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Schiano-Phan, Rosa. "The development of passive downdraught evaporative cooling systems using porous ceramic evaporators and their application in residential buildings." Thesis, Open University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417587.
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Passive Evaporative Cooling is a method that uses the evaporation of water to cool the air. It is traditionally used and is most suitable in hot and dry climates. Its application is based on the availability of water resources and the creation of air movement through the building. The use of clay and porous ceramic in passive downdraught evaporative cooling has a track record in the vernacular architecture of hot and dry climatic regions. As part of this project, an improved design for porous ceramic evaporators has been developed for integration into a perimeter cavity wall system, as an alternative form of passive evaporative cooling. This research demonstrates that passive evaporative cooling using porous ceramic can provide thermal comfort conditions inside residential buildings in hot dry climates. Porous ceramic components can be integrated simply and effectively within existing housing of 1940s to 1970s which are due for refurbishment. Performance simulations on a case study building in Seville demonstrated that the system can provide comfort conditions after a series of energy saving strategies were applied to reduce cooling loads. An applicability study focusing on the residential stock of Seville assessed that the proposed system can avoid the need for mechanical cooling in 70% of the existing buildings. This could result in substantial energy and CO2 savings, contributing to Spain’s commitment to reduce greenhouse gas emissions by 2010. An outline specification of a typical wall-integrated Porous Ceramic System (PCS) was set out and costed. A Life Cycle Cost analysis over 25 years compared the proposed PCS with a conventional room air-conditioning unit, demonstrating that its cost is half of the conventional option. The application of the proposed passive cooling system to apartment buildings in Southern European cities could considerably improve comfort and living conditions of the occupants, as well as reduce the use of room air-conditioning. If applied on a large scale, this could produce substantial energy savings and reduce greenhouse gas emissions in the atmosphere.
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Sovernigo, Enrico. "Influence of nanostructured heterojunctions on the electrical properties of photovoltaic cells." Doctoral thesis, Università degli studi di Trieste, 2011. http://hdl.handle.net/10077/4480.
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2009/2010Le celle fotovoltaiche basate su strati sottili di materiali organici hanno raggiunto efficienze dell' 8.3% ed hanno le potenzialità per diventare un'alternativa a basso costo delle celle basate su silicio amorfo. Alcune delle problematiche legate alle proprietà intrinseche di generazione, separazione e trasporto delle cariche possono essere affrontate non solo con lo studio della chimica e dei processi per materiali organici e fullerene, ma anche con lo sviluppo di nuove architetture delle celle basate sul controllo e l'organizzazione alla scala del nanometro. Il presente lavoro di tesi è basato sulla convinzione che quest'ultimo approccio, complementare a quello basato sul miglioramento delle proprietà intrinseche dei materiali, contribuirà sostanzialmente al progresso di questo campo della ricerca applicata. L'obiettivo di questo lavoro è quello di dimostrare il principio di funzionamento di una serie di diversi e nuovi prototipi di dispositivi basati su micro- e nano-architetture. In particolare, abbiamo realizzato: un nanomodulo di 1 cm2 che mostra una tensione di circuito aperto di quasi 1 kV, una cella solare basata su un'eterogiunzione con interfaccia avente strutture di 20 nm interpenetrate, e abbiamo ottimizzato deposizione di ossido di indio stagno (ITO) per lo sviluppo di un nostro dispositivo di intrappolamento della luce basato su serie di microlenti. Tuttatavia, riteniamo che ulteriori sforzi nella stessa direzione siano necessari per dimostrare l'utilità delle nano-architetture nel fotovoltaico organico. Parte del lavoro di ricerca è stato dedicato allo sviluppo e messa in opera di strumentazione specifica per la lavorazione e caratterizzazione per il fotovoltaico come un evaporatore in vuoto ad angolo inclinato connesso ad una camera a guanti in azoto per la deposizione di metalli e di organici.
Thin-film photovoltaic (PV) cells based on the bulk hetero-junction of organic materials reached a record efficiency of 8.3% and have the potential to become a lower-cost alternative to amorphous silicon. Some of the issues related to the intrinsic properties of generation, separation and transport of charges, may be addressed not just by working on the details of the chemistry and processing of the organic/fullerenes materials, but also by implementing new cell architectures organized and well controlled down to the nanoscale. The present work of thesis is based on the conviction that the latter approach, complementary to that focused on the improvement of the intrinsic properties of the materials, will substantially contribute to the progress of this field of applied research. The goal of this work is that of demonstrating the working principle of a series of different and new micro- and nano-architectures into prototypical organic solar devices. In particular, we realized: a 1 cm2 nanomodule with almost 1 kV of open circuit voltage, a solar cell with a controlled nanostructured interface heterojunction with interpenetrating features of 20 nm, and we optimized the sputtering deposition of indium tin oxide (ITO) for our light trapping device based on microlenses array. However, we believe that additional efforts in the same direction will be necessary to demonstrate the usefulness of nanoarchitectures in organic photovoltaics. Part of the research work was devoted to the development and the commission of specific instrumentation for PV processing and characterization as an oblique angle vacuum evaporator connected to a nitrogen glove-box for the deposition of metals and organics.
XXIII Ciclo
1980
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Howell, John Michael. "Whey permeate fouling of evaporators." Thesis, University of Canterbury. Chemical and Process Engineering, 1998. http://hdl.handle.net/10092/10686.
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Whey permeate fouling was studied to gain a better understanding of the processes involved and find methods of alleviation. An apparatus was built which allowed study of fouling under industrial conditions. It was found that pretreatment by heating at 80°C for two minutes and then centrifuging at 630 g reduced fouling in the apparatus by 94%. This was attributed to precipitation of calcium phosphate in the solution bulk during preheating, which reduced the level of supersaturation. Heat treatment with the same conditions but without centrifuging reduced fouling by only 39%. Precipitate which forms in the bulk of solution fouls in later heat treatment processes and separation of the precipitated mineral is needed to minimise fouling.
Storage time affected fouling. In the short term (about 2 weeks), fouling slightly increased with storage time. When held for longer times (about 1 month) whey permeate did not appreciably foul.
The use of additives was also found to be an effective alleviation method, reducing fouling by 66% with 0.1% addition (by dry weight) of tetrasodium pyrophosphate. This addition would increase the price of a ton of lactose by $16.32 /ton.
Nanoftltration, ion dialysis and electrodialysis were also examined, but rejected as being uneconomic.
By observing the effect of preheating and storage time it was proposed that calcium phosphate exists in whey in two forms. The majority of the minerals are associated with non-protein nitrogen (NPN) species, which tends to provide stability and prevent precipitation. In the other form the calcium phosphate is in solution as free ions. When the NPN species release minerals due to cleavage by enzymes or denaturation by heat, the concentration of ionic species increases past the solubility product and precipitation occurs.
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Quy, Tiffany Anne. "Characterization of micro-capillary wicking evaporators." Online access for everyone, 2006. http://www.dissertations.wsu.edu/Thesis/Fall2006/T_Quy_081806.pdf.
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Lagos, Arcangel. "Heat transfer enhancement in DX evaporators." Thesis, London South Bank University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311210.
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Karpiscak, Martin, and Mary H. Marion. "Evaporative Cooler Water Use." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 1994. http://hdl.handle.net/10150/146414.
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McCafferty, J. B. "Refrigerant distribution in shell and tube evaporators." Thesis, Heriot-Watt University, 1991. http://hdl.handle.net/10399/1027.
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Wadell, Robert Paul. "Experimental Investigation of Compact Evaporators for Ultra Low Temperature Refrigeration of Microprocessors." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7198.
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It is well known that microprocessor performance can be improved by lowering the junction temperature. Two stage cascaded vapor compression refrigeration (VCR) is a mature, inexpensive, and reliable cooling technology that can offer chip temperatures down to ?? C. Recent studies have shown that for a power limited computer chip, there is a non-linear scaling effect that offers a 4.3X performance enhancement at ?? C. The heat transfer performance of a compact evaporator is often the bottleneck in sub-ambient heat removal. For this reason, the design of a deep sub-ambient compact evaporator is critical to the cooling system performance and has not been addressed in the literature.
