Tesis sobre el tema "Heat engineering"

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.

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.

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.

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.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 130-133).
The effects on pool boiling characteristics such as critical heat flux and the heat transfer coefficient of different surface characteristics such as surface wettability, roughness, morphology, and porosity are not well understood. Layer-by-layer nanoparticle coatings were used to modify the surface of a sapphire heater to control the surface roughness, the layer thickness, and the surface chemistry. The surface was then tested in a water boiling test at atmospheric pressure while imaging the surface with high speed infrared thermography yielding a 2D time dependent temperature profile. The critical heat flux and heat transfer coefficient were enhanced by over 100% by optimizing the surface parameters. It was found that particle size of the nanoparticles in coating, the coating thickness, and the wettability of the surface have a large impact on CHF and the heat transfer coefficient. Surfaces were also patterned with hydrophobic "islands" within a hydrophilic "sea" by coupling the Layer-by-layer nanoparticle coatings with an ultraviolet ozone technique that patterned the wettability of the surface. The patterning was an attempt to increase the nucleation site density with hydrophobic dots while still maintaining a large hydrophilic region to allow for rewetting of the surface during the ebullition cycle and thus maintaining a high critical heat flux. The patterned surfaces exhibited similar critical heat fluxes and heat transfer coefficients to the surfaces that were only modified with layer-by-layer nanoparticle coatings. However, the patterned surfaces also exhibited highly preferential nucleation from the hydrophobic regions demonstrating an ability to control the nucleation site layout of a surface and opening an avenue for further study.
by Bren Andrew Phillips.
S.M.

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

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.

The work performed can be divided into three stages. The first stage involved the development and study of a transparent heat pipe which served to illustrate the principles of heat pipes, specifically, thermosyphons or wickless heat pipes. The second stage dealt with the conception, construction and study of a laboratory scale heat pipe injection lance. The knowledge gained in the laboratory was used to build two pilot scale heat pipe injection lances, Mark I and Mark II, in the third stage of this work. These lances were tested in the copper converting furnace at the Kidd Creek smelter. Through the development of pilot scale heat pipe injection lances, it is shown that a self-cooled heat pipe lance has a furnace life orders of magnitude greater than a conventional stainless steel lance, with its exact location relative to the molten copper bath surface known.

Sweden has been one of the first countries in the world to use ground-source heat pumps (GSHP) to supply heating and cooling to its buildings. Today, it is the leading country in Europe and new installations tend to have larger capacities. The use of deeper borehole heat exchangers (BHE) is an opportunity to extract larger amounts of heat over small land areas. However, there are only few case studies on BHE deeper than 300 m, hence such systems may be optimized. This study focuses on a deep GSHP system recently installed in central Stockholm, composed of four 510 m deep BHE. The objectives were to get the system ready for monitoring and to analyze the first sets of data recorded. First, a review of all the sensors already installed, of the data needed, and of the different ways to extract it, has been led. Practically, an acquisition system has been set up and connected to new and existing sensors such as thermometers and flow-meters. Theoretically, a method to derive the thermodynamic cycles of the different heat pumps has been determined. It led to the determination of COPs for several days during late spring 2017. The system globally showed reasonable efficiency, with an overall performance factor (equivalent to SPF2) of 3.42 including the circulation pumps of the ground loop. However, it could certainly be improved in several ways, for example by avoiding short cycles or by finding an optimum flow in the secondary ground loop. Furthermore, these results should be juxtaposed with those that will be obtained during winter, when the heating demand will be the highest.
Sverige var ett av de första länderna i världen som använt bergvärmepumpar (GSHP) för att täcka värme- och kylbehoven i byggnader. Sverige är, idag, det ledande landet i Europa och nya bergvärmeanläggningar tenderar att vara större, åtminstone kapacitetsmässigt. Användningen av djupa borrhålsvärmeväxlare (BHEs) ger möjligheten att extrahera en större mängd värme i areabegränsade egendomar. Det finns dock bara få studiefall om anläggningar med borrhål djupare än 300 m och de anläggningarna skulle därför kunna optimeras. Den här studien fokuserar på ett GSHP system med djupa borrhål som nyligen installerades i centrala Stockholm och som består av fyra 510 m djupa borrhål, bland annat. Målen var att förberedda prestandauppföljningssystemet och analysera de första insamlade mätningarna. Första steget var att samla information om de sensorerna som redan var installerade, bestämma vilka mätvärde var nödvändiga och hur skulle de kunna mättas. Praktiskt har en datainsamlingsenhet iordningställts och anslutits till befintliga och nya sensorer såsom temperaturgivare och flödesmätare. Teoretiskt har en metod frambringats för att bestämma den termodynamiska cykeln av varje värmepump. Det möjliggjorde beräkningen av COP:n under vissa dagar under våren 2017. Globalt visade systemet rimlig prestanda med en prestandafaktor (likvärdig SPF2) på 3.42, inklusive cirkulationspumpar i bergvärmeskretsen. Det skulle dock kunna förbättras på olika sätt, t.ex. genom att undvika kort-cykling av kompressorer eller gnom att hitta ett optimalt köldbärarflöde i bergvärmeskretsen. Resultaten som det här arbetet kom fram till borde dessutom jämföras med en liknande analys under vintertid, då värmebehovet är högst.

