Dissertations / Theses on the topic 'Low grade heat'
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1
Sansom, Robert. "Decarbonising low grade heat for low carbon future." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/25503.
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More energy is consumed in the UK for heat than either transport or electricity and yet until recently little attention has been given to decarbonising heat to meet the UK's 2050 greenhouse gas targets. The challenges are immense as over 80% of households in the UK use gas for space and water heating. To achieve the UK's greenhouse gas targets will necessitate heat to be almost completely decarbonised and will thus require a transition from gas for heating to a low carbon alternative. However, there is a lack of consensus over which low carbon heat technologies householders should be encouraged to adopt as projections of these vary significantly. This thesis commences by reviewing those projections and identifying the possible reasons for the variations. Low carbon heat technologies suitable for large scale deployment are identified and a heat demand model developed from which demand profiles can be constructed. An integrated heat and electricity investment model is then developed which includes electricity generation assets but also district heating assets such as combined heat and power plant, network storage and large network heat pumps. A core input into this model is the heat demand profiles. The investment model enables the interaction between heat and electricity assets to be evaluated and so using scenarios combined with sensitivities examines the economics and carbon emissions of the low carbon residential heating technologies previously identified. Throughout this analysis the equivalent cost for gas heating is used as a comparator. The results suggest that district heating is an attractive option which is robust under most outcomes. However, its economic viability is crucially dependent on a financing regime that is compatible with other network based assets. Also identified is a role for electric storage heaters for buildings with low heat demand.
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Gude, Veera Gnaneswar. "Desalination using low grade heat sources." access full-text online access from Digital Dissertation Consortium, 2007. http://libweb.cityu.edu.hk/cgi-bin/er/db/ddcdiss.pl?3296129.
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Li, Chennan. "Innovative Desalination Systems Using Low-grade Heat." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4126.
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Water and energy crises have forced researchers to seek alternative water and energy sources. Seawater desalination can contribute towards meeting the increasing demand for fresh water using alternative energy sources like low-grade heat. Industrial waste heat, geothermal, solar thermal, could help to ease the energy crisis.
Unfortunately, the efficiency of the conventional power cycle becomes
uneconomically low with low-grade heat sources, while, at the same time, seawater desalination requires more energy than a conventional water treatment process. However, heat discarded from low-grade heat power cycles could be used as part of desalination energy sources with seawater being used as coolant for the power cycles. Therefore a study of desalination using low-grade heat is of great significance.
This research has comprehensively reviewed the current literature and
proposes two systems that use low-grade heat for desalination applications or even desalination/power cogeneration. The proposed two cogeneration systems are a supercritical Rankine cycle-type coupled with a reverse osmosis (RO) membrane desalination process, and a power cycle with an ejector coupled with a multi-effect distillation desalination system. The first configuration provides the advantages of
making full use of heat sources and is suitable for hybrid systems. The second system has several advantages, such as handling highly concentrated brine without external electricity input as well as the potential of water/power cogeneration when it is not used to treat concentrated brine. Compared to different stand-alone power cycles, the proposed systems could use seawater as coolant to reject low-grade heat from the power cycle to reduce thermal pollution.
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Kishore, Ravi Anant. "Low-grade Thermal Energy Harvesting and Waste Heat Recovery." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/103650.
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Low-grade heat, either in the form of waste heat or natural heat, represents an extremely promising source of renewable energy. A cost-effective method for recovering the low-grade heat will have a transformative impact on the overall energy scenario. Efficiency of heat engines deteriorates with decrease in hot-side temperature, making low-grade heat recovery complex and economically unviable using the current state-of-the-art technologies, such as Organic Rankine cycle, Kalina cycle and Stirling engine. In this thesis, a fundamental breakthrough is achieved in low-grade thermal energy harvesting using thermomagnetic and thermoelectric effects. This thesis systematically investigates two different mechanisms: thermomagnetic effect and thermoelectric effect to generate electricity from the low-grade heat sources available near ambient temperature to 200�[BULLET]C. Using thermomagnetic effect, we demonstrate a novel ultra-low thermal gradient energy recovery mechanism, termed as PoWER (Power from Waste Energy Recovery), with ambient acting as the heat sink. PoWER devices do not require an external heat sink, bulky fins or thermal fluid circulation and generate electricity on the order of 100s μW/cm3 from heat sources at temperatures as low as 24�[BULLET]C (i.e. just 2�[BULLET]C above the ambient) to 50�[BULLET]C. For the high temperature range of 50-200�[BULLET]C, we developed the unique low fill fraction thermoelectric generators that exhibit a much better performance than the commercial modules when operated under realistic conditions such as constant heat flux boundary condition and high thermally resistive environment. These advancements in thermal energy harvesting and waste heat recovery technology will have a transformative impact on renewable energy generation and in reducing global warming.PHD
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Hedström, Sofia. "Thermal energy recovery of low grade waste heat in hydrogenation process." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-32335.
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The waste heat recovery technologies have become very relevant since many industrial plants continuously reject large amounts of thermal energy during normal operation which contributes to the increase of the production costs and also impacts the environment. The simulation programs used in industrial engineering enable development and optimization of the operational processes in a cost-effective way. The company Chematur Engineering AB, which supplies chemical plants in many different fields of use on a worldwide basis, was interested in the investigation of the possibilities for effective waste heat recovery from the hydrogenation of dinitrotoluene, which is a sub-process in the toluene diisocyanate manufacture plant. The project objective was to implement waste heat recovery by application of the Organic Rankine Cycle and the Absorption Refrigeration Cycle technologies. Modeling and design of the Organic Rankine Cycle and the Absorption Refrigeration Cycle systems was performed by using Aspen Plus® simulation software where the waste heat carrier was represented by hot water, coming from the internal cooling system in the hydrogenation process. Among the working fluids investigated were ammonia, butane, isobutane, propane, R-123, R-134a, R-227ea, R-245fa, and ammonia-water and LiBr-water working pairs. The simulations have been performed for different plant capacities with different temperatures of the hydrogenation process. The results show that the application of the Organic Rankine Cycle technology is the most feasible solution where the use of ammonia, R-123, R-245fa and butane as the working fluids is beneficial with regards to power production and pay-off time, while R-245fa and butane are the most sustainable choices considering the environment.
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Lee, Dongwook Ph D. Massachusetts Institute of Technology. "Low-grade heat conversion into electricity by thermoelectric and electrochemical systems." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120186.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
Developing cost effective technologies that convert low-grade heat into electricity is essential to meet the increasing demand for renewable energy systems. Thermoelectric and recently emergent electrochemical heat conversion devices are promising candidates for this purpose. However, current performance and cost of these devices limit their widespread application. In this thesis, we investigate design guidelines for heterostructured thermoelectric systems and electrochemical heat energy harvesters to address these challenges. Material cost and scarcity of elements in state-of-the-art thermoelectric materials are current limitations. Conductive polymers has become an attractive alternative to those materials, however they suffer from low Seebeck coefficient. Nanoscale composites of inorganic semiconductors with conductive polymers could improve low Seebeck coefficients and power factors of conductive polymers, however quantitative understandings on the mechanisms lying behind the enhancements were often missing. In our research, thin film heterostructures of a conductive polymer, PEDOT:PSS / undoped Si or undoped Ge were selected as templates for mechanistic investigations on thermoelectric performance enhancements. With the combination of experiments and simulation, it was determined that p-type PEDOT:PSS transferred holes to the interfaces of adjacent Si and Ge, and these holes could take advantage of higher hole mobility of Si and Ge. This phenomenon called modulation doping, was responsible for thermoelectric power factor enhancements in Si / PEDOT:PSS and Ge / PEDOT:PSS heterostructures. Another technology to transform low-grade heat into electricity is electrochemical heat conversion. Traditionally, the electrochemical heat conversion into electricity suffered from low conversion efficiency originating from low ionic conductivity of electrolytes, even though high thermopowers often reaching several mV/K has been an alluring advantage. Recently developed breakthrough on operating such devices under thermodynamic cycles bypassed low ionic conductivity issue, thereby improving the conversion efficiency by multiple orders of magnitude. In this study, we focused on improving efficiency by increasing thermopowers and suppressing heat capacity of the system, while maintaining the autonomy of thermodynamic cycles without need for recharging by external sources of electricity. These detailed interpretations on nanoscale composite thermoelectric systems and electrochemical heat harvester provide insights for the design of next-generation thermoelectric and electrochemical heat energy harnessing solutions.
by Dongwook Lee.
Ph. D.
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Soleimanikutanaei, Soheil. "Modelling, Design, and Optimization of Membrane based Heat Exchangers for Low-grade Heat and Water Recovery." FIU Digital Commons, 2018. https://digitalcommons.fiu.edu/etd/3921.
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Transport Membrane Condenser (TMC) is an innovative technology based on the property of a nano-scale porous material which can extract both waste heat and water from exhaust gases. This technology tremendously improves the efficiency of boilers and gas/coal combustors by lowering waste heat and increasing water recovery. Contaminants in the flue gases, such as CO2, O2, NOx, and SO2 are inhibited from passing through the membrane by the membrane’s high selectivity. The condensed water through these tubes is highly pure and can be used as the makeup water for many industrial applications. The goal of this research is to investigate the heat transfer, condensation rate, pressure drop and overall performance of crossflow heat exchangers. In this research, a numerical model has been developed to predict condensation of water vapor over and inside of nano-porous layers. Both capillary condensation inside the nanoscale porous structure of the TMC and the surface condensation were considered in the proposed method using a semi-empirical model. The transport of the water vapor and the latent heat of condensation were applied in the numerical model using the pertinent mass, momentum, turbulence and energy equations.
By using the proposed model and simulation procedure, the effect of various inlet parameters such as inlet mass flow rate, inlet temperature, and water vapor content of the inlet flow on the performance of the cross-flow TMC heat exchanger was studied to obtain the optimum performance of the heat exchangers at different working conditions. The performance of the TMC heat exchangers for inlet flue gas rate 40 to 120 kg/h, inlet water rate 60 to 140 kg/h, inlet flue gas relative humidity 20 to 90%, and tube pitch ratio 0.25 to 2.25 has been studied. The obtained results show that the water condensation flux continuously increases with the increase of the inlet flue-gas flow rate, water flow rate, and the flue-gas humidity. The total heat flux also follows the same trend due to the pronounced effect of the latent heat transfer from the condensation process. The water condensation flux and the overall heat transfer increase at the beginning for small values of the tube pitches and then decreases as the tube pitch increases furthermore. In addition to the cross-flow TMC heat exchangers, the performance of a shell and tube TMC heat exchanger for high pressure and temperature oxy-combustion applications has been investigated. The performance analysis for a 6-heat exchanger TMC unit shows that heat transfer of the 2-stage TMC unit is higher than the 2-stage with the same number of the heat exchanger in each unit.
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Stürzebecher, Wolfgang. "Absorption cooling from low grade heat sources in the range 10kW - 100kW." Thesis, Sheffield Hallam University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442471.
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Chen, Huijuan. "The Conversion of Low-Grade Heat into Power Using Supercritical Rankine Cycles." Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3447.
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Low-grade heat sources, here defined as below 300 ºC, are abundantly available as industrial waste heat, solar thermal, and geothermal, to name a few. However, they are under-exploited for conversion to power because of the low efficiency of conversion. The utilization of low-grade heat is advantageous for many reasons. Technologies that allow the efficient conversion of low-grade heat into mechanical or electrical power are very important to develop.
This work investigates the potential of supercritical Rankine cycles in the conversion of low-grade heat into power. The performance of supercritical Rankine cycles is studied using ChemCAD linked with customized excel macros written in Visual Basic and programs written in C++.
The selection of working fluids for a supercritical Rankine cycle is of key importance. A rigorous investigation into the potential working fluids is carried out, and more than 30 substances are screened out from all the available fluid candidates. Zeotropic mixtures are innovatively proposed to be used in supercritical Rankine cycles to improve the system efficiency.
Supercritical Rankine cycles and organic Rankine cycles with pure working fluids as well as zeotropic mixtures are studied to optimize the conversion of lowgrade heat into power. The results show that it is theoretically possible to extract and convert more energy from such heat sources using the cycle developed in this research than the conventional organic Rankine cycles. A theory on the selection of appropriate working fluids for different heat source and heat sink profiles is developed to customize and maximize the thermodynamic cycle performance.