Four compact evaporator designs were investigated as feasible designs - a baseline case with no enhancement structures, micro channels, inline pin fin arrays, and alternating pin fin arrays. A parametric experimental investigation of four compact evaporator designs has been performed aiming at enhancing heat transfer. Each evaporator consists of oxygen free copper and has a footprint of 20 mm x 36 mm, with a total thickness of 3.1 mm. The micro channel evaporator contains 13 channels that are 400 um wide by 1.2 mm deep, and the pin fin evaporators contain approximately 80 pin fins that are 400 um wide by 1.2 mm tall with a pitch of 800 um. Two phase convective boiling of R508b refrigerant was investigated in each evaporator at flow rates of 50 - 70 g/min and saturation temperatures of ??to ??C. Pressure drop and local heat transfer measurements are reported and used to explain the performance of the various evaporator geometries. The results are compared to predictions from popular macro- and micro-channel heat transfer and pressure drop correlations. The challenges of implementing a two stage cascade VCR systems for microprocessor refrigeration are also discussed.
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Jin, Dae-Hyun. "Investigation on refrigerant distribution in evaporator manifolds." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3845.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Shepherd, Adrian M. "Safeguarding of evaporator operations in reprocessing plant." Thesis, London South Bank University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.411377.
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Dalili, Farnosh. "Humidification in Evaporative Power Cycles." Doctoral thesis, KTH, Chemical Engineering and Technology, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3469.
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Evaporative gas turbine cycles (EvGT) show an exceptionalexhaust heat recovery potential, which makes them a strongcompetitor to other advanced gas turbine cycles, especiallyfrom small to intermediate sizes. Evaporative gas turbines aredistinguished by humidifying the working fluid beforecombustion at temperatures below the boiling point of water;and the heat required for evaporation of water is partly takenout of the exhaust gas. Thus, humidification is a key operationin these cycles. This thesis investigates, both theoreticallyand experimentally, two alternative approaches tohumidification: the packed-bed humidification tower and thetubular humidifier. Both these equipments involvecountercurrent contact between water and the working fluid.Humidifier design criteria are developed and criticalparameters such as flooding, wetting rate and entrainment arediscussed. The experimental parts were carried out on thepacked-bed tower in the EvGT pilot plant, and on a tubularhumidifier test rig especially erected for this purpose. Thetheoretical models were confirmed by the experiments.
The height of a transfer unit, necessary for designingpacked beds, was calculated for the packing employed in theEvGT pilot plant. It was found that the data provided by themanufacturer may be used with minor corrections.
The tubular test rig operated satisfactorily delivering hothumid air. The theoretical models coincided well with theexperimental results, verifying the design criteria developedhere. The heat transfer calculations indicated that mostresistance to heat transfer is on the exhaust gas side. Thus, asurface extended tube (Sunrod) was used in the test rig. Itcould be concluded that the tubular humidifier is a strongalternative to the packed-bedtower, especially in smallhigh-pressure gas turbines.
Furthermore, the importance of the non-ideality of theair-water vapor mixture in modeling evaporative cycles wasfirst highlighted in this work. Through applying realthermodynamic properties of air-water vapor mixtures in cyclecalculations, it was found that the compressed air contains ahigher amount of moisture than indicated by the ideal gasmixture model. This affects the design of the heat recoverysystem and cannot be neglected.
Key words:evaporative gas turbine, indirect-fired gasturbine, humidification, packed bed, tubular humidifier,evaporator, saturator.
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Davis, Kendall Bruce. "Evaporative cooling of sodium atoms." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11384.
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Uguz, Kamuran Erdem. "Evaporative instability in binary mixtures." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112169/document.
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Cette étude concerne la physique des écoulements convectifs résultant d’une instabilité d’évaporation de fluides binaires. Ce problème a de nombreuses applications, l’enrobage par centrifugation, le dépôt de films, les caloducs, etc, pour lesquels le changement de phase et la convection jouent un rôle prépondérant dans la conception et la qualité des procédés. Le système physique étudié est un mélange liquide sous sa propre vapeur, confiné par deux plaques conductrices de chaleur et des bords latéraux isolants. Les plaques sont utilisées pour appliquer un gradient thermique. Aucun gradient de concentration n’est imposé au système. Ces gradients sont induits par les différentes vitesses d’évaporation des composés. Dans ce système, il est important de comprendre comment la dynamique des fluides et les transferts de masse et de chaleur entrent en compétition pour la formation de structures. Le principal objectif de ce travail est d’identifier les conditions pour que le système évolue d’un état conductif vers un état de convection lorsque le gradient vertical de température dépasse une certaine valeur critique.Dans le système, la convection s’installe par trois mécanismes distincts : évaporation, gradients de densité et gradients de tension interfaciale. Trois forces convectives s’opposent aux effets de diffusion qui tendent à garder le système en état conductif. Le seuil d’apparition de la convection dépend de quelques variables, comme les dimensions du contenant, les propriétés thermophysiques des phases liquide et vapeur, la fraction massique, et les caractéristiques de perturbations. L’effet de chacune de ces variables sur le seuil est étudié en présence ou non de gravité.Pour représenter la physique, un modèle mathématique non linéaire complet est développé, basé sur les conservations de quantité de mouvement, d’énergie et de masse dans chaque phase avec les conditions aux limites appropriées. Le fluide binaire est composé de deux alcools légers comme l’éthanol et le sec-butanol. Dans les équations du modèle, la masse volumique ainsi que la tension interfaciale sont fonctions à le fois de la température et de la concentration. Pour la recherche du seuil de transition, les équations sont linéarisées autour d’un état de base connu. Dans notre cas, il s’agit de l’état conductif. Le système d’équations linéaires résultant est résolu par une méthode de collocation spectrale Chebyshev.Nous obtenons quatre résultats principaux. Premièrement, dans un système multi-composants sans gravitation, une instabilité n’apparaît que lorsque le système est chauffé du côté de la phase vapeur contrairement à un système mono-composant. Cela implique que, si on souhaite éviter les instabilités, il vaut mieux un apport de chaleur par la phase liquide en cas de processus d’évaporation en couches minces ou en micro-gravité.Deuxièmement, en présence de gravité, un système multi-composants peut devenir instable quelle que soit la direction du chauffage. Si la convection thermique est négligeable, alors nous montrons que le chauffage par la phase vapeur est la configuration la plus instable. Sinon, les deux modes de chauffage sont à même de produire une instabilité. Ce résultat implique que le gradient thermique appliqué doit être inférieur à une valeur seuil pour éviter les instabilités quelle que soit la direction du chauffage.Troisièmement, lorsque l’instabilité apparaît en absence de gravité, des structures n’apparaitront pas dans le cas de fluide pur mais apparaitront dans le cas d’un fluide multi-composants. De même, des structures apparaitront en présence de gravité en fonction du facteur d’aspect du confinement. Les facteurs d’aspect peuvent être choisis pour éviter des structures multi-cellulaires même en cas d’apparition d’instabilités durant l’évaporation.Enfin, des structures oscillantes ne sont pas prédites de façon générale malgré les effets opposés des convections solutale et thermique dans le problème d’évaporationThis study focuses on understanding the physics of the convective flow resulting from evaporative instability in binary mixtures. This problem has wide applications in spin coating, film deposition, heat pipes, etc. where phase change and convection play a very important role in the design process and also final quality of the product. The physical system of interest consists of a liquid mixture underlying its own vapor sandwiched between two conducting plates with insulated sidewalls in a closed container. The conducting plates are used to apply a vertical temperature gradient while there is no applied concentration gradient in the system. Concentration gradients are induced by the different evaporation rate of the components. In this system it is important to understand how the fluid dynamics and the heat and mass transfer interact competitively to form patterns. The main goal of this work is to identify the conditions for the system going from the conductive no-flow state to a convection state when the applied vertical temperature gradient exceeds a certain value called the critical value.In the system convection arises due to three distinct phenomena; evaporation, density gradients, and interfacial tension gradients. These convective forces are opposed by the diffusion effects that try to keep the system in the conductive no-flow state. The onset point depends upon several variables such as the dimensions of the container, thermo-physical properties of both liquid and vapor phases, mass fraction, and the characteristic of the disturbance given to the system. The effects of each of these variables on the onset point are investigated both in the presence and in the absence of gravity. To represent the physics a complete non-linear mathematical model is developed including momentum, energy, and mass balances in both phases with appropriate boundary conditions. The binary mixture is assumed to be made up of two low weight alcohols such as ethanol and sec-butanol. In the modeling equations the density and the interfacial tension are taken to be function of both temperature and concentration. To identify the onset point the non-linear equations are linearized around a known base state. In this case the base state is the conductive no-flow state. The resulting set of linear equations is solved using a spectral Chebyshev collocation method. Four major results arise from this work. First, in a multi-component system in the absence of gravity, an instability arises only when the system is heated from the vapor side as opposed to evaporation in a single-component. The implication is that evaporative processes in thin layers or in micro-gravity are best conducted with heat from the liquid side if instabilities are to be avoided.Second, in the presence of gravity, a multi-component system may become unstable no matter the direction of heating. If thermal buoyancy is negligible then it is shown in this study that heating from the vapor side is the unstable arrangement. Otherwise either heating style can produce an instability. This result means that the applied temperature difference must be kept below a threshold in order to avoid flow instabilities no matter the heating direction.Third, whenever instability occurs in the absence of gravity, patterns will not result in the case of a pure component but may result in the case of multi-components. Likewise, patterns will result when gravity is taken into account provided the aspect ratio of the container lies in a suitable range. As a result, aspect ratios can be chosen to avoid multi-cellular patterns even if convective flow instabilities arise during evaporation.Lastly, oscillations are not ordinarily predicted despite opposing effects of solutaland thermal convection in the evaporation problem
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Alexseev, Alexandre Viktorovich. "Micro loop heat pipe evaporator coherent pore structures." Texas A&M University, 2003. http://hdl.handle.net/1969.1/1303.
