Дисертації з теми "Heat"

A detailed investigation of novel air-coupled absorbers for use in a diesel engine exhaust-driven ammonia-water absorption system operating in extreme ambient conditions was conducted. Electrically driven vapor-compression systems are under scrutiny due to the environmental impact of synthetic refrigerants and the exacerbation of electric utility loads during peak demand periods. One alternative to vapor-compression systems is the absorption heat pump that uses environmentally benign working fluids and can be driven by a variety of heat sources, including waste heat and solar thermal processes. Direct air coupling of the absorber and condenser instead of indirect hydronic coupling can reduce absorption system size, complexity, and inefficiency, but materials compatibility issues with ammonia-water and the poor heat transfer properties of air present challenges. Heat and mass transfer modeling was used to predict the performance of round-tube corrugated-fin and compact tube-array absorbers designed for a 2.64-kW absorption chiller operated in high ambient temperature (51.7°C) conditions. A single-pressure ammonia-water test facility was constructed and used in conjunction with a temperature- and humidity-controlled air-handling unit to evaluate the absorbers at design and off-design operating conditions. Absorber performance was recorded over a range of air temperatures (35-54.4°C), air flow rates (0.38-0.74 m3 s-1), inlet solution temperatures (92-102°C), concentrated solution flow rates (0.006-0.010 kg s-1), and concentrated solution concentrations (38-46%). At design conditions, round-tube corrugated-fin absorbers of 394 and 551 Fins Per Meter (FPM) demonstrated comparable performance (Q394-FPM,exp = 4.521±0.271 kW; Q551-FPM,exp = 4.680±0.260 kW), and measured heat transfer rates were 0.7-1.9% AAD higher than those predicted through modeling. The measured heat transfer rate in the prototype tube-array absorber was significantly lower than the values predicted at design conditions (Qprot,exp = 2.22±0.24 kW; Qprot,mod = 4.33 kW). Maldistribution of the two-phase flow in the tube array is the probable cause of the disparity between the prototype absorber data and model predictions. Results from this investigation can be used to guide the development of air-coupled heat and mass exchangers for compact absorption heat pumps.

This study investigates the change in thermal resistance due to fouling in drain water pipes. As insulation of houses and energy efficiency of appliances improve, the importance of Drain Water Heat Recovery (DWHR) is growing steadily. In older houses, the relative heat loss through drain water is smaller than in newly built houses, but should still be considered. For example, 17 % of the total heat loss in Swedish multi-family houses built before 1940 was transported with the drain water (Ekelin et al., 2006). The average temperature of drain blackwater is between 23 °C and 26 °C (Seybold & Brunk, 2013), and a part of its heat can be recovered in DWHR systems. This allows cold incoming water to houses and buildings to be pre-heated by drain water before it is heated in the heat pump. Depending on the system, 30 % to 75 % of the heat from drain water can be recovered (Zaloum et al., 2007b). A threat to heat exchanger performance is that additional materials, so called fouling, accumulate on the surfaces of the heat exchangers and increases its thermal resistance. This resistance can be described by a fouling resistance and can be very costly due to losses in heat transfer and required cleaning. To quantify the fouling resistance, experiments were conducted in a climate chamber on Brinellvägen 66, using a pipe that had been installed for 3 years in the sewage system from the men’s toilet on Brinellvägen 64B. The installed pipe was compared with a pipe from the same manufacturer with the same dimensions. The pipes were sealed and filled with water at about 20 °C. Thermocouples were used to measure the decrease in water temperature over time in both pipes. Based on these measurements, the difference in thermal resistance was found, using curve fitting and the Lumped Capacitance Method. The fouling resistance was quantified by comparing the thermal resistances of the test pipe with and without fouling. The main findings were firstly that fouling significantly increases the thermal resistance of aluminium pipes. Secondly, corrosion causes a significant decrease in the pipes’ thermal resistance. The combination of these effects led to a decrease of 14 % in thermal resistance in the examined system after three years compared to the time of installation. The decrease in thermal resistance due to corrosion in the test pipe was 44 % compared to the time of installation. Furthermore, the thermal resistance of the test pipe decreased by 51 % when it was cleaned from the fouling. The fouling resistance of the 0.81 mm fouling layer was found to be 0.03068 m2K/W.
Denna studie undersöker den ökade termiska resistansen i avloppsrör på grund av beläggningar. Idag lägg stor vikt vid bra isolering och energieffektiv utrustning i nybyggda hus, vilket även sätter press på värmeåtervinning av avloppsvatten. Värmeåtervinningen av avloppsvatten är mindre viktig i äldre hus, då den relativa värmeförlusten av avloppsvatten är lägre än i nybyggda hus, men bör likväl tas i akt vid utvärderingen av värmeanvändning. I ett svenskt flerfamiljshus byggt före 1940 stod värmeförlusten på grund av varmt avloppsvatten för 17 % av den totala värmeförlusten (Ekelin et al., 2006). Den genomsnittliga temperaturen för svartvatten ligger på 23 °C till 26 °C (Seybold & Brunk, 2013), varav delar av värmen kan återvinnas i värmeväxlare. Detta bidrar till att det kalla ingående vattnet till värmepumpen förvärms av värmen från avloppsvattnet. Beroende på system och material kan 30 % till 75 % av värmen från avloppsvatten återvinnas (Zaloum et al., 2007b). Ett hot mot prestandan av värmeväxlare är att beläggning formas på de värmeöverförande ytorna i värmeväxlaren. Detta bidrar till en ökad termisk resistans och kan vara mycket kostsam på grund av minskning av värmeöverföring och nödvändig rengöring av anordningen. För att undersöka omfattningen av den ökade termiska resistansen utfördes en rad experiment i en klimatkammare på Brinellvägen 66. En jämförande metod användes där ett aluminiumrör, som tidigare installerats i avloppssystemet från herrarnas toalett i korridoren på Brinellvägen 64B, jämfördes med ett identiskt rör av samma tillverkare. Rören var tätade och fyllda med 20-gradigt kranvatten. Termoelement användes för att, över tid, mäta minskningen av vattentemperaturen i rören. Temperaturskillnaden användes för att beskriva skillnaden i termisk resistans genom att utföra kurvanpassning och tillämpa Lumped Capacitance Method. Skillnaden i termisk resistans mellan de båda rören antogs vara lika med beläggningens motstånd för värmeöverföring. Två huvudsakliga resultat kom av studien. Det första var att beläggning bidrar till ökad termisk resistans av aluminiumrör. Den andra var att korrosion tillsammans med andra externa faktorer orsakar en märkbar minskning av rörens termiska resistans. Totalt sett orsakade beläggningen tillsammans med korrosion en minskning av 14 % av den termiska resistansen i provröret, jämfört med den termiska resistansen vid installationstillfället. Vidare låg minskningen i termisk resistans på grund av korrosion i teströret på 44 % jämfört med den termiska resistansen vid installationstillfället och den genomsnittliga termiska resistansen av det rengjorda teströret låg på 51 % lägre än den genomsnittliga resistansen av teströret innan rengöring. Den beräknade resistansen för ett 0.81 mm tjockt lager av beläggning var 0.03068 m2K/W.