The outcomes of this research will eventually contribute to the utilization of low-grade waste heat more efficiently.
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Meyer, Adriaan Jacobus. "Steam jet ejector cooling powered by low grade waste or solar heat." Thesis, Stellenbosch : University of Stellenbosch, 2006. http://hdl.handle.net/10019.1/2012.
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Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006.A small scale steam jet ejector experimental setup was designed and manufactured. This ejector setup is of an open loop configuration and the boiler can operate in the temperature range of Tb = 85 °C to 140 °C. The typical evaporator liquid temperatures range from Te = 5 °C t o 10 °C while the typical water cooled condenser presure ranges from Pc = 1 . 70 kPa t o 5. 63 kPa (Tc = 15 °C to 35 °C). The boiler is powered by by two 4kW electric elements, while a 3kW electric element simulates the cooling load in the evaporator. The electric elements are controlled by means of variacs. The function ...
Centre for Renewable and Sustainable Energy Studies
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Solanki, Roochi. "Modelling of a two-phase thermofluidic oscillator for low-grade heat utilisation." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/24563.
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The Non-Inertive-Feedback Thermofluidic Engine (NIFTE) is a two-phase thermofluidic oscillator which, by means of persistent periodic thermal-fluid oscillations when placed across a steady temperature difference, is capable of utilising low-grade (i.e., low temperature) heat to induce a fluid motion. Innovative devices which comprise no or few moving parts and that can operate utilising low-grade heat for fluid pumping and/or pressurisation are currently under development based on the NIFTE concept to: (i) understand the fundamental principle of operation of this novel technology; (ii) construct reliable, simple models that capture the first-order dominant underlying processes that govern its operation and performance for the purpose of early-stage engineering design; and (iii) to investigate the potential of this technology in specific fluid-pumping applications. Three spatially lumped linearised models of the NIFTE are developed through the use of electrical analogies. The first model (LTP) imposes a static (i.e. steady) linear temperature profile along the surface of the heat exchangers, the second model (CTD) imposes a constant-temperature difference between the surface of the heat exchanger and the working fluid, the third model (DHX) allows the solid heat exchanger blocks to store and release heat dynamically as they interact thermally with the working fluid. Through carrying out a parametric study on the LTP model, with and without inertial effects in the liquid phase it is shown that the inclusion of inertia has a significant effect on the trends and magnitudes of key performance indicators, namely the temperature gradient along the heat exchangers, oscillation frequency and exegetic efficiency. In addition, much improved predictions of the oscillation frequency and temperature gradient are possible when using the inertive LTP model. Following from this, a parametric study on the three models, all including inertia, is used to show that the CTD model predicts unrealistically high exergetic efficiencies, and as such is omitted from any further studies. A dissipative thermal loss parameter that can account for the exergetic losses due to the parasitic, cyclic phase change and heat exchange within the device is included in the LTP and DHX models in an effort to make realistic predictions of the exergetic efficiencies. A parametric study on the LTP and DHX models, including and excluding the thermal loss parameter is carried out and the results are compared to experimental data. It is found that the inclusion of the thermal loss parameter greatly improves the prediction of the exergetic efficiency in both the LTP and DHX models, both in trend and approximate magnitude. From the results it is concluded that, on accounting for thermal losses, the DHX model achieves the best predictions of the key performance indicators of the NIFTE, that is, of the oscillation frequency and exergetic efficiency of the device. An investigation on the applicability of different working fluids for the NIFTE, based on the dynamic heat exchanger model including thermal losses, with emphasis on the effects of key thermodynamic properties on the maximum thermal efficiency of an idealised cycle and the predicted exergetic efficiency of the device is also carried out. The change in specific volume due to vaporisation and the maximum saturation pressure of the working fluid in the cycle are found to have a dominant role in determining these efficiencies. Thirty one pure working fluids are studied, under a given set of scenarios, each representing a different practical application for the NIFTE device. For the scenario where the maximum pressure of the engine is defined by the pumping application, higher efficiencies are predicted for wet and isentropic fluids. For the scenario where the hot and cold heat exchanger temperatures are set by the external heat source and sink, higher efficiencies are predicted by dry and isentropic fluids. In this work, it is estimated that, with optimised designs and well-selected working fluids, the NIFTE may be capable of thermal efficiencies in the range 1 - 5 % when operating with low-grade heat at temperatures from 50 to 100°C, with current best performance of 1.5% at 80°C.
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Al-Kharabsheh, Saleh A. "Theoretical and experimental analysis of water desalination system using low grade solar heat." [Gainesville, Fla.] : University of Florida, 2003. http://purl.fcla.edu/fcla/etd/UFE0000982.
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Albatati, Faisal Ali S. "Investigation of environmentally friendly power generation systems for low-grade waste heat recovery." Thesis, University of Nottingham, 2015. http://eprints.nottingham.ac.uk/28990/.
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From the point of view of energy importance and the environmental impacts associated with conventional energy production methods, and for the purpose of low-grade waste heat recovery, this thesis demonstrates an investigative approach to develop and test a novel, environmentally friendly small-scale Rankine based power generation prototype system. To fulfil the aim, a range of systems of different technologies, and employing different working fluids were investigated to identify the most efficient, cost-effective system for the application. These systems are the absorption power generation system, and the flood expansion power generation system employing CO2/Lubricant mixture as the working fluid, the CO2 SRC power system, and finally the ORC system employing newly developed HFOs and HCFOR1233zd(E) refrigerants. The CO2/lubricant working fluid mixture was experimentally investigated and thermodynamically modelled. The performance of the investigated systems was theoretically evaluated by computer simulations. The results revealed that the ORC outperformed all other investigated systems, achieving thermal efficiency and net thermal power output of 14.36% and 4.81 kW respectively with R1233zd(E). In addition, the evaluation confirmed the capability of the new refrigerants to replace conventional refrigerants. A small-scale R1233zd(E) ORC prototype system utilising a specially developed scroll expander was constructed and tested. In the First Experiment, an automotive motor was utilised as the electric generator. The system’s optimum performance was 7.87% thermal efficiency, 1.39 kW expander power output, and 180 W electric power output. The main source of performance limitation was identified as the lower capability of the steam humidifier heat source, in addition to the speed mismatch between the expander and the motor, the poor performance of the circulation pump, and the piping configuration in relation to the positions of heat exchangers. Piping and the position of heat exchangers were altered, the motor was replaced by an alternator and the second experiment commenced in which the best overall experimental performance of 7.6% thermal efficiency, 1 kW expander power output, 246 W electric power output, was achieved. Very poor pump efficiency and a large power loss through the power transmission mechanism to the alternator were observed. Upon completion of the experiments, the theoretically predicted performance was validated, and the experimentally obtained results were compared to those of similar ORCs from literature. The comparison revealed that for the utilised expander type, a mass flow rate of 0.074 kg/s, and a pressure ratio of 4.5, achieves the best expander efficiency of 75%. From an economic point of view, the R1233zd(E) ORC was shown to be a very attractive and safe investment even for scaled- up systems. The thesis concluded that the ORC technology remains the most efficient, flexible technology for low-grade heat recovery, and the evaluation of R1233zd(E) for the first time expressed the attractive potentials of the refrigerant in ORC applications. Finally, justified recommendations were made to replace the heat source and refrigerant pump and to test other types of expander in order to improve the performance of the R1233zd(E) ORC prototype system.
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Müller, Holger. "Solar process heat in the food industry : methodological analysis and design of a sustainable process heat supply system in a brewery and a dairy." Thesis, De Montfort University, 2016. http://hdl.handle.net/2086/12489.
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The food industry is a large consumer of industrial energy. A very large portion of this energy is needed in the form of thermal energy at medium to low temperatures. Fossil fuels remain the dominant sources of this energy. This combination provides various possibilities to reduce energy consumption and CO2 emissions with heat recovery, but also with the integration of solar process heat. Energy efficiency must provide the context, or background, of such considerations, and is therefore a very important aspect of them. It is a complex task to design an efficient heat supply with a variety of energy sources. An analysis of standards for energy audits, guides for energy efficiency and guides for solar process heat integration confirms that complexity. However, no available methodology considers all the necessary steps. These must range from analysis of the existing heat supply to the redesign of an efficient heat supply system. The focus must be on heat sources with waste heat and on solar process heat that might be used to complement the conventional sources. The design of a process heat system is mainly the task of design engineers in engineering offices. Specific tools and measures are needed to support these experts. However, the companies of the food industry sector employ their own energy engineers for energy issues. These people are actually the decision makers responsible for the configuration of the company energy supply systems, who also possess knowledge of the processes in their industry subsector. The expertise of the energy engineers varies within a broad range and is also connected to their area of responsibility. Therefore, it is important to consider these energy engineers when developing a methodology. The development of the methodology proposed herein consists first of the configuration of the tools and measures, which were assigned to four elements and functions. Second, the methodology so developed was applied at two companies in cooperation with their energy engineers, in detailed case studies. The feedback from the energy engineers is therefore a main objective and provides a background for evaluation of the usability of the methodology. It demonstrates the expertise required of the energy engineers, for the application of the tools and measures provided. Moreover, the development and application of the methodology involving real companies demonstrates the necessity of getting feedback from energy engineers. That finding is very important, and has been insufficiently considered in previous guides or methodologies. It is proposed that further work be aimed at providing additional case studies to extend the use of this methodology to other parts of the food industry.
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Bryson, Matthew John, and mbryson@bigpond net au. "The conversion of low grade heat into electricity using the Thermosyphon Rankine Engine and Trilateral Flash Cycle." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080130.162927.
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Low grade heat (LGH) sources, here defined as below 80ºC, are one group of abundant energy sources that are under-utilised in the production of electricity. Industrial waste heat provides a convenient source of concentrated LGH, while solar ponds and geothermal resources are examples of sustainable sources of this energy. For a number of years RMIT has had two ongoing, parallel heat engine research projects aimed at the conversion of LGH into electricity. The Thermosyphon Rankine Engine (TSR) is a heat engine that uses water under considerable vacuum. The other research stream uses a hydrocarbon based working fluid in a heat engine employing the Trilateral Flash Cycle (TFC). The TSR Mk V was designed and built as a low cost heat engine for the conversion of LGH into electricity. Its main design advantages are its cost and the employment of only one moving part. Using the data gained from the experimental rig, deviations from the expected results (those derived theoretically) were explored to gain insight for further development. The results from the TSR rig were well below those expected from the design specifications. Although the experimental apparatus was able to process the required heat energy, the efficiency of conversion fell well below the expected 3% and was approximately 0.2%. The inefficiency was explained by a number of contributing factors, the major being form drag upon the rotor that contributed around 2/3 of the losses. Although this was the major cause of the power loss, other factors such as the interference with the rotor by the condensate on its return path contributed to the overall poor performance of the TSR Mk V. The RMIT TFC project came about from exploration of the available academic literature on the subject of LGH conversion. Early work by researchers into applying Carnot's theory to finite heat sources led them to explore the merits of sensible heat transfer combined with a cycle that passes a liquid (instead of a gas) though an expander. The results showed that it was theoretically possible to extract and convert more energy from a heat source of this type using this method than using any other alternative. This previous research was targeted at heat sources above 80ºC and so exploration of the theoretical and empirical results for sources below this temperature was needed. Computer models and an experimental rig using isopentane (with a 28ºC boiling point at atmospheric pressure) were produced to assess the outcomes of employing low temperature heat sources using a TFC. The experimental results from the TFC research proved promising with the efficiency of conversion ranging from 0.8% to 2.4%. Although s uch figures seem poor in isolation, it should be noted that the 2.4% efficiency represents an achievement of 47% of the theoretical ideal conversion efficiency in a rig that uses mainly off-the-shelf components. It also confirms that the TFC shows promise when applied to heat sources less than 80ºC.
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Ayou, Dereje Sendeku. "Combined absorption power and refrigeration systems driven by low and mid-grade heat sources." Doctoral thesis, Universitat Rovira i Virgili, 2014. http://hdl.handle.net/10803/306436.