Includes bibliographical references.
A case study was thus carried out at an applicable local industry (brewery) to assess the feasibility of implementing the heat pump for waste heat recovery. Through analysis, the focus was narrowed down from a site wide audit, to a departmental breakdown and then eventually to a specific process; the wort boiler. Three different alternatives were investigated and the performance and economic viability compared; a simple waste heat recovery solution involving a vapour condenser (vq, a mechanical vapour recompression (MVR) heat pump and a thermal vapour recompression (TVR) heat pump. It was found that the MVR system yielded the greatest energy savings, followed by the VC and then the TVR system. All three systems had positive rates of return, with the VC and TVR systems being tied for first place.

An experimental study of the effect of axial flux distribution (AFD) on critical heat flux (CHF) was conducted in directly heated tubes at the Freon-equivalent CANDU reactor conditions of interest. CHF measurements were obtained on test sections with four nonuniform AFD profiles as well as a uniform AFD profile using HFC-134a as a test fluid. Each of the non-uniform AFD test sections had a stepped cosine heat flux profile with approximately 16 heat flux steps. The test conditions covered a pressure range of 1662 to 2389 kPa, a mass flux range of 2827 to 4648 kg m-2 s -1 and an inlet quality range of -0.909 to -0.002. The results showed that the AFD has a strong effect on CHF at high dryout qualities. (Abstract shortened by UMI.)

With the widespread deployment of solar photovoltaic (PV) and thermal devices imminent, this research aims to resolve some engineering barriers to the existing solar photovoltaic/thermal (PV/T) technologies by incorporating an innovative loop heat pipe (LHP) and a typical heat pump. In addition, a coated aluminium-alloy (Al-alloy) sheet replaces the conventional baseboard for the PV cells to improve heat exportation. As a result, this research has developed a novel solar PV/LHP heat pump system to maximise the electrical output of a PV module and generate an additional amount of heat simultaneously. The overall investigation followed the basic methodology of combined theoretical and experimental analysis, including procedures for a critical literature review, optimal concept design, mathematical derivation, the development of simulation models, prototype fabrication, laboratory-controlled and field testing, simulation model validation and socio-economic analysis. A full range of specialised simulation models was developed to predict the system performance with reasonable accuracy. The proposed LHP device has a maximum heat transfer limit of about 900W. The Al-alloy baseboard improved PV efficiency by nearly 0.26% when compared with a traditional PV baseboard. During the real-time measurement conditions, the mean electrical, thermal and overall energetic/exergetic efficiencies of the PV/LHP module were 9.13%, 39.25% and 48.37%/15.02%, respectively. The basic thermal and advanced system coefficients of performance (COPth/COPPV/T) were almost 5.51 and 8.71, respectively. The test results indicated that this system performed better than conventional solar/air energy systems. The feasibility analysis illustrated that this system could generate a substantial amount of energy in subtropical climatic regions, such as Hong Kong. It is cost effective to operate this system in areas with high energy charging tariffs, such as London and Hong Kong. The research results are expected to configure feasible solutions for future PV/T technologies and develop a new solar-driven heating system. The core technologies may enable a significant reduction in or even elimination of the carbon footprint in the built environment.

