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1
Garcia, Ramon. "Contributions on Closed System Transformations Based Thermal Cycles". British Journal of Applied Science & Technology 4, nr 19 (10.01.2014): 2821–36. http://dx.doi.org/10.9734/bjast/2014/10074.
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Ferreiro Garcia, Ramon, i Dr Jose Carbia Carril. "Analysis of a thermal cycle that surpass Carnot efficiency undergoing closed polytropic transformations". JOURNAL OF ADVANCES IN PHYSICS 15 (19.02.2019): 6165–82. http://dx.doi.org/10.24297/jap.v15i0.8029.
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This research work deals with a feasible non-regenerative thermal cycle, composed by two pairs of closed polytropic-isochoric transformations implemented by means of a double acting reciprocating cylinder which differs basically from the conventional Carnot based thermal cycles in that:
-it consists of a non condensing mode thermal cycle
-all cycle involves only closed transformations, instead of the conventional open processes of the Carnot based thermal cycles,
-in the active processes (polytropic path functions), as heat is being absorbed, mechanical work is simultaneously performed, avoiding the conventional quasi-adiabatic expansion or compression processes inherent to the Carnot based cycles and,
-during the closed polytropic processes, mechanical work is also performed by means of the working fluid contraction due to heat releasing.
An analysis of the proposed cycle is carried out for helium as working fluid and results are compared with those of a Carnot engine operating under the same ratio of temperatures. As a result of the cycle analysis, it follows that the ratio of top to the bottom cycle temperatures has very low dependence on the ideal thermal efficiency, but the specific work, and, furthermore, within the range of relative low operating temperatures, high thermal efficiency is achieved, surpassing the Carnot factor.
3
Dumitrașcu, Gheorghe, Michel Feidt i Ştefan Grigorean. "Finite Physical Dimensions Thermodynamics Analysis and Design of Closed Irreversible Cycles". Energies 14, nr 12 (9.06.2021): 3416. http://dx.doi.org/10.3390/en14123416.
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This paper develops simplifying entropic models of irreversible closed cycles. The entropic models involve the irreversible connections between external and internal main operational parameters with finite physical dimensions. The external parameters are the mean temperatures of external heat reservoirs, the heat transfers thermal conductance, and the heat transfer mean log temperatures differences. The internal involved parameters are the reference entropy of the cycle and the internal irreversibility number. The cycle’s design might use four possible operational constraints in order to find out the reference entropy. The internal irreversibility number allows the evaluation of the reversible heat output function of the reversible heat input. Thus the cycle entropy balance equation to design the trigeneration cycles only through external operational parameters might be involved. In designing trigeneration systems, they must know the requirements of all consumers of the useful energies delivered by the trigeneration system. The conclusions emphasize the complexity in designing and/or optimizing the irreversible trigeneration systems.
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Rogalev, Nikolay, Andrey Rogalev, Vladimir Kindra, Olga Zlyvko i Pavel Bryzgunov. "Review of Closed SCO2 and Semi-Closed Oxy–Fuel Combustion Power Cycles for Multi-Scale Power Generation in Terms of Energy, Ecology and Economic Efficiency". Energies 15, nr 23 (5.12.2022): 9226. http://dx.doi.org/10.3390/en15239226.
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Today, with the increases in organic fuel prices and growing legislative restrictions aimed at increasing environmental safety and reducing our carbon footprint, the task of increasing thermal power plant efficiency is becoming more and more topical. Transforming combusting fuel thermal energy into electric power more efficiently will allow the reduction of the fuel cost fraction in the cost structure and decrease harmful emissions, especially greenhouse gases, as less fuel will be consumed. There are traditional ways of improving thermal power plant energy efficiency: increasing turbine inlet temperature and utilizing exhaust heat. An alternative way to improve energy efficiency is the use of supercritical CO2 power cycles, which have a number of advantages over traditional ones due to carbon dioxide’s thermophysical properties. In particular, the use of carbon dioxide allows increasing efficiency by reducing compression and friction losses in the wheel spaces of the turbines; in addition, it is known that CO2 turbomachinery has smaller dimensions compared to traditional steam and gas turbines of similar capacity. Furthermore, semi-closed oxy–fuel combustion power cycles can reduce greenhouse gases emissions by many times; at the same time, they have characteristics of efficiency and specific capital costs comparable with traditional cycles. Given the high volatility of fuel prices, as well as the rising prices of carbon dioxide emission allowances, changes in efficiency, capital costs and specific greenhouse gas emissions can lead to a change in the cost of electricity generation. In this paper, key closed and semi-closed supercritical CO2 combustion power cycles and their promising modifications are considered from the point of view of energy, economic and environmental efficiency; the cycles that are optimal in terms of technical and economic characteristics are identified among those considered.
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Dumitrascu, Gheorghe, Michel Feidt i Stefan Grigorean. "Closed Irreversible Cycles Analysis Based on Finite Physical Dimensions Thermodynamics". Proceedings 58, nr 1 (11.09.2020): 37. http://dx.doi.org/10.3390/wef-06905.
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The paper develops generalizing entropic approaches of irreversible closed cycles. The mathematical models of the irreversible engines (basic, with internal regeneration of the heat, cogeneration units) and of the refrigeration cycles were applied to four possible operating irreversible trigeneration cycles. The models involve the reference entropy, the number of internal irreversibility, the thermal conductance inventory, the proper temperatures of external heat reservoirs unifying the first law of thermodynamics and the linear heat transfer law, the mean log temperature differences, and four possible operational constraints, i.e., constant heat input, constant power, constant energy efficiency and constant reference entropy. The reference entropy is always the entropy variation rate of the working fluid during the reversible heat input process. The amount of internal irreversibility allows the evaluation of the heat output via the ratio of overall internal irreversible entropy generation and the reference entropy. The operational constraints allow the replacement of the reference entropy function of the finite physical dimension parameters, i.e., mean log temperature differences, thermal conductance inventory, and the proper external heat reservoir temperatures. The paper presents initially the number of internal irreversibility and the energy efficiency equations for engine and refrigeration cycles. At the limit, i.e., endoreversibility, we can re-obtain the endoreversible energy efficiency equation. The second part develops the influences between the imposed operational constraint and the finite physical dimensions parameters for the basic irreversible cycle. The third part is applying the mathematical models to four possible standalone trigeneration cycles. It was assumed that there are the required consumers of the all useful heat delivered by the trigeneration system. The design of trigeneration system must know the ratio of refrigeration rate to power, e.g., engine shaft power or useful power delivered directly to power consumers. The final discussions and conclusions emphasize the novelties and the complexity of interconnected irreversible trigeneration systems design/optimization.
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Shen, Qiang, Chang Lian Chen, Fei Chen, Qi Wen Liu i Lian Meng Zhang. "Thermal Shock Behavior of Calcia Stabilized Zirconia Ceramics with Porosity Gradient Structure". Materials Science Forum 631-632 (październik 2009): 435–40. http://dx.doi.org/10.4028/www.scientific.net/msf.631-632.435.
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Porous calcia stabilized zirconia ceramics (CSZC) with closed pores were presurelessly sintered by adding different contents of zirconia hollow balls. CSZC FGM with porosity gradient structure was then fabricated by laminating five layers with designed contents of zirconia hollow balls. The porosity, microstructure, and bending strength of the obtained CSZC samples were characterized. The results show that the hollow balls distribute uniformly and are well bonded with the matrix, and the porous structure is mainly composed of closed pores. The porosity of the CSZC increases linearly from 5.7 % to 31.6 % when the content of zirconia hollow balls increases from 0 % to 30 %, and the bending strength decreases rapidly from 297 MPa to 30 MPa. The thermal shock behavior of the CSZC and FGM was evaluated using air-quenching technique. It is shown that the residual bending strength of the quenched samples increases after several quenching cycles, and the samples are damaged by thermal shock after eight thermal cycles because of the production of monoclinic zirconia. FGM samples with porosity gradient structure can endure above twelve thermal shock cycles and exhibits better thermal shock resistance.