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Hi ha una gran abundància de fonts de calor de baixa i mitja temperatura (<300 ° C), com pot ser la solar tèrmica, geotèrmica o calor residual de diversos processos tèrmics. Els principals serveis energètics com l'aire condicionat, la refrigeració o l'electricitat es generen en general per separat mitjançant diverses tecnologies de conversió d'energia independents. La majoria dels usuaris finals necessiten almenys més d'un servei energètic: un exemple típic d'això ho constitueix el servei energètic a edificis. La producció combinada d'electricitat (descentralitzada) i de fred mitjançant sistemes eficients de conversió d'energia accionats tèrmicament és una de la solució tecnològica adequada per fer front als actuals reptes relacionats amb l'energia a nivell mundial.
L'objectiu d'aquesta tesi és el desenvolupament d'una nova classe de cicles d'absorció per a la producció d'energia mecànica o elèctrica i refrigeració mitjançant fonts d'energia de baixa i mitjana temperatura. Per aconseguir aquest objectiu, es presenta primer una revisió dels cicles d'absorció combinats proposats a la literatura. Es presenten i discuteixen més els criteris d'acompliment utilitzats en la literatura. A continuació, es proposen diversos nous cicles d'absorció combinats. Aquests són analitzats i discutits des del punt de vista energètic i exergètic per a la utilització eficaç de les fonts de calor de baixa i mitjana temperatura. Com fluids de treball s’han utilitzat mescles a base d'amoníac: NH3 / H2O, NH3 / LiNO3 i NH3 / NaSCN. S'ha desenvolupat un model semi-empíric per a un expansor de desplaçament utilitzant amoníac (i barreja d’amoníac / aigua amb alta concentració d'amoníac) com a fluid de treball. Aquest model s'ha integrat en alguns dels cicles d'absorció combinats proposats en aquesta tesi. Posteriorment, s'ha realitzat un model de sistema d'absorció per a la producció de potència i refrigeració solar (SAPCS) per usar-lo en l'eina de simulació dinàmica TRNSYS com un cas representatiu per a la integració dels cicles d'absorció combinats amb una planta termosolar.Existe una gran abundancia de fuentes de calor de baja y media temperatura (<300 ° C), como puede ser la solar térmica, geotérmica o calor residual de diversos procesos térmicos. Los principales servicios energéticos como el aire acondicionado, la refrigeración o la electricidad se generan por lo general por separado mediante diversas tecnologías de conversión de energía independientes. La mayoría de los usuarios finales necesitan por lo menos más de un servicio energético: un ejemplo típico de esto lo constituye el servicio energético a edificios. La producción combinada de electricidad (descentralizada) y de frío mediante sistemas eficientes de conversión de energía accionados térmicamente es una de la solución tecnológica adecuada para hacer frente a los actuales desafíos relacionados con la energía a nivel mundial. El objetivo de esta tesis es el desarrollo de una nueva clase de los ciclos de absorción para la producción de energía mecánica o eléctrica y refrigeración mediante fuentes de energía de baja y media temperatura. Para lograr este objetivo, se presenta primero una revisión de los ciclos de absorción combinados propuestos en la literatura. A continuación, se proponen varios nuevos ciclos de absorción combinados. Estos son analizados y discutidos desde el punto de vista energético y exergético para la utilización eficaz de las fuentes de calor de baja y media temperatura. Como fluidos de trabajo se utilizaron mezclas a base de fluidos de trabajo de amoníaco: NH3 / H2O, NH3 / LiNO3 y NH3 / NaSCN. Se ha desarrollado un modelo semi-empírico para un expansor de desplazamiento usando amoniaco (y mezcla de amoniaco / agua con alta concentración de amoniaco) como fluido de trabajo. Este modelo se ha integrado en algunos de los ciclos de absorción combinados propuestos en esta tesis. Posteriormente, se ha realizado un modelo de sistema de absorción para la producción de potencia y refrigeración solar (SAPCS) para usarlo en la herramienta de simulación dinámica TRNSYS como un caso representativo para la integración de los ciclos de absorción combinados con una planta termosolar. En conclusión esta tesis contribuirá al desarrollo de una nueva clase de sistemas de absorción capaces de proporcionar energía y refrigeración de forma simultánea y/o alternativamente, mediante la utilización de fuentes de calor
Low and mid-grade heat sources (< 300 °C), such as solar thermal, geothermal and waste heat from various thermal processes are abundantly available. Air-conditioning, refrigeration and electricity are useful forms of energy products, usually produced using separate energy conversion technologies. Most end-users need at least dual energy products: typical example could be buildings applications. The combined production of electricity (decentralized) and cold using efficient thermally-driven energy conversion systems are one of the suitable technological solution to address the current global energy related challenges. The aim of this thesis is the development of a new class of absorption cycles to produce mechanical or electrical energy and cooling using energy sources at low or medium temperature. To achieve this aim, first combined absorption cycles proposed in the literature are reviewed. The concept of combined absorption cycles are explained in terms of idealized energy conversion systems. Performance criteria used in the literature are presented and discussed. Then, several new combined absorption cycles are proposed, analysed and discussed from the energetic and exergetic viewpoints for the effective utilization of low and mid-grade heat sources. Ammonia based working fluid mixtures were used: NH3/H2O, NH3/LiNO3 and NH3/NaSCN. A semi-empirical model for a scroll expander using ammonia (and ammonia/water mixture with high concentration of ammonia) as working fluid is developed. It is integrated into some of the proposed combined absorption cycles in this Thesis. Then, a Solar Absorption Power and Cooling System (SAPCS) model is developed for its use in TRNSYS software as a simulation tool and it is used to demonstrate a representative case for the integration of combined absorption cycles with solar thermal plant. In conclusion this thesis will contribute to the development of new class of absorption systems able to provide power and refrigeration simultaneously and/or alternatively by utilizing low and mid-grade heat sources.
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Law, Richard. "A knowledge-based system for low-grade waste heat recovery in the process industries." Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2541.
Full textAbstract:
The ever-increasing price of energy, combined with increasingly stringent legislation to reduce greenhouse gas emissions, is driving the UK process industries toward increasing energy efficiency. Significant gains can be made in this sector, as up to 11.4TWh per annum (4% of total energy use) of the UK process industries’ energy consumption is lost as recoverable waste heat. Substantial recovery of this waste heat would have economic benefits of the order of £100s of million/year, and environmental benefits of the order of 100s of thousands of tonnes of carbon dioxide equivalent per year. This thesis describes the development of a knowledge-based system for the selection and preliminary design of equipment for low-grade waste heat recovery in the process industries. The system addresses two of the key barriers to low-grade waste heat recovery in the UK. Firstly, it provides a readily accessible and zero cost tool to replace expensive, time-consuming expert consultancy in the initial stages of waste heat recovery projects, and, secondly, it educates users regarding the range and benefits of novel waste heat recovery technologies. The system requires an input of easy-to-access data from the user. Based on this data, it then selects the most appropriate technologies for waste heat recovery for the case study in question from a database including various types of heat exchanger, vapour compression heat pumps, mechanical vapour recompression and organic Rankine cycles. It also generates a preliminary design including equipment size, efficiency/effectiveness, capital cost, cost savings, payback time and potential reductions in carbon emissions. This provides sufficient information to allow the user to make an educated decision regarding whether or not waste heat recovery is suitable for their needs. The knowledge-base of the system was built using a decision tree method that has been proven to be successful in the building of decision making tools for various engineering applications. The software is programmed using the Java language which allows widespread free dissemination to computers running all common operating systems. The system was tested using case studies based on data from both existing publications and collaborating companies. The results were validated against published results, common modelling software results and the views of expert consultants. Broadly, in terms of equipment specification and cost, the knowledge-based system produced the same results as the other methods. Furthermore, the preliminary designs generated were generally within 5% of the final figures from the other sources. In certain cases, the knowledge-based system suggested alternative technologies that were more viable (economically and/or practically) than those considered by the authors of published case studies. In all cases, system operating time (data input, and processing of results) was of the order of minutes, whereas studies by consultants or the use of existing modelling packages would be significantly more time-consuming (of the order of hours or days). Hence, the system can be used as a rapid optioneering tool for investigation of waste heat recovery technologies, requiring substantially less time than current available methods.
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Yuan, Ziwen. "Multifunctional membrane distillation for hypersaline brine treatment, low-grade heat harvesting and lithium recovery." Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/24775.
Full textAbstract:
Membrane distillation (MD), a thermally driven technology capable of desalinating hypersaline brine, has become increasingly attractive. However, the widespread industrial application of MD has been hindered by its low energy utilization efficiency. Adding new functions to MD by integrating other emerging processes can improve MD's energy utilization efficiency. This thesis investigated two derivations of MD: pressure-retarded membrane distillation (PRMD) and thermo-osmosis coupled thermally regenerative electrochemical cycle (TO-TREC).
PRMD has the potential to recover the low-grade heat in terms of electricity by applying hydraulic pressure at the cold permeate side. Here, the feasibility of using PRMD for both desalination of hypersaline water and harvesting of low-grade heat was evaluated experimentally for the first time. Highly concentrated NaCl solution (4 M) can be desalinated with the salt rejection >99.9%, and electricity is generated in PRMD at the same time. However, the results also showed that the experimental PRMD performance was significantly affected by the pressure-induced membrane deformation. Thus, improving the mechanical stability of membranes would be the first critical step to improve PRMD performance. Further, controlling internal scaling and fouling is also critical for PRMD.
TO-TREC is a new process in which the electrochemical process is integrated with the MD process for efficient lithium recovery. TO-TREC system extracted Li+ selectively from hypersaline brine and then released it into a recovery solution as LiCl with a high production rate. TREC harvests thermal energy from low-grade heat, saving >20% of electrical energy compared to conventional electrochemical methods. Li source solutions can be continuously concentrated by the coupled MD process, making it possible to utilize sources with low lithium concentration. The new process has an excellent potential to meet the growing global Li demands for various energy applications
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Worall, Mark. "An investigation of a jet-pump thermal (ice) storage system powered by low-grade heat." Thesis, University of Nottingham, 2001. http://eprints.nottingham.ac.uk/11111/.
Full textAbstract:
This thesis investigates a novel combination of a jet-pump refrigeration cycle and a thermal (ice) storage (TIS) system that could substantially reduce the electrical energy requirements attributable to comfort cooling.Two methods of TIS were identified; spray ice TIS would use evaporative freezing to store ice on a vertical surface,and encapsulated ice TIS would freeze a bed of encapsulated elements by sublimation freezing.Thestudy also investigates jet-pump refrigeration at partload and a convergent-divergent design manufactured from a thermoset plastic to make recommendations for performance enhancement for a system that has a low COP. An experimental rig was built to investigate the novel concepts in the laboratory. Encapsulated ice TIS was superior to spray ice TIS because, for the same nominal secondary flow, sublimation freezing causes an increase in coolth storage rate of about 10 % compared to evaporative freezing. Encapsulated ice stores experience difficulties in fully discharging their coolth (approximately 6% in this case), but spray ice TIS can be used to produce an ice/brine slurry enabling all of the ice to be used, and so may be more suitable if the unmelted ice represents a large proportion of the cooling capacity. Approximately 85 % to 90 % of the ice formed on the vertical surface during spray ice TIS testing was formed by evaporative freezing from a falling film. At high saturation conditions, heat is transferred mainly by conduction across the falling film. Both the growth of an ice layer on a vertical surface and freezing of encapsulated elements were found to be successful, but a large data spread was observed during spray ice TIS testing. It was thought that a variation in the steady-state saturation conditions in the evaporator/ice store was caused by variability of droplet size distribution from the spray nozzle flow, which may make a full-scale system unreliable. The COP of the spray ice TIS system was approximately 0.15 compared to a COP of approximately 0.25 found during encapsulated ice TIS testing. The difference was because of the use of an over-expanded primary nozzle, which restricted secondary flow and increased momentum losses. A primary nozzle that expands close to the design evaporator saturation conditions should be used to maximise entrainment ratio. The COP of a jet-pump TIS is low, but a system designed to operate at off-peak periods could increase the COP to about 0.8 by taking advantage of the lower ambient conditions. The measurement of entrainment ratio was used successfully to determine ice storage rate and COP. This was valid because of the assumption that the saturation conditions in the evaporator/ice store approached steady-state. However, over longer periods that would be found in large-scale systems, the ice storage rate and entrainment ratio may fall substantially. The steady-state assumption could still be used to observe the change in evaporator conditions by sampling over short time intervals (30 minutes). At part-load, increases in evaporator saturation temperature could increase entrainment ratio substantially (50 % increase) for only a small reduction in critical pressure lift ratio Ns *(15 % reduction). A variation in chilled water temperature could be used to boost entrainment ratio at the peak demand. The variation in Ns* is too small to use this strategy to control the jet-pump with respect to condenser operating conditions. The entrainment ratio is approximately proportional to the diff-user to primary nozzle area ratio. A doubling of entrainment ratio was attained for only a 15% reduction in Ns*. The change in geometry from a constant area throat to a convergent-divergent design caused the flow through the jet-pump to vary with outlet conditions indicating that secondary flow was not choked. Higher entrainment ratios and pressure lift ratios were observed, but the entrainment ratio varied with outlet conditions in the form of peaks and troughs, making its operation unpredictable. This was thought to be caused by the restriction in secondary flow area due to the interaction of the primary jet and the curved wall. The convergent-divergent design manufactured from a thermoset plastic was successfully tested, showing that a plastic material can be used as a material of construction. In principle, a large number of jet-pump units could be manufactured from a single mould, reducing the first cost. The investigation proved the concept of jet-pump TIS. Waste-heat could be utilised over 24 hours and year round, increasing the efficiency of the process. The use of a convergent-divergent throat design, multiple geometry jet-pumps and operation at off-peak periods can maximise the performance over a cooling season, and be competitive with other TIS and chiller systems. The mass production of jet-pumps using injection moulding techniques could reduce substantially the capital cost of a system. All of these factors should encourage the development of such systems, so that the harmful emissions caused by the use of air conditioning systems can be minimised.