Many of the projects utilizing Grade 91 steel are large in scale, therefore it is necessary to assemble on site. The assembly of the major pieces often requires welding in the assembly; welding drastically changes the superior mechanical properties of Grade 91 steel that it was specifically developed for. Therefore, because of the adverse effects of welding on the mechanical properties of Grade 91, it is necessary to do a localized post weld heat treatment. In this study a localized post weld heat treatment is used to gather experimental data. The data is then used to derive unknown heat transfer coefficients that are necessary for theoretically modeling heat treatments. With the derived coefficients that have been found one can theoretically model heat treatment scenarios specific to the situations and provide results that are reliable and provide insight as to what parameters will provide the best results. This research is very beneficial to the joining of metals industry because it provides a way to ensure the method used to heat treat the welded section is being properly done, and the required heat treatment is achieved. It is applicable to many different geometries so that it can be modified to specific situations.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 55).
Many applications, such as laser diode technology, utilize components (eg. resistors) which have performance characteristics heavily dependent on temperature, and therefore, maintaining constant temperature is essential in order to eliminate drift in device efficiency. Constant temperature controllers, however, can often be complicated and only stay within a certain range of a set temperature. If temperature needs to be maintained, this thesis suggests a model instead to use ice as an isothermal heat sink. The model proposes to make use of thermodynamics and stabilize an isothermal solid-liquid interface created during ice formation, which will lead to having an isothermal free surface in the liquid phase. The model was validated using a Peltier device to freeze water by applying a constant DC current, and because the inefficiency of the module decreases with decreasing temperature, the heat dissipating power of the thermoelectric eventually equalizes with the ambient losses, stabilizing a solid-liquid interface. This stabilized interface was able to be maintained in experiments using deionized (DI) water, DI water with polystyrene (PS) micro-beads, and DI water with Pseudomonas syringae, a gram-negative bacteria. Pseudomonas syringae is known as an ice-nucleating agent that can reduce the amount of supercooling needed to nucleate ice. Experiments using the bacteria were observed to stabilize a solid-liquid interface faster than the control experiments, and this phenomenon was modeled as a two-fold reason: (1) by increasing nucleation temperature using the bacteria, a reduced input Peltier power is needed to nucleate ice, thereby making the Peltier device reach the steady-state heat losses faster; and (2) a possible decreased enthalpy of fusion caused by the bacteria leads to less latent heat released during the freezing process, putting less heat load on the Peltier device and allowing it to reach steady-state faster. This prediction regarding decreased enthalpy of fusion was validated using a heat flux sensor, as the preliminary results for a mixture of DI water with bacteria yielded an enthalpy of fusion of (199.1±20.2) kJ/kg, whereas the values for DI water and DI water with PS beads were (345.1±15.6) kJ/kg and (328.3±31.2) kJ/kg respectively.
by Vu Anh Hong.
S.B.