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Burugupally, Sindhu Preetham. "Evaluation of a Combustion-Based Mesoscale Thermal Actuator in Open and Closed Operating Cycles". Actuators 8, nr 4 (23.10.2019): 73. http://dx.doi.org/10.3390/act8040073.
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A combustion-based mesoscale thermal actuator is proposed and its performance is studied in both open and closed cycle operations using a physics-based lumped-parameter model. The actuator design is unique as it implements a free-piston complaint architecture where the piston is free to move in a linear direction. Our objective is to study the actuator behavior in both the cycles to help identify the benefits and highlight the differences between the two cycles. The actuator is modeled as a spring-mass-damper system by taking an air standard cycle approach. Three observations are reported: (1) for nominal heat inputs (140 J/cycle), the actuator can produce large displacement strokes (16 cm) that is suitable for driving mesoscale robots; (2) the efficiency of the actuator depends on the heat input; and (3) for a specific heat input, both the open and closed cycles operate differently—with different stroke lengths, peak pressures, and thermal efficiencies. Our study reveals that the performance metrics of the actuator make it an ideal candidate for high speed, large force, and large displacement stroke related applications.
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Itoh, Y. Z., i H. Kashiwaya. "A Study of Cyclic Thermal Straining in a Welded Joint, Using a Closed-Loop, Servo-Controlled Testing Machine". Journal of Pressure Vessel Technology 114, nr 4 (1.11.1992): 422–27. http://dx.doi.org/10.1115/1.2929249.
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For investigating the origin of residual stresses in welded joints, the transient thermal stresses in a carbon-manganese-silicon steel (JIS SM41B), a cast martensitic stainless steel (JIS SCS5), an austenitic stainless steel (JIS SUS304), and a titanium alloy (Ti-6Al-4V) were investigated by subjecting round bar specimens, in which both ends were fixed, to thermal of cycles. The specimens were heated in air by high-frequency induction. The cyclic thermal straining tests were conducted for the case of a single thermal cycle and the case of multiple thermal cycles, using a closed loop, servo-controlled testing machine. The experimental results made clear that the transient thermal stress behavior was dependent on metallurgical effects, such as phase transformations, strain hardening, the Bauschinger effect, etc. The effects on phase transformation on the transient thermal stress behavior of SCS5 and SM41B were especially remarkable. However, the effects of phase transformations on the residual stresses due to the thermal straining cycle were negligible in SM41B and not observed in both SUS304 and Ti-6Al-4V. The residual stresses tended to increase with increase of the peak temperature of thermal cycles in SM41B, SUS304 and Ti-6Al-4V. However, when the peak temperature increased above 600°C in SCS5, the residual stress rapidly decreased and became compressive because of the expansion due to the martensite transformation. This study led to the conclusion that the transient thermal stresses for various peak temperatures could easily be obtained by an incremental step test using a single specimen and that this incremental step test could simply estimate the residual stress character of butt-welded joints.
9
Amann, Charles A. "Applying Thermodynamics in Search of Superior Engine Efficiency". Journal of Engineering for Gas Turbines and Power 127, nr 3 (24.06.2005): 670–75. http://dx.doi.org/10.1115/1.1804537.
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Historically, a succession of thermodynamic processes has been used to idealize the operating cycles of internal combustion engines. In this study, the 256 possible combinations of four reversible processes—isentropic, isothermal, isochoric, and isobaric—are surveyed in search of cycles promising superior thermal efficiency. Regenerative cycles are excluded. The established concept of the air-standard cycle, which mimics the internal combustion engine as a closed-cycle heat engine, is used to narrow the field systematically. The approach relies primarily on graphical interpretation of approximate temperature-entropy diagrams and is qualitative only. In addition to identifying the cycles offering the greatest efficiency potential, the compromise between thermal efficiency and mean effective pressure is addressed.
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Khaliq, A. "Finite-Thermal Reservoir Effects on Ecologically Optimized Closed Regenerative Joule-Brayton Power Cycles". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 220, nr 5 (11.07.2006): 425–34. http://dx.doi.org/10.1243/09576509jpe189.
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Leung, E. Y. W. "A Universal Correlation for the Thermal Efficiency of Open Gas Turbine Cycle With Different Fuels". Journal of Engineering for Gas Turbines and Power 107, nr 3 (1.07.1985): 560–65. http://dx.doi.org/10.1115/1.3239772.
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It is well known that, unlike the thermal efficiency of closed gas turbine cycles, the thermal efficiency of open gas turbine cycles varies with the fuel used in the combustion process. Presented in this paper is a thorough investigation of the effects of hydrocarbon fuels and alcohol fuels on the thermal efficiency of open gas turbine cycle. Among the open cycles with different fuels and otherwise identical specifications, the computed thermal efficiencies show a variation of about 2 percent between the extremes, which is appreciable. It was found that the thermal efficiency increases with a parameter of the fuel, c1 + c2, taken from the equation of reaction, c(Fuel)+O2→c1(CO2)+c2(H2O), and that the thermal efficiency of open gas turbine cycles is likely to be higher if the original fuel is replaced by a fuel which has a higher fuel parameter, c1 + c2. A universal correlation for both hydrocarbon fuels and alcohol fuels is presented in Fig. 1, plotting the thermal efficiency maximized from the pressure ratio variation, versus the parameter, c1 + c2. Alternatively, this correlation is also generalized by equation (2).
12
Tacconi, J., W. P. J. Visser i D. Verstraete. "Multi-objective optimisation of semi-closed cycle engines for high-altitude UAV propulsion". Aeronautical Journal 123, nr 1270 (7.08.2019): 1938–58. http://dx.doi.org/10.1017/aer.2019.62.
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ABSTRACTThe maximum attainable performance of small gas turbines represents a strong limitation to the operating altitude and endurance of high-altitude unmanned aerial vehicles (UAVs). Significant improvement of the cycle thermal efficiency can be achieved through the introduction of heat exchangers, with the consequent increase of the overall engine weight. Since semi-closed cycle engines can achieve a superior degree of compactness compared to their open cycle counterparts, their use can offset the additional weight of the heat exchangers. This paper applies semi-closed cycles to a high-altitude UAV propulsion system, with the objective of assessing the benefits introduced on the engine performance and weight. A detailed model has been created to account for component performance and size variation as function of thermodynamic parameters. The sizing has been coupled with a multi-objective optimisation algorithm for minimum specific fuel consumption and weight. Results of two different semi-closed cycle configurations are compared with equivalent state-of-the-art open cycles, represented by a recuperated and an intercooled-recuperated engine. The results show that, for a fixed design power output, engine weight is approximately halved compared to state-of-the-art open cycles, with slightly improved specific fuel consumption performance. Optimum semi-closed cycles furthermore operate at higher overall pressure ratios than open cycles and make use of recuperators with higher effectiveness as the mass penalty of the recuperator is smaller due to the lower engine mass flow rates.
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Liu, Weimin, Xiaojian Xu, Fengyun Chen, Yanjun Liu, Shizhen Li, Lei Liu i Yun Chen. "A review of research on the closed thermodynamic cycles of ocean thermal energy conversion". Renewable and Sustainable Energy Reviews 119 (marzec 2020): 109581. http://dx.doi.org/10.1016/j.rser.2019.109581.
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Carril, José Carbia, Álvaro Baaliña Insua, Javier Romero Gómez i Manuel Romero Gómez. "HTR-Based Power Plants’ Performance Analysis Applied on Conventional Combined Cycles". Science and Technology of Nuclear Installations 2015 (2015): 1–11. http://dx.doi.org/10.1155/2015/716572.
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In high temperature reactors including gas cooled fast reactors and gas turbine modular helium reactors (GT-MHR) specifically designed to operate as power plant heat sources, efficiency enhancement at effective cost under safe conditions can be achieved. Mentioned improvements concern the implementation of two cycle structures: (a), a stand alone Brayton operating with helium and a stand alone Rankine cycle (RC) with regeneration, operating with carbon dioxide at ultrasupercritical pressure as working fluid (WF), where condensation is carried out at quasicritical conditions, and (b), a combined cycle (CC), in which the topping closed Brayton cycle (CBC) operates with helium as WF, while the bottoming RC is operated with one of the following WFs: carbon dioxide, xenon, ethane, ammonia, or water. In both cases, an intermediate heat exchanger (IHE) is proposed to provide thermal energy to the closed Brayton or to the Rankine cycles. The results of the case study show that the thermal efficiency, through the use of a CC, is slightly improved (from 45.79% for BC and from 50.17% for RC to 53.63 for the proposed CC with He-H2O operating under safety standards).