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Loop heat pipes seem a promising approach for application in modern technologies where such thermal devices as cooling fans and radiators cannot satisfy overall requirements. Even though a loop heat pipe has a big potential to remove the thermal energy from a high heat flux source, the heat removal performance of heat pipes cannot be predicted well since a first principles of evaporation has not been established. An evaporation model based on statistical rate theory has been recently suggested by Ward and developed for a single pore by Oinuma. A loop heat pipe with coherent pore wick structure has been proposed as a design model.
To limit product development risk and to enhance performance assurance, design model features and performance parameters have been carefully reviewed during the concept development phase and have been deliberately selected so as to be well-founded on the limited existing loop heat pipe knowledge base. A first principles evaporation model has been applied for evaporator geometry optimization. A number of iteration calculations have been performed to satisfy design and operating limitations. A set of recommendations for design optimization has been formulated. An optimal model has been found and proposed for manufacture and experimental investigation.
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Ingebrigtsen, Vegard Byre. "Energy Analysis of Evaporator System in Fertilizer Production." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18410.
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Yara Glomfjord is the north most production facility of compound fertilizer in the world and produces annually about 500 000 tons NPK and 200 000 tons CN. The general energy system of the process plant utilizes steam as the main energy carrier for the entire production site. Yara Glomfjord has today a general lack of steam, and steam is produced in EGA boilers approximately 75% of operational time to cover all heating tasks. The main objective of this Master thesis is to analyze energy flow in in the factory to identify energy saving potential, and later to suggest improvements for the CN-evaporator system in order to retire the use of EGA boilers and supply excess heat for other heating tasks in the factory.First off analysis was made on general energy flows in the factory. This was done in order to reveal potential for energy savings and to clarify which paths to choose for further heat integration. The result of the analysis shows that latent heat flows are of far greater importance than sensible heat flows to the general steam balance at Yara Glomfjord. It was also identified that the large potential for latent heat recovery lies within the evaporator equipment.Next up this text suggests investment in evaporator equipment in order to integrate latent heat, so that the overall steam consumption goes down. Three different suggestions were presented and analyzed in detail in the document: CN-Evaporator System Design. The most proving suggestions are new equipment coupled in cascade with old evaporators or a new independent MVR evaporator in front of old solution. Both suggestions are found to retire EGA boilers completely and also supply excess heat for other heating tasks. This text recommends one of these two suggestions.To suggest new improvements in the CN-evaporator system Epcon Evaporation Technology AS were involved. Testing at Epcon’s facilities in Trondheim indicate a new possibility. For the suggested retrofit cascade evaporation system, submergence of boiling pressure is possible. These findings supports the recommendations from this text to invest in a new evaporator coupled in cascade with the old solution with submergence of boiling pressure. In this way the energy savings in question can be implemented with only a small investment and almost no energy cost in a vacuum pump.As a huge potential for energy savings was found possible at reasonable cost and at a manageable technical level, the findings of this Master thesis hopefully settles the steam issues of the Yara Glomfjord compound fertilizer plant once and for all.In light of the late findings of this project, with the possibility of submergence of boiling pressure a hint is also sent to Yara Porsgrunn. As a great role model for Yara Glomfjord they utilize latent heat, but at the cost of expensive compressor work and not with submergence of boiling pressure which this text clearly states to be the superior technology.
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Suren, Aydin. "Scaling of black liquor in falling film evaporator." Thesis, Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/10147.
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Young, B. R. "Modelling and identification of a climbing film evaporator." Thesis, University of Canterbury. Chemical and Process Engineering, 1992. http://hdl.handle.net/10092/7522.
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The objective of this work is the characterisation of a model to describe the dynamics of a climbing film evaporator over a wide operating range. The model should be sufficiently simple so that the calculation of control action is straight-forward. The hypothesis of this thesis is that such a model may be constructed to describe the dynamics of a climbing film evaporator well.
The first chapter introduces the topics of climbing film evaporation, two-phase flow
and modelling and identification.
The second chapter describes the climbing film evaporator used in this study. For this purpose, the evaporator was fully instrumented with temperature sensors, conductivity cells and flow-meters. The instrumentation was commissioned and calibrated.
In the next chapter a distributed parameter model of the climbing film evaporator is
derived from the one-dimensional homogeneous two-phase flow equations, the parameters of which were to be determined by identification.
The next two chapters summarise the field of identification. The fourth chapter presents and develops identification techniques for lumped parameter models, and the fifth chapter describes and constructs identification methods for distributed parameter
models.
The methods described in the lumped parameter identification section were recursive, so that they could be used in real-time to track time-varying parameters – a feature that is useful in the design of self tuning regulators. These identification methods used a UD factorisation algorithm and were found to be robust for inappropriate choices of system dead-time. Accurate estimates of dead-time were obtained from either method.
The distributed parameter identification methods investigated were optimisation schemes to minimise an output least square error criterion. Methods for solving the distributed parameter identification problem using the method of characteristics were investigated and developed. Identification using the method of characteristics is appropriate as the partial differential equations describing the climbing film evaporator are hyperbolic in nature.
Chapter six presents the identification strategy adopted to model the evaporator using the techniques described and developed in chapters four and five. The experiments for the collection of data to be used in the various models are designed.
A range of models of the climbing film evaporator were identified. The simplest models for the evaporator were global black-box linear models. Gain-scheduled linear models were identified to attempt compensation for system non-linearity. Finally the parameters of distributed parameter models for the climbing film evaporator were investigated. These models are presented and discussed in chapters seven, eight and nine respectively.
The thesis is organised so that pages are numbered within chapters, with nomenclature and references listed at the end of each chapter.
The paper entitled "Multi-input, multi-output identification of a pilot-plant climbing film evaporator" is based upon this work (Appendix VI). The paper has been accepted for presentation at the 12th World Congress of the International Federation of Automatic Control, Sydney Convention and Exhibition Centre, Darling Harbour, Sydney, Australia, 19th-23rd July 1993.
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Smith, Patrick D. "Control and optimization of a multiple-effect evaporator." Master's thesis, University of Cape Town, 2000. http://hdl.handle.net/11427/5397.