The aim of this thesis is to study and explain the purpose and the function of drain water heat exchangers. The thesis goes over theory behind heat transfer and heat exchangers and presents the general solutions of domestic drain water heat recovery systems. Systems gone over in detail are the different general shower drain water heat recovery systems. Another part of the thesis is a case study of an actual shower drain water heat recovery system of a Finnish household. The purpose of the case study is to study the actual temperature increase of cold water in a drain water heat recovery unit and efficiency of such heat exchanger. An alternate goal is to study the difference in efficiency values and temperature gains between two heat exchangers of the same model, where the other has been used significantly more than the other. In other words, another target is to study the fouling effect. The calculations are done using real measurement data. The most important findings are that utilizing a shower drain heat recovery unit provides real energy savings in the long run, and that there is a significant difference of efficiency between a dirty and a clean heat exchanger. Drain water heat recovery systems provided as high as 15 °C increase in the temperature of cold water. A clean heat exchanger boasts an impressive 50.4% efficiency, whereas the dirtier heat exchanger provides a 36.1% efficiency. The results can be further used to calculate the energy savings of the household on a yearly basis. Furthermore, the results show that domestic drain water heat recovery could potentially make a significant difference in national energy usage if implemented nationwide.

Heat flux and heat conductance at the metal mold interface plays a key role in controlling the final metal casting strength. It is difficult to obtain these parameters through direct measurement because of the required placement of sensors, however they can be obtained through inverse heat conduction calculations. Existing inverse heat conduction methods are analyzed and classified into three categories, i.e., direct inverse methods, observer-based methods and optimization methods. The solution of the direct inverse methods is based on the linear relationship between heat flux and temperature (either in the time domain or in the frequency domain) and is calculated in batch mode. The observer-based method consists on the application of observer theory to the inverse heat conduction problem. The prominent characteristic in this category is online estimation, but the methods in this category show weak robustness. Transforming estimation problems into optimization problems forms the methods in the third category. The methods in third category show very good robustness property and can be easily extended to multidimensional and nonlinear problems. The unknown parameters in some inverse heat conduction methods can be obtained by a proposed calibration procedure. A two-index property evaluation (accuracy and robustness) is also proposed to evaluate inverse heat conduction methods and thus determine which method is suitable for a given situation. The thermocouple dynamics effect on inverse calculation is also analyzed. If the thermocouple dynamics is omitted in the inverse calculation, the time constant of thermocouple should be as small as possible. Finally, a simple model is provided simulating the temperature measurement using a thermocouple. FEA (Finite Element Analysis) is employed to simulate temperature measurement.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.
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 (pages 181-195).
Radiative heat transfer is the process by which two objects exchange thermal energy through the emission and absorption of electromagnetic waves. It is one of nature's key fundamental processes and is ubiquitous in all facets of daily life from the light we receive from the Sun to the heat we feel when we place our hands near a fire. Fundamentally, radiative heat transfer is governed by the photonic dispersion, which describes all the electromagnetic states that can exist within a system. It can be modified by the material, the shape, and the environment. In this thesis, morphological effects are used to modify the photonic dispersion in order to explore alternative methods to spectrally shape, tune, and enhance radiative heat transfer from the near-field to the far-field regimes. We start by investigating the application of thin-film morphologies to different types of materials in the near-field regime using a rigorous fluctuational electrodynamics formalism. For thin-film semiconductors, trapped waveguide modes are formed, which simultaneously enhance radiative transfer at high frequencies where these modes are resonant and suppress radiative transfer at low frequencies where no modes are supported. This spectrally selective behavior is applied to a theoretical thermophotovoltaics (TPV) system where it is predicted the energy conversion efficiency can be improved. In contrast, thin-films of metals supporting surface plasmon polariton (SPP) modes will exhibit the opposite effect where the hybridization of SPP modes on both sides of the film will lead to a spectrally broadened resonant mode that can enhance near-field radiative transfer by over an order of magnitude across the infrared wavelength range. In order to observe these morphological spectral effects, suitable experimental techniques are needed that are capable of characterizing the spectral properties of near-field radiative heat transfer. To this end, we developed an experimental technique that consists of using a high index prism in an inverse Otto configuration to bridge the momentum mismatch between evanescent near-field radiative modes and propagation in free space in conjunction with a Fourier transform infrared (FTIR) spectrometer. Preliminary experimental results indicate that this method can be used to measure quantitative, gap-dependent near-field radiative heat transfer spectrally. While utilizing near-field radiative transfer remains a technologically challenging regime for practical application, morphological effects can still be used to modify the optical properties of materials in the far-field regime. As an example, we use polyethylene fibers to design an infrared transparent, visibly opaque fabric (ITVOF), which can provide personal cooling by allowing thermal radiation emitted by the human body to directly transmit to the surrounding environments while remaining visible opaque to the human eye.
by Jonathan Kien-Kwok Tong.
Ph. D.