15
Newaz, G. M., B. S. Majumdar i F. W. Brust. "Thermal Cycling Response of Quasi-Isotropic Metal Matrix Composites". Journal of Engineering Materials and Technology 114, nr 2 (1.04.1992): 156–61. http://dx.doi.org/10.1115/1.2904155.
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In this study, thermal cycling response of quasi-isotropic metal-matrix composite (MMC) with a stacking sequence of [0/ ± 45/90]s was investigated. The thermal cycles were imposed between temperatures of 316–649° C. Metallography of the samples at the edge has shown the presence of fiber-matrix debonding and ply-to-ply separation (delamination) in the 45 and 90 deg plies. The propensity for debonding was found to be greater when fibers are too close in any of these plies. Both closed form elastic analysis and linear finite element analysis using temperature dependent material properties were undertaken to evaluate the criticality of local stresses and strains in the constituent materials. Inelastic deformation around fiber-matrix interface leading to cracking in the 90 deg ply was best simulated by higher local variation in fiber volume fraction in the composite and the presence of initial process induced defect.
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Florez, Frank, Pedro Fernández de Córdoba, José Luis Higón, Gerard Olivar i John Taborda. "Modeling, Simulation, and Temperature Control of a Thermal Zone with Sliding Modes Strategy". Mathematics 7, nr 6 (2.06.2019): 503. http://dx.doi.org/10.3390/math7060503.
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To reduce the energy consumption in buildings is necessary to analyze individual rooms and thermal zones, studying mathematical models and applying new control techniques. In this paper, the design, simulation and experimental evaluation of a sliding mode controller for regulating internal temperature in a thermal zone is presented. We propose an experiment with small physical dimensions, consisting of a closed wooden box with heat internal sources to stimulate temperature gradients through operating and shut down cycles.
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Bontempo, R., i M. Manna. "Efficiency optimisation of advanced gas turbine recuperative-cycles". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 234, nr 6 (1.10.2019): 817–35. http://dx.doi.org/10.1177/0957650919875909.
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The paper presents a theoretical analysis of three advanced gas turbine recuperative-cycles, that is, the intercooled, the reheat and the intercooled and reheat cycles. The internal irreversibilities, which characterise the compression and expansion processes, are taken into account through the polytropic efficiencies of the compressors and turbines. As customary in simplified analytical approaches, the study is carried out for an uncooled closed-circuit gas turbine without pressure losses in the heat exchangers and using a calorically perfect gas as working fluid. Although the accurate performance prediction of a real-gas turbine is prevented by these simplifying assumptions, this analysis provides a fast and simple approach which can be used to theoretically explain the main features of the three advanced cycles and to compare them highlighting pros and contra. The effect of the heat recuperation is investigated comparing the thermal efficiency of a given cycle type with those of two reference cycles, namely, the non-recuperative version of the analysed cycle and the simple cycle. As a result, the ranges of the intermediate pressure ratios returning a benefit in the thermal efficiency in comparison with the two reference cycles have been obtained for the first time. Finally, for the sole intercooled and reheat recuperative-cycle, a novel analytical expression for the intermediate pressure ratios yielding the maximum thermal efficiency is also given.
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Оvchinnikova, M. V., A. G. Mikhailova, D. M. Karlinsky, V. А. Gorlenko i L. D. Rumsh. "Reversible Cyclic Thermal Inactivation of Oligopeptidase B from Serratia proteamaculans". Acta Naturae 10, nr 2 (15.06.2018): 65–70. http://dx.doi.org/10.32607/20758251-2018-10-2-65-70.
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A unique property was found for oligopeptidase B from Serratia proteamaculans (PSP) as well as its mutants: they can undergo reversible thermal inactivation at 37C, with activity being restored or even increased with respect to the initial one upon subsequent cooling. The process can be repeated several times, with the same results achieved (up to 5 cycles). This effect can be explained by a shift in the equilibrium between the inactive open form of the enzyme and the active closed one upon variation of the incubation temperature.
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Agazzani, A., A. F. Massardo i T. Korakianitis. "An Assessment of the Performance of Closed Cycles With and Without Heat Rejection at Cryogenic Temperatures". Journal of Engineering for Gas Turbines and Power 121, nr 3 (1.07.1999): 458–65. http://dx.doi.org/10.1115/1.2818495.
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This paper presents optimized cycle performance that can be obtained with systems including a closed cycle gas turbine (CCGT). The influence of maximum temperature, minimum temperature, and recuperator effectiveness on cycle performance is illustrated, Several power-plant arrangements are analyzed and compared based on thermodynamic performance (thermal efficiency and specific work); enabling technologies (available at present); and developing technologies (available in the near term or future). The work includes the effects of utilization of high temperature ceramic heat exchangers and of coupling of CCGT systems with plants vaporizing liquid hydrogen (LH2) or liquefied natural gas (LNG). Given the versatility of energy addition and rejection sources that can be utilized in closed gas-cycle systems, the thermodynamic performance of power plants shown in this paper indicate the remarkable capabilities and possibilities for closed gas-cycle systems.
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Hofer, Markus, Frieder Hecker, Michael Buck i Jörg Starflinger. "Start-up, operation and thermal-hydraulic analysis of a self-propelling supercritical CO2 heat removal system coupled to a pressurized water reactor". EPJ Nuclear Sciences & Technologies 8 (2022): 34. http://dx.doi.org/10.1051/epjn/2022039.
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The supercritical carbon dioxide (sCO2) heat removal system, which is based on a closed Brayton cycle with sCO2 as a working fluid, is an innovative, self-propelling and modular heat removal system for existing and future nuclear power plants. By changing the number of CO2 cycles, the heat removal capacity can be adapted. In this paper, up to four sCO2 cycles are analyzed in interaction with a pressurized water reactor, using the thermal-hydraulic system code ATHLET and considering a long-term station blackout and loss of ultimate heat sink scenario with conservatively high and low decay heat curves. The presented start-up procedure for the heat removal system might require further optimization due to the non-linear thermal gradients. Independent from the start-up, a heat removal system with three or four CO2 cycles keeps the primary loop temperatures sufficiently low. However, with only three cycles, the core is almost uncovered, and the danger of recriticality may occur due to cold leg deboration. Controlling the turbine inlet temperature via the turbomachinery speed and subsequent shutdown of single cycles successfully adapts the operation of the heat removal system to the declining decay heat. This enables reliable decay heat removal for more than 72 h.
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Invernizzi, Costante Mario, i Gioele Di Marcoberardino. "An Overview of Real Gas Brayton Power Cycles: Working Fluids Selection and Thermodynamic Implications". Energies 16, nr 10 (9.05.2023): 3989. http://dx.doi.org/10.3390/en16103989.
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This paper discusses and reviews the main real gas effects on the thermodynamic performance of closed Brayton cycles. Cycles with carbon dioxide as working fluids are taken as a reference and a comparison of the thermodynamic cycle efficiencies that are made with other possible working fluids (pure fluids and fluid mixtures). We fixed the reduced operating conditions, in optimal conditions, so that all working fluids had the same thermodynamic global performances. Therefore, the choice of the working fluid becomes important for adapting the cycle to the different technological requirements. The positive effects of the real gas properties in supercritical cycles were approximately maximal at reduced minimum cycle temperatures of about 1.01 to 1.05, with maximum to minimum cycle temperatures of about 2.2. The use of mixtures furthers widens the application of the field of closed Brayton cycles, thereby allowing a continuous variation in the critical temperature of the resulting working fluid and, in some cases, also making it possible to take the condensation with a significant further increase in the thermodynamic cycle efficiency. The paper also demonstrates the thermodynamic convenience of resorting to mixtures of carbon dioxide and inert gases. Extensive measurements of vapour–liquid equilibria and analysis of the thermal stability and material compatibility are essential for a practical and full use of the real gas Brayton cycles.