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Bibliography: leaves 117-125.Falling commodity prices have reduced the profit margins of Southern African sugar producers. Although these price falls have been severe, they reflect a long-term trend of reducing margins for basic commodity producers during the 20th Century. This trend has forced. producers to closely examine their processes and to look for areas in which improvements in productivity, yield and efficiency can be achieved. Evaporation is the most energy intensive unit operation in the sugar factory, and it is responsible for the removal of most of the water from sugar solution, or juice, which is extracted from the sugar cane. There is also a large potential to lose sucrose at the evaporators due to the high temperatures and long residence times employed there. The smooth control of the evaporators is thus vital to consistent factory operation, and the evaporators are commonly a sugar factory bottleneck. This study developed a control strategy for the particular evaporator configuration found at Triangle Sugar Mill in south eastern Zimbabwe. There are currently several evaporator control strategies being used in the sugar industry. Most of these are an assembly of single loop Proportional Integral Derivative (PID) controllers, which cannot optimally account for the interactions encountered in most evaporator stations. Ideally, any evaporator control system should be able to handle the multiple input multiple output problem while anticipating and handling constraints on inputs and outputs. Several multivariable approaches have been tried, but these usually require a great deal of expensive instrumentation.After a review of the multivariable control literature and testing of several alternative control systems, Dynamic Matrix Control (DMC) was chosen as the bestwsuited control algorithm for the Triangle control problem. A dynamic model of the Triangle evaporator station was, developed to formulate and test the DMC and other controllers. The model was based on a set of differential equations involving mass and energy balances through the evaporators. Real plant data were collected from the SCADA system and the model was tested against this data. After validation the model was. used to record step responses of the process to key input variables. The control system had nine (9) measurable inputs, and three (3) controlled outputs. The objective of the control system was to deliver the maximum amount of consistently high quality symp, within plant constraints. This was formulated in an objective function which seeks to minimize a weighted sum of the errors of syrup concentration from a setpoint, and the fluctuations in juice flowrates. Two alternative formulations were developed, and tested on the plant model.
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Qiu, Guoquan. "A novel evaporative/desiccant cooling system." Thesis, Nottingham Trent University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.444606.
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Guerra, Zuimdie. "Evaporative air conditioner for automotive application." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/35980.
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Dreyer, Andre Alexis. "Analysis of evaporative coolers and condensers." Thesis, Stellenbosch : Stellenbosch University, 1988. http://hdl.handle.net/10019.1/66038.
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Thesis (MEng.) -- Stellenbosch University, 1988.ENGLISH ABSTRACT: In this report various mathematical models for the thermal evaluation of evaporative coolers and condensers are presented. These models range from the exact model based on the work by Poppe [84P01] to the simplified logarithmic models based on the work of McAdams [54Mcl] and Mizushina et al. [67MI1], [68MI1]. Various computer programs were written to perform rating and selection calculations on cross-flow and counterflow evaporative coolers and condensers. Experimental tests were conducted on a cross-flow evaporative cooler to determine the governing heat and mass transfer coefficients. The experimentally determined coefficients were cqrrelated and these correlations are compared to the existing correlations. The two-phase pressure drop across the tube bundle was also measured and a correlation for two-phase pressure drop across a tube bundle is presented.
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Giacomelli, Gene, and Kathryn Hahne. "Evaporative Cooling in Semi-Arid Climates." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2008. http://hdl.handle.net/10150/146294.
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2 pp.In the semi-arid climate of southern AZ, evaporative cooling systems are commonly used and very effective for cooling homes (swamp coolers), outdoor areas (misters), and for greenhouses used for commercial and horticultural plant production (pad-and-fan, high-pressure-fog). The purpose of this brochure is to educate users about strategies they can employ to save water and improve the performance of evaporative cooling systems. Principles of operation, a list of advantages and disadvantages, and a comparison of common systems is also included, to help users decide the best system for them.
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Smith, Jason Berndt. "Sodium salt scaling in falling film black liquor evaporators." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/10263.
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Broome, Steven. "Liquid Distribution And Falling Film Wetting In Dairy Evaporators." Thesis, University of Canterbury. Department of Chemical and Process Engineering, 2005. http://hdl.handle.net/10092/4027.
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Niro designed and built five near-identical milk evaporators for Fonterra’s production site at Clandeboye and five at the Edendale site. Tubes in the Clandeboye evaporators often fouled excessively and occasionally blocked, requiring water blasting to clear them. Large amounts of undesirable foam from milk were observed in the second effect of some evaporators. This was known to be related to fouling and early shutdowns. The fouling increased the cleaning chemical and utility usage, and the evaporator downtime. The problems were believed to be related to the liquid distribution system at the top of the tubes. Evaporator liquid distribution has received relatively little research but it has been shown that the efficiency of evaporation reduces when there is poor wetting. Some estimates were available from previous work for the minimum flowrates required to obtain a complete falling film inside a tube. Many tasks were performed to assess the performance of the liquid distribution systems. The minimum wetting rates of three different milks were found in a model evaporator tube under isothermal, heat transfer and evaporation conditions at 60ºC. Numerous measurements of evaporators at Clandeboye were made to thoroughly analyse the evaporator performance. The overall heat transfer coefficients and wetting rates were calculated throughout the evaporators. Physical measurements were taken of the dimensions of the distribution systems in every evaporator. Many potential problems were found including warping, inconsistent hole sizes and fabrication faults. An analysis of the tube and distribution hole arrangements showed that every pass had some liquid misdistribution which was confirmed by a water trial. The evaporators were inspected before cleaning after 22 hours of whole milk production and after 5 hours of milk protein concentrate (MPC) production. There was considerable fouling at the bottom of some tubes that received low whole milk flows and large particles of MPC were blocking distribution plate holes. Observation and analysis showed that the foaming was likely to be caused by an upward flow of vapour from some passes which disrupted the downward flow of milk. As a result of this project there is sufficient confidence to justify modification of effects 2 and 4 of the evaporators. Sixteen tubes in effect 4 will be welded shut and the distribution systems in effects 2 and 4 will be redesigned to give a better liquid distribution. For effect 2, vertical tubes called ‘vapour risers’ should be installed to allow the vapour to flow upwards through the distribution plate without creating foam. The heights of the partitions dividing the effect 2 passes will be modified to encourage any foam in pass 1 to flow preferentially to pass 2. Installing a filter after the MPC direct steam injector will reduce the number of blocked distribution plate holes. Both modifications are expected to enable the evaporators to run continuously for 20 hours instead of 15 hours, giving up to 33% fewer cleans. The cleaning costs are approximately $700 and milk losses are approximately $200 per clean. The modifications should save up to $438,000, based on cleaning and water blasting in the 2003-2004 milk powder season. The design of future evaporator distribution systems must be improved to avoid retrofitting.
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Farnham, Taylor A. "Design and fabrication of evaporators for thermo-adsorptive batteries." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92611.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.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 (page 61).
Current heating and cooling within electric vehicles places a significant demand on the battery, greatly reducing their potential driving range. An Advanced Thermo- Adsorptive Battery (ATB) reduces this load by storing thermal energy within a bed of adsorptive sheets. A phase change heat exchanger capable of delivering the required cooling via liquid-vapor phase change was designed and prototyped for ATB. The thermal performance and fluid flow within the phase change heat exchanger were characterized for both coolant and refrigerant. A full-scale and quarter-length prototype was designed within the desired geometric and operating condition constraints. In order to build the phase change heat exchanger, fabrication techniques, including brazing, copper sintering, and bonding porous media were explored and characterized. In addition, the quarter-length design was fabricated and insights from its construction are proposed as recommendations for future work.
by Taylor A. Farnham.
S.B.
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Sandström, Camilla. "Frosting and Defrosting on Air Source Heat Pump Evaporators." Thesis, KTH, Energiteknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-299880.