High grade energy, which is primarily derived from hydrocarbon fuels, is in short supply; therefore alternative energy sources such as renewable and recycled energy sources are gaining significant attention. Pyro-metallurgical processes are large consumers of energy. They in return generate large quantities of waste heat which goes un-recovered. The overall theme of this research is to capture, concentrate and convert some of this waste heat to a valuable form. The main objective is to characterize and develop heat pipe technology (some of which originated at McGill) to capture and concentrate low grade heat. Heat pipe employs boiling as the means to concentrate the energy contained in the waste heat and transfers it as higher quality energy. The distinct design features of this device (separate return line and flow modifiers in the evaporator) maximize its heat extraction capacity. During the testing the main limitations within the heat pipe were identified. Different test phases were designed throughout which the configuration of the system was modified to overcome these limitations and to increase the amount of extracted heat.
L'énergie d'haut grade de nos jours est produite principalement à base de combustion d'hydrocarbure et les réserves de cette énergie deviennent de plus en plus rare, mais certaines énergies alternatives connues gagnent des forces parmi les marchés incluant les sources d'énergie renouvelables et recyclées. Les usines pyrométallurgiques sont des consommateurs significatifs d'énergie d'haut grade. Ces procédés industriels relâches un montant important de chaleurs (perte) à l'environnement sans aucune récupération. Le but du projet est de concentrer, capturer et convertir cette chaleur résiduelle de basse qualité en énergie valable. Par contre, l'objectif principal du projet comme tel est de développer et de perfectionner un caloduc capable d'extraire cette chaleur parvenant des gaz effluents. Le point d'ébullition d'une substance (vapeur) est utilisé comme moyen de concentrer l'énergie contenu dans les effluents avec la technologie des caloducs. Pour maximiser les gains énergétiques, la conception de ce caloduc en particulier utilise des canaux de retour indépendant ainsi qu'un modificateur de débit dans l'évaporateur, lui permettant d'extraire un niveau supérieur de chaleur. Pendant les essais lors du projet, les éléments limitants des systèmes de caloducs ont été identifiés. Les configurations du système ont été ajustées et modifiés dans la phase expérimentale d'essai pour surmonter ces limitations et maximiser l'extraction de chaleur.

Refrigerant charge minimization is one of the most important targets for heating and air conditioning applications when using natural refrigerants like hydrocarbons or ammonia to cope with the new environmental challenges. Some applications of minichannels for charge minimization in heat pumps are presented and discussed in this thesis. The design of an innovative condenser, an evaporator and an internal heat exchanger is presented. These devices are shell-and-tube heat exchangers using 2 mm i.d. minichannels and realized for the use with propane. Computational procedures based on empirical correlations available in the literature and a simplified model of the heat transfer and pressure drop processes have been developed and used for the design. Experimental performance data of the heat exchangers when using R22 and propane is reported and compared against the predictions given by the computational procedures. The shell-and-tube minichannel heat exchangers have been installed in a 100 kW heat pump using propane as the refrigerant. The unit has been designed for laboratory tests and the minichannel shell-and-tube heat exchangers have been installed in the facility together with a conventional plate condenser and an evaporator. Different configurations have been tested in order to quantify the advantages of operating the heat pump using the low charge heat exchangers, with regard to both energy performance and propane charge. In particular, the experimental performance when using the minichannel condenser is compared to the one obtained when using the plate condenser, and the influence of the internal heat exchanger on the performance of the equipment is measured and discussed. Experimental data about the efficiency with propane of the semihermetic compressor installed in the heat pump is also reported. Besides empirical correlations to predict the global thermal performance, a more complete understanding of the two-phase flow and heat transfer in minichannels is needed for the design and optimization of heat exchangers. Some CFD simulations are presented in this thesis using the innovative Volume Of Fluid (VOF) method, which is able to directly compute multiphase flows without using any empirical closure law to model the interaction between the phases. In order to assess the capability of the method to compute the motion of the gas-liquid interface, which is crucial for two-phase flow and heat transfer, simulations of the adiabatic churn flow regime of air-water mixture at different pipe diameters and liquid and gas superficial velocities have been initially performed. A comparison of the numerical results with experimental visualizations is reported and a simplified theoretical model of the wave levitation process has been developed and used to explain the numerical results. The VOF simulations were then extended to the study of condensation of R134a inside a minichannel with 1 mm internal diameter. Computational results about the evolution of the vapour-liquid interface and the heat transfer coefficient along the channel are reported.
La riduzione della carica di refrigerante nelle applicazioni di condizionamento e riscaldamento è uno dei vincoli di progetto principali quando vengono utilizzati, per motivi di carattere ambientale, refrigeranti naturali come idrocarburi ed ammoniaca. Alcune applicazioni dei minicanali per la minimizzazione della carica nelle pompe di calore vengono presentate e discusse nella presente tesi. Viene presentato il progetto di un condensatore, un evaporatore ed uno scambiatore di calore rigenerativo innovativi. Questi componenti sono degli scambiatori di calore a fascio tubiero utilizzanti minicali del diametro di 2 mm e progettati per l’uso con propano. Delle procedure di calcolo basate su di correlazioni disponibili in letteratura ed un modello semplificato del processo di scambio termico sono state utilizzate per il progetto. Le prestazioni sperimentali degli scambiatori con R22 e propano vengono riportate e confrontate con le stime fornite dalle procedure di calcolo. Gli scambiatori di calore sono stati installati in una pompa di calore della capacità termica di 100 kW utilizzante propano come fluido frigorigeno. Nell’impianto della pompa di calore, destinata a test di laboratorio, sono stati installati anche un condensatore ed un evaporatore a piastre convenzionali. In questo modo è stato possibile confrontare diverse configurazioni al fine di quantificare in via sperimentale i vantaggi apportati dall’utilizzo degli scambiatori a minicanali, in termini sia di prestazioni energetiche, sia di carica di propano richiesta. In particolare, le prestazioni delle configurazioni utilizzanti il condensatore a minicanali vengono confrontate con quelle delle configurazioni utilizzanti lo scambiatore a piastre, e l’influenza sulle prestazioni energetiche dello scambiatore rigenerativo viene misurata e discussa. Vengono inoltre riportati dati sperimentali relativi all’efficienza con propano del compressore semiermetico installato nella pompa di calore. Oltre a correlazioni empiriche in grado di stimare le prestazioni termiche globali, il progetto e l’ottimizzazione di scambiatori di calore richiede una più approfondita conoscenza del deflusso e dello scambio termico all’interno di minicanali. Vengono presentate in questa tesi delle simulazioni di termofluidodinamica computazionale tramite l’innovativo metodo VOF (Volume Of Fluid) in grado di simulare direttamente deflussi multifase senza la necessità di utilizzare correlazioni empiriche per la modellazione dell’interazione tra le fasi. Al fine di validare l’efficacia di questo metodo nel calcolare il moto dell’interfaccia gas-liquido, il quale è un aspetto cruciale nello scambio termico bifase, sono state in un primo momento eseguite delle simulazioni del regime di deflusso ”churn flow” per una miscela aria-acqua nel caso di un tubo liscio verticale adiabatico, a differenti valori di diametro del tubo e di velocità superficiale delle due fasi. I risultati sono stati confrontati con visualizzazioni sperimentali ed un modello teorico semplificato del processo di levitazione delle onde è stato sviluppato ed utilizzato per commentare i risultati numerici. Le simulazioni con il metodo VOF sono state in un secondo momento estese allo studio della condensazione di R134a all’interno di un minicanale del diametro di 1 mm. Vengono riportati risultati computazionali relativi all’evoluzione dell’interfaccia vapore-liquido e dei coefficienti di scambio termico lungo il minicanale.