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KIM, YOUNG MIN, DONG GIL SHIN, SANG TAE LEE i DANIEL FAVRAT. "THERMODYNAMIC ANALYSIS OF A CLOSED BRAYTON/ERICSSON CYCLE ENGINE WITH SCROLL MACHINES". International Journal of Air-Conditioning and Refrigeration 18, nr 04 (grudzień 2010): 279–87. http://dx.doi.org/10.1142/s2010132510000277.
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Stirling and Ericsson engines have great potential for many applications, including micro-cogeneration, solar power, and biomass. However, ideal cycles of both types of engines are difficult to achieve in practice because neither isothermal compression nor isothermal expansion is practical with reciprocating piston engines or with turbomachinery. On the other hand, scroll compressor and expander can be very suitable for effective cooling and heating because of the high area-to-volume ratio of scroll geometry or the application of two-phase flow. To achieve quasi-isothermal compression, either a large amount of liquid is injected into the inlet of the compressor or the compressor is externally cooled by liquid. Similarly, for quasi-isothermal expansion, either hot liquid, such as thermal oil, is injected into the inlet of the expander or the expander is externally heated by a heat source. In this current study, we have undertaken a theoretical investigation of thermodynamic analyses of several kinds of scroll-type engines, in particular with regard to associated compression and expansion processes, adiabatic or quasi-isothermal processes, and the highest cycle temperature. We selected power density, or thermal efficiency, as an objective function, and then deduced optimal design parameters for the scroll-type engine.
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Kubíková, Tereza. "ORC and sCO2 cycle for high temperature WHR applications". MATEC Web of Conferences 367 (2022): 00016. http://dx.doi.org/10.1051/matecconf/202236700016.
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This article suggests a suitable closed thermodynamic cycle for waste heat from a cement plant by using alternative working fluids. A pair of closed working cycles is compared: supercritical CO2 cycle (sCO2) and the Organic Rankine Cycle (ORC). In the case of ORC, it was necessary to choose a suitable working fluid. The goal is to minimize the ODP (Ozone Depletion Potential) and GWP (Global Warming Potential), to maximize the thermal efficiency and to optimize the minimum working temperature difference (pinch points, approach points), the temperature profiles of the heat exchangers and their working pressure and temperature, which affects the cost. Both cycles (ORC and sCO2) including a detailed component analysis are calculated using Python in Spyder IDE, which includes all the libraries for this task. According to the results of the calculations, the ORC cycle was chosen for further calculations of the components (condenser and turbine). The most suitable working fluids with high efficiency are hexamethyldisiloxane (MM), ethylbenzene and toluene, from which toluene was selected.
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Ibrahim, O. M., S. A. Klein i J. W. Mitchell. "Optimum Heat Power Cycles for Specified Boundary Conditions". Journal of Engineering for Gas Turbines and Power 113, nr 4 (1.10.1991): 514–21. http://dx.doi.org/10.1115/1.2906271.
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Optimization of the power output of Carnot and closed Brayton cycles is considered for both finite and infinite thermal capacitance rates of the external fluid streams. The method of Lagrange multipliers is used to solve for working fluid temperatures that yield maximum power. Analytical expressions for the maximum power and the cycle efficiency at maximum power are obtained. A comparison of the maximum power from the two cycles for the same boundary conditions, i.e., the same heat source/sink inlet temperatures, thermal capacitance rates, and heat exchanger conductances, shows that the Brayton cycle can produce more power than the Carnot cycle. This comparison illustrates that cycles exist that can produce more power than the Carnot cycle. The optimum heat power cycle, which will provide the upper limit of power obtained from any thermodynamic cycle for specified boundary conditions and heat exchanger conductances is considered. The optimum heat power cycle is identified by optimizing the sum of the power output from a sequence of Carnot cycles. The shape of the optimum heat power cycle, the power output, and corresponding efficiency are presented. The efficiency at maximum power of all cycles investigated in this study is found to be equal to (or well approximated by) η=1−TL,in/φTH,in where φ is a factor relating the entropy changes during heat rejection and heat addition.
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Langston, Lee S. "Is there a Supercharged Gas Turbine in your Future?" Mechanical Engineering 137, nr 05 (1.05.2015): 58–59. http://dx.doi.org/10.1115/1.2015-may-5.
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This article discusses various features of supercharged gas turbine and supercharged analysis. One 400 MW supercharged gas turbine power plant variant analysed by Wettstein yielded a predicted thermal efficiency of 60 percent, rivaling current combined cycle values. The supercharged gas turbine power plant proposed by Wettstein is a semi-closed (SC) cycle. The SC cycle is an amalgamation of closed and open cycles. It consists of a gas turbine having an internal combustor for energy input to the cycle. With a SC cycle, a designer now has some of the best features of both open and closed to move SC power plant operation in different directions. With internal combustion, the SC cycle is not constrained by the temperature limitations of the closed cycle. The supercharged gas turbine power plant looks very promising. In another ASME paper, Wettstein shows how gas turbine supercharging could benefit marine propulsion.
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Di Ronco, Andrea, Francesca Giacobbo, Guglielmo Lomonaco, Stefano Lorenzi, Xiang Wang i Antonio Cammi. "Preliminary Analysis and Design of the Energy Conversion System for the Molten Salt Fast Reactor". Sustainability 12, nr 24 (15.12.2020): 10497. http://dx.doi.org/10.3390/su122410497.
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The unique design features of the molten salt fast reactor (MSFR) should enable higher coolant temperatures than in conventional water reactors, with a significant improvement in the achievable thermodynamic performance. The use of a molten salt as both fuel and coolant, however, poses several advanced heat transfer challenges, such as the design of innovative heat exchangers and energy conversion systems. In this work, we address a preliminary but quantitative analysis of the energy conversion system for the MSFR, based on reference design data from the SAMOFAR H2020-EURATOM project. We consider three main technologies, i.e., the supercritical steam cycle, the closed helium cycle and the helium/steam combined cycle. Preliminary design results are presented for each technology, based on a simplified modelling approach. The considered cycles show promising efficiency improvements, with the best performance being proven by the supercritical steam cycle. The analysis also highlights the critical issue related to the risk of freezing of the molten salts within the secondary heat exchangers, due to the low inlet temperatures of the working fluids. Results show potential incompatibility between the freezing point of molten salts and the temperatures typical of steam cycles, while helium cycles offer the best chances of freezing avoidance. The combined cycle promises intermediate performance in terms of thermodynamic efficiency and thermal compatibility with molten salts comparable with closed helium cycles.
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Langwieser, Johanna, Andrea Schweighuber, Alexander Felgel-Farnholz, Christian Marschik, Wolfgang Buchberger i Joerg Fischer. "Determination of the Influence of Multiple Closed Recycling Loops on the Property Profile of Different Polyolefins". Polymers 14, nr 12 (15.06.2022): 2429. http://dx.doi.org/10.3390/polym14122429.
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In a circular economy, polymeric materials are used in multiple loops to manufacture products. Therefore, closed-loops are also envisaged for the mechanical recycling of plastics, in which plastic is used for products that are in turn collected and reprocessed again and again to make further products. However, this reprocessing involves degradation processes within the plastics, which become apparent through changes in the property profile of the material. In the present paper, the influence of multiple recycling loops on the material properties of four different polyolefins was analyzed. Two different closed-loop cycles with industrially sized processing machines were defined, and each polyolefin was processed and reprocessed within the predefined cycles. For the investigation of the effect of the respective loops, samples were taken after each loop. The samples were characterized by high-pressure liquid chromatography coupled to a quadru-pole time-of-flight MS, high-temperature gel permeation chromatography, melt flow rate measurements, infrared spectroscopy, differential thermal analysis, and tensile tests. With increasing number of processing loops, the tested polyolefins showed continuous material degradation, which resulted in significant changes in the property profiles.
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Chen, Lingen, Chenqi Tang, Huijun Feng i Yanlin Ge. "Power, Efficiency, Power Density and Ecological Function Optimization for an Irreversible Modified Closed Variable-Temperature Reservoir Regenerative Brayton Cycle with One Isothermal Heating Process". Energies 13, nr 19 (2.10.2020): 5133. http://dx.doi.org/10.3390/en13195133.