Turbocharging is a way to stay competitive on the market where there are increasing demands on fuel consumption and engine performance. Turbocharging lets the engine work closer to its maximum power and thereby reduces the relative losses due to pumping and friction. The turbocharger is exposed to big temperaturedifferences and heat flows will occur both internally between the turbine and the compressor as well as between the turbocharger and its surroundings. Away to get a better understanding of the behaviour of the turbocharger is to understand the heat flows better. This thesis is therefore aimed at investigating theeffect of heat transfer on the turbocharger. In the thesis, different ways of accountfor the heat transfer within the turbocharger is investigated and a heat transfermodel is presented and validated. The model can be used as a tool to estimate theimportance of different heat flows within the turbocharger. A set of heat transfer coefficients are estimated and the heat transfer is modelled with good accuracyfor high engine loads and speeds.

Analytical, numerical and experimental analyses have been performed to investigate the effects of thermocouple wire electrical insulation on the temperature measurement of a reference surface. Two diameters of K-type thermocouple, 80μm and 200μm, with different exposed stripped wire lengths (0 mm, 5mm, 10mm, 15mm and 20mm) were used to measure various surface temperatures (4oC, 8oC, 15oC, 25oC and 35oC). Measurements were made when the thermocouple probe is in direct contact with the surface and the wires are extended vertically and exposed to natural convection from outside environment. Experimental results confirmed that the thermal effect from the electrical insulation on temperature measurement was within -0.5oC and therefore it can be neglected. Moreover, the experimental results agree well with those obtained by both the analytical and numerical methods and further confirm that the diameter of the thermocouple has an impact on the temperature measurement. Analytical results of the thermocouple wire with insulation confirm that there is no specific value for the critical radius and the rate of heat flux around the thermocouple wire continuously increases with the wire radius even when this is larger than the critical radius. Experimental and numerical analyses have been performed to investigate the heating impact of using thermocouples for the temperature measurement of small volumes of cold water. Two sizes of K-type thermocouple have been used: 80μm and 315μm to measure the temperature of the cold water inside a small chamber while the thermocouple wires were extended vertically in the outside environment. For this study, the chamber temperature was adjusted to 4oC. The results show that the heating effect of the thermocouple decreases for the greater depth measurements and this effect is eliminated when the thermocouple junction is close to the chamber bottom surface. The increase in the thermal resistance between the bottom surface and the thermocouple junction raises the heating effect of the thermocouple impact. Moreover, the exposed length of thermocouple wires to the environment has no effect over a specific length where the wire end temperature is equal to that of the environment. Experimental and numerical analyses have been carried out to study the effect of using subchannels in heat sink to minimise the effect of hotspots generated on a chip circuit. Two devices of heat sink – with and without subchannels – were fabricated in order to investigate this effect. The first device was manufactured with a normal parallel channel while the second one was designed to extract more heat by dividing the main channels above the hotspot into two subchannels. A hotspot heat flux (16.7×104 [W/m2]) was applied at the centre of the channels while a uniform heat flux (4.45×104 [W/m2]) was applied at upstream and downstream of the channels. Five mass flow rates have generated under gravity force to investigate the performance of devices under different operating conditions. The results showed the maximum surface temperature was reduced by 4oC the temperature uniformity was improved. Moreover, thermal resistance was reduced by 25% but the pumping power was increased as a result of the presence of the subchannels.