Thesis (MScIng)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: As the demand for less expensive energy is increasing world-wide, energy conservation is becoming a more-and-more important economic consideration. In light of this, means to recover energy from waste fluid streams is also becoming more-and-more important. An efficient and cost effective means of conserving energy is to recover heat from a low temperature waste fluid stream and use this heat to preheat another process stream. Heat pipe heat exchangers (HPHEs) are devices capable of cost effectively salvaging wasted energy in this way. HPHEs are liquid-coupled indirect transfer type heat exchangers except that the HPHE employs heat pipes or thermosyphons as the major heat transfer mechanism from the high temperature to the low-temperature fluid. The primary advantage of using a HPHE is that it does not require an external pump to circulate the coupling fluid. The hot and cold streams can also be completely isolated preventing cross-contamination of the fluids. In addition, the HPHE has no moving parts. In this thesis, the development of a range of air-to-air HPHEs is investigated. Such an investigation involved the theoretical modelling of HPHEs such that a demonstration unit could be designed, installed in a practical industrial application and then evaluated by considering various financial aspects such as initial costs, running costs and energy savings. To develop the HPHE theoretical model, inside heat transfer coefficients for the evaporator and condenser sections of thermosyphons were investigated with R134a and Butane as two separate working fluids. The experiments on the thermosyphons were undertaken at vertical and at an inclination angle of 45° to the horizontal. Different diameters were considered and evaporator to condenser length ratios kept constant. The results showed that R134a provided for larger heat transfer rates than the Butane operated thermosyphons for similar temperature differences despite the fact that the latent heat of vaporization for Butane is higher than that of R134a. As an example, a R134a charged thermosyphon yielded heat transfer rates in the region of 1160 W whilst the same thermosyphon charged with Butane yielded heat transfer rates in the region of 730 W at 23 °C . Results also showed that higher heat transfer rates were possible when the thermosyphons operated at 45°. Typically, for a thermosyphon with a diameter of 31.9 mm and an evaporator to condenser length ratio of 0.24, an increase in the heat transfer rate of 24 % could be achieved. Theoretical inside heat transfer coefficients were also formulated which were found to correlate reasonably well with most proposed correlations. However, an understanding of the detailed two-phase flow and heat transfer behaviour of the working fluid inside thermosyphons is difficult to model. Correlations proposing this behaviour were formulated and include the use of R134a and Butane as the working fluids. The correlations were formulated from thermosyphons of diameters of 14.99 mm, 17.272 mm, 22.225 mm and 31.9 mm. The evaporator to condenser length ratio for the 31.9 mm diameter thermosyphon was 0.24 whilst the other thermosyphons had ratios of 1. The heat fluxes ranged from 1800-43500 W/m2. The following theoretical inside heat transfer coefficients were proposed for vertical and inclined operations (READ CORRECT FORMULA IN FULL TEXT ABSTRACT) φ = 90° ei h = 3.4516x105Ja−0.855Ku1.344 φ = 45° ei h = 1.4796x105Ja−0.993Ku1.3 φ = 90° l l l ci l l v h x k g 1/ 3 2.05 2 4.61561 109Re 0.364 ν ρ ρ ρ − ⎡ ⎡ ⎛ ⎞⎤ ⎤ = ⎢ ⎢ ⎜ ⎟⎥ ⎥ ⎢ ⎢ ⎜ − ⎟⎥ ⎥ ⎣ ⎣ ⎝ ⎠⎦ ⎦ φ = 45° l l l ci l l v h x k g 1/ 3 1.916 2 3.7233 10 5Re 0.136 ν ρ ρ ρ − ⎡ ⎡ ⎛ ⎞⎤ ⎤ = ⎢ ⎢ ⎜ ⎟⎥ ⎥ ⎢ ⎢ ⎜ − ⎟⎥ ⎥ ⎣ ⎣ ⎝ ⎠⎦ ⎦ The theoretically modelled demonstration HPHE was installed into an existing air drier system. Heat recoveries of approximately 8.8 kW could be recovered for the hot waste stream with a hot air mass flow rate of 0.55 kg/s at an inlet temperature of 51.64 °C and outlet temperature of 35.9 °C in an environment of 20 °C. Based on this recovery, energy savings of 32.18 % could be achieved and a payback period for the HPHE was calculated in the region of 3.3 years. It is recommended that not withstanding the accuracies of roughly 25 % achieved by the theoretically predicted correlations to that of the experimental work, performance parameters such as the liquid fill charge ratios, the evaporator to condenser length ratios and the orientation angles should be further investigated.
AFRIKAANSE OPSOMMING: As gevolg van die groeiende aanvraag na goedkoper energie, word die behoud van energie ‘n al hoe belangriker ekonomiese oorweging. Dus word die maniere om energie te herwin van afval-vloeierstrome al hoe meer intensief ondersoek. Een effektiewe manier om energie te herwin, is om die lae-temperatuur-afval-vloeierstroom (wat sou verlore gaan) se hitte te gebruik om ‘n ander vloeierstroom mee te verhit. Hier dien dit dan as voorverhitting van die ander, kouer, vloeierstroom. Hittepyp hitteruilers (HPHR’s) is laekoste toestelle wat gebruik kan word vir hierdie doel. ‘n HPHR is ‘n vloeistof-gekoppelde indirekte-oordrag hitteruiler, behalwe vir die feit dat dié hitteruiler gebruik maak van hittepype (of hittebuise) wat die grootste deel van sy hitteoordragsmeganisme uitmaak. Die primêre voordele van ‘n HPHR is dat dit geen bewegende dele het nie, die koue- en warmstrome totaal geïsoleer bly van mekaar en geen eksterne pomp benodig word om die werkvloeier mee te sirkuleer nie. In hierdie tesis word ‘n ondersoek gedoen oor die ontwikkeling van ‘n bestek van lug-totlug HPHR’s. Hierdie ondersoek het die teoretiese modellering van so ‘n HPHR geverg, sodat ‘n demonstrasie eenheid ontwerp kon word. Hierdie demonstrasie eenheid is geïnstalleer in ‘n praktiese industriële toepassing waar dit geïvalueer is deur na aspekte soos finansiële voordele en energie-besparings te kyk. Om die teoretiese HPHR model te kon ontwikkel, moes daar gekyk word na die binnehitteoordragskoëffisiënte van die verdamper- en kondensordeursneë, asook R134a en Butaan as onderskeie werksvloeiers. Die eksperimente met die hittebuise is gedoen in die vertikale en 45° (gemeet vanaf die horisontaal) posisies. Verskillende diameters is ook ondersoek, maar met die verdamper- en kondensor-lengteverhouding wat konstant gehou is. Die resultate wys dat R134a as werksvloeier in die hittebuise voorsiening maak vir groter hitteoordragstempo’s in vergelyking met Butaan as werksvloeier by min of meer dieselfde temperatuur verskil – dít ten spyte van die feit dat Butaan ‘n hoër latente-hittetydens- verdampings eienskap het. As voorbeeld gee ‘n R134a-gelaaide hittebuis ‘n hitteoordragstempo van omtrent 1160 W terwyl dieselfde hittebuis wat met Butaan gelaai is, slegs ongeveer 730 W lewer by 23 °C. Die resultate wys ook duidelik dat hoër hitteoordragstempo’s verkry word indien die hittebuis bedryf word teen ‘n hoek van 45°. ‘n Tipiese toename in hitteoordragstempo is ongeveer 24 % vir ‘n hittebuis met ‘n diameter van 31.9 mm en ‘n verdamper- tot kondensor-lengteverhouding van 0.24. Teoretiese binne-hitteoordragskoëffisiënte is ook geformuleer. Dié waardes stem redelik goed ooreen met die meeste voorgestelde korrelasies. Nieteenstaande die feit dat gedetailleerde twee-fase-vloei en die hitteoordragsgedrag van die werksvloeier binne hittebuise nog nie goed deur die wetenskaplike wêreld verstaan word nie. Korrelasies wat hierdie gedrag voorstel is geformuleer en sluit weereens die gebruik van R134a en Butaan as werksvloeiers in. Die korrelasies is geformuleer vanaf hittebuise met diameters van onderskeidelik 14.99 mm, 17.272 mm, 22.225 mm en 31.9 mm. Die verdamper- tot kondensor-lengteverhoudings vir die 31.9 mm deursnit hittebuis was 0.24 terwyl die ander hittebuise ‘n verhouding van 1 gehad het. Die hitte-vloede het gewissel van 1800-45300 W/m2. Die volgende teoretiese geformuleerde binne-hitteoordragskoëffisiënte word voorgestel vir beide vertikale sowel as nie-vertikale toepassing (LEES KORREKTE FORMULE IN VOLTEKS OPSOMMING) φ = 90° ei h = 3.4516x105Ja−0.855Ku1.344 φ = 45° ei h = 1.4796x105Ja−0.993Ku1.3 φ = 90° l l l ci l l v h x k g 1/ 3 2.05 2 4.61561 109Re 0.364 ν ρ ρ ρ − ⎡ ⎡ ⎛ ⎞⎤ ⎤ = ⎢ ⎢ ⎜ ⎟⎥ ⎥ ⎢ ⎢ ⎜ − ⎟⎥ ⎥ ⎣ ⎣ ⎝ ⎠⎦ ⎦ φ = 45° l l l ci l l v h x k g 1/ 3 1.916 2 3.7233 10 5Re 0.136 ν ρ ρ ρ − ⎡ ⎡ ⎛ ⎞⎤ ⎤ = ⎢ ⎢ ⎜ ⎟⎥ ⎥ ⎢ ⎢ ⎜ − ⎟⎥ ⎥ ⎣ ⎣ ⎝ ⎠⎦ ⎦ Die wiskundig-gemodelleerde demostrasie HPHR is geïnstalleer binne ‘n bestaande lugdroër-sisteem. Drywing van om en by 8.8 kW kon herwin word vanaf die warm-afvalvloeierstroom met ‘n massa vloei van 0.55 kg/s teen ‘n inlaattemperatuur van 51.64 °C en ‘n uitlaattemperatuur van 35.9 °C binne ‘n omgewing van 20 °C. Na aanleiding van hierdie herwinning, kan energiebesparings van tot 32.18 % verkry word. Die HPHR se installasiekoste kan binne ‘n berekende tydperk van ongeveer 3.3 jaar gedelg word deur hierdie besparing. Verdamper- tot kondensator-lengteverhouding, vloeistofvulverhouding en die oriëntasiehoek vereis verdere ondersoek, aangesien daar slegs ‘n akkuraatheid van 25 % verkry is tussen teoretiese voorspellings en praktiese metings.