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Ajimotokan, Habeeb A. "A study of trilateral flash cycles for low-grade waste heat recovery-to-power generation." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/9202.
Full textAbstract:
There has been renewed significance for innovative energy conversion
technologies, particularly the heat recovery-to-power technologies for
sustainable power generation from renewable energies and waste heat. This is
due to the increasing concern over high demand for electricity, energy shortage,
global warming and thermal pollution. Among the innovative heat recovery-to-
power technologies, the proposed trilateral flash cycle (TFC) is a promising
option, which presents a great potential for development. Unlike the Rankine
cycles, the TFC starts the working fluid expansion from the saturated liquid
condition rather than the saturated, superheated or supercritical vapour phase,
bypassing the isothermal boiling phase. The challenges associated with the
need to establish system design basis and facilitate system configuration
design-supporting analysis from proof-of-concept towards a market-ready TFC
technology are significant. Thus, there is a great need for research to improve
the understanding of its operation, behaviour and performance. The objective of
this study is to develop and establish simulation tools of the TFCs for improving
the understanding of their operation, physics of performance metrics and to
evaluate novel system configurations for low-grade heat recovery-to-power
generation. This study examined modelling and process simulation of the TFC
engines in order to evaluate their performance metrics, predictions for guiding
system design and parameters estimations. A detailed thermodynamic analysis,
performance optimization and parametric analysis of the cycles were
conducted, and their optimized performance metrics compared. These were
aimed at evaluating the effects of the key parameters on system performances
and to improve the understanding of the performance behaviour. Four distinct
system configurations of the TFC, comprising the simple TFC, TFC with IHE,
reheat TFC and TFC with feed fluid-heating (or regenerative TFC) were
examined. Steady-state steady-flow models of the TFC power plants,
corresponding to their thermodynamic processes were thermodynamically
modelled and implemented using engineering equation solver (ESS). These
models were used to determine the optimum synthesis/ design parameters of the cycles and to evaluate their performance metrics, at the subcritical operating
conditions and design criteria. Thus, they can be valuable tools in the
preliminary prototype system design of the power plants. The results depict that
the thermal efficiencies of the simple TFC, TFC with IHE, reheat TFC and
regenerative TFC employing n-pentane are 11.85 - 21.97%, 12.32 - 23.91%,
11.86 - 22.07% and 12.01 - 22.9% respectively over the cycle high temperature
limit of 393 - 473 K. These suggest that the integration of an IHE, fluid-feed
heating and reheating in optimized design of the TFC engine enhanced the heat
exchange efficiencies and system performances. The effects of varying the
expander inlet pressure at the cycle high temperature and expander isentropic
efficiency on performance metrics of the cycles were significant. They have
assisted in selecting the optimum-operating limits for the maximum performance
metrics. The thermal efficiencies of all the cycles increased as the inlet
pressures increased from 2 - 3 MPa and increased as the expander isentropic
efficiencies increased from 50 - 100%, while their exergy efficiencies increased.
This is due to increased net work outputs that suggest optimal value of pressure
ratios between the expander inlets and their outlets. A comprehensive
evaluation depicted that the TFC with IHE attained the best performance
metrics among the cycles. This is followed by the regenerative TFC whereas
the simple TFC and reheat TFC have the lowest at the same subcritical
operating conditions. The results presented show that the performance metrics
of the cycles depend on the system configuration, and the operating conditions
of the cycles, heat source and heat sink. The results also illustrate how system
configuration design and sizing might be altered for improved performance and
experimental measurements for preliminary prototype development.
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Charalambous, Constantinos. "An investigation of an adsorption cogeneration system for power and cooling using low grade heat." Thesis, University of Newcastle upon Tyne, 2015. http://hdl.handle.net/10443/2891.
Full textAbstract:
Cogeneration is a hot topic in the efforts to reduce dependence on fossil fuel usage and to reduce greenhouse gas emissions by replacing the primary energy source with a low-grade heat source. Cogeneration simultaneously produces power and cooling using a low-grade heat source (e.g. solar energy, geothermal energy or waste heat), which ideally provides a renewable carbon-free solution for implementation in domestic, industrial as well as isolated areas. This research thesis describes for the first time the development and construction of the Low Heat cogeneration chemisorption system, explores its potential and makes suggestions for its future development based on the experience gained during the experiments. The design uses two adsorption cycles operating out of phase and alternatively connected to a scroll expander in order to reach 3kW of cooling and 1kW of electricity. Each adsorption cycle consists of a reactor, a condenser and an evaporator. Each reactor contains a composite mixture of CaCl2 and activated carbon at a ratio of 4:1 by mass. The system was experimentally investigated for its cooling as well as for its cogeneration performance. Experimental investigations were performed for different heating and cooling temperatures, cycle times and the optimum overall ammonia for the system. The maximum refrigeration coefficient of the performance (COPref) of the machine was found to be 0.26 when the refrigeration power was 3.52kW. At the same time, the specific cooling power (SCP) per side was 201.14W/kg (402.28W/kg per cycle) and the cooling capacity 168.96kJ/kg (337.92kJ/kg per cycle). During the cogeneration experiments it was found that the expander affected the pressure and temperature; the refrigerant flow rate and the pressure across the expander were important for the system’s power production. The maximum power recorded was 486W which provides a power coefficient of performance (COPW) of 0.048. A model to describe the desorption power generation as well as the evaporation refrigeration process was developed using the ECLIPSE software. The cooling model was validated from the experimental results and later the power model was used for ii further investigation of the system power performance. The optimisation of the machine completes the study by using both experimental and simulation data.
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Ottaviano, Saverio <1988>. "Test bench development, experimental analysis and modelling of micro-organic Rankine cycle for low-grade heat recovery." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amsdottorato.unibo.it/9784/1/saverio_ottaviano_PhD_thesis_.pdf.
Full textAbstract:
This thesis presents the detailed experimental and numerical analysis conducted on a prototype of micro-scale organic Rankine cycle (ORC) power system. The system is conceived for stationary co-generative applications in the residential sector, since it is characterized by a power output in the kW-scale. Suitable heat sources are low-enthalpy geothermal energy, biomass combustion, solar thermal collectors or low-temperature waste heat recovery. The system is driven by a reciprocating piston expander prototype, and uses HFC-134a as working fluid, hence it is suitable for temperature of heat source in the range 60-90 °C. The micro-ORC has been tested in a wide range of operating conditions, with the aim of deeply characterizing the system behavior and understanding the effect of each process variable on the performance of the power plant. The main objectives of this thesis are:
- presenting the characteristics and performance of the prototypal micro-ORC system
- assessing the dependencies of the micro-ORC system steady-state performance from the off-design operating conditions, by analyzing the behavior of each component;
- estimating experimentally the system response to transient variations of the operating conditions, in order to deduce guidelines for the control system design;
- developing and validating a charge-sensitive thermodynamic model to simulate the ORC system in stationary and dynamic conditions.
The analysis here presented aims at providing a contribution to the research field of micro-scale and low-temperature organic Rankine cycles, especially from the experimental point of view. The improvement of micro-ORC performance and reliability is one of the key factor for the market spread of this technology, helping to enhance the global electricity generation efficiency, save primary resources and greenhouse gases emissions, and increase the exploitation of renewable thermal sources.
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Lindqvist, Jakob, and Niklas Faber. "Performance evaluation in post integrated organic Rankine cycle systems : A study on operational systems utilizing low grade heat." Thesis, Linköpings universitet, Mekanisk värmeteori och strömningslära, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-150371.
Full textAbstract:
Organic Rankine cycles can be integrated with district heating systems and in applications of biogas digestion. Evaluating the performance of the installations by Againity AB in Ronneby and Norrköping, Sweden, is a unique opportunity which can support the establishment of ORC technology in the waste heat recovery market, unveiling its feasibilities and limitations. Operational data gathered from October 2017 until April 2018, provides this thesis with information about the ORC-systems. A method using Coolprop and Matlab has been used to detect steady-state series in the Ronneby installation using moving standard deviation and inclination criteria. By screening the data and selecting these series, analytical equations can be used to determine the performance of the installations and map the linear relationship between variables like pressure and generator power. The largest impact on the system in Ronneby is developed in the condenser. Large coolant volume flow creates large heat sink capacity and higher generator efficiency and power. However, with increasing generator power the condenser pressure decrease. Lower condenser pressure results in a decreased evaporation pressure, which could be maintained if the pump was able to run at higher frequencies. The Plant in Norrköping needs further studies and a review of its sensors. The code in Matlab is a resource to Againity and Linköpings university for future work in performance evaluation. It can be used to detect errors in energy balance, local readings, and picture the machines' performance graphically.
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Yang, Chen. "Novel cycles using carbon dioxide as working fluid : new ways to utilize energy from low-grade heat sources." Licentiate thesis, KTH, Energy Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4055.
Full textAbstract:
This licentiate thesis proposes and analyzes three carbon dioxide novel cycles, namely: the carbon dioxide transcritical power cycle, the carbon dioxide Brayton cycle and the carbon dioxide cooling and power combined cycle. Due to the different characteristics of each cycle, the three cycles are suitable for different applications. The CO2 transcritical power cycle is suitable for harvesting energy from low-grade heat sources, near which a low temperature heat sink is accessible. The CO2 Brayton cycle is suitable for harvesting the energy from relatively high-grade heat sources when there is no low temperature heat sink available. The CO2 cooling and power combined cycle is suitable for applications, where both power and cooling are needed (e.g. automobile applications, in which the cycle can utilize the energy in the engine exhaust gasses to produce power and provide cooling/heating to the mobile compartment room at the same time).
Several models have been developed using the software known as Engineering Equation Solver (EES)1 for both cycle analysis and computer aided heat exchanger design. Different cycle working conditions have been simulated and different working parameters’ influence on the cycle performance has been explained. In addition, Refprop 7.02 is used for calculating the working fluid properties and the CFD tool Femlab has been employed to investigate the particular phenomena influencing the heat exchanger performance.
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Chen, Yang. "Novel cycles using carbon dioxide as working fluid : new ways to utilize energy from low-grade heat sources." Licentiate thesis, Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4055.
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Vidhi, Rachana. "Organic Fluids and Passive Cooling in a Supercritical Rankine Cycle for Power Generation from Low Grade Heat Sources." Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5322.