Seasonal heat storage, which is used to balance the supply of and demand for heat, e.g. in district heating networks, is necessary for the large-scale utilization of solar heat. The aim of this thesis was to study and develop seasonal heat storage to a point where it, if possible, would be an option in Swedish heating systems. Initial theoretical calculations indicated that the borehole heat store was feasible for seasonal heat storage. In the borehole heat store sensible heat is stored in the bedrock. The bedrock is penetrated by evenly spaced vertical boreholes, which are drilled within a square or circular land area. The holes work as heat exchangers between a heat carrier (normally water), which is pumped through the pipe system of the boreholes and the storage volume. Performed measurements in a pilot plant verified the predicted thermal behaviour of the store. A pre-design of a large-scale heat store, within the University area, was performed. After assuming the operation cycle and the properties of the store, the thermal behaviour of the Luleå heat store was simulated. The construction work of this large-scale borehole heat store (120,000 m 3) was studied in detail and the performance was evaluated during the first five years of operation. It was found that there were several short-comings in design, construction and operation. The operation of the heat pumps caused problems. The borehole pipes were incorrectly installed, which decreased the charged heat by 23% and recovered heat by about 34%. Without changing the storage task the store could have been built at a cost of 4.5 MSEK instead of 6.3 MSEK. A model was developed to determine the optimum design of borehole heat stores. The optimum design was defined as the design that fulfils the storage task at a minimum annual storage cost, i.e. the sum of the annual costs of the investment, operation, maintenance and heat loss. The optimum and actual designs of three stores were evaluated and compared. The more recently constructed plants differed less from the optimum design than the oldest plant, situated in Luleå. The main reason was the increasing engineering experience, which influenced the design of the later stores. Typical data for the optimum design are drilling depths of 125 m and a borehole spacing of 4 m. In a 1.6 GWh store, 65 boreholes result in a storage volume of about 125,000 m3. The specific construction cost, which decreases with increasing heat extraction capacity, is 1.50 SEK/ KWh or 20 SEK/m3 at an heat extraction capacity of 7 GWh. The annuity method (6%, 25 y) was used to calculate the annual investment cost, which stood for approximately 65% of the total annual storage cost. The sensitivity of the different parameters was investigated with the optimization model. It was demonstrated that the technical design of the store was greatly influenced by the cost parameters. For example, small changes in the drilling cost could mean a very different design. It was also found that it was cost-effective to investigate the soil depth and the rock thermal conductivity in detail before the design of the borehole heat store was performed.
Godkänd; 1994; 20070209 (ysko)

Thermal analysis is a non-destructive and quantitative technique used to assess the quality of the liquid metal prior to casting. The method has been used in the aluminum foundry to assess the extent of grain refining and the degree of eutectic modification. Although the method has been, to a certain extent, successfully used, it has some serious drawbacks. The most apparent include: (a) poor reproducibility, (b) poor control over heat extraction and cooling rates, (c) a batch operation, and (d) a manual operation which is difficult to automate and computerize.
To overcome these shortcomings associated with current thermal analysis methods, a new technique of performing thermal analysis on aluminum alloys has been devised. Besides being semi-continuous, the new system is easier to use, more dependable and, most importantly, capable of performing thermal analysis tests at controlled and variable cooling rates throughout the entire solidification process.
The new thermal analysis technique is based on heat pipe principles in which a small quantity of a melt, residing in the core of a heat pipe probe, is solidified, and its cooling curve is acquired. Once the cooling curve has been acquired, the probe is instructed to remelt the sample and await instructions to run another test. The new probe, which resides in the melt and need not be withdrawn, is used to solidify the sample under predetermined and controlled conditions.
The operating principles of the new thermal analysis device are based on heat pipe technology. In simple terms, a heat pipe is a high heat transfer device capable of transferring large amounts of heat from a source to a sink by taking advantage of the high heat transfer rates associated with the evaporation and condensation of a working fluid placed inside the pipe. Heat is absorbed at the heat source (evaporator) and dissipated at the heat sink (condenser) at approximately isothermal conditions, and hence the thermal gradient from one extreme end of the pipe to the other is minimal, the amount of heat transferred is large, and the thermal resistance is small.
The new thermal analysis device has been used to produce cooling curves of various aluminum alloys. The device has also been shown to detect the extent of grain refinement, degree of eutectic modification, and formation of intermetallic phases. In addition, the device has been used to quantify the amount of iron in aluminum melts. Thermal analysis results obtained with the new technique are in good agreement with those of conventional thermal analysis. In conjunction with the new device, a control scheme has been devised to control the heat extraction and cooling rates during cooling of aluminum alloys. Finally, a heat transfer and solidification model of the heat pipe thermal analyzer is derived and validated based on the acquired experimental data.
Thermal analysis results are reported for pure aluminum, three casting alloys: hypeoeutectic aluminum silicon (A356 and A319), and a eutectic aluminum silicon (413) alloy, and a wrought alloy of the 6000 series (6061).