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One or more isothermal heating process was introduced to modify single and regenerative Brayton cycles by some scholars, which effectively improved the thermal efficiency and significantly reduced the emissions. To analyze and optimize the performance of this type of Brayton cycle, a regenerative modified Brayton cycle with an isothermal heating process is established in this paper based on finite time thermodynamics. The isothermal pressure drop ratio is variable. The irreversibilities of the compressor, turbine and all heat exchangers are considered in the cycle, and the heat reservoirs are variable-temperature ones. The function expressions of four performance indexes; that is, dimensionless power output, thermal efficiency, dimensionless power density and dimensionless ecological function are obtained. With the dimensionless power density as the optimization objective, the heat conductance distributions among all heat exchangers and the thermal capacitance rate matching among the working fluid and heat reservoir are optimized. Based on the NSGA-II algorithm, the cycle’s double-, triple- and quadruple-objective optimization are conducted with the total pressure ratio and the heat conductance distributions among heat exchangers as design variables. The optimal value is chosen from the Pareto frontier by applying the LINMAP, TOPSIS and Shannon entropy methods. The results show that when the pressure ratio in the compressor is less than 12.0, it is beneficial to add the regenerator to improve the cycle performance; when the pressure ratio is greater than 12.0, adding the regenerator will reduce the cycle performance. For single-objective optimization, the four performance indexes could be maximized under the optimal pressure ratios, respectively. When the pressure ratio is greater than 9.2, the cycle is simplified to a closed irreversible simple modified Brayton cycle with one isothermal heating process and coupled to variable-temperature heat reservoirs. Therefore, when the regenerator is used, the range of pressure ratio is limited, and a suitable pressure ratio should be selected. The triple objective (dimensionless power output, dimensionless power density and dimensionless ecological function) optimization’ deviation index gained by LINMAP or TOPSIS method is the smallest. The optimization results gained in this paper could offer some new pointers for the regenerative Brayton cycles’ optimal designs.
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Patel, Raj C., Diego C. Bass, Ganza Prince Dukuze, Angelina Andrade i Christopher S. Combs. "Analysis and Development of a Small-Scale Supercritical Carbon Dioxide (sCO2) Brayton Cycle". Energies 15, nr 10 (13.05.2022): 3580. http://dx.doi.org/10.3390/en15103580.
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Carbon dioxide’s (CO2) ability to reach the supercritical phase (7.39 MPa and 304.15 K) with low thermal energy input is an advantageous feature in power generation design, allowing for the use of various heat sources in the cycle. A small-scale supercritical carbon dioxide (sCO2) power cycle operating on the principle of a closed-loop Brayton cycle is currently under construction at The University of Texas at San Antonio, to design and develop a small-scale indirect-fired sCO2 Brayton cycle, acquire validation data of the cycle’s performance, and compare the cycle’s performance to other cycles operating in similar conditions. The power cycle consists of four principal components: A reciprocating piston compressor, a heating source, a reciprocating piston expander to produce power, and a heat exchanger to dissipate excess heat. The work explained in the present manuscript describes the theory and analysis conducted to design the piston expander, heating source, and heat exchanger in the cycle. Theoretical calculations indicate that using sCO2 for the Brayton cycle generates 4.5 kW of power with the inlet pressure and temperature of 17.23 MPa and 358.15 K to the piston expander. Based on the fully isentropic conditions, the thermal efficiency of the system is estimated to be 12.75%.
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Alhmoud, Lina, i Ali Khudhair Al-Jiboory. "Insulated-gate bipolar transistor junction temperature estimation based on ℋ∞ robust controller in wind energy applications". Wind Engineering 44, nr 5 (27.09.2019): 548–58. http://dx.doi.org/10.1177/0309524x19877645.
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This article presents lifetime estimation using robust control based on thermal path degradation condition of insulated-gate bipolar transistor wind power modules. Online measurements of the on-state voltage [Formula: see text] are considered to be a promising method for obtaining a thermal-sensitive electrical parameter for wire-bond lift-off. This parameter demonstrates a good correlation with junction temperature. Due to the harsh environment, disturbances and uncertain parameters are founded within the compact set of wind energy generation systems. The uncertainty sacrifices some degree of accuracy of junction temperature measurements. Hence, robust control theory has been utilized to synthesize [Formula: see text] controller for the thermal impedance of high-power insulated-gate bipolar transistors. To study this reliability problem, an integrated model of wind energy generation system is built in MATLAB/Simulink for the closed-loop system. Simulation results show the benefit of the designed controller compared to the open-loop system in terms of thermal cycles of junction temperature and lifetime estimation.
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Choi, Sungwook, In Woo Son i Jeong Ik Lee. "Comparative Performance Evaluation of Gas Brayton Cycle for Micro–Nuclear Reactors". Energies 16, nr 4 (20.02.2023): 2065. http://dx.doi.org/10.3390/en16042065.
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Gas Brayton cycles have been considered the next promising power cycles for microreactors. Especially the open-air and closed supercritical CO2 (S-CO2) Brayton cycles have received attention due to their high thermal efficiency and compact component sizes when compared to the steam Rankine cycle. In this research, the performances of the open-air and closed S-CO2 Brayton cycle at microreactor power range are compared with polytropic turbomachinery efficiency. When optimizing the cycle, three different optimization parameters are considered in this paper: maximum efficiency, maximum cycle specific work, and maximum of the product of both indicators. For the air Brayton cycle, the maximum of the product of both indicators allows to consider both efficiency and specific work while optimizing the cycle. However, for the S-CO2 Brayton cycle, the best performing conditions follow either maximum efficiency or the maximum cycle specific work conditions. In general, the S-CO2 power cycle should be designed and optimized to maximize the cycle specific work for commercial-scale application. The results show that the air Brayton cycle can achieve near 45% efficiency when it can couple with a microreactor with a core outlet temperature higher than 700 °C. However, the S-CO2 power cycle can still achieve above 30% efficiency when it is coupled with a microreactor with a core outlet temperature higher than 500 °C, whereas the air Brayton cycle cannot even reach breakeven condition.
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RUSU, MIHAELA, IULIA SALAORU, M. E. POPA i G. I. RUSU. "ON THE OPTICAL CHARACTERISTICS OF CdS THIN FILMS DEPOSITED BY QUASI-CLOSED VOLUME TECHNIQUE". International Journal of Modern Physics B 18, nr 09 (10.04.2004): 1287–97. http://dx.doi.org/10.1142/s0217979204024616.
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Cadmium sulfide (CdS) thin films (d=0.15–1.15 μ m ) were deposited onto glass substrates by the quasi-closed volume technique under vacuum. The investigations shown that the films are polycrystalline and have a hexagonal structure. It was experimentally established that the films with stable structure can be obtained if they are submitted to a heat treatment, consisting of several succesive heating/cooling cycles within a given temperature range (ΔT=300–600 K ), the temperature dependence of the electrical conductivity becomes reversible. For heat-treated samples, the values of thermal activation energy calculated from the temperature dependence of the electrical conductivity, ranged between 2.30–2.45 eV. The spectral dependences of the transmission and absorption coefficients were studied in the range 500–1400 nm. The influence of heat treatment on the shape of the absorption spectra and dispersion index of refraction is studied for samples with different thickness. Optical energy gap, calculated from the absorption spectra was in the range 2.30–2.5 eV.
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Skaltsounis, Panagiotis, George Kokkoris, Theodoros G. Papaioannou i Angeliki Tserepi. "Closed-Loop Microreactor on PCB for Ultra-Fast DNA Amplification: Design and Thermal Validation". Micromachines 14, nr 1 (10.01.2023): 172. http://dx.doi.org/10.3390/mi14010172.