Heat exchanger network retrofit plays an important role in energy saving in process industry. Many design methods for the retrofit of heat exchanger networks have been proposed during the last three decades. Conventional retrofit methods rely heavily on topology modifications which often results in a long retrofit duration and high initial costs. Moreover, the addition of extra surface area to the heat exchanger can prove difficult due to topology, safety and downtime constraints. These problems can be avoided through the use of heat transfer enhancement in heat exchanger network retrofit. This thesis develops a heuristic methodology and an optimization methodology to consider heat transfer enhancement in heat exchanger network retrofit. The heuristic methodology is to identify the most appropriate heat exchangers requiring heat transfer enhancements in the heat exchanger network. From analysis in the heuristic roles, some great physical insights are presented. The optimisation method is based on simulated annealing. It has been developed to find the appropriate heat exchangers to be enhanced and to calculate the level of enhancement required. The new methodology allows several possible retrofit strategies using different retrofit methods be determined. Comparison of these retrofit strategies demonstrates that retrofit modification duration and pay-back time are reduced significantly when only heat transfer enhancement is utilised. Heat transfer enhancement may increase pressure drop in a heat exchanger. The fouling performance in a heat exchanger will also be affected when heat transfer enhancement is used. Therefore, the implications of pressure drop and fouling are assessed in the proposed methodology predicated on heat transfer enhancement. Methods to reduce pressure drop and mitigate fouling are developed to promote the application of heat transfer enhancement in heat exchanger network retrofit. In optimization methodology considering fouling, the dynamic nature of fouling is simulated by using temperature intervals. It can predict fouling performance when heat transfer enhancement is considered in the network. Some models for both heat exchanger and heat transfer enhancement are used to predict the pressure drop performance in heat exchanger network retrofit. Reducing pressure by modifying heat exchanger structure is proposed in this thesis. From case study, the pressure drop increased by heat transfer enhancement can be eliminated by modifying heat exchanger structure.

Abstract The LNG production plant processing natural gas from the Snøhvit field outside Hammerfest in northern Norway utilizes heat and power produced locally with gas turbines. Building a new production train supplied with electricity from the power grid is being evaluated as a possible solution for reducing CO2 emissions from the plant. Buying electricity from the grid rather than producing it in a combined heat and power plant makes it necessary to find new ways to cover the heat loads at the production plant. A project thesis was written in the fall semester 2010 evaluating the possibility of generating the necessary heat with heat pumps. It was concluded that parts of the required heat could be delivered with reasonable efficiencies using heat pumps. Further, a heat pump delivering heat to the CO2-removal system was analyzed. Simulations showed that the required heat load, reaching approximately 62 MW at full production, could be delivered from a heat pump using butane as working fluid. The electrical power consumption for the compressors would be 23.3 MW, giving the heat pump a COP of 2.66. In this master thesis the heat pump suggested earlier is analyzed, focusing on identifying losses. Several possible changes that will enhance the heat pump’s efficiency are suggested. The use of other workings fluids and mixed refrigerants are analyzed as well, using the process simulation software Pro/II. The simulations indicates that the heat pump should be equipped with a flash tank at middle pressure, thereby reducing throttling losses and required mass flows through the evaporators. In addition, the suction gas should be overheated as much as possible. Using mixed refrigerants lowers the efficiency of the heat pump. Finally, two new systems are suggested: One with butane as workings fluid and one with pentane, both with flash tank at middle pressure and superheated suction gas. The pentane-system gives the highest system COP, but requires much bigger compressors than the butane-system. The table shows the most important results. Working fluid Electrical power consumption [MW] Volume flow suction gas [m3/h] COP Butane (C4H10) 18.6 55000 3.35 Pentane (C5H12) 17.5 150000 3.54 The power grid electricity is assumed to have been produced without any CO2 emissions. Covering the heat required by the CO2 removal system with a gas fired furnace would generate CO2 emissions of approximately 120,000 tons per year. Heat pumps are a good solution because they deliver relatively cheap heat without these CO2 emissions.

Hot water plays an import role in modem life. The consumption of hot water represents a significant part of the nation's energy consumption. One way of reducing the energy consumption involved, and hence the cost of that energy, is to reclaim heat from the waste warm water that is discharged to the sewer each day. The potential for economic waste water heat recovery depends on both the quantity available and whether the quality fits the requirement of the heating load. To recover heat from waste water in residential and commercial buildings is hard to achieve in quality because of its low temperature range. Nevertheless, efforts to recycle this waste energy could result in significant energy savings. The objective of this research was to develop a multiple panel thermosyphon heat exchanger for a waste water heat recovery system. The advantage of the system proposed in this work is that it not only provides useful energy transfer during simultaneous flow of cold supply and warm drain water but also has the ability to store recovered energy at the bottom of a hot water storage tank for later use. While this concept is not new, the design of the heat exchanger proposed for the present study is significantly different from those used previously. Component experiments were carried out to determine the performance characteristics of a single thermosyphon panel. By changing the inclination angle of the single panel heat exchanger and varying its working condition, it was found that the inclination angle of 10° could be identified as the minimum inclination angle at which good performance was still obtained. The close values of the overall heat transfer coefficients between top surface of the panel insulated and both top and bottom surfaces of the panel uninsulated shows that the overall heat transfer coefficient of the single panel was dominated by the bottom surface of the panel. Even if in a worst case the top surface of the panel might be possibly covered by the deposits from the waste water, it would not affect much on the heat transfer performance of the panel. Measurements of hot water usage and waste water temperature and flow rates were obtained for a potential application of the proposed exchanger (the dishwasher for the kitchen in the University Halls of Residence). A model of a multi-panel thermosyphon heat exchanger was also developed to predict the energy savings that would be expected if such a heat exchanger was used in this situation. The result indicated that an overall electricity of 7500 kWh could be saved annually from the dishwasher system by employing a four-panel thermosyphon heat exchanger.

Disertační práce je zaměřena na kovové a polymerní výměníky tepla. Hlavním předmětem zkoumání je optimalizace teplosměnných ploch za účelem zvýšení účinnosti výměníku tepla. Tyto cíle byly dosaženy experimentálně a numericky pomocí modelování v ANSYS. Na základě dosažených výsledků byla rozpracována technologie křížového navíjení polymerních výměníků z dutých vláken. Experimentální zařízení původně určené pro navíjení tlakových nádrží bylo modifikované pro automatizovanou výrobu polymerních výměníků z dutých vláken, ježto může být použita při jejich masové výrobě. Tato práce se také zabývala výměníky tepla pro klimatizační systémy. Byly zkoumány možnosti využití polymerních výměníků z dutých vláken v těchto systémech. Mimo jiné byla provedena studie vlivu cyklického tepelného zatížení standardního kovového žebrovaného tepelného výměníku.