An experimental investigation of the effects of axial flux distribution (AFD) and obstacles on film-boiling heat transfer was performed in a vertical tube using HFC-134a as coolant. The following parameters were examined: (1) Axial flux profiles (uniform, inlet-peak and outlet-peak), (2) Flow-blockage ratios (12% and 24%), (3) Obstacle pitches (150 mm and 300 mm), (4) Obstacle shapes (blunt and round). Test conditions covered the pressure 1665 and 2389 kPa (water-equivalent value: 10 and 14 MPa), a mass-flux range from 1395 to 3575 kg.m-2.s -1 (water-equivalent value: 2000 to 5000 kg.m-2.s -1) and an inlet-fluid temperature range from 30 to 70°C (water-equivalent value: 229 to 324°C). Film-boiling temperature measurements were recorded for all possible heat-flux levels, up to a limiting surface temperature of 240°C to avoid Freon decomposition. Inside wall temperature distributions of the obstacle-equipped test sections were compared against those of a reference bare tube at similar flow conditions. Flow obstacles were found to have a significant influence on film-boiling heat-transfer. Film-boiling wall temperatures along the test section were reduced significantly by decreasing the obstacle pitch, by increasing the obstacle size and by using a blunt instead of streamline-shaped obstacle. The effect of AFD on film-boiling heat transfer is noticeable in the developing film-boiling region and can be attributed mainly to the variation in critical heat flux (CHF) occurrence. However, the AFD effect appears to be less obvious in the fully developed film-boiling region. Since the literature suggested that the single-phase pressure-loss coefficient of the flow obstructions could be an important parameter in correlating the film-boiling heat-transfer enhancement, this parameter was also measured and correlated. Previously derived prediction methods for obstacle-enhanced film-boiling heat transfer did not provide satisfactorily agreement with the data; therefore, a new prediction method was derived to predict the film-boiling heat-transfer augmentation for uniform AFD tubes. The new equation accounts for the enhancement in film-boiling heat transfer due to turbulence generated by (i) liquid-film termination at the dryout point and (ii) the upstream flow obstructions. The new correlation was applied to non-uniform AFD data. It was concluded that (i) this new prediction method is also applicable to non-uniform AFD tubes, (ii) the new prediction method has the correct asymptotic trends and (iii) single-phase pressure-loss coefficients cannot be used directly to predict the heat-transfer enhancement for both blunt and rounded obstacles.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007.
Includes bibliographical references (p. 283-289).
Passive cooling via natural circulation of gas after a loss of coolant (LOCA) accident is one of the major goals of the Gas-cooled Fast Reactor (GFR). Due to its high surface heat flux and low coolant velocities under natural circulation in post-LOCA scenarios, the capability of turbulent gas flow to remove heat from the GFR core can be impaired by either a buoyancy effect or an acceleration effect. These phenomena lead to a Deteriorated Turbulent Heat Transfer (DTHT) regime. To predict accurately the cladding temperature at the hot spot, reliable heat transfer correlations that account correctly for these effects are needed. This work addresses this need by experimentally obtaining heat transfer data and developing new heat transfer correlations that can be used in system analysis codes, such as RELAP5-3D, to reduce uncertainties of predictions in these DTHT regimes. An experimental facility was designed and built using similitude analysis to match key experimental loop parameters to the GFRs' Decay Heat Removal (DHR) system operating conditions to the largest extent possible. Through a thorough literature survey two non-dimensional numbers namely (1) the buoyancy parameter (Bo*) and (2) the acceleration parameter (K,) were identified as important indicators of the DTHT regime. The experimental data was collected for a range of (1) inlet Reynolds number from 1800 to 42,700, (2) inlet Bo* up to 1X10-5 (3) and inlet Kv up to 5x10-6. The data showed significantly higher reduction of the Nusselt number (up to by 70%) than previously reported (up to 50%). Also, the threshold at which DTHT regime occurs was found to be at smaller non-dimensional numbers than previously reported. A new phenomenon "re-turbulization", where the laminarized heat transfer recovers back to turbulent flow along the channel, was observed in the experiment.
(cont.) A new single phase gas flow heat transfer map is proposed based on the non-dimensional heat flux and the Reynolds number in our data, and is shown to compare well with data in the literature. Three sets of new correlations were developed, which reflect both the buoyancy and acceleration effects and have better accuracy as well as ease of numerical implementation than the existing correlations. The correlations are based on the Gnielinski correlation and replace the Reynolds number subtracting constant by a functional form that accounts for the buoyancy and acceleration effects separately, or in the combined form through a newly introduced non-dimensional "DTHT" number. The three correlation types have different complexity level, with the first being the most complex and the third being the most simple and easy to apply without any need for iterations. Additional runs with natural circulation showed that the friction factor in the DTHT regime could be significantly higher than predicted by conventional friction factor correlations, although more experiments will be needed to develop reliable correlations for pressure drop in these regimes. Overall, it is concluded that due to the low heat transfer coefficient and increased friction factor in the DTHT regime, the GFR DHR system should be ideally designed to operate outside the DTHT regime to (1) avoid reduction of heat transfer capability, (2) avoid increase of pressure drop, and (3) reduce uncertainties in predictions of the cladding temperature.
by Jeongik Lee.
Ph.D.