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Air source heat pumps has become increasingly popular for residential households as they are considered an energy efficient alternative on the heating market. The air source heat pumps use the outdoor air as heat source and can operate in cold climates around -15 to -20°C, but as the temperatures drops below 6°C the heat pump experiences problems with frost accumulating on the heat exchanger. The frost collected on the heat exchanger lowers the heat pump performance and can in worst case cause a malfunction. Therefore, frost suppression and defrost strategies are important to increase efficiency. This thesis will though an experimental setup of a 5kW air-to-water heat pump investigate frosting behaviour on the evaporator under different ambient conditions. The frost will be analysed through thermodynamic measurement data as well as frost weight measurement and image analysis of the frost growth and thickness on the fins. Two evaporators were used for comparison, one treated with a hydrophobic nano-coating and the other without any treatment. Measurements showed that the coated evaporator effectively suppressed the frost from affecting the heat transfer for temperatures above the freezing point with longer time between defrosts and slower frost growth. Measurements at ambient temperatures of 5.5 and 2.0°C resulted in a 54% and 7%, respectively, longer time between defrosts for the coated evaporator compared to the uncoated one, as well as 35% and 14% slower growth rate of the ice layer thickness. As the ambient temperature decrease frost suppression loses its efficiency and at ambient air temperatures below the freezing point the uncoated evaporator achieved longer time durations between the defrosts and slower ice layer thickness growth compared to the coated evaporator. The first recorded attachment of frost on the fins of the evaporator was delayed for all measurements with the coated evaporator compared to the uncoated evaporator. The air side pressure drop over the heat exchanger, due to frost growth at the air inlet, followed a non-linear behaviour starting with an increase as the frost attached to the fins and tubes of the evaporator, followed by a decrease in the middle of the measurement and ending with an increase until the heat pump initiated defrost. Fan power consumption followed the same pattern, but no apparent cause for the pressure drop could be found in the data collected during the measurements.
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O'Halloran, Steven Patrick. "Experimental measurements and numerical analyses of an automotive evaporator /." Search for this dissertation online, 2006. http://wwwlib.umi.com/cr/ksu/main.
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Day, Benjamin Marc. "An Evaluation and Redesign of a Thermal Compression Evaporator." ScholarWorks@UNO, 2009. http://scholarworks.uno.edu/td/926.
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Evaporators separate liquids from solutions. For maximum efficiency, designers reduce the temperature difference between the heating and heated media using multiple-stage evaporators. This efficiency requires increased size and bulk. A vendor claimed its thermal compression evaporator achieved high efficiency with only two stages. It did not function as claimed. This project investigated the evaporator's design to identify its problems and propose an alternative design with a minimized footprint. The analysis showed theoretical flaws and design weaknesses in the evaporator, including violation of the first law of thermodynamics. An alternative thermal compressor design was created through computational fluid dynamics using spreadsheet methods developed in house, aided by the software product FLUENT. Detailed component sizing was done using the software product HYSYS. The proposed redesign achieved four to one efficiency with two stage thermal compression, using one half of the space of a traditional system of similar performance.
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Van, den Dool Kari. "Evaporative cooling of apple and pear orchards." Thesis, Link to the online version, 2006. http://hdl.handle.net/10019/1251.
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Musa, Mu'azu. "Novel evaporative cooling systems for building applications." Thesis, University of Nottingham, 2009. http://eprints.nottingham.ac.uk/10674/.
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The technology and applications of evaporative cooling to provide human comfort in buildings is not new and has been used in different places based on different methods and materials. Conventional air conditioning systems overshadowed the application of evaporative cooling for buildings despite their ozone layer depletion. Evaporative cooling using porous ceramic evaporators were experimentally investigated. Encouraging results in terms of temperature reduction and cooling effectiveness were reported. In this work also thermoelectric unit was integrated in to the evaporative cooling system containing porous ceramic evaporators. The warm inlet air cooled in the evaporative cooling chamber was passed over the hot-side fins of the thermoelectric cooling device to act as a better heat sink. Typical test results showed that the cold side temperature of thermoelectric unit was 5Deg.C lower and the hot side was 10Deg.Clower, respectively when operated on the wet and dry porous ceramics evaporative cooling chamber. Direct evaporative cooling is often associated with the rise in relative humidity which may result in uncomfortable feeling due to unwanted increase in moisture. Indirect evaporative cooling offers a solution but still requires improvements in the effectiveness. There is also need for using cheap and readily available materials for the construction, requiring simple fabrication technology without very complex engineering infrastructure. Most widely used common fibrous materials have very limited capillary effect. So a periodic water spray system with an automatic control is required for running the cooler which adds to the power consumption, rise in operation costs as well as construction and operational difficulties. As a compromise using horizontal arrangement was considered. Use of pump for supplying water required to moisten the evaporative cooling surface was eliminated. The system was constructed and tested under varying temperature, relative humidity and air flow rates. Results showed significant temperature reduction accompanied with acceptable increase in relative humidity. Temperature drop of 6-10Deg.C between the inlet and outlet temperatures of the product or supply air was recorded. Increase in relative humidity of the supply air was 6 - 10% less than the working air. Application of this novel system was demonstrated in the parasol self-cooling arrangement. The fibre tube vaporative cooler has the potential of cooling a building space to the acceptable comfort limits. The application of porous ceramics for building space cooling, integrating the system to be used as a heat sink and the use of horizontal fibre tubes for evaporative cooling are all novel ideas in this field of research. Other novel features also include the ability to minimise energy consumption by eliminating common methods of continuous water circulation.
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Hudson, David Mark. "The high temperature evaporative refining of metals." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.330210.
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Hall, Carsie Alvin. "Evaporative cooling effects in precision machine tools." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/36012.
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Ciccone, Brianne N. "Modeling of Evaporative Losses in Industrial Pasteurization." Youngstown State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1339587036.
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Sahu, Srikrishna. "Experimental study of isothermal and evaporative sprays." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/7076.
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The present research focuses on studying an isothermal spray to understand the mechanism of interaction between droplets and turbulent air flow, and an evaporative spray to evaluate the group evaporation of droplets as opposed to single droplet evaporation. The thesis describes the development and application of two novel experimental techniques for simultaneous characterization of droplet and gaseous phases in isothermal and evaporative sprays respectively. Both approaches use the out-of-focus imaging technique, Interferometric Laser Imaging for Droplet Sizing (ILIDS), for planar measurements of droplet size and velocity. The in-focus imaging techniques Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) are respectively combined with ILIDS for simultaneous measurement of gas flow characteristics in an isothermal spray and vapour concentration distribution in an evaporative spray. Combination of either of the two optical arrangements results in a discrepancy in the location of the centre of a droplet leading to erroneous identification of the droplets in the PIV/PLIF images. This issue has been addressed and a method is proposed to reduce the droplet positioning error. The coupling between the droplet and gas phases in the isothermal spray is explained by evaluating several statistical quantities, the most important being the spatial correlation coefficients of the droplet-gas velocity fluctuations obtained conditional on droplet size classes. The effect of anisotropy and gravity on the momentum transfer between the two phases are studied. The gas flow eddy structures are extracted by applying Proper Orthogonal Decomposition (POD) on the instantaneous gas velocity data and the selective influence of the large scale eddy structures of the gas phase flow on the droplet-gas flow interaction are examined. In order to study the effect of inter droplet spacing on the droplet evaporation rate, experiments are first performed for the mono-sized droplet stream. The smaller inter droplet spacing of the larger droplet sizes causes the vapour to surround the droplet stream leading to droplet group evaporation. The smaller magnitude of the mean group evaporation number, evaluated at different radial locations in the evaporative acetone spray, suggests the mode of evaporation is in the range of regimes of individual to group evaporation. It is shown that the assumption of uniform droplet spacing in the theoretical expressions for the evaluation of the group evaporation number always leads to overestimation of the group evaporation number.
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Caravello, Victor. "Total evaporative resistance of selected clothing ensembles." [Tampa, Fla.] : University of South Florida, 2004. http://purl.fcla.edu/fcla/etd/SFE0000452.
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Agartan, Yigit Ata. "Experimental Comparison Of Different Minichannel Geometries For Use In Evaporators." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614095/index.pdf.
Full textAbstract:
This thesis investigates the refrigerant (R-134a) flow in three minichannels having
different geometries experimentally. During the last 40 years heat transfer in
small scales has been a very attractive research area. Improvements in heat
transfer in the refrigeration applications by means of usage of micro/minichannels
provide significant developments in this area. Also it is known that experimental
studies are very important to constitute a database which is beneficial for new
developments and research. During the two-phase flow experiments conducted
in the minichannels, low mass flow rates and constant wall temperature
approach, which are the conditions in the evaporators of the refrigerator
applications were applied because one of the purposes of this study is to
determine the most ideal minichannel among the tested minichannels for usage
in the evaporator section of the refrigerators. Two-phase flow experiments were
made with refrigerant R134a in the three minichannels having hydraulic
diameters of 1.69, 3.85 and 1.69 mm respectively. As distinct from the others, the
third minichannel has a rough inner surface. Comparison of the experimental
results of the three minichannels was made in terms of forced convection heat
transfer coefficients and pressure drop at constant quality and mass flux values.