Full textAbstract:
Low grade heat sources have a large amount of thermal energy content. Due to low temperature, the conventional power generation technologies result in lower efficiency and hence cannot be used. In order to efficiently generate power, alternate methods need to be used. In this study, a supercritical organic Rankine cycle was used for heat source temperatures varying from 125°C to 200°C. Organic refrigerants with zero ozone depletion potential and their mixtures were selected as working fluid for this study while the cooling water temperature was changed from 10-25°C. Operating pressure of the cycle has been optimized for each fluid at every heat source temperature to obtain the highest thermal efficiency. Energy and exergy efficiencies of the thermodynamic cycle have been obtained as a function of heat source temperature.
Efficiency of a thermodynamic cycle depends significantly on the sink temperature. At areas where water cooling is not available and ambient air temperature is high, efficient power generation from low grade heat sources may be a challenge. Use of passive cooling systems coupled with the condenser was studied, so that lower sink temperatures could be obtained. Underground tunnels, buried at a depth of few meters, were used as earth-air-heat-exchanger (EAHE) through which hot ambient air was passed. It was observed that the air temperature could be lowered by 5-10°C in the EAHE. Vertical pipes were used to lower the temperature of water by 5°C by passing it underground. Nocturnal cooling of stored water has been studied that can be used to cool the working fluid in the thermodynamic cycle. It was observed that the water temperature can be lowered by 10-20°C during the night when it is allowed to cool. The amount of water lost was calculated and was found to be approximately 0.1% over 10 days.
The different passive cooling systems were studied separately and their effects on the efficiency of the thermodynamic cycle were investigated. They were then combined into a novel condenser design that uses passive cooling technology to cool the working fluid that was selected in the first part of the study. It was observed that the efficiency of the cycle improved by 2-2.5% when passive cooling system was used.
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Schmidt, Joel Edward. "The Use of Ammonium Carbamate as a High Specific Thermal Energy Density Material for Thermal Management of Low Grade Heat." University of Dayton / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1310666985.
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Landelle, Arnaud. "Experimental and numerical study of transcritical Organic Rankine Cycles for low-grade heat conversion into electricity from various sources." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI090/document.
Full textAbstract:
Le Cycle Organique de Rankine (abrégé ORC de l’anglais Organic Rankine Cycle) est une technologie permettant la conversion de chaleur basse température en électricité. L’ORC transcritique a été identifié comme une solution prometteuse pour la valorisation de la chaleur fatale. Cependant, peu d’installations expérimentales ont permis de confirmer ces performances. Ce travail de thèse présente le fonctionnement et l’optimisation d’ORC sous-critique et transcritique pour la conversion de chaleur basse température en électricité à partir de différentes sources. Premièrement, les contextes thermodynamique et technologique de l’ORC sont présentés. Des critères de performance énergétiques et exergétiques sont définis et appliqués à une base de données d’installations expérimentales afin d’exposer l’état de l’art actuel des ORC. Deuxièmement, les outils numériques et expérimentaux, spécifiquement développés ou utilisé pour ces travaux, sont présentés. Trois installations expérimentales d’ORC transcritique complet ou incomplet fournissent les données expérimentales. Différents modèles numériques sont utilisés : sous l’environnement Matlab pour la modélisation en permanent, l’analyse des données expérimentales et l’analyse énergétique/exergétique ; L’environnement Modelica/Dymola pour l’analyse des transitoires et de la dynamique du système. Dans un troisième temps, ces différents outils sont utilisés pour étudier quatre différentes problématiques : - Le fonctionnement de la pompe de circulation est étudié, d’un point de vue énergétique et volumétrique. Des modèles semi-empiriques et des corrélations de performance sont présentés. - Les transferts thermiques en supercritique sont examinés, en local et en global. Les coefficients de transfert thermique sont comparés avec différentes corrélations de la littérature. - L’influence de la charge de réfrigérant sur les performances et le comportement de l’ORC est analysée. La charge optimale est estimée pour différentes conditions de fonctionnement et des mécanismes de régulation de la charge sont présentés. - Les performances énergétiques et exergétiques de l’ORC sont comparées avec la base de données. Une analyse exergétique du procédé a permis d’identifier des voies d’améliorationThe Organic Rankine Cycle (ORC) is a technology used for low-grade thermal energy conversion into electricity. Transcritical ORC has been identified as a solution for efficient waste heat recovery. However, few experimental tests have been conducted to confirm the interest of transcritical ORC and investigate its operational behaviors. The work presented focuses on the operation and the optimization of subcritical and transcritical Organic Rankine Cycles for low-grade heat conversion into electricity from various heat sources (solar, industrial waste heat). First, the thermodynamic framework of ORC technology is presented. Energetic and exergetic performance criteria, appropriate to each type of input source, are introduced and selected. The criteria are later applied to a database of ORC prototypes, in order to objectively analyze the state-of-the-art. In a second step, the experimental and numerical tools, specifically developed or used in the present thesis, are presented. Three subcritical and transcritical ORC test benches (hosted by CEA and AUA) provided experimental data. Numerical models were developed under different environments: Matlab for steady-state modeling, data processing and energy/exergy analysis. The Modelica/Dymola environment for system dynamics and transient operations. Lastly, the different tools are exploited to investigate four different topics: - The ORC pump operation is investigated, both under an energetic and volumetric standpoint, while semi-empirical models and correlations are exposed. - Supercritical heat transfers are explored. Global and local heat transfer coefficients are estimated and analyzed under supercritical conditions, while literature correlations are introduced for comparison. - Working fluid charge influence over the ORC performance and behavior is investigated. Optimal fluid charge is estimated under various operating conditions and mechanisms for charge active regulation are exposed. - ORC system performances and behavior are discussed. Through both an energetic and exergetic standpoint, performances are compared with the state-of-the-art, while optimization opportunities are identified through an exergetic analysis
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Scott, Grant. "Microwave pretreatment of a low grade copper ore to enhance milling performance and liberation." Thesis, Link to the online version, 2006. http://hdl.handle.net/10019/123.
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Peris, Pérez Bernardo. "Thermo-economic assessment of small-scale organic Rankine cycle for low-grade industrial waste heat recovery based on an experimental application." Doctoral thesis, Universitat Jaume I, 2017. http://hdl.handle.net/10803/456991.
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This thesis focuses on the use of small-scale Organic Rankine Cycles (ORC) to produce electricity from low-grade waste heat recovery of industrial processes. In particular, a thermo-economic (combination of thermodynamic and economic) optimization is conducted to achieve more cost-effective systems and, thus, to contribute to the ORC adoption in practical applications. As a novelty, this investigation is based on an experimental application case, which allows developing a comprehensive model of the system and its subsequent validation from actual data. Thereby, more realistic results are reached, which underline the most relevant topics to pay attention to improve the economic feasibility of new projects.Esta tesis se centra en el uso de sistemas de pequeña escala basados en el ciclo Rankine orgánico (ORC por las siglas en ingles) para la producción de electricidad a partir de la recuperación de calor residual de baja temperatura en procesos industriales. En concreto, se lleva a cabo una optimización termoeconómica (combinación entre termodinámica y económica) como método para mejorar la rentabilidad de los proyectos y, de esta forma, favorecer el uso de los sistemas ORC en aplicaciones prácticas. Como novedad, la investigación se lleva a cabo en torno a un caso experimental de aplicación, lo que permite desarrollar un modelo íntegro del sistema y posteriormente validarlo con datos reales. De este modo, se alcanzan resultados más realistas que ponen de relieve los aspectos clave para mejorar la viabilidad económica de nuevos proyectos.
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Green, Jeffrey Andrew. "IMPROVING THE ENERGY EFFICIENCY OF A MID-SIZE POWER PLANT BY REDUCTION IN AUXILIARY POWER AND IMPROVED HEAT TRANSFER." OpenSIUC, 2014. https://opensiuc.lib.siu.edu/theses/1502.
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This study incorporates the potential use of Variable Frequency Drives on various motors as well as areas of improved heat transfer in an older, mid-sized coal fired power plant. In power plants, fluid flow rates are often controlled using dampers or valves while the motors that power the pumps stay at full speed resulting in a significant amount of wasted electrical power; energy is also lost due to poor heat recovery prior to gases leaving the system. By examining pump usage as well as additional heat available for recovery, potential energy savings will be determined. Preliminary results of five motors suggested for variable frequency drive application show annual savings that total 31.1 GWh, resulting in a 1.66% increase in overall plant efficiency. Total project costs are near $2 million resulting in a simple payback period of less than two years assuming 0.04 $/kWh. For every degree reduction of the flue gas temperature by means of heat recovery that is reused elsewhere in the cycle, 2 Billion BTU of coal would be saved annually. One realistic scenario suggested heat recovery resulting in a 120°F degree reduction of flue gas temperature amounting to a 2.54% increase in cycle efficiency.
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Li, Liang. "Experimental and theoretical investigation of CO2 trans-critical power cycles and R245fa organic Rankine cycles for low-grade heat to power energy conversion." Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/14766.
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Globally, there are vast amounts of low-grade heat sources from industrial waste and renewables that can be converted into electricity through advanced thermodynamic power cycles and appropriate working fluids. In this thesis, experimental research was conducted to investigate the performance of a small-scale Organic Rankine Cycle (ORC) system under different operating conditions. The experimental setup consisted of typical ORC system components, such as a turboexpander with a high speed generator, a scroll expander, a finned-tube condenser, an ORC pump, a plate evaporator and a shell and tube evaporator. R245fa was selected as the working fluid, on account of its appropriate thermophysical properties for the ORC system and its low ozone depletion potential (ODP). The test rig was fully instrumented and extensive experiments carried out to examine the influences of several important parameters, including heat source temperature, ORC pump speed, heat sink flow velocity, different evaporators and with or without a recuperator on overall R245fa ORC performances. In addition, in terms of the working fluid’s environmental impact, temperature match of the cycle heat processes and system compactness, CO2 transcritical power cycles (T-CO2) were deemed more applicable for converting low-grade heat to power. However, the system thermal efficiency of T-CO2 requires further improvement. Subsequently, a test rig of a small-scale power generation system with T-CO2 power cycles was developed with essential components connected; these included a plate CO2 supercritical heater, a CO2 transcritical turbine, a plate recuperator, an air-cooled finned-tube CO2 condenser and a CO2 liquid pump. Various preliminary test results from the system measurements are demonstrated in this thesis. At the end, a theoretical study was conducted to investigate and compare the performance of T-CO2 and R245fa ORCs using low-grade thermal energy to produce useful shaft or electrical power. The thermodynamic models of both cycles were developed and applied to calculate and compare the cycle thermal and exergy efficiencies at different operating conditions and control strategies. In this thesis, the main results showed that the thermal efficiency of the tested ORC system could be improved with an increased heat source temperature in the system with or without recuperator. When the heat source temperature increased from 145 oC to 155 oC for the system without recuperator, the percentage increase rates of turbine power output and system thermal efficiency were 13.6% and 14% respectively while when the temperature increased from 154 oC to 166 oC for the system with recuperator, the percentage increase rates were 31.2% and 61.97% respectively. In addition, the ORC with recuperator required a relative higher heat source temperature, which is comparable to a system without recuperator. On the other hand, at constant heat source temperatures, the working fluid pump speed could be optimised to maximise system thermal efficiency for ORC both with and without recuperator. The pressure ratio is a key factor impacting the efficiencies and power generation of the turbine and scroll expander. Maximum electrical power outputs of 1556.24W and 750W of the scroll expander and turbine were observed at pressure ratio points of 3.3 and 2.57 respectively. For the T-CO2 system, the main results showing that the CO2 mass flow rate could be directly controlled by varying the CO2 liquid pump speeds. The CO2 pressures at the turbine inlet and outlet and turbine power generation all increased with higher CO2 mass flow rates. When CO2 mass flow rate increased from 0.2 kg/s to 0.26kg/s, the maximum percentage increase rates of measured turbine power generation was 116.9%. However, the heat source flow rate was found to have almost negligible impact on system performance. When the thermal oil flow rate increased from 0.364kg/s to 0.463kg/s, the maximum percentage increase rate of measured turbine power generation was only 14.8%. For the thermodynamic analysis, with the same operating conditions and heat transfer assumptions, the thermal and exergy efficiencies of R245fa ORCs are both slightly higher than those of T-CO2. However, the efficiencies of both cycles can be enhanced by installing a recuperator at under specific operating conditions. The experiment and simulation results can thus inform further design and operation optimisations of both the systems and their components.