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Polymerase chain reaction (PCR) is the most common method used for nucleic acid (DNA) amplification. The development of PCR-performing microfluidic reactors (μPCRs) has been of major importance, due to their crucial role in pathogen detection applications in medical diagnostics. Closed loop (CL) is an advantageous type of μPCR, which uses a circular microchannel, thus allowing the DNA sample to pass consecutively through the different temperature zones, in order to accomplish a PCR cycle. CL μPCR offers the main advantages of the traditional continuous-flow μPCR, eliminating at the same time most of the disadvantages associated with the long serpentine microchannel. In this work, the performance of three different CL μPCRs designed for fabrication on a printed circuit board (PCB) was evaluated by a computational study in terms of the residence time in each thermal zone. A 3D heat transfer model was used to calculate the temperature distribution in the microreactor, and the residence times were extracted by this distribution. The results of the computational study suggest that for the best-performing microreactor design, a PCR of 30 cycles can be achieved in less than 3 min. Subsequently, a PCB chip was fabricated based on the design that performed best in the computational study. PCB constitutes a great substrate as it allows for integrated microheaters inside the chip, permitting at the same time low-cost, reliable, reproducible, and mass-amenable fabrication. The fabricated chip, which, at the time of this writing, is the first CL μPCR chip fabricated on a PCB, was tested by measuring the temperatures on its surface with a thermal camera. These results were then compared with the ones of the computational study, in order to evaluate the reliability of the latter. The comparison of the calculated temperatures with the measured values verifies the accuracy of the developed model of the microreactor. As a result of that, a total power consumption of 1.521 W was experimentally measured, only ~7.3% larger than the one calculated (1.417 W). Full validation of the realized CL μPCR chip will be demonstrated in future work.
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Hahn, Jaeseung, i William M. Shih. "Thermal cycling of DNA devices via associative strand displacement". Nucleic Acids Research 47, nr 20 (4.10.2019): 10968–75. http://dx.doi.org/10.1093/nar/gkz844.
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Abstract DNA-based devices often operate through a series of toehold-mediated strand-displacement reactions. To achieve cycling, fluidic mixing can be used to introduce ‘recovery’ strands to reset the system. However, such mixing can be cumbersome, non-robust, and wasteful of materials. Here we demonstrate mixing-free thermal cycling of DNA devices that operate through associative strand-displacement cascades. These cascades are favored at low temperatures due to the primacy of a net increase in base pairing, whereas rebinding of ‘recovery’ strands is favored at higher temperatures due to the primacy of a net release of strands. The temperature responses of the devices could be modulated by adjustment of design parameters such as the net increase of base pairs and the concentrations of strands. Degradation of function was not observable even after 500 thermal cycles. We experimentally demonstrated simple digital-logic circuits that evaluate at 35°C and reset after transient heating to 65°C. Thus associative strand displacement enables robust thermal cycling of DNA-based devices in a closed system.
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Altgen, Michael, i Holger Militz. "Influence of process conditions on hygroscopicity and mechanical properties of European beech thermally modified in a high-pressure reactor system". Holzforschung 70, nr 10 (1.10.2016): 971–79. http://dx.doi.org/10.1515/hf-2015-0235.
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Abstract European beech (Fagus sylvatica L.) was thermally modified in a closed reactor system under various process conditions. Sorption cycles, dynamic vapor sorption (DVS) measurements, and a three-point bending test were performed on thermally modified wood (TMW) to assess hygroscopicity and mechanical properties. As a function of mass loss (ML), the initial equilibrium moisture content (EMC) measured at 20°C/65% relative humidity (RH) directly after the process was strongly influenced by the RH during the process. This effect is explained by realignments of amorphous polymers in the cell wall ultra-structure in the course of thermal modification (TM). However, the EMC of TMW gradually increased after sorption cycles consisting of conditioning over liquid water and water-soaking. This increase was most distinct for TMW modified at low RH, which is an indication for reversible ultra-structural realignments. Results of the bending test suggest that structural realignments also hindered the plastic flow of amorphous cell wall polymers, thereby reducing inelastic toughness and inelastic deflection, while other bending properties were solely affected by ML alone. Process conditions in a closed reactor systems have a profound impact on resulting wood properties, and thus, the partial reversibility of these property changes need to be considered during the application.
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Sammoutos, Christos, Angeliki Kitsopoulou, Panagiotis Lykas, Evangelos Bellos i Christos Tzivanidis. "Dynamic Investigation of a Solar-Driven Brayton Cycle with Supercritical CO2". Applied System Innovation 6, nr 4 (10.08.2023): 71. http://dx.doi.org/10.3390/asi6040071.
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The exploitation of solar irradiation is a critical weapon for facing the energy crisis and critical environmental problems. One of the most emerging solar technologies is the use of solar towers (or central receiver systems) coupled with high-performance thermodynamic cycles. In this direction, the present investigation examines a solar tower coupled to a closed-loop Brayton cycle which operates with supercritical CO2 (sCO2) as the working medium. The system also includes a storage system with two molten salt tanks for enabling proper thermal storage. The sCO2 is an efficient fluid that presents significant advancements, mainly reduced compression work when it is compressed close to the critical point region. The novelty of the present work is based on the detailed dynamic investigation of the studied configuration for the year period using adjustable time step and its sizing for achieving a continuous operation, something that makes possible the establishment of this renewable technology as a reliable one. The analysis is conducted with a developed model in the Modelica programming language by also using the Dymola solver. According to the simulation results, the yearly solar thermal efficiency is 50.7%, the yearly thermodynamic cycle efficiency is 42.9% and the yearly total system efficiency is 18.0%.
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Walker, H. A., i J. H. Davidson. "Analysis and Simulation of a Two-Phase Self-Pumping Water Heater". Journal of Solar Energy Engineering 112, nr 3 (1.08.1990): 153–60. http://dx.doi.org/10.1115/1.2930474.
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The thermal performance of a two-accumulator self-pumping solar water heater is characterized in a daily simulation. The passive vapor transport system operates in cycles, alternating between run, pressurizing, and pump phases. Three isothermal closed-system thermodynamic models characterize the operational phases of the system. The applicable conservation of mass and energy equations of each model are combined in the numerical simulation. Instantaneous temperature and heat transfer rates, as well as integrated energy quantities and thermal efficiencies, are compared to experimental values. The qualitative behavior of the analytical model agrees with that of the physical system. Multiplying thermal loss coefficients by 2.5 and adjusting the theoretical solar model to correspond with measured insolation forces quantitative agreement of overall daily performance. The simulation reveals the impact of the duration of the pressurizing and pumping phases on overall performance. The volume and thermal capacitance of the components used during the pressurizing and pump phases should be minimized, while the insulation on those components should be maximized to optimize system performance. The validated model will be used in future work to optimize system design.
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Dwijayanto, R. Andika Putra. "Sustainability of Nuclear Fuel Resources in Indonesia with Open and Closed Fuel Cycle". Sustainability Science and Resources 4 (15.07.2023): 47–59. http://dx.doi.org/10.55168/ssr2809-6029.2023.4004.
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In the wake of climate change and global warming, various alternatives are being considered as a potential replacement for fossil fuels. Despite often being overlooked, nuclear power offers many benefits as a low-carbon energy source. Being a thermal power plant, nuclear power can generate energy reliably without relying on weather without emitting greenhouse gases during its operation. Serialised construction can reduce the capital cost, which often touted as expensive. Due to the commitment to the Paris Protocol, Indonesia is obliged to achieve carbon neutrality in its energy generation, and nuclear power is a plausible option to replace fossil fuel generation. One of the questions regarding nuclear power deployment in Indonesia is the sustainability of the nuclear fuel, especially considering its domestic resources both uranium and thorium. This study estimates how long uranium and thorium resources in Indonesia will last when used to power the nuclear power plants with open and closed fuel cycles. Several reactor designs were considered. The calculation result shows that domestic nuclear fuel resources in Indonesia can be sustainable enough, provided that closed nuclear fuel cycle is deployed.
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Ma, Zheshu, i Jieer Wu. "Efficiency optimization of a closed indirectly fired gas turbine cycle working under two variable-temperature heat reservoirs". Archives of Thermodynamics 32, nr 2 (1.08.2011): 3–20. http://dx.doi.org/10.2478/v10173-011-0006-4.