The residential and service sector amounts to approximately 40 percent of Sweden’s entire energy demand. In which 90 percent of that is used by households and non-residential buildings. All in all about 80 TWh are used for heating and the provision of hot water in households and non-residential buildings. Since heating has always been such a large part of the energy consumption for buildings in Sweden, it is only natural that there have been several improvements along the way. There’s a new facility just installed last year in the building Pennfäktaren 11, a horizontal wastewater heat recovery heat exchanger. This thesis study will be focused on creating a TRNSYS model of a waste water heat exchanger, where the crucial parameters such as water flow rate, temperature, and more can be used as inputs to assess the technical performance of the heat exchanger. The model developed in TRNSYS can simulate the performance of a single heat exchanger unit, with a few input parameters needed. The model was developed by using measurement data from the facility in Stockholm to get realistic results depending on time and actual measurements. From the measured data, there were a few parameters that needed to be calculated, first off the mass flow rate of the waste water flow, this was done by an energy balance over the heat exchanger. Following the mass flow rate the cold water set point had to be determined, so that the heat recovered was not larger than the heat that could be utilized by the building. Since data was available from a single site, there was not much else to do than accept the data as true, there were some data points that had to be sorted out however, such as negative flow rates and flow rates much higher than should be possible. The finished model uses all the data from the measurements as well as the calculated values, it provided heat transfer rate along with the outgoing temperatures of both waste water and the preheated water. The first reference scenario provided 25,3 MWh of recovered energy, but the best scenario with an increased waste water temperature as well as increased flow rate it could provide a total of 47,2 MWh, almost twice the original value. To conclude the model seems to simulate a waste water heat exchanger well and returns feasible data. It should be possible to use the model to see if a building is a good “candidate” to install a waste water heat exchanger in.
Byggnads och servicesektorn står för cirka 40 procent av Sveriges energibehov. Av de 40 procenten består 90% av energibehov ifrån hushåll och kontorsbyggnader. Totalt sett 80 TWh används för uppvärmning av byggnader samt varmvatten. Då uppvärmning alltid varit en stor del av energibehovet i Sverige är det naturligt att det skett en rad förbättringar på vägen. Det finns en ny anläggning på Pennfäktaren 11 i Stockholm, en horisontell värmeväxlare för avloppsvatten. Den här uppsatsen fokuserar på att skapa en modell i TRNSYS av en värmeväxlare där parametrar som vattenflöde, temperatur, och mer kan användas för att bedöma den tekniska aspekten av en installation av värmeväxlare i en byggnad. Modellen kan simulera prestandan av en ensam värmeväxlare, med endast ett fåtal parametrar som behövs. Modellen baseras på mätdata ifrån anläggningen på Pennfäktaren, denna mätdata har sedan använts för att beräkna först massflödet av avloppsvatten men också för att bestämma hur mycket värme som är möjligt att återvinna utan att överskrida det byggnaden faktiskt kan använda. Då det bara finns data ifrån en källa fick den anses som korrekt, dock gjordes en del ändringar där data helt enkelt var omöjligt, t.ex. negativa avloppsflöden och flödesmängder så höga att de inte ska kunna vara möjliga. Den färdiga modellen använder mätdata tillsammans med de beräknade värdena. Detta används för att genom modellen beräkna temperaturvärden för utgående vatten och avlopp samt den totala mängden återvunnen värme. I referensscenariot kunde totalt 25,3 MWh värme återvinnas men det bästa scenariot med ökad avloppstemperatur och avloppsflöde kunde närmare 47,2 MWh återvinnas, nästan det dubbla från referensvärdet. För att sammanfatta ger modellens simulationer rimliga värden för värmeväxlaren. Det bör därför vara fullt möjligt att använda modellen för att bedöma ett hus rimlighet till en värmeväxlarinstallation.

This thesis examined thermoregulatory responses in heart failure (HF) patients during exercise at a fixed relative intensity, and at an intensity that elicited a fixed rate of metabolic heat production (Hprod) in a warm environment (30°C). Additionally, the efficacy of a chronic, high-dose (5mg/d for 6wk) pharmacological intervention (folic acid supplementation) as a strategy for improving skin blood flow (SkBF) responses and thus, thermoregulatory control in these patients during exercise was assessed. The findings of three experiments conducted to achieve these aims are presented in this thesis. Experiment #1 was designed to compare thermoregulatory responses in HF and controls (CON) during exercise in the heat. Ten HF (New York Heart Association [NYHA] class I-II), and eight CON were included in the study. Core temperature (Tc), skin temperature (Tsk), and cutaneous vascular conductance (CVC – and index of SkBF) were assessed at rest and during one hour of cycling exercise at 60% of maximal oxygen uptake. Hprod and the evaporative requirements for heat balance (Ereq) were also calculated. Whole-body sweat rate (WBSR) was determined from pre-post nude body mass corrected for fluid intake. While Hprod (HF: 3.9 ± 0.9; CON: 6.4 ± 1.5 W/kg) and Ereq (HF: 3.3 ± 0.9; CON: 5.6 ± 1.4 W/kg) were lower (p < 0.01) for HF compared to CON, both groups demonstrated a similar rise in Tc (HF: 0.9 ± 0.4; CON: 1.0 ± 0.3°C). Despite this similar rise in Tc, Tsk (HF: 1.6 ± 0.7; CON: 2.7 ± 1.2°C), and the elevation in CVC (HF: 1.4 ± 1.0; CON: 3.0 ± 1.2 au/mmHg) were lower (p < 0.05) in HF compared to CON. Additionally, WBSR (HF: 0.36 ± 0.15; CON: 0.81 ± 0.39 L/h) was lower (p = 0.02) in HF compared to CON; however, was similar when corrected for differences in Ereq (p = 0.83). Collectively, these data suggest that patients with HF maybe limited in their ability to manage a thermal load and distribute heat content to the body surface (i.e., skin), secondary to impaired circulation to the periphery. Experiment #2 was designed to examine thermoregulatory responses in HF and CON during exercise at a fixed rate of Hprod, and therefore Ereq, in a 30°C environment. A total of 20 men; 10 HF and 10 CON similar in body size, were included in the study. Rectal temperature (Trec), local sweat rate (LSR), and CVC were measured throughout 60-min of cycle ergometry. WBSR was estimated from pre-post nude body weight corrected for fluid intake. Despite exercising at the same rate of Hprod (HF: 338 ± 43; CON: 323 ± 31 W, p = 0.25), the rise in Trec was greater (p < 0.01) in HF (0.81 ± 0.16°C) than CON (0.49 ± 0.27°C). In keeping with a similar Ereq (HF: 285 ± 40; CON: 274 ± 28 W, p = 0.35), no differences in WBSR (HF: 0.45 ± 0.11; CON: 0.41 ± 0.07 L/h, p = 0.38) or LSR (HF: 0.96 ± 0.17; CON: 0.79 ± 0.15 mg/cm2 /min, p = 0.50) were observed between groups. However, the rise in CVC was lower in HF than CON (HF: 0.83 ± 0.42; CON: 2.10 ± 0.79 au/mmHg, p < 0.01). Additionally, the cumulative body heat storage estimated from partitional calorimetry was similar between groups (HF: 154 ± 106; CON: 196 ± 174 kJ, p = 0.44). Collectively, these findings demonstrate that HF patients exhibit a blunted SkBF response, but no differences in sweating. Given that HF had similar body heat storage to controls at the same Hprod, their greater rise in core temperature can be attributed to a less uniform internal distribution of heat between the body core and periphery. In light of the findings of Experiments #1 and #2, Experiment #3 was subsequently designed to examined the effect of folic acid supplementation (5mg/d for 6wk) on vascular function (brachial artery flow-mediated dilation [FMD]), and SkBF responses (CVC) during 60-min of exercise at a fixed Hprod (300 W) in a 30°C environment in 10 HF (NYHA class I-II) patients and 10 CON. Serum folic acid concentration increased in HF (pre-intervention: 1.4 ± 0.2; post-intervention: 8.9 ± 6.7 ng/ml, p = 0.01) and CON (pre-intervention: 1.3 ± 0.6; post-intervention: 5.2 ± 4.9 ng/ml, p = 0.03). FMD improved by 2.1 ± 1.3% in HF (p < 0.01), but no change was observed in CON postintervention (p = 0.20). During exercise, the external workload performed on the cycle ergometer to attain the fixed level of Hprod for exercise was similar between groups (HF: 60 ± 13; CON: 65 ± 20 W, p = 0.52). Increases in CVC during exercise were similar in HF (pre: 0.89 ± 0.43; post: 0.83 ± 0.45 au/mmHg, p = 0.80) and CON (pre: 2.01 ± 0.79; post: 2.03 ± 0.72 au/mmHg, p = 0.73), although the values were consistently lower in HF for both pre- and post-intervention measurement intervals (p < 0.05). Furthermore, mean arterial pressure was similar in HF (pre: 98 ± 5; post: 94 ± 5 mmHg, p = 0.53) and CON (pre: 102 ± 3; post: 100 ± 3 mmHg, p = 0.65), and no differences were observed between groups during both exercise trials (all p > 0.05). These findings demonstrate that folic acid improves vascular endothelial function in patients with HF, but does not enhance SkBF during exercise at a fixed Hprod in a warm environment. The work presented in this thesis serves to expand our current understanding of the mechanisms responsible for impaired thermoregulatory control, particularly during exercise in the heat, in patients with HF. Furthermore, whilst folic acid did not serve to improve thermoregulatory SkBF during exercise in HF, folic acid improved vascular endothelial function to a greater extent in HF than CON. These data indicate that while folic acid does not alleviate the development of thermal strain during exercise in HF, its utility as a viable treatment option for reducing and/or preventing disease-related changes in vascular endothelial function in these patients warrants further investigation.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School Allied Health Sciences
Griffith Health
Full Text