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Grove, Elmi. "Feasibility study on the implementation of a boiling condenser in a South African fossil fuel power plant." Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/61293.
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The South African electricity mix is highly dependent on subcritical coal-fired power stations.
The average thermal efficiency of these power plants is low. Traditional methods to increase
the thermal efficiency of the cycle have been widely studied and implemented. However,
utilising the waste heat at the condenser, which accounts for the biggest heat loss in the cycle,
presents a large potential to increase the thermal efficiency of the cycle. Several methods can
be implemented for the recovery and utilisation of low-grade waste heat.
This theoretical study focuses on replacing the traditional condenser in a fossil fuel power
station with a boiling condenser (BC), which operates in a similar manner to the core of a
boiling water reactor at a nuclear power plant (Sharifpur, 2007). The system was theoretically
tested at the Komati Power Station, South Africa's oldest power station. The power station
presented an average low-grade waste heat source. The BC cycle was theoretically tested with
several working fluids and numerous different configurations. Several of the theoretical
configurations indicated increased thermal efficiency of the cycle. The BC cycle configurations
were also tested in two theoretical scenarios.
Thirty configurations and 103 working fluids were tested in these configurations. The
configuration that indicated the highest increase in thermal efficiency was the BC cycle with
regeneration (three regenerative heat exchangers) from the BC turbine. A 2.4% increase in
thermal efficiency was obtained for the mentioned theoretical implementation of this
configuration. The working fluid tested in this configuration was ethanol. This configuration
also indicated a 7.6 MW generating capacity.
The increased thermal efficiency of the power station presents benefits not only in increasing
the available capacity on South Africa's strained grid, but also environmental benefits. The
mentioned reduction of 7.6 MW in heat released into the atmosphere also indicated a direct environmental benefit. The increase in thermal efficiency could also reduce CO2 emissions
released annually in tons per MW by 5.74%.
The high-level economic analysis conducted, based on the theoretically implemented BC cycle
with the highest increase in thermal efficiency, resulted in a possible saving of R46 million per
annum. This translated to a saving of R19.2 million per annum for each percentage increase
in thermal efficiency brought about by the BC cycle.
The theoretical implementation of the BC, with regeneration (three regenerative heat
exchangers) from the BC turbine and ethanol as a working fluid, not only indicated an increase
in thermal efficiency, but also significant economic and environmental benefits.Dissertation (MEng)--University of Pretoria, 2016.
Mechanical and Aeronautical Engineering
MEng
Unrestricted
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Borgogno, Remy. "Procédé thermo-hydraulique solaire appliqué à la trigénération dans le secteur résidentiel." Thesis, Perpignan, 2017. http://www.theses.fr/2017PERP0025/document.
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Un nouveau procédé de trigénération thermo-hydraulique fonctionnant à partir d'énergie thermique basse température (80 à 110 °C) a été étudié pour assurer les différents besoins du secteur résidentiel. Le terme "thermo-hydraulique" se réfère à l'utilisation d'un liquide incompressible qui permet de transférer le travail hydrauliquement entre différents composants ou sous-systèmes, permettant d'améliorer l'efficacité de la chaine de conversion énergétique. Un modèle quasi-statique a été développé pour évaluer les performances énergétiques des différentes variantes du procédé. Ces calculs ont permis de définir parmi un large choix, quels fluides de travail étaient les plus appropriés. Ces calculs ont été complétés par une étude quasi-dynamique et dynamique permettant un meilleur dimensionnement du procédé. Enfin, une étude de fonctionnement annuel a été réalisée à partir du modèle quasi-statique pour évaluer l'évolution des performances ainsi que sa production d'énergie sur une année complète de fonctionnement. Ces études montrent que le couple fluide R1234yf/R1233zd semble le plus approprié à un fonctionnement en climat méditerranéen. L'étude annuelle montre qu'en considérant les données climatiques de la ville de Perpignan, le procédé permet d'amplifier l'énergie solaire collectée d'un facteur de 1,32 en moyenne et permet d'atteindre un COP solaire de 0,24 en mode rafraichissement. Quand les besoins thermiques sont satisfaits, l'intégralité de l'énergie solaire captée est valorisée pour produire de l'électricité avec un rendement moyen annuel de 4,2%A new process based on thermal-hydraulic conversion actuated by low-grade thermal energy (80–110 °C) is investigated and aims at providing trigeneration energy features for the residential sector. "Thermo-hydraulic" term refers to a process involving an incompressible fluid used as an intermediate medium to transfer work hydraulically between different thermal operated components or sub-systems allowing to improve the efficiency of the energy conversion chain. A model, assuming steady-state operations, is developed to assess the energy performances of different variants of this thermo-hydraulic process as well as various pairs of working fluids. These calculations were completed by a quasi-dynamic and dynamic models allowing a better sizing of the process. Finally, an annual study was realized from the quasi-static model in order to estimate the evolution of the performances as well as its power production over a complete year of functioning. For instance, in the frame of a single-family home, located in the Mediterranean region, the working fluid pair (R1234yf/R1233zd) is investigated in detail in order to estimate the annual performances. For domestic houses, the process aims at amplifying the solar energy collected by a factor of 1.32 for heating purpose, provides a cold production with a solar COP of 0.24 and generates electricity from the remaining solar energy with an efficiency of 4.2%
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Hansen, Per. "Potentiell koppling mellan elektrolys och landbaseradfiskodling : En analys av behov och tillgång på syrgas och värme." Thesis, Högskolan i Gävle, Miljövetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-36512.
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Det kommer ske en stor utbyggnad av elektrolys för produktion av vätgas i Sverigeoch övriga världen. För att sänka produktionskostnaden och därmed göra vätgasenbilligare analyserar denna rapport vilket behov av syrgas och värme som en landbaserad fiskodling har, samt hur mycket syrgas och värme fiskodlingen skulle behövaköpa från en elektrolysör. Analysen visar att de arter som används i studien - tilapia(Oreochromis, Oreochromis,. Alcolapia), regnbåge (Oncorhynchus mykiss) och lax(Salmo salar) - i en odling som producerar 40 ton fisk om året skulle förbruka cirka1,16 procent av syrgasen och cirka 0,35 procent av värmen från en 3 MW PEMelektrolysör. Försäljningsvärdet av syrgasen och värmen från en 3 MW elektrolysörberäknas till cirka 695 000 SEK/år för syrgasen och cirka 1 830 000 SEK/år för värmen. Den genomsnittliga kostnaden för syrgas och värme för arterna i studien i enodling på 40 ton/år beräknas till 8900 SEK/år för syrgasen och 6400 SEK/år förvärmen i en landbaserad fiskodling.There will be a major expansion of electrolysis for production of hydrogen in Sweden and the rest of the world. To reduce production costs and thus make hydrogencheaper, this report analyzes how much oxygen and heat a fish farm consumes andtherefore would need to buy from an electrolyser. The analysis shows that the species used in the study - tilapia (Oreochromis, Oreochromis, Alcolapia), rainbow(Oncorhynchus mykiss) and salmon (Salmo salar) - in a farm that produces 40 tonsof fish per year would consume 1.16 percent of the oxygen and 0,35 percent of theheat produced from a 3 MW PEM electrolyzer. The value of the oxygen and theheat from a 3 MW electrolyser is calculated at SEK 694,939/year for the oxygenand SEK 1,829,813/year for the heat. The average cost for the species in the studyin a 40 tonne/year fish farm is calculated at SEK 8,900/year for the oxygen and SEK6,400/year for the heat in a land-based fish farm.
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Al-Anfaji, Ahmed Suaal Bashar. "The optimization of combined power-power generation cycles." Thesis, University of Hertfordshire, 2015. http://hdl.handle.net/2299/15485.
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An investigation into the performance of several combined gas-steam power generating plants’ cycles was undertaken at the School of Engineering and Technology at the University of Hertfordshire and it is predominantly analytical in nature. The investigation covered in principle the aspect of the fundamentals and the performance parameters of the following cycles: gas turbine, steam turbine, ammonia-water, partial oxidation and the absorption chiller. Complete thermal analysis of the individual cycles was undertaken initially. Subsequently, these were linked to generate a comprehensive computer model which was employed to predict the performance and characteristics of the optimized combination. The developed model was run using various input parameters to test the performance of the cycle’s combination with respect to the combined cycle’s efficiency, power output, specific fuel consumption and the temperature of the stack gases. In addition, the impact of the optimized cycles on the generation of CO2 and NOX was also investigated. This research goes over the thermal power stations of which most of the world electrical energy is currently generated by. Through which, to meet the increase in the electricity consumption and the environmental pollution associated with its production as well as the limitation of the natural hydrocarbon resources necessitated. By making use of the progressive increase of high temperature gases in recent decades, the advent of high temperature material and the use of large compression ratios and generating electricity from high temperature of gas turbine discharge, which is otherwise lost to the environment, a better electrical power is generated by such plant, which depends on a variety of influencing factors. This thesis deals with an investigation undertaken to optimize the performance of the combined Brayton-Rankine power cycles' performance. This work includes a comprehensive review of the previous work reported in the literature on the combined cycles is presented. An evaluation of the performance of combined cycle power plant and its enhancements is detailed to provide: A full understanding of the operational behaviour of the combined power plants, and demonstration of the relevance between power generations and environmental impact. A basic analytical model was constructed for the combined gas (Brayton) and the steam (Rankine) and used in a parametric study to reveal the optimization parameters, and its results were discussed. The role of the parameters of each cycle on the overall performance of the combined power cycle is revealed by assessing the effect of the operating parameters in each individual cycle on the performance of the CCPP. P impacts on the environment were assessed through changes in the fuel consumption and the temperature of stack gases. A comprehensive and detailed analytical model was created for the operation of hypothetical combined cycle power and power plant. Details of the operation of each component in the cycle was modelled and integrated in the overall all combined cycle/plant operation. The cycle/plant simulation and matching as well as the modelling results and their analysis were presented. Two advanced configurations of gas turbine cycle for the combined cycle power plants are selected, investigated, modelled and optimized as a part of combined cycle power plant. Both configurations work on fuel rich combustion, therefore, the combustor model for rich fuel atmosphere was established. Additionally, models were created for the other components of the turbine which work on the same gases. Another model was created for the components of two configurations of ammonia water mixture (kalina) cycle. As integrated to the combined cycle power plant, the optimization strategy considered for these configurations is for them to be powered by the exhaust gases from either the gas turbine or the gases leaving the Rankine boiler (HRSG). This included ChGT regarding its performance and its environmental characteristics. The previously considered combined configuration is integrated by as single and double effect configurations of an ammonia water absorption cooling system (AWACS) for compressor inlet air cooling. Both were investigated and designed for optimizing the triple combination power cycle described above. During this research, tens of functions were constructed using VBA to look up tables linked to either estimating fluids' thermodynamic properties, or to determine a number of parameters regarding the performance of several components. New and very interesting results were obtained, which show the impact of the input parameters of the individual cycles on the performance parameters of a certain combined plant’s cycle. The optimized parameters are of a great practical influence on the application and running condition of the real combined plants. Such influence manifested itself in higher rate of heat recovery, higher combined plant thermal efficiency from those of the individual plants, less harmful emission, better fuel economy and higher power output. Lastly, it could be claimed that various concluding remarks drawn from the current study could help to improve the understanding of the behaviour of the combined cycle and help power plant designers to reduce the time, effort and cost of prototyping.
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Charalambous, Charithea. "Temperature swing adsorption process for carbon dioxide capture, purification and compression directly from atmospheric air." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/33311.