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Efficiency optimization of a closed indirectly fired gas turbine cycle working under two variable-temperature heat reservoirsIndirectly or externally fired gas turbines (IFGT or EFGT) are interesting technologies under development for small and medium scale combined heat and power (CHP) supplies in combination with micro gas turbine technologies. The emphasis is primarily on the utilization of the waste heat from the turbine in a recuperative process and the possibility of burning biomass even "dirty" fuel by employing a high temperature heat exchanger (HTHE) to avoid the combustion gases passing through the turbine. In this paper, finite time thermodynamics is employed in the performance analysis of a class of irreversible closed IFGT cycles coupled to variable temperature heat reservoirs. Based on the derived analytical formulae for the dimensionless power output and efficiency, the efficiency optimization is performed in two aspects. The first is to search the optimum heat conductance distribution corresponding to the efficiency optimization among the hot- and cold-side of the heat reservoirs and the high temperature heat exchangers for a fixed total heat exchanger inventory. The second is to search the optimum thermal capacitance rate matching corresponding to the maximum efficiency between the working fluid and the high-temperature heat reservoir for a fixed ratio of the thermal capacitance rates of the two heat reservoirs. The influences of some design parameters on the optimum heat conductance distribution, the optimum thermal capacitance rate matching and the maximum power output, which include the inlet temperature ratio of the two heat reservoirs, the efficiencies of the compressor and the gas turbine, and the total pressure recovery coefficient, are provided by numerical examples. The power plant configuration under optimized operation condition leads to a smaller size, including the compressor, turbine, two heat reservoirs and the HTHE.
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Nicoletto, Carlo, Valentina Falcioni, Silvia Locatelli i Paolo Sambo. "Non-Thermal Plasma and Soilless Nutrient Solution Application: Effects on Nutrient Film Technique Lettuce Cultivation". Horticulturae 9, nr 2 (4.02.2023): 208. http://dx.doi.org/10.3390/horticulturae9020208.
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Soilless cultivation is one of the best examples of the sustainable intensification concept due to the high use efficiency of its inputs. Managing the nutrient solution through a closed cycle system represents a crucial objective to be pursued, but the recovery of the nutrient solution requires chemical correction and sanitization. The application of non-thermal plasma (NTP) in agriculture promotes the safety of the nutrient solution, decreasing the use of chemicals. The aim of this study was to evaluate the effects of cold plasma on the nutrient depletion, yield, and qualitative traits of lettuce. A closed soilless system (nutrient film technique) was used to compare different NTP treatments: control, low ionization (LI), and high ionization (HI) in two successive lettuce cycles. No significant differences within the nutrient depletion trends were observed. The treated lettuce’s yield was 12% higher than that of the control, characterized by a higher total soluble solid content and a significantly higher electrical conductivity and titratable acidity than the control. The ion content was higher in HI plants, as were the contents of nitrogen, phosphorous, and potassium. In HI plants, the leaf pigments were higher, but no significant changes were observed for the antioxidant content. Cold plasma is a promising strategy that brings benefits to the crop.
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Komarov, Ivan, Vladimir Kindra, Dmitry Pisarev, Dmitriy Kovalev i Dmitriy Lvov. "Thermodynamic Analysis of the Low-Grade Heat Sources for the Improvement in Efficiency of Oxy–Fuel Combustion Power Cycles". Inventions 8, nr 1 (10.01.2023): 16. http://dx.doi.org/10.3390/inventions8010016.
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Today, most of the electrical energy in the world is generated by fossil fuel incineration. This causes significant emissions of harmful substances into the atmosphere. The noted problem can be solved by switching to power plants with zero emissions, operating in semi-closed cycles, and producing electricity through oxygen combustion of fuel. A significant drawback of most of the known oxygen–fuel cycles is the lack of useful utilization of various sources of low-grade heat, which is especially typical for power plants operating on gasified coal fuel; as a result of the gasification process, a significant amount of excess heat is released into the atmosphere. This paper presents the results of the development and study of oxygen–fuel cycle thermal schemes of increased efficiency with coal gasification. It was determined that the modernization of the scheme using the carbon dioxide Rankine cycle for the utilization of low-grade heat makes it possible to achieve an increase in the net electrical efficiency equal to 1.2%.
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Mills, Brantley H., Clifford K. Ho, Nathaniel R. Schroeder, Reid Shaeffer, Hendrik F. Laubscher i Kevin J. Albrecht. "Design Evaluation of a Next-Generation High-Temperature Particle Receiver for Concentrating Solar Thermal Applications". Energies 15, nr 5 (23.02.2022): 1657. http://dx.doi.org/10.3390/en15051657.
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High-temperature particle receivers are being developed to achieve temperatures in excess of 700 °C for advanced power cycles and solar thermochemical processes. This paper describes designs and features of a falling particle receiver system that has been evaluated and tested at the National Solar Thermal Test Facility at Sandia National Laboratories. These advanced designs are intended to reduce heat losses and increase the thermal efficiency. Novel features include aperture covers, active air flow, particle flow obstructions, and optimized receiver shapes that minimize advective heat losses, increase particle curtain opacity and uniformity, and reduce cavity wall temperatures. Control systems are implemented in recent on-sun tests to maintain a desired particle outlet temperature using an automated closed-loop proportional–integral–derivative controller. These tests demonstrate the ability to achieve and maintain particle outlet temperatures approaching 800 °C with efficiencies between 60 and 90%, depending on incident power, mass flow, and environmental conditions. Lessons learned regarding the testing of design features and overall receiver operation are also presented.
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Stachowicz, M., i K. Granat. "Possibilities of Reclamation Microwave-Hardened Molding Sands with Water Glass". Archives of Metallurgy and Materials 59, nr 2 (1.06.2014): 757–60. http://dx.doi.org/10.2478/amm-2014-0127.
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Abstract The paper presents results of a research on identifying opportunities for effective reclamation of waste molding sand with water-glass, hardened by microwave heating. The molding sand applied in the tests was prepared with use of selected type 145 of sodium water-glass. The sand was sequentially processed by microwave hardening, cooling, thermal loading to 800°C, cooling to ambient temperature, crushing and mechanical reclamation. These stages create a closed processing loop. After each cycle, changes of tensile strength and bending strength were determined. Results of the study show that it is possible to activate surface of high-silica grains of waste foundry sand hardened with microwaves, provided that applied are appropriate processing parameters in successive operation cycles.
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Piwowarski, Marian. "Design analysis of ORC micro-turbines making use of thermal energy of oceans". Polish Maritime Research 20, nr 2 (1.04.2013): 48–60. http://dx.doi.org/10.2478/pomr-2013-0016.
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Abstract The article presents the results of the analysis of energy conversion cycles making use of thermal energy of oceans. The objects of analysis were two cases of closed Organic Rankine Cycle (ORC) power plants, which were: the cycle in which the vapour of the working medium was produced by warm oceanic water in the circum-equatorial zone, and the so-called “arctic” cycle in which this vapour was produced by non-frozen water in the circumpolar zone. Between ten and twenty low-boiling media were examined for which operating parameters were optimised to obtain the highest cycle efficiency. A preliminary design of an ORC turbine which was obtained by optimising basic design parameters is included. It has been proved that realisation of the Ocean Thermal Energy Conversion (OTEC) cycle is possible both in the warm and permanently frozen regions. The results of the calculations have also revealed that the efficiency of the OTEC cycle is higher in the circumpolar zone. Selecting a low-boiling medium and designing a highly efficient turbine operating in both abovementioned regimes is technically realisable.
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Podolak, Marian, Dariusz Mana i Stanislaw Przestalski. "ESR Study of the Liposome Membrane Physical Parameters in the Heating-Cooling Cycles". Zeitschrift für Naturforschung C 53, nr 3-4 (1.04.1998): 191–96. http://dx.doi.org/10.1515/znc-1998-3-408.