As a result of the experiments, the most ideal minichannel among the tested
minichannels was determined for the evaporator applications in the refrigerators.
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Behbahani, Reza M. "Heat transfer and heat transfer fouling in phosphoric acid evaporators." Thesis, University of Surrey, 2003. http://epubs.surrey.ac.uk/842710/.
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The primary problem in concentrating phosphoric acid is due to fouling on the tube-side of the heat exchangers of the evaporators. Scaling on the heat transfer surfaces occurs because of high supersaturation of phosphoric acid liquor with respect to calcium sulfate. A review of the existing literature reveals that no information is available on heat transfer and on crystallisation fouling of phosphoric acid solutions. Solubility of calcium sulfate is very important with regards to the scaling problems in phosphoric acid concentration plants. Hence, the solubility of different calcium sulfate types in phosphoric acid solution was studied and their dependency on acid concentration and temperature were investigated. A large number of measurements of heat transfer coefficient for water and phosphoric acid solutions under forced convective, subcooled flow boiling and pool boiling conditions at different temperatures, flow velocities, heat fluxes and concentrations were performed. The results show that the modified Gnielinski and Petukhov and Popov con-elations fit the experimental results for forced convective heat transfer to phosphoric acid solutions better than the other correlations. The Chen model and associated correlations were found suitable for the prediction of subcooled flow boiling heat transfer coefficients for phosphoric acid solutions. Applying the actual temperature driving force (Tw-Ti) instead of (Tw-Tb), a theoretical model was proposed, which permits the prediction of pool boiling heat transfer coefficients of phosphoric acid solutions with good accuracy. A large number of fouling experiments were carried out at different flow velocities, surface temperatures and concentrations to determine the mechanisms, which control deposition process. After clarification of the effect of operational parameters on the deposition process, a mathematical model was developed for prediction of fouling resistance. The activation energy evaluated for the surface reaction of the deposit formation was found to be 56,829 J/mol. The predicted fouling resistances were compared with the experimental data. Quantitative and qualitative agreement for measured and predicted fouling rates, is good. Also, a kinetic model for crystallization fouling was developed, using the field data. The predictions of the suggested model are in good agreement with the plant operating data. Finally, a numerical model was developed for computer simulation of shell and tube heat exchangers. The agreement between the field data and the prediction of the model was very satisfactory.
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Зубков, О. В., І. В. Свид, and О. С. Мальцев. "Features of the use of PID controllers when controlling evaporators." Thesis, MC&FPGA, 2020. https://mcfpga.nure.ua/conf/2020-mcfpga/10-35598-mcfpga-2020-001.
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In the work, the features of the use of PID regulators for controlling evaporators are theoretically and experimentally analyzed, an algorithm for controlling the heating element of the evaporator is developed, and practical recommendations are given for choosing the parameters of the PID controller.
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Elliott, Matthew Stuart. "Decentralized model predictive control of a multiple evaporator HVAC system." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3001.
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Bérubé, Pierre. "High temperature biological treatment of foul evaporator condensate for reuse." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0028/NQ48606.pdf.
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Chaer, Issa Namr. "Refrigeration performance with electrically enhanced heat transfer at the evaporator." Thesis, London South Bank University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313001.
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PRUZAESKY, FRANK CHAVIANO. "THEORETICAL AND EXPERIMENTAL STUDY OF A SHELL AND COIL EVAPORATOR." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2001. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=1770@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORO presente trabalho diz respeito ao desenvolvimento de um modelo de simulação para evaporadores do tipo casco e serpentina, com aplicações para resfriadores de água. O modelo considera o trocador de calor como divido em duas zonas: uma de evaporação e outra de superaquecimento. Diferentes mecanismos de transferência de calor, existentes em cada zona, foram, portanto, levados em consideração. Definidas as condições de entrada de ambos os fluidos e a geometria do evaporador,um programa escrito em FORTRAN foi desenvolvido para calcular o desempenho térmico do evaporador, incluindo a capacidade térmica, condições de saída do refrigerante e água e distribuição de área de troca pelas duas zonas. Propriedades do refrigerantes foram calculadas com subrotinas do pacote REFPROP, desenvolvido no NIST, EUA, permitindo a modelagem de equipamentos operando com uma vasta gama de refrigerantes, incluindo hidrocarbonetos e misturas não azeotrópicas. Em virtude da ausência de informação na literatura, um aparato experimental foi construído para a determinação do coeficiente de transferência de calor no lado da carcaça, por onde escoa a água.
The present work is concerned with the development of a simulation model for shell and coil heat exchangers with first application in water-chillers. The model considers the heat exchanger as divided into two zones: two-phase region (boiling) and superheating region. Different refrigerant properties and heat transfer mechanisms are thus taken into account for each zone. For prescribed heat exchanger's geometry and water and efrigerant inlet conditions, a program in FORTRAN calculates the evaporator's performance which includes: refrigerant and water outlet conditions, evaporator's thermal capacity, and tube distribution for each zone. The REFPROP code programmed in FORTRAN was used for getting the local refrigerant properties, and the new kattan et al. s model for refrigerants boiling, including the new flow pattern map, was used for predicting the internal convective coefficient of heat transfer at the boiling region. A simple correlation was obtained for predicting the water convective coefficient depending on Reynolds number for the specific geometry at tested ranges of temperature. An evaporator was manufactured and an accurate test rig that included two controlled temperature baths and a data acquisition system was used for obtaining used data. The model is able to deal with a number of pure refrigerants and refrigerant blends.
El presente trabajo discute el desarrollo de un modelo de simulación para evaporadores de tipo casco y serpentina, con aplicaciones para refrigeradores de agua. El modelo considera que el agente de intercambio de calor está divido en dos zonas: una de evaporación y otra de supercalentamiento. Por esto, se consideraron los diferentes mecanismos de transferencia de calor existentes en cada zona. Definidas las condiciones de entrada de ambos fluidos y la geometría del evaporador, se desarrolló un programa en FORTRAN para calcular el desempeño térmico del evaporador, incluyendo la capacidad térmica, condiciones de salida del refrigerante y agua y distribución de área de intercambio térmico por las dos zonas. Las popriedades del refrigerante fueron calculadas con subrutinas del paquete REFPROP, desarrollado en el NIST, EUA, lo que permitió modelar los equipos operando con una vasta gama de refrigerantes, incluyendo hidrocarbonetos y mezclas no azeotrópicas. En virtud de la ausencia de información en la literatura, se construyó un aparato experimental para la determinación del coeficiente de transferencia de calor en el lado del casco, por donde sale el agua.
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Hassan, Abdelrahman Hussein Abdelhalim. "Development and Validation of a Minichannel Evaporator Model under Dehumidification." Doctoral thesis, Universitat Politècnica de València, 2016. http://hdl.handle.net/10251/71357.
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[EN] In the first part of the current thesis, two fundamental numerical models (Fin2D-W and Fin1D-MB) for analyzing the air-side performance of minichannel evaporators were developed and verified. The Fin2D-W model applies a comprehensive two-dimensional scheme to discretize the evaporator. On the other hand, the Fin1D-MB model is based on the one-dimensional fin theory in conjunction with the moving boundaries technique along the fin height. The first objective of the two presented models is to identify and quantify the most influential phenomena encountered in the process of cooling and dehumidification. The second objective is to study the impact of the classical modeling assumptions on the air-side performance of minichannel evaporators. Different comparative studies between the traditional Effectiveness-NTU approach and the proposed numerical models were implemented to achieve the mentioned goals. The results revealed that the modeling assumptions which have the most significant impacts on the heat and mass transfer rates are: the uniform air properties along the fin height, adiabatic-fin-tip at half the height, and negligence of partial dehumidification scenarios. These widely used assumptions resulted in substantial deviations in total heat transfer rate, up to 52%, between the Effectiveness-NTU approach and Fin2D-W model.