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Many reports, scientific papers, patents, and scientific news investigate the feasibility and affordability of direct carbon dioxide capture from the atmospheric air (DAC). Since carbon dioxide (CO2) is extremely diluted in the atmosphere, large volumes of air have to be handled to capture comparable amounts of CO2. Therefore, both the energy consumption and the plant size are expected to be 'prohibitive'. On the other hand, some analyses have shown that DAC is feasible and can become affordable with essential research and development. DAC has been regarded as an optional bridging or a transitional technology for mitigating CO2 emissions in the medium-term. Priorities include investing in renewable and low-carbon technologies, efficiency and integration of energy systems, and realisation of additional environmental benefits. A heavy reliance on negative emission technologies (NETs), and consequently DAC, may be extremely risky as NETs interact with a number of societal challenges, i.e. food, land, water and energy security. Although, "... capturing carbon from thin air may turn out to be our last line of defence, if climate change is as bad as the climate scientists say, and if humanity fails to take the cheaper and more sensible option that may still be available today" MacKay (2009). Certainly, more research is necessary to bring down both cost and energy requirements for DAC. This work firstly predicts the adsorption equilibrium behaviour of a novel temperature swing adsorption process, which captures carbon dioxide directly from the air, concentrates, and purifies it at levels compatible to geological storage. The process consists of an adsorption air contactor, a compression and purification train, which is a series of packed beds reduced in size and connected in-line for the compression and purification purposes, and a final storage bed. The in-line beds undergo subsequent adsorption and desorption states. The final desorbed stream is stored in a storage bed. This cyclic process is repeated for a number of times imposed by the required purity and pressure in the final bed. The process is been thermodynamically verified and optimised. Since, the overall performance of this process does not only depend on the design of the process cycle and operating conditions but also on the chosen adsorbent material, further optimisation of the adsorptive and physical properties of the solid adsorbent is investigated. Thus, the optimal parameters of the potentially used porous materials is identified. Continuing the research on different adsorbent materials, an experimental investigation on the equilibrium properties of two competitive adsorbents is also performed. Besides the thermodynamic analysis, a dynamic model is presented for the investigation of the mass and heat transfer and its influence on the adsorption rate and consequently on the overall process performance. Since the initial stream is very dilute, it is expected that the adsorption rate will be low compared to other temperature swing processes and the capture rate will be affected by the heat transfer. Finally, the design and development of an experimental laboratory-scale apparatus is presented and analysed. Future design improvements are also discussed.
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Cederblad, Lena. "Aspects on Head and neck Cancer with special reference to Salivary Gland Tumours and Single Nucleotide Polymorphism." Doctoral thesis, Uppsala universitet, Institutionen för immunologi, genetik och patologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-332192.
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A thesis on Head and neck cancer focusing on dose planning, salivary gland carcinoma and Single nucleotide polymorphism. For dose planning PET/CT (Positron emissions tomography/computed tomography) with tracer gave more precise information in comparison dose planning with CT. More primary tumours and metastases were found with the acetate tracer than with glucose tracer. Acetate PET/CT also showed larger volume of tumours attributed to lipid metabolism. In a retrospective study salivary gland cancer 5-year overall survival (OS) was 53 %. Salivary gland carcinoma consists of many histopathological groups, the two largest groups being mucoepidermoid carcinoma (MEC) and adenoid cystic carcinoma (ASCC). For ACC, having the best 5-year OS, it was 70 percent. Facial palsy, advanced stage disease, lymph node metastases worsened prognosis. ACC and polymorphous low grade carcinoma (PLGA) expressed c-myc and cyclin D1 to a larger extent than MEC. In squamous cell carcinoma of the head and neck we examined the occurrence of Single Nucleotide polymorphism, SNP. We found that the SNPs in male and female patients differed from each other. In male patients the SNPs were associated with immune response while in female patients the association was to SNPs concerning inflammation. This means that different pathways were engaged in cancer development for men and women. We also found that the SNPs in patients were different from those expressed in the healthy controls.
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Савлук, Сергій Валерійович, Сергей Валерьевич Савлук, and S. V. Savluk. "Обґрунтування параметрів забезпечення синхронізації двухвальних інерційних віброзбуджувачів." Thesis, Видавництво НГУ, 2012. http://ir.nmu.org.ua/handle/123456789/183.
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Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.02.09 – динаміка і міцність машин. Державний вищий навчальний заклад «Національний гірничий університет» МОНмолодьспорту України, Дніпропетровськ, 2012.Диссертация на соискание ученой степени кандидата технических наук по специальности 05.02.09 – динамика и прочность машин. Государственное высшее учебное заведение «Национальный горный университет» МОНмолодежиспорта Украины, Днепропетровск, 2012.
A thesis for a competition for a candidate of engineering sciences degree on speciality 05.02.09 – Dynamics & durability of machines. State Higher Educational Institution «National Mining University», Dnipropetrovsk, 2012.
У дисертації вирішена наукова задача забезпечення синхронно-синфазного режиму обертання валів віброзбуджувача. Розроблена математична модель, що описує динаміку системи «робочий орган – віброзбуджувач – синхронізатор – привод» у вібраційних технологічних машинах із спрямованими коливаннями робочого органу. Отримані залежності враховують розкид параметрів тертя, відхилення коефіцієнтів тертя в підшипникових вузлах віброзбуджувача, вплив технологічного навантаження і наявність синхронізатора з пружним елементом. Викладені рекомендації щодо вибору параметрів інерційного самосинхронізовного віброзбуджувача спрямованих коливань і методика розрахунку синхронізатора з пружним елементом. Результати досліджень упроваджені й пройшли апробацію при розрахунку і виборі параметрів грохота ГСЛ-42 СЭ.
В диссертации решена научная задача обеспечения синхронного режима вращения валов вибровозбудителя с учетом положения центра масс рабочего органа, характеристик привода (мощность, скорость вращения валов, погрешность изготовления двигателей, расположение вибровозбудителей на рабочем органе), а также разброса параметров трения в подшипниковых узлах и параметров синхронизатора с упругим элементом. В работе проведен анализ существующих исследований динамики системы «рабочий орган – вибровозбудитель – привод» в технологических машинах с направленными колебаниями рабочего органа, оснащенных инерционными вибровозбудителями. Выполнена постановка задач исследования и разработана математическая модель, описывающая динамику системы «рабочий орган – вибровозбудитель – синхронизатор – привод» в вибрационных технологических машинах с направленными колебаниями рабочего органа, с учетом положения центра масс рабочего органа, характеристик привода, разброса параметров трения в подшипниковых узлах, параметров синхронизатора с упругим элементом. В результате проведения лабораторных экспериментов, промышленных испытаний и теоретических исследований определены фактические режимы работы двухвального инерционного вибровозбудителя в условиях самосинхронизации и применения синхронизатора с упругим элементом в конструкции возбудителя. Получены зависимости, устанавливающие области синхронного вращения валов вибровозбудителя для параметров характеристик трения в подшипниковых узлах, угла наклона вибровозбудителей к горизонту, использование синхронизатора с упругим элементом, отношения расстояний от осей вращения до центра масс рабочего органа. Установлено, что режим синхронного вращения валов обеспечивается допустимым углом рассогласования фаз вращения, который линейно зависит от характеристик трения в подшипниковых узлах. Определен параметр, учитывающий влияние силы тяжести дебалансных грузов на режим синхронизации, который находится в степенной зависимости от угла наклона вибровозбудителей к горизонту. Установлено, что использование синхронизатора с упругим элементом обеспечивает режим синхронного вращения валов вибровозбудителя при разбросе параметров до 10 раз по сравнению с режимом самосинхронизации. Обосновано, что рациональную жесткость упругого элемента синхронизатора необходимо определять как отношение разности критического момента двигателя и момента сопротивлений в подшипниковых узлах к параметру, который характеризуется расстоянием между осями валов и радиусом эксцентриситета синхронизатора. Исследование на лабораторном стенде подтвердило правильность исходных допущений и полученные результаты. Изложены рекомендации по выбору параметров самосинхронизирующегося инерционного вибровозбудителя направленных колебаний и методика расчета синхронизатора с упругим элементом для вибровозбудителя направленных колебаний. Результаты исследований внедрены и прошли апробацию при расчете и выборе параметров грохота ГСЛ-42 СЭ.
The dissertation is about the development of methods for choice the parameters of a vibrator and a synchronizer with an elastic element. Vibrating machines use this vibrator and synchronizer for receiving directed fluctuations on a movable operating element. New method enables to design the vibrator for the vibrating equipment. If design was bad, then that method enables to design the synchronizer with an elasticity element.
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Baeza, Román Anna. "Tratamiento médico e intervencionista de los pacientes diabéticos con síndrome coronario agudo." Doctoral thesis, Universitat Jaume I, 2017. http://hdl.handle.net/10803/400870.
Full textAbstract:
La cardiopatía isquémica supone la principal causa de muerte en los países desarrollados, con una alta tasa de morbilidad, gran demanda asistencial y consumo de recursos. La diabetes mellitus tiene una alta prevalencia entre los pacientes con SCA. Esta Tesis estudia diferentes aspectos que pueden estar implicados en esta peor evolución.
En primer lugar, analiza las características de los pacientes diabéticos manejados de forma conservadora e identifica determinantes del uso de una estrategia invasiva frente al manejo conservador. En segundo lugar, mide la accesibilidad al sistema sanitario de los pacientes diabéticos, y estudia la repercusión sobre la mortalidad de estas diferencias de accesibilidad detectadas. Por último, estudia la validez del score de riesgo isquémico GRACE en la población española actual con síndrome coronario agudo y en el subgrupo de pacientes diabéticos, y valora si la inclusión de la variable DM en el modelo puede mejorar el poder pronóstico del mismo.Ischemic heart disease is the leading cause of death in developed countries, with a high rate of morbidity, high healthcare demand and resource consumption. Diabetes mellitus has a high prevalence among patients with ACS. This thesis studies different aspects that may be involved in this worse evolution. First, it analyzes the characteristics of conservatively managed diabetic patients and identifies determinants of the use of an invasive strategy versus conservative management. Secondly, it measures accessibility to the health system of diabetic patients, and studies the impact on mortality of these differences in accessibility. Finally, it studies the validity of the ischemic risk score GRACE in the current Spanish population and in the subgroup of diabetic patients, and assesses whether the inclusion of the DM variable in the model can improve its prognostic power.
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Chiang, Jia-Juen, and 江家諄. "Optimization of Multi-Effect Evaporation Desalination System for Low Grade Sensible Heat." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/s2aegs.
Full textAbstract:
碩士國立臺灣大學
化學工程學研究所
106
In recent years, water stress becomes more severe in southern Taiwan due to climate change and reservoir siltation. Desalination technology can mit- igate this upcoming issue and supply fresh water persistently. Multi-Effect Evaporation (MEE) system is one of thermal desalination technologies which has features of high efficiency in power consumption. A mathematical model ofMEEsystemisdevelopedtoeffectivelyutilizethesensiblelowgradewaste heat. The model is based on mass and energy balances and it is highly non- linear. Besides conventional configuration, an advanced process, namely the Boosted MEE (BMEE) is also investigated on the basis of waste heat perfor- mance ratio. Waste heat performance ratio is defined as the ratio of the en- thalpy of the distillate to the maximum exploitable energy of the heat source. For MEE system, the leaving temperature of waste heat is quite high and waste heat can not be efficiently exploited. To improve the operating effi- ciency, BMEE system is studied and the results show that the BMEE system is superior to the conventional MEE system in both waste heat performance ratio (up to 8%) and heat transfer area (up to 14%). The BMEE system has shown the capability to fully utilize the sensible waste heat at specified low waste heat outlet temperature. Moreover, the outlet temperature of waste heat is the key to choose either MEE system or BMEE system in terms of fresh- water production. While the specified waste heat outlet temperature is higher than the lowest possible temperature of the MEE system, it becomes more appropriate to use the MEE system rather than the BMEE system.
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Tobias, Benjamin C. "Biaxial fatigue behavior of commercially pure titanium Ti-50A (Grade 2) and low-alloy titanium Ti-Code 12 (Grade 12) heat exchanger materials." Thesis, 1985. http://hdl.handle.net/1957/32368.
Full textAbstract:
Material failures in heat exchangers are often
closely tied to events associated with the conditions
of service and operating parameters. These events can
generally be attributed to adverse load application and
higher than optimum operating temperatures that could
lead to changes in the microstructure of the materials
and fatigue failure of the component. However, fatigue
failure in heat exchangers is usually associated with
the presence of a biaxial stress condition. Two nonparallel
forces create a two-dimensional stress field
at the free surface of the structural element where
the process and mechanism of fatigue failure normally
initiate.