The trend towards improving building airtightness to save energy has increased the incidence of poor indoor air quality and associated problems, such as condensation on windows, mould, rot and fungus on window frames. Mechanical ventilation/heat recovery systems, combined with heat pumps, offer a means of significantly improving indoor air quality, as well as providing energy efficient heating and cooling required in buildings. This thesis is concerned with the development of a novel mechanical ventilation heat recovery/heat pump system for the domestic market. Several prototypes have been developed to provide mechanical ventilation with heat recovery. These systems utilise an annular array of revolving heat pipes which simultaneously transfer heat and impel air. The devices, therefore, act as fans as well as heat exchangers. The heat pipes have wire finned extended surfaces to enhance the heat transfer and fan effect. The systems use environmentally friendly refrigerants with no ozone depletion potential and very low global warming potential. A hybrid system was developed which incorporated a heat pump to provide winter heating and summer cooling. Tests were carried out on different prototype designs. The type of tinning, the working fluid charge and the number and geometry of heat pipes was varied. The prototypes provide up to 1000m3/hr airflow, have a maximum static pressure of 220Pa and have heat exchanger efficiencies of up to 65%. At an operating supply rate of 200m3/hr and static pressure 100Pa, the best performing prototype has a heat exchanger efficiency of 53%. The heat pump system used the hydrocarbon isobutane as the refrigerant. Heating COPs of up to 5 were measured. Typically the system can heat air from 0°C to 26°C at 200m3/hr with a whole system COP of 2. The contribution to knowledge from this research work is the development of a novel MVHR system and a novel MVHR heat pump system and the establishment of the performances of these systems.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 205-211).
Modern computer processors require significant cooling to achieve their full performance. The "efficiency" of heat sinks is also becoming more important: cooling of electronics consumes 1% of worldwide electricity use by some estimates. Unfortunately, current cooling technologies often focus on improving heat transfer at the expense of efficiency. The present work focuses on a unique, compact, and efficient air cooled heat sink which addresses these shortcomings. While conventional air cooled heat sinks typically use a separate fan to force air flow over heated fins, the new design incorporates centrifugal fans directly into the body of a loop heat pipe with multiple planar condensers. These "integrated fans" rotate between the planar condensers, in close proximity to the hot surfaces, establishing a radially outward flow of cooling air. The proximity of the rotating impellers to the condenser surfaces results in a marked enhancement in the convective heat transfer coefficient without a large increase in input power. To develop an understanding of the heat transfer in integrated fan heat sinks, a series of experiments was performed to simultaneously characterize the fan performance and average heat transfer coefficients. These characterizations were performed for 15 different impeller profiles with various impeller-to-gap thickness ratios. The local heat transfer coefficient was also measured using a new heated-thin-film infrared thermography technique capable of applying various thermal boundary conditions. The heat transfer was found to be a function of the flow and rotational Reynolds numbers, and the results suggest that turbulent flow structures introduced by the fans govern the transport of thermal energy in the air. The insensitivity of the heat transfer to the impeller profile decouples the fan design from the convection enhancement problem, greatly simplifying the heat sink design process. Based on the experimental results, heat transfer and fan performance correlations were developed (most notably, a two-parameter correlation that predicts the dimensionless heat transfer coefficients across 98% of the experimental work to within 20% relative RMS error). Finally, models were developed to describe the scaling of the heat transfer and mechanical power consumption in multi-fan heat sinks. These models were assessed against experimental results from two prototypes, and suggest that future integrated fan heat sink designs can achieve a 4x reduction in thermal resistance and 3x increase in coefficient of performance compared to current state-of-the-art air cooled heat sinks.
by Wayne L. Staats, Jr.
Ph.D.

This experimental study explores the heat transfer from heated bare and finned tubular surfaces to particulates in packed bed cross flow. The results from this experiment will be used to help select the type of particulates that will be used. Additionally, these results will assist in estimating heat transfer in prototype and commercial particle to fluid heat exchangers (PFHX). This research is part of larger effort in the use of particulates in concentrating solar power technology. These solid particles are heated by concentrated sunlight to very high temperatures at which they are a suitable heat source for various thermal power and thermochemical cycles. Furthermore, one of the advantages of this concept is the ability to store thermal energy in the solid particles at relatively low cost. However, an important feature of any Particle Heat Receiver (PHR) system is the PFHX, which is the interface between the solar energy system and the thermal power or chemical system. In order to create this system material data is needed for the design and optimization of this PFHX. The paper focuses on the heat transfer properties of particulates to solid surfaces under plug flow conditions. The particulates will be evaluated for three grain sizes of sand and two grain sizes of proppants. These two materials will be tested at one, five and ten millimeters per second in order to see how the various flow rates, which will be required for different loads, will affect the heat transfer coefficient. Finally the heat transfer coefficient will also be evaluated for both finned and non-finned heat exchangers to see the effect that changes in the surface geometry and surface area have on the heat transfer coefficient. The heat transfer coefficient will help determine the appropriate material that will be used in the PHR system.

Heat waves represent a public health challenge that requires multiple responses and warnings to protect vulnerable populations. Although studies have reported an increasing trend of heat wave occurrence in many areas of the world, no clear trend exists in East Tennessee. Using data from Parameter-elevated Relationships on Independent Slope Models (PRISM), CDC WONDER and the United States Census Bureau, the relationship between mortality rates and year was estimated during heat wave events between 1999 and 2010. Five heat wave definitions were tested. Overall, 2007 and 2010 stand out as the years with the highest number of heat wave days in East Tennessee. August could be described as the hottest month. Three of the heat wave definitions tested show increasing non-accidental mortality rates with year. The relative risk for cardiovascular mortality is elevated among females compared to males for one of the heat wave definitions (Relative Risk (RR) = 1.33, CI= 1.08-1.65).

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.

Heat stress is a common physical agent associated with many occupations. The most commonly used method of assessing heat stress exposure is an empirical method using the Wet Bulb Globe Temperature Index but his method is limited in its ability to parse out individual contributors to the heat stress. The International Organization for Standardization (ISO) published a rational model called Predicted Heat Strain (PHS) in 2004, and rational methods have the advantage of separating out the individual pathways for heat exchange. The objective of this research was a performance assessment of the current PHS model. This experimental design consisted of 15 trials (3 clothing ensembles and 5 heat stress levels) involving 12 men and women. The clothing ensembles were work clothes, NexGen® (microporous) coveralls, and Tychem® QC (vaporbarrier) coveralls. The heat stress levels were 1.0 , 2.0 , 3.5 , 5.5 and 9.0 °CWBGT above the average critical environment for each ensemble determined in prior studies. The metabolic rate was 190 W/m2. The two outcomes of each trial were an exposure time when core temperature reached 38 °C (ET38) and a Safe Exposure Time (SET) defined as the amount of time required to reach either a core temperature (Tre) = 38.5 ºC, a heart rate of 85% age-estimated maximum, or fatigue. ix Trial data for environment, metabolic rate and clothing were inputs to the (PHS) model to determine a predicted amount of time for the participants to reach a Tre = 38 ºC, which was the limiting condition in PHS for acute exposures. The first consideration was predictive validity for which PHS-Time was compared to ET38. The expectation would be that PHS-Time would predict the mean ET response. Results for predictive validity indicated a moderate agreement between ET38 and PHS-Time (r2 of 0.34 and Intraclass Correlation Coefficient at 0.33). When the method for accounting for clothing was changed to that recommended by ISO, the PHS predicted times moved systematically toward a shorter exposure time and modest agreement (r2 of 0.39 and Intraclass Correlation Coefficient at 0.31). Protective validity was the ability of the PHSTime to predict an exposure time that would be safe for most people. In this case, PHS-Time was compared to SET. The PHS was protective for 73% of the cases. When it was modified to account for clothing following the ISO method, the protective outcomes were 98%. In addition, the PHS model examined with respect to starting core temperature and fixed height and weight. Using the actual core temperature improved the outcomes somewhat, but changing from 36.8 to 37.0 would be sufficient. There is a strong tendency to over-predict PHS-Time for individuals with a low body surface area, usually short and lower than average weight.