In the second part of the thesis, the Fin1D-MB model was integrated into the IMST-ART® simulation tool to evaluate the global performance of minichannel evaporators (air- and refrigerant-side). The Fin1D-MB model was selected because of its simplicity, calculation speed, and reasonable solution accuracy relative to the Fin2D-W model. The validation of the complete Fin1D-MB model was conducted against many experimental data and numerical models available in the literature. The validation process was achieved for different heat exchanger geometries, refrigerants, and operating conditions. The results showed that for the R134a minichannel evaporators studied, the Fin1D-MB model successfully predicted the Inlet refrigerant and outlet air temperatures, cooling capacity, and refrigerant-side pressure drop within error bands of ±0.5 ºC, ±5%, and ±20%, respectively. For the CO2 (R744) minichannel evaporator studied, the presented model estimated the cooling capacity and outlet air temperature within error bands of ±10% and ±1.0 ºC, respectively. Regarding the CO2 pressure drop, the Fin1D-MB model generally underpredicted the pressure drop values compared to the experimental data, with a maximum deviation of 11 kPa.[ES] En la primera parte de la tesis actual, dos modelos numéricos fundamentales (Fin2D-W y Fin1D-MB) para analizar el lado del aire de los evaporadores de minicanales se han desarrollado y verificado. El modelo Fin2D-W aplica un esquema detallado de dos dimensiones para discretizar el evaporador mientras que el modelo Fin1D-MB se basa en la teoría de la aleta unidimensional junto con la técnica de fronteras móviles para el lado del aire. El primer objetivo de los dos modelos presentados es identificar y cuantificar los fenómenos más influyentes encontrados en el proceso de enfriamiento y deshumidificación. El segundo objetivo es estudiar el impacto de las hipótesis comúnmente usadas en el modelado de la transmisión de calor del aire de los evaporadores de minicanales. Se implementaron diferentes estudios comparativos entre el enfoque tradicional Effectiveness-NTU y los modelos numéricos propuestos para alcanzar los objetivos mencionados. Los resultados muestran que las hipótesis que provocan una mayor desviación con respecto a la solución detallada en la transferencia de calor y masa son: propiedades de aire uniforme a lo largo de la altura de la aleta, extremo adiabático de aleta a mitad de su longitud, y no contemplar el supuesto de deshumidificación parcial en la aleta. Estas hipótesis ampliamente utilizadas han resultado en errores importantes en la transferencia de calor total, hasta un 52%, entre el enfoque Effectiveness-NTU y el modelo Fin2D-W. En la segunda parte de la tesis, el modelo Fin1D-MB se integró en la herramienta de simulación IMST-ART® para evaluar el rendimiento global de los evaporadores de minicanales (en el lado del aire y del refrigerante). El modelo Fin1D-MB se seleccionó gracias a su simplicidad, velocidad de cálculo, y solución de una precisión razonable relativa al modelo Fin2D-W. Se realizó una validación del modelo completo Fin1D-MB con la ayuda de datos experimentales y modelos numéricos ya disponibles en la literatura. El modelo se ha validado para diferentes geometrías de intercambiadores de calor, refrigerantes y condiciones de funcionamiento. Los resultados han mostrado que para los evaporadores de minicanales funcionando con el refrigerante R134a, el modelo Fin1D-MB predice de manera correcta las temperaturas de entrada del refrigerante y de salida del aire, la capacidad de enfriamiento, y la caída de presión del lado de refrigerante dentro de las bandas de error de ±0.5 ºC, ±5%, y ±20%, respectivamente. Para el evaporador de minicanales con CO2 (R744) estudiado, el modelo estima la capacidad de refrigeración y la temperatura de salida del aire dentro de las bandas de error de ±10% y ±1.0 ºC, respectivamente. En cuanto a la caída de presión de CO2, el modelo Fin1D-MB generalmente predice a la baja los valores de la caída de presión en comparación con los datos experimentales, con una desviación máxima de 11 kPa.
[CAT] A la primera part de la tesi actual, dos models numèrics fonamentals (Fin2D-W i Fin1D-MB) per analitzar el costat de l'aire dels evaporadors de minicanals s'han desenvolupat i verificat. Al model Fin2D-W s'aplica un esquema detallat de dues dimensions per discretitzar l'evaporador mentre que al model Fin1D-MB es basa en la teoria d'aleta unidimensional juntament amb la tècnica de frontera mòbil per al costat de l'aire. El primer objectiu dels dos models presentats és identificar i quantificar els fenòmens més influents trobats en el procés de refredament i deshumidificació. El segon objectiu és estudiar l'impacte de les hipòtesis comunament utilitzades en el modelatge de la transmissió de calor de l'aire dels evaporadors de minicanals. Es van implementar diferents estudis comparatius entre l'enfocament tradicional Effectiveness-NTU i els models numèrics proposats per assolir els objectius esmentats. Els resultats mostren que les hipòtesis que provoquen una major desviació respecte a la solució detallada a la transferència de calor i massa són: propietats d'aire uniforme al llarg de l'altura de l'aleta, extrem adiabàtic d'aleta a la meitat de la seua longitud, i no contemplar el supòsit de deshumidificació parcial en l'aleta. Aquestes hipòtesis àmpliament utilitzades donen errors importants en la transferència de calor total, fins a un 52%, entre l'enfocament Effectiveness-NTU i el model Fin2D-W. A la segona part de la tesi, el model Fin1D-MB es va integrar en l'eina de simulació IMST-ART® per avaluar el rendiment global dels evaporadors de minicanals (al costat de l'aire i del refrigerant). El model Fin1D-MB es va seleccionar gràcies a la seva simplicitat, velocitat de càlcul, i solució d'una precisió raonable relativa al model Fin2D-W. Es va realitzar una validació del model complet Fin1D-MB amb l'ajuda de dades experimentals i models numèrics ja disponibles a la literatura. El model s'ha validat per a diferents geometries d'intercanviadors de calor, refrigerants i condicions de funcionament. Els resultats mostren que per als evaporadors de minicanals funcionant amb el refrigerant R134a, el model Fin1D-MB prediu de manera correcta les temperatures d'entrada del refrigerant i de sortida de l'aire, la capacitat de refreda-ment, i la caiguda de pressió del costat de refrigerant dins de les bandes d'error de ±0.5 ºC, ±5%, i ±20%, respectivament. Per a l'evaporador de minicanals amb CO2 (R744) estudiat, el model estima la capacitat de refrigeració i la temperatura de sortida de l'aire dins de les bandes d'error de ±10% i ±1.0 ºC, respectivament. Pel que fa a la caiguda de pressió de CO2, el model Fin1D-MB generalment prediu a la baixa els valors de la caiguda de pressió en comparació amb les dades experimentals, amb una desviació màxima d'11 kPa.
Hassan, AHA. (2016). Development and Validation of a Minichannel Evaporator Model under Dehumidification [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/71357
TESIS
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Yang, Jianxin. "A study of heat pump fin staged evaporators under frosting conditions." [College Station, Tex. : Texas A&M University, 2004. http://hdl.handle.net/1969.1/555.
Full textAbstract:
Thesis (Ph.D.)--Texas A&M University, 2003."Major Subject: Mechanical Engineering" Title from author supplied metadata (record created on Jul. 18, 2005.) Vita. Abstract. Includes bibliographical references.
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Kriesi, Ruedi. "Critical operation parameters of solar multi-stage evaporators with self regulation /." Lausanne, 1985. http://library.epfl.ch/theses/?nr=461.
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SOTOMAYOR, PAUL ORTEGA. "MODELING OF EVAPORATORS TYPE LAMINATED PLATE FOR AUTOMOTIVE AIR CONDITIONING SYSTEMS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2008. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=12431@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOÉ desenvolvido um modelo de simulação de evaporadores automotivos tipo placa (Brazed Laminated Plate), para o resfriamento de ar úmido. O modelo estudado adota o método de análise local, onde o trocador de calor é dividido em um número de elementos de troca de calor, para os quais as equações de troca de calor e de conservação de energia são aplicadas. Para efeito da determinação do coeficiente local de troca de calor e do fator de atrito, o modelo considera duas regiões na troca de calor. Pelo lado do refrigerante foi considerada uma região bifásica (líquido - vapor) e outra, de superaquecimento (vapor). No lado do ar têm-se duas condições: com a superfície do evaporador seca ou molhada. Para cada zona foram levados em conta diferentes mecanismos de transferência de calor. Também foi estudada a queda de pressão do lado do refrigerante e do lado do ar, utilizando, para tal, as respectivas correlações de queda de pressão. Para a simulação foram consideradas definidas as condições de entrada dos fluídos e a geometria do evaporador. Um programa foi desenvolvido em FORTRAN para calcular os estados termodinâmicos de saída dos dois fluidos. As propriedades do refrigerante foram calculadas utilizando o software REFPROP versão 7.0, desenvolvido no NIST, EUA, o que permitiu a modelagem do trocador de calor operando com uma vasta gama de refrigerantes. Novos refrigerantes, H e 1234yf, ainda não constantes da biblioteca REFPROP v07, foram também testados. Os resultados da simulação foram comparados com dados experimentais disponíveis.