An experimental investigation was conduct6d to
evaluate the biaxial fatigue behavior of commercially
pure titanium Ti-50A (Grade 2) and low-alloy titanium
Ti-Code 12 (Grade 12) heat exchanger materials. The
biaxial state of stress was composed of an axial stress
and a superimposed torsional stress, applied in a thin-wall
tubular specimen machined from titanium tubing.
Torsional stress was applied independently using a torsion
machine and a torque fixer assembly devised as part of
this study. After applying the desired torsion, the
torsionally stressed specimen was mounted on a closed-loop
electrohydraulic machine for the application of
axial cyclic loading. A minimum of four tests were
conducted for each of three alternating stress levels at
both high and low torsional stresses. The biaxial
fatigue test under load control condition was done under
fully reversed cycles equivalent to a biaxiality ratio
of -1. These test parameters were determined from an
analytical formulation based on Mohr's circle.
The results are presented in terms of the various
measured or calculated quantities versus number of cycles
to fracture. Biaxial fatigue curves were drawn through the
experimental points corresponding to Weibull's mean life
criterion. The four data points exhibit scatter that
appears to be related to the applied stress amplitude. It
was also found that a correlation exists between the magnitude
of applied cyclic biaxial stress and fatigue life to
failure. In addition, the results have been discussed
taking existing failure criteria into account.Graduation date: 1985
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(7518488), Michael D. Ozeh. "Design And Fabrication Of A Hybrid Nanoparticle-Wick Heat Sink Structure For Thermoelectric Generators In Low-Grade Heat Utilization.pdf." Thesis, 2019.
Find full textAbstract:
Waste heat recovery is a multi-billion-dollar industry with a compound annual growth rate of 8.8% assessed between 2016 to 2024 and low-grade waste heat (< 230oC ± 20oC) makes up 66% of this ubiquitous resource. Thermoelectric generators are preferred for the recovery process because they are cheap and are well suited for this temperature range. They generate power by converting thermal potential to electric potential, known as the Seebeck effect. Since they have no moving parts, they are inherently immune to mechanical failure or an intermittent need for maintenance. However, the challenge has been to effectively harvest waste heat with these modules to generate power, using passive processes. This work is focused on designing a device for optimized harvesting of waste energy from the ambient with a custom, evaporatively-cooled heat sink. This heat sink is designed to passively handle the cooling of the other side of the thermoelectric module so as to enable the attainment of a minimum of 5V, which is the minimum voltage required to power small mobile devices. The heat sink model is similar to a loop heat pipe but engineered for compactness. To ensure this level of efficacy is attained, several studies are made to optimize the wick. Non-metal wicks were considered as they do not contribute to an increase in temperature of the compensation chamber in loop heat pipes. A non-metal wick integrated with nanoparticles is tested and results show a clear thermal management enhancement over similar but virgin non-metal wicks, at over 16%. The heat source section of the device is optimized for energy-harvesting in low grade temperature regimes by incorporating a near-black body coating on the metal heat source section. Experimental results show that both the heat source and sink sections were able to induce sufficient thermal potential for the thermoelectric modules to passively generate up to 5V using eight 40mm by 40mm Bismuth Telluride modules in 3.5 minutes. The prototype is relatively cheap, inherently reliable and presents the possibility of passively harvesting low-grade waste heat for later use, including powering small electronic devices.
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林志宏. "The optimal design of Low-grade waste heat trasferring power using organic rankine cycle." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/29669149775765481387.
Full text
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MORADI, RAMIN. "Object-oriented modeling of micro-ORC systems for low-grade waste heat recovery applications." Doctoral thesis, 2021. http://hdl.handle.net/11573/1549644.
Full textAbstract:
Organic Rankine Cycle (ORC) systems are one of the most suitable technologies to produce electricity from low-temperature sources. A comprehensive understanding of these systems is necessary for their further deployment especially in micro scales, in which the intrinsic issues such as low isentropic efficiency and unreliability arise more severely.
In this thesis, the components of a non-regenerative, micro-scale ORC unit are modeled empirically using the experimental data. The components models are used as functions in the system-level solver. The system solver uses a novel approach, in which no assumption is made for the modeling and only the components specifications and the real system boundaries that an operator has during the system run are put as inputs. This assumption-free, object-oriented model follows the two fundamental conservation laws of thermodynamics that are the conservation of energy and the conservation of mass. The developed mass-sensitive model is a robust solver that leads to a full understanding of the system limitations and losses using the empirical models of the main system components.
In addition to the system modeling, the thesis theoretically studies the impact of the expander lubricant oil on the system performance using the empirical lubricant-refrigerant miscibility model and a data reconciliation method. The impact of the expander’s lubricant is found significantly effective on the performances of the heat exchangers, the expander, and the overall system especially in micro-scales, despite its influence has been mostly neglected in the literature so far.
Since the use of micro-scale ORC systems for low-temperature waste heat recovery (WHR) applications is investigated, a novel kind of expander for such systems has been here analyzed using computational fluid dynamics (CFD). The regenerative flow turbine (RFT) is found particularly interesting due to its good and reliable performance in very low-pressure ratios making the machine suitable as an alternative expansion.
Finally, a biomass-fed integrated system is studied in detail. The integrated system consists of a dual-fluidized-bed gasifier, a hot gas conditioning unit, a steam-injected-micro gas turbine, and an ORC as the bottom cycle. This system-level study shows the performance of the integrated system when full conservation of energy and mass is applied. The results show that the overall system efficiency improvement by the ORC is limited to 1-2 % using the wet gas turbine compared to 5-8% without the steam injection. Nevertheless, the produced thermal power in the condenser of the ORC unit shows the ability of the integrated system to meet higher users’ thermal demands in small-scale CHP applications.
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Hsu, Sung Wei, and 徐菘蔚. "Performance Analyses and Experimental Studies on Screw-Expander ORCs for Low grade Heat to Power." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/01744559166134786366.
Full textAbstract:
博士國立清華大學
動力機械工程學系
103
To date, ORC is the most efficient and economical approach for the recovery of low-to-medium heat to power. In general, a volumetric-type screw-expander is selected as the ORC’s engine core for power capacity less than 300 kW due to its superior performance and competitive cost. This thesis theoretically and experimentally studies on the system characteristics and performance behaviors of screw-expander ORCs. Steady-state models of the ORC’s components are theoretically developed and experimentally validated. Then, the model of the ORC system is established to predict its performance. In view of practical and economical applications of an ORC, a trade-offs analysis between cycle efficiency and amount of power output is performed for system optimization under limited heat source for subcritical ORCs and trans-critical ORCs. Two sets of ORCs are designed and developed, and a series of performance tests are done to explore the characteristics of these two ORC systems. (1)20kW screw-expander ORC: using R134a as working fluid, converted the heat of 60~85°C hot water into power. (2) 50kW screw-expander ORC: using R245fa as working fluid, converted the heat of 90~105°C hot water into power. A theoretical expansion model of screw expander is developed and compared with experimental data. The achieved performance of these two ORCs are promising, with expander efficiency of 72.5% and cycle efficiencies higher than the typical efficiencies reported for the considered temperature range. The ORCs can be used to exploit the low temperature heat, as low as 60°C, with high performance which predict their wide application and potential energy saving.
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Chuang, I.-Yuan, and 莊翼遠. "Evaporation parametric optimization of sub- and supercritical organic Rankine cycle for low-grade waste heat recovery system." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/05514826373324513899.
Full textAbstract:
碩士國立中央大學
機械工程學系
105
As industry develops, there is an increasing demand on energy. The development of energy-saving devices and renewable energy have been emerging issues around the world. Organic Rankine cycle, ORC, is a technique to generate power from low temperature heat sources. ORC is used in recycling industrial waste heat, solar energy and geothermal power generation. Waste heat below 230°C is called low-grade waste heat. Low-grade waste heat cannot be efficiently reused in process, so it is usually exhausted into the environment. In this research, we perform thermodynamic analysis on low-grade waste heat recycling ORC systems. R134a,R1234yf, R227ea, R245fa, and Propane are used as working fluids and their max system thermal efficiency and net power output is calculated. We discuss the effect of different evaporation pressure and evaporation temperature to the system performance with different conditions of three heat source temperatures, 100°C, 150°C,and 200°C, and four pinch point temperature differences, 5°C,10°C,15°C, and20°C by iteration methods to find the optimum parameters. The result shows that R245fa has the highest net work output of 505.5kW and system thermal efficiency of 15% at heat source temperature of 200°C. In this research, we use brazed plate heat exchangers as example. We use the optimum conditions to calculate the total heat transfer area and evaluate the constructing costs of the heat exchanger. It is found that the higher heat source temperature, the lower cost it needs. When the propane is used as working fluid, the lowest cost can be achieved with heat source temperature at 150°C、200°C.
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PALOMBA, VALERIA. "Thermal energy storage systems for low-grade heat applications: Design and experimental testing of lab-scale prototypes." Doctoral thesis, 2017. http://hdl.handle.net/11570/3116364.
Full textAbstract:
The main objective of this thesis is the development of prototypes of thermal energy storages
suitable for coupling with low-grade waste heat (e.g. non-concentrating solar, industrial
process heat) and their experimental testing.
Benefits of thermal energy storages are several, but the experience in non-sensible heat
storage is still limited, especially in the design of prototypes. High temperature heat storage
(T >150°C) has been the subject of a quite extensive research, but low-grade heat sources are
still not fully exploited, due to the competition with water, that is available at a risible cost.
In the present thesis, two different technologies were investigated, latent heat and adsorption
heat, by design and experimental testing of lab-scale storages. In particular, data from
experimental testing on Phase Change Materials carried out at CNR-ITAE were used for the
development of thermal energy storages using latent heat technology (with phase change
materials). Since only limited data on PCM-based devices in the investigated temperature
range were available, two approaches were followed: a custom fin-and-tube heat exchanger
and a commercial plate heat exchanger were tested with the same PCM (a paraffin) and the
results used for a design analysis. In order to complete the analysis, a simplified numerical
model was developed through the commercial software COMSOL Multiphysics and validated
against experimental results. The model was able to describe the behaviour of the
fin-and-tube system with low computational effort, showing good possibility for a future
design optimization and easy adaptability to different configurations.
Measurement on adsorption equilibrium curves available for adsorbent materials, instead,
were used as the input for the development of a thermal energy storage making use of
adsorption technology. While the storage was designed to use the same heat sources as the
latent thermal ones, different operating conditions on the user-side were considered, taking
into account both cold or hot storage possibilities.
The experimental measurements on both the technologies highlighted the good potential
of the investigated systems and therefore that further research in the specific temperature range
analysed is feasible and will allow overcoming the limitations that still exist. However, the
intense research activity that is on-going in the field of thermal energy storage cannot preclude
from a standardization, both in the definition of relevant indicators and the assessment of the systems. To this aim, an attempt has been made at comparing the developed storages (2
latent heat storages and 1 adsorption storage), by defining common performance indicators
and evaluating whether they can be applied to such different cases, in terms of characteristics,
sizes and application.
Results obtained have shown that both technologies allow reaching a higher energy
storage density than water, under all the examined conditions (i.e. charging temperature of
75°C to 90°C), with values up to 900 kJ/kg in the case of the adsorption heat storage. The
operating parameters affecting storage operation were analysed as well: indeed, it was found
that the performance of the storages is strongly dependent not only on the heat sources and
external ambient conditions, but also on the control of the system (i.e. the flow rate imposed,
the part load operation) and the construction features, such as the material used for the shells
or the insulation.
Finally, the methodology suggested for the evaluation of the storage could be successfully
applied to all the systems, allowing a qualitative and quantitative comparison.
The main outcomes of the work here reported can then lead the path towards the optimization
of the heat storage systems, from lab-scale to pre-commercial ones, thus increasing
the technology readiness level and making a step forward towards practical application.
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Shai, Tzer-Yuan, and 薛澤源. "Theoretical Analysis and Preliminary Test Results of the Experimental Loop for an Organic Rankine Cycle in Recovering Low-Grade Waste Heat." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/39965865702365692456.
Full text