Uptake of geothermal heat pump (GSHP) systems has been slow in some parts of the world due to the unpredictable operational performance, large installation space requirement and high installation costs. Therefore, design modification was searched in order to improve the feasibility. With regard to relatively small impact of the construction costs, efficient thermal energy collection was targeted in horizontal ground-loop systems with shallow underground construction. The research started with a sensitivity analysis of the underground heat collection system using computational fluid dynamics (CFD). The results indicated essential design parameters to enhance the performance. Strategies to improve one of the parameters, thermal conductivity of soil surrounding the heat exchanger, were investigated through lab experiments. Subsequently, further design optimisation with the CFD intended to select the most competitive modified design against the existing design. It was discovered that an indication to achieve economic and practical modifications for efficient heat collection was to increase the moisture content of sub-soil up to the optimum moisture content (OMC). Annual operation analysis with the CFD disclosed that additional costs for even simple design modifications could easily worsen the payback period. Consequently, solutions to improve the performance of the GSHP within reasonable payback period were proposed.

Energy is largely invisible to users. It has been argued that employing technologies to visualise energy will assist people in conserving energy. Energy visibility interventions have largely focussed on appliance use and electricity consumption. This thesis aims to firstly explore whether making heat visible, using thermal images, promotes heat (and thereby energy) conservation. Secondly using a multiple method approach, it explores how. Five studies were employed. Study One and Three investigated whether using thermal images as a tailored antecedent intervention would promote energy conservation behaviours. The results confirmed that the images led to a reduction in Kg CO2 emissions attributed to domestic energy use. Study One and Three indicated that householders undertook more energy saving behaviours in relation to those aspects that were visible in the images. These actions were attributed to simple, energy saving behaviours such as proofing draughts. Study Two investigated how people make sense of the images and how behaviours are promoted by the images. Study two suggested that the images provide a unique medium through which factors which contribute to energy saving can be combined and reasoned by the viewer. It suggests the psychological factors in a pathway from prompt to behaviour. Study Four established that showing the images in an information presentation was not as effective when influencing participants’ ideas about energy conservation. Finally, Study Five explored participants gaze and demonstrated how features of the images, can attract the viewer. The novel contribution of this thesis is in establishing that ‘making heat visible’ through a tailored thermal imaging prompt can increase the likelihood of a householder taking simple energy saving actions, by providing a novel medium through which householders attend to heat and energy use.

The heat exchanger is a device that transfers heat from one fluid to another or between fluid and the environment. Over the last few decades, the role of heat exchangers has increased in the process of heat recovery and introduction of new energy sources. Surface roughness of heat exchanger wall plays a vital role in the efficiency of heat transfer. Therefore, significance of surface roughness is examined by many researchers applying different shapes of roughness. Roughness is the variation in the height of a surface. It could be either a part of the geometry or due to deposition of undesired materials (which decreases the thermal function of the heat exchanger, increases the pressure drop and could cause corrosion). Dimensionless heat transfer correlations such as Nusselt number provides a clear view about the effect of heat transfer by surface roughness. This thesis combines different Nusselt correlations for distinct shapes of surface roughness and investigates the suitability of them on a test experiment by comparing the values gotten. From this investigation it was clear that the value of Nunner correlation delivers the most reasonable results for a fouled layer formed by means of crystallization. Also the Nusselt correlation by Saini et al. could be more suitable for artificial surface roughness than for a fouled surface
Lämmönvaihdin on laite, joka siirtää lämpöä fluidista toiseen tai fluidin ja ympäristön välillä. Viimeisimpien vuosikymmenten aikana lämmönvaihtimien rooli on kasvanut lämmön talteenottoprosesseissa ja uusien energialähteiden käyttöönotossa. Lämmönvaihtimien pinnankarheudella, jolla tarkoitetaan seinämän pintakuvion korkeuden muutosta verrattuna tasaiseen pintaan, on merkittävä rooli lämmönvaihtimen tehokkuudessa. Pinnankarheuden vaikutusta lämmönsiirtoon onkin tarkasteltu useissa tutkimuksissa. Pinnankarheus voi olla osa lämmönvaihdinrakennetta tai johtua ei haluttujen materiaalien kerrostumisesta pinnalle. Tällöin puhutaan likaantumisesta, joka heikentää lämmönvaihtimen lämmönsiirtoa, lisää painehäviötä ja voi aiheuttaa korroosiota. Dimensiottomat korrelaatiot, kuten Nusseltin luku antavat tietoa pinnankarheuden aiheuttamasta vaikutuksen lämmönsiirtoon. Tässä kandidaatintyössä on tarkasteltu kirjallisuudessa esitettyjä Nusseltin luvun korrelaatioita ja niiden soveltuvuutta eri pinnankarheuden muotoihin sekä tutkittu niiden soveltuvuutta todellisen lämmönvaihtimen tapauksessa. Tästä tutkimuksessa tarkastelluista korrelaatioista Nunnerin korrelaatio soveltui parhaiten likaantuneen lämmönvaihtimen lämmönsiirron tarkasteluun. Sainin ym. korrelaatio arvioitiin soveltuvan paremmin keinotekoisen pinnankarheuden kuin likaantuneen pinnan lämmönsiirron tarkasteluun

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Dr. Yogendra Joshi; Committee Member: Dr. S. Mostafa Ghiaasiaan; Committee Member: Dr. Sheldon Jeter. Part of the SMARTech Electronic Thesis and Dissertation Collection.

An average heat transfer coefficient, h_bar, is often used to solve heat transfer problems. It should be understood that this is an approximation and may provide inaccurate results, especially when the temperature field is of interest. The proper method to solve heat transfer problems is with a conjugate approach. However, there seems to be a lack of clear explanations of conjugate heat transfer in literature. The objective of this work is to provide a clear explanation of conjugate heat transfer and to determine the discrepancy in the temperature field when the interface boundary condition is approximated using h_bar compared to a local, or variable, heat transfer coefficient, h(x). Simple one-dimensional problems are presented and solved analytically using both h(x) and h_bar. Due to the one-dimensional assumption, h(x) appears in the governing equation for which the common methods to solve the differential equations with an average coefficient are no longer valid. Two methods, the integral equation and generalized Bessel methods are presented to handle the variable coefficient. The generalized Bessel method has previously only been used with homogeneous governing equations. This work extends the use of the generalized Bessel method to non-homogeneous problems by developing a relation for the Wronskian of the general solution to the generalized Bessel equation. The solution methods are applied to three problems: an external flow past a flat plate, a conjugate interface between two solids and a conjugate interface between a fluid and a solid. The main parameter that is varied is a combination of the Biot number and a geometric aspect ratio, A_1^2 = Bi*L^2/d_1^2. The Biot number is assumed small since the problems are one-dimensional and thus variation in A_1^2 is mostly due to a change in the aspect ratio. A large A_1^2 represents a long and thin solid whereas a small A_1^2 represents a short and thick solid. It is found that a larger A_1^2 leads to less problem conjugation. This means that use of h_bar has a lesser effect on the temperature field for a long and thin solid. Also, use of ¯ over h(x) tends to generally under predict the solid temperature. In addition is was found that A_2^2, the A^2 value for the second subdomain, tends to have more effect on the shape of the temperature profile of solid 1 and A_1^2 has a greater effect on the magnitude of the difference in temperature profiles between the use of h(x) and h_bar. In general increasing the A^2 values reduced conjugation.