A simulation model for automotive brazed laminate plate evaporators, for humid air cooling, was developed. The model adopts the local analysis method, where the heat exchanger is divided into a number of elemental control volumes, for which the equations of heat transfer and conservation of energy are applied. In order to determine the local heat transfer coefficient and friction factor, the model considers different regions in the heat exchanger. In the refrigerant side, two-phase or superheated flows were considered. In the air side, dry or wet surface conditions were modeled. For each zone different mechanisms of heat transfer and pressure drop were taken in account. The simulation model assumed prescribed evaporator geometry and inlet conditions for both fluids. A computer program was developed in FORTRAN to calculate overall thermodynamic outlet states of both fluids. Refrigerant properties were calculated using the software REFPROP version 7.0, developed by the NIST, U.S.A.. It allowed the modeling of the evaporator, operating with a vast range of refrigerants. New refrigerants, fluids H and 1234yf, (still not available in REFPROP v07 libraries) also were tested. The results of the simulation were compared with available experimental data.
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ZANETTI, EMANUELE. "EXPERIMENTAL AND NUMERICAL STUDY OF EVAPORATORS FOR MULTI-SOURCE HEAT PUMPS." Doctoral thesis, Università degli studi di Padova, 2022. https://hdl.handle.net/11577/3460845.
Full textAbstract:
The present thesis aims at describing the operation of innovative evaporators employed in multi-source heat pumps. The exploitation of multiple sources at the low-pressure side of a heat pump is recently considered to be a good solution to air source heat pumps, whose performance is limited to the external air temperature and to the necessity of periodic defrosting cycles.
In order to study the advantage of using multi-source heat pumps, it is necessary to investigate the performance of the selected evaporators at the desired operative conditions: to accomplish this purpose, the results of both experimental activities and simulations realized with ad hoc developed numerical tools are presented in this work.
First, a 16 kW air/ground dual-source heat pump working with R32 for heating, cooling and DHW production has been experimentally characterized. The advantage of such configuration is that it is possible to extract or dissipate heat with the most convenient thermal source and the possibility to undersize the ground loop compared to a conventional ground-coupled system. In the framework of this activity, a novel minichannels air-to-refrigerant heat exchanger has been mounted on the heat pump and used as the evaporator.
A 5 kW air/solar dual-source heat pump for water heating has also been experimentally studied in this work. When operating in solar-assisted mode, the evaporator consists of three PV-T (photovoltaic-thermal) solar collectors connected in parallel, where the refrigerant (CO2) is directly sent after the throttling process. The main advantage of using a solar evaporator is that, since the solar radiation can be considered as a forced heat flux, the evaporation temperature can be higher than that obtained in an air-to-refrigerant heat exchanger when the solar irradiance is high. Furthermore, the use of a PV-T device can reduce the global power consumption, due to PV electricity production. The presented heat pump prototype has been also designed to work in an innovative flooded-evaporation configuration: in this case, liquid CO2 enters the collectors and the flow is ensured by a natural circulation loop. The main advantage is the possibility to eliminate the maldistribution issues occurring in heat pump evaporators.
All the heat exchangers used analyzed experimentally have been numerically modelled in this work. A model of a brazed plate heat exchange, of a conventional finned coil heat exchanger, of an air-to-refrigerant minichannels heat exchanger and of a PV-T evaporator have been realized. The models have been developed in Matlab environment, following a distributed parameters approach: each discretized element is treated as an independent heat exchanger where continuity, momentum and energy equations are solved; in this sense, a “physical” approach has been used. This managed to investigate the operation of the studied heat pumps in non-tested conditions to further optimize the design and functioning of their components.
However, all the developed evaporators models are partly based on empirical correlations, in particular for the determination of the heat transfer coefficients on the refrigerant side. Empirical correlations are not always accurate and a well-established predictive model is not available in the literature. For this reason, a section of the present manuscript has been dedicated to presenting the description and the first results of a new CFD method for modelling the evaporation phenomenon in small channels during annular flow with refrigerants. The simulations have been realized in OpenFOAM environment and are based on the application of the Volume of Fluid method.The present thesis aims at describing the operation of innovative evaporators employed in multi-source heat pumps. The exploitation of multiple sources at the low-pressure side of a heat pump is recently considered to be a good solution to air source heat pumps, whose performance is limited to the external air temperature and to the necessity of periodic defrosting cycles. In order to study the advantage of using multi-source heat pumps, it is necessary to investigate the performance of the selected evaporators at the desired operative conditions: to accomplish this purpose, the results of both experimental activities and simulations realized with ad hoc developed numerical tools are presented in this work. First, a 16 kW air/ground dual-source heat pump working with R32 for heating, cooling and DHW production has been experimentally characterized. The advantage of such configuration is that it is possible to extract or dissipate heat with the most convenient thermal source and the possibility to undersize the ground loop compared to a conventional ground-coupled system. In the framework of this activity, a novel minichannels air-to-refrigerant heat exchanger has been mounted on the heat pump and used as the evaporator. A 5 kW air/solar dual-source heat pump for water heating has also been experimentally studied in this work. When operating in solar-assisted mode, the evaporator consists of three PV-T (photovoltaic-thermal) solar collectors connected in parallel, where the refrigerant (CO2) is directly sent after the throttling process. The main advantage of using a solar evaporator is that, since the solar radiation can be considered as a forced heat flux, the evaporation temperature can be higher than that obtained in an air-to-refrigerant heat exchanger when the solar irradiance is high. Furthermore, the use of a PV-T device can reduce the global power consumption, due to PV electricity production. The presented heat pump prototype has been also designed to work in an innovative flooded-evaporation configuration: in this case, liquid CO2 enters the collectors and the flow is ensured by a natural circulation loop. The main advantage is the possibility to eliminate the maldistribution issues occurring in heat pump evaporators. All the heat exchangers used analyzed experimentally have been numerically modelled in this work. A model of a brazed plate heat exchange, of a conventional finned coil heat exchanger, of an air-to-refrigerant minichannels heat exchanger and of a PV-T evaporator have been realized. The models have been developed in Matlab environment, following a distributed parameters approach: each discretized element is treated as an independent heat exchanger where continuity, momentum and energy equations are solved; in this sense, a “physical” approach has been used. This managed to investigate the operation of the studied heat pumps in non-tested conditions to further optimize the design and functioning of their components. However, all the developed evaporators models are partly based on empirical correlations, in particular for the determination of the heat transfer coefficients on the refrigerant side. Empirical correlations are not always accurate and a well-established predictive model is not available in the literature. For this reason, a section of the present manuscript has been dedicated to presenting the description and the first results of a new CFD method for modelling the evaporation phenomenon in small channels during annular flow with refrigerants. The simulations have been realized in OpenFOAM environment and are based on the application of the Volume of Fluid method.
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Gentine, Pierre. "Analysis of the diurnal behavior of Evaporative Fraction." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/34605.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2006.Includes bibliographical references (leaves 153-160).
In this thesis, the diurnal behavior of Evaporative Fraction (EF) was examined. EF was shown to exhibit a typical concave-up shape, with a minimum usually reached in the middle of the day. The influence of the vegetation cover and the soil moisture conditions on EF diurnal shape was also investigated. We also checked the repercussion of a change in environmental conditions on EF. This study will finally allow a better understanding of EF and suggests some new methods to obtain a good estimate of EF and of evapotranspiration.
by Pierre Gentine.
S.M.
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Al-Shooshan, Ahmad A. "Nozzle type evaporative cooling system in the greenhouse." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1291124029.
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Sait, Hani. "Analytical and experimental study of thin film evaporation in heat pipes /." free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p3164540.
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