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Abstract Changes of dynamic and structural parameters of egg yolk lecithin (EYL) liposome membranes in the heating-cooling cycles have been studied using the E S R spin probe method. The investigations were conducted in the range of temperatures from -18 °C to +60 °C. It has been found that in the range of temperatures -15 °C to +45 °C in both the heating and the cooling run the spectroscopic parameters changed practically along the same curve (reversible changes). However, after exceeding this range of temperatures one of the parameters (partition coefficient of the spin probe 2,2,6,6 -tetramethylpiperidine -1-oxyl; TEMPO) changed along a closed curve, showing the phenomenon of thermal hysteresis. In the heating process the TEMPO content in liposome membranes was smaller than this in the cooling process. We assume that during the heating, the lipid molecules of the outer liposome layers dissolve in the aqueous medium. In the cooling process they can aggregate and form new liposomes, what in turn increases the surface of liposome membranes, accessible for the TEMPO probe (active surface).
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Traverso, Alberto, Federico Calzolari i Aristide Massardo. "Transient Analysis of and Control System for Advanced Cycles Based on Micro Gas Turbine Technology". Journal of Engineering for Gas Turbines and Power 127, nr 2 (1.04.2005): 340–47. http://dx.doi.org/10.1115/1.1839918.
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Microturbines have a less complex mechanical design than large-size gas turbines that should make it possible to fit them with a more straightforward control system. However, these systems have very low shaft mechanical inertia and a fast response to external disturbances, such as load trip, that make this very difficult to do. Furthermore, the presence of the recuperator requires smooth variations to the Turbine Outlet Temperature (TOT), when possible, to ensure reduced thermal stresses to the metallic matrix. This paper, after a brief overview of microturbine control systems and typical transients, presents the expected transient behavior of two advanced cycles: the Externally Fired micro Gas Turbine (EFmGT) cycle, where the aim is to develop a proper control system set-up to manage safe part-load operations at constant rotational speed, and a solar Closed Brayton Cycle (CBC), whose control system has to ensure the maximum efficiency at constant rotational speed and constant Turbine Inlet Temperature (TIT).
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Sohn, Yoonchul, Dongouk Kim, Sangeui Lee, Jae Yong Song, Sunghoon Park, Hajin Kim, Youngchul Ko, Kunmo Chu i Intaek Han. "Correlation between Thermo-mechanical Reliability and Superhydrophobic Nature of CNT Composite Coatings". International Symposium on Microelectronics 2014, nr 1 (1.10.2014): 000086–91. http://dx.doi.org/10.4071/isom-ta34.
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One of the most important applications for superhydrophobic coatings is anti-frosting for safety and energy conservation. Safety concerns are especially critical in cold-climate regions where the daily temperature fluctuation is large. However, superhydrophobic coatings have not been studied in terms of their thermomechanical reliability. In this study, wetting characteristics and stress relaxation behavior were quantitatively investigated with multi-walled carbon nanotube (MWNT)–silicone composite films under thermal cycling condition. It is concluded that an open structure with numerous nanopores among the fillers, constituting air pockets described as the “Cassie structure,” is of great importance not only for developing a film's superhydrophobic nature but also for accommodation of thermal stress that evolved from different coefficients of thermal expansion between the coating and the substrate. The amount of stress relaxation for a 30 vol% MWNT–silicone composite film with open structure reaches ~80% of the value for its counterpart with a closed structure and no pores. A superhydrophobic MWNT–silicone composite film that can endure over 4000 thermal cycles (−30°C to room temperature) is fabricated by controlling the composition and microstructure of the composite. In addition, the importance of size and shape of nanofillers in delaying nucleation and growth of frost on superhydrophobic coatings is also discussed.
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Beck, Tilmann, Karl-Heinz Lang, Otmar Vöhringer i Detlef Löhe. "Experimental Analysis of the Interaction of “Hot” and “Cold” Volume Elements during Thermal Fatigue of a Cooled Component Made from AISI 3161 Steel". International Journal of Materials Research 92, nr 8 (1.08.2001): 875–81. http://dx.doi.org/10.1515/ijmr-2001-0160.
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Abstract Start-stop and load change procedures of combustion engines result in inhomogenous and instationary temperature fields, which induce cyclic mechanical loadings, e. g., in solid and cooled turbine blades and vanes. The present study shows results of so-called “complex thermal-mechanical fatigue” (CTMF) tests carried out with a two specimen testing system in order to simulate the interaction of the “hot” outer and the “cold” inner side of a cooled turbine blade. The test samples were made from the austenitic steel AISI 316 L. Specimen 1 represents the “hot” and specimen 2 the “cold” side of the blade, respectively. Both specimens were loaded by individual thermal cycles with closed loop control of the temperature. The mechanical interaction of the “hot” and the “cold” side was simulated by keeping the total strains of both specimes at identical values and keeping the sum of the forces at a value of zero at every moment throughout the tests. The results are discussed on the background of the microstructures resulting from the individual loadings of specimen 1 and 2.
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Angelino, G., i C. Invernizzi. "Real gas Brayton cycles for organic working fluids". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 215, nr 1 (1.02.2001): 27–38. http://dx.doi.org/10.1243/0957650011536543.
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Organizing a closed Brayton cycle in such a way that the compression process is performed in the vicinity of the critical point where specific volumes are a fraction of those of an ideal gas yields performance indices particularly attractive, mainly at moderate top temperatures. Cycle thermodynamic analysis requires the development of adequate methods for the computation of thermodynamic properties above the vapour saturation curve about the critical point. Working fluids suitable for the proposed cycle can be found in the class of organics, in particular among the newly developed, zero ozone depletion potential, chlorine-free compounds. The numerous technical and environmental requirements which a fluid must meet for practical use combined with the peculiar thermodynamic restraints limit the number of suitable fluids. Mixing two substances of different critical temperatures yields an indefinite number of fluids with tailor-made thermodynamic properties. One such mixture 0.93 HFC23 + 0.07 HFC125 (molar fraction), having tcr = 30°C, at tmax = 400°C, pmax = 150 bar, gives an efficiency above 27 per cent with heat rejection temperatures between 89 and 33°C. With a different mixture composition with a 50°C critical temperature, at the same tmax and pmax, an efficiency of 25.1 per cent is attained in a combined heat and power generation cycle with heat available in the range 53-103°C. An experimental programme to test the thermal stability of organic fluids showed that top temperatures of 380-450°C are achievable with some commercially available fluoro-substituted hydrocarbons. In view of practical applications a conversion unit based on a reciprocating engine could handle without problems the pressures and temperatures involved. The use of turbomachinery would lead to power plant of large capacity for the usual rotor dimensions or to micro-turbines at high rotating speed in the low power range.
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Gorokhovsky, Alexander V., Gleb Yu Yurkov, Igor N. Burmistrov, Angel F. Villalpando-Reyna, Denis V. Kuznetsov, Alexander A. Gusev, Bekzod B. Khaidarov, Yuri V. Konyukhov, Olga V. Zakharova i Nikolay V. Kiselev. "Glass-Ceramic Protective Coatings Based on Metallurgical Slag". Coatings 13, nr 2 (24.01.2023): 269. http://dx.doi.org/10.3390/coatings13020269.
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Pyroxene glass-ceramic enamels based on combinations of blast furnace slag and some additives were produced and investigated. The batch compositions and technological regimes of enameling were developed to produce high temperature protective coatings for carbon steel (ASTM 1010/1008). The composition of raw materials was selected to match the values of the thermal expansion coefficients of the glass-ceramic coating (~11∙10−6 K−1) and metal substrate (~12∙10−6 K−1) taking into account the temperatures of fluidization (Tf ~ 800°) and crystallization (Tc = 850−1020 °C) of the corresponding glasses. The covered and thermally treated samples of carbon steel were produced using single-layer enameling technology and investigated to specify structure, phase composition and properties of the coating and coating-steel interface. The obtained coatings were characterized with excellent adhesion to the steel (impact energy ~3 J) and protective properties. The closed porous structure of the coatings promoted low thermal conductivity (~1 W/(m·K)) and high (up to 1000 °C) thermal resistance, whereas the pyroxene-like crystalline phases supported high wear and chemical resistance as well as micro-hardness (~480 MPa) and thermal shock resistance (>30 cycles of 23–700 °C). The obtained cheap coatings and effective protective coatings could be used at the temperatures up to 1100 °C in the corrosive atmosphere and under the action of abrasive particles.