碩士
國立臺灣大學
園藝學研究所
94
Summary To develop the heat-tolerance indicators of petunia (Petunia ×hybrida Hort.), differential morphological and physiological responses to four temperatures regimes between seven heat-tolerant (HT) or heat-sensitive (HS) petunia cultivars were investigated. While grown at 27℃, the shoot dry weights of HT cultivars Wave Blue and Tidal Wave Silver increased as compared with grown at 16℃. HT cultivars maintained more branches and root dry weight than the HS cultivars did. The relative injury (RI) values of all cultivars tested decreased significantly as growing mean temperature increased from 16℃ to 33℃, and the reduction of RI values was more obvious in HT cultivars. While grown at 27℃, RI values of the tested cultivars were the most distinct, and were positively related to the reduction of branches (R2 = 0.79, P < 0.001). Thus, a mean of 27℃ was a suitable growing temperature to screen the heat-tolerant petunias, which had lower RI values and more branches. The most effective treatment to distinguish RI values between HT and HS petunia cultivars was 50℃ water bath for 30 minutes. The RI values of HT cultivars Happy Dream Blue and Tidal Wave Silver grown at 29℃ root temperature were smaller than those at 21℃ or 26℃, while RI values of HS cultivars grown at all root temperatures were constant. Unlike the traditional cultivars, HT cultivars Wave Blue and Tidal Wave Silver produced similar or more branches and flowers under LD treatments. The LD treatments increased shoot dry weight in HT cultivar Tidal Wave Silver, but decreased dry weight in HS cultivar Fantasy Ivory. All cultivars had less root dry weight under LD than SD, but Tidal Wave Silver maintained more root dry weight than HS cultivars. Despite of the differential vegetative growth responses, flowering was all promoted under LD in three cultivars tested The pollens of ‘Tidal Wave Silver’ and ‘Fantasy Ivory’ petunia were subjected to 45℃ for 0, 1, or 2 hours to determine the effects of heat treatment on pollen viability and germination percentage. After heated for 1 or 2 hours, both pollen viability and germination percentage of both cultivars declined significantly. However, ‘Fantasy Ivory’ exhibited more decline in pollen viability and germination percentage than ‘Tidal Wave Silver’. A linear relationship existed between pollen viability and germination percentage (R2 = 0.87, P < 0.0001), indicating that pollen viability could be used to measure germination. The pollen viability after treated with 45℃ for 1 hour could also be used for screening heat-tolerant petunias. Neither the percentage of seed germination, the percentage of cotyledon expansion, the time to 50% or 90% of seed germination or cotyledon expansion could be used to distinguish heat-tolerance in four petunia cultivars. At 30℃, the first leaves of HT cultivars Tidal Wave Silver and Wave Blue emerged, while those of HS cultivars did not. Thus, the first leaf emergence at 30℃ could be used for screening heat-tolerant petunias.

The dimensional and dimensionless model formulating the melting and freezing processes in the melting and freezing rotating device (MFRD) are presented. The heat transfer process between the two concentric cylinders with D/r o < 0.01 may be considered as that between two parallel plates with a distance of D between them. The theoretical analysis about solidification or melting of a slab at a constant boundary temperature, which is greater or lower than the melting point, is conducted. The theoretical and numerical analysis of the Quasi-Steady state with the moving phase boundaries of the melting and freezing processes in the dimensionless system are performed. Moreover, the properties in MFRD are analyzed. The use of MFRD in the aerospace is discussed.

The Marnoch heat engine (MHE) is a new type of power generation device that is under research and development at the University of Ontario Institute of Technology. In this thesis, the transient heat transfer behaviour of the source heat exchanger of the Marnoch heat engine is studied, and its operation for laminar and turbulent flows is modelled. The temperature variations of the working fluid, the heating fluid and the wall, are calculated. The temperature distribution of the fluids and the wall over the length of the heat exchanger is also calculated. It is found that the temperature of the working fluid rises sharply to a peak and then gradually decreases. The wall temperature decreases exponentially, and the temperature of the heating fluid falls sharply, and then gradually decreases. A base model for the step change in the mass flow of the working fluid is developed and compared against past works for the purpose of validation.
UOIT

碩士
國立中央大學
能源工程研究所
95
This article is trying to develop a new kind heat spreader, which were used the theory of pulsating heat pipes. Channels were manufactured on copper plate, to finish the flat plate pulsating heat pipes. When heat input, fluid makes phase changes, produce the vapor pressure difference between the evaporation area and condensation area, the major heat transfer mechanism in a pulsating heat pipe is the sensible heat of liquid. Channels arrangement designed to two types, which were single loop and double side loop. In order to understand the influence by the wide of channel, there are two kinds of channel size, which wide were 0.5 mm and 1 mm. In this article, also experiment three fill rate, which were 20 %、50 % and 80 %. The heat transfer characteristics of flat plat pulsating heat pipes were investigated experimentally. The experimental results at the same input heat and same fill rate, the single loop design which heat transfer performance better than the double side loop. When fix the fill rate as 50 %, the minimum heating power is 15 W at 1 mm wide channel, 20 W at 0.5 mm wide channel. In the experiment of different fill rate, when fill rate 20 %, pulsation only occurs at heating power 15 W, as the heating power increase, pulsation stop. Also found that the optimal fill rate is around 50 % and 80 %. The drag force which caused by the channel walls will decrease the liquidity, also decrease the range of pulsation. In order to decrease the spreading resistance, we should make the design of channel better.

碩士
大同工學院
機械工程學系
84
This study presents the distribution of temperature of microstructureand the variation of heat flux and velocity of fluid during the cooling process.Numerical simulation method is used in studying the effect of cooling, and isothermal figures are also used to describe the temperature distribution.Finally, the temperature difference between the highest temperature of theoutlet of solid and the temperature of the inlet of fluid. It can be concludedthat the temperature difference can be controlled under a acceptable range bychaning the velocity of fluid.

碩士
亞洲大學
光電與通訊學系
102
Since LED chip is smaller than conventional light source, it is easy to distribute and accumulate heat. This can reduce its brightness, shorten its life time and drift wavelength spectrum. So in manufacturing LED products, cooling mechanism is a very important issue. In this study, academia partners developed LED Down Light was used to simulate the behavior of heat distribution. At first we use Autodesk Inventor to draw heat sink mechanism solid model, i.e., heat sink mechanism, then it is imported to CF Design heat flow analysis simulation software. After setting the coefficient of its materials, boundary conditions and meshing and following steps, we get thermal simulation analysis data. Alternating the different required conditions, we get some useful results. The heat sink material is one of the important factors for cooling because of its heat transfer parameters. The 5mm spacing of the heat sink’s fins will get the best cooling condition in this case. Tilting heat sink in 90 degrees, the heat temperature will rise 8.64 percent, and this is obvious impact of the cooling effect. Finally, two cooling heat sink models with the similar volume show a significant difference in the cooling effect. Through this study, we can see the design of the cooling mechanism (material, spacing, number of fins, fin configuration), and fixture orientation will affect the thermal performance of LED lamps. We hope the study methods, processes and conclusions can provide some useful information to LED lighting products.

碩士
東南科技大學
機械工程研究所
104
This study aimed to develop and design the new type condenser of heat pipe by lead to improve the Coefficient of Performance (COP) of the R-22 room air conditioner. First of all, this study was implemented by reviewing related literatures and researches to understand heat pipe and vapor compression refrigeration (VCR) cycle. Then, the heat pipe condenser will be installed to the VCR system, and to match compressor and throttling element by trial and error, which lead to construct the new type R-22 room air conditioner. The heat pipe condenser can successfully applied in R-22 room air conditioner, it proved to improve the COP and achieve energy-saving. The results show that compressor power consumption can be reduced to 490 W from 1200 W, the condenser cooling area can be reduced 6.52 times, and the COP can be increased to 3.576 from 3.603. Keywords: heat pipe, evaporator, condenser, heat exchanger.