The demand for lower emission engines forces the car industry to build moreefficient engines. Turbocharged engines are on the rise, and better understandingof the heat transfer and efficiency of the turbocharger is needed to build better ones. A lot is known about the overall efficiency of the turbocharger, but not much is known about where the heat losses are located and how they interact with each other. This thesis presents a one dimensional model for heat exchange in the tur-bocharger and investigates how the heat flows from the hot exhaust gases to the cold intake air. Data is gathered by performing tests on a single scroll turbocharger in an engine test bench at Linköping University. The tests are focused on operating points where the air mass flow is low and neither the compressor nor the turbine works adiabatically. The results show that it is possible to estimate the heat flows together withthe efficiency of the turbine and compressor using only known parameters, elim-inating the need to add any new sensors to the engine.

Presented in this study is an experimental investigation of heat transfer in a model of the 37-rod CANDU reactor bundle. Localized heat was provided by a narrow heated strip mounted on the central rod, which could be traversed within the duct and rotated about its axis. The relative variation of the "apparent" local heat transfer coefficient around the central rod was determined for various rod-wall proximities including two limiting cases of rod-wall contact and rod-rod-wall contact. The flow temperature measurements were concentrated on the rod-wall gap variation. The statistics of the temperature fluctuations showed a deviation from Gaussianity, that was more pronounced as the gap diminished. Asymmetry of the mean temperature and the temperature fluctuation contours is observed with the heater near the gap as well as facing the sub-channel centre. (Abstract shortened by UMI.)

A heat pipe is a heat transfer device of very high thermal conductance that features two-phase flow. Research at McGill University has led to the development of the McGill Heat Pipe which includes an internal flow modifier. Such a heat pipe can be operated at very high heat fluxes. This area of heat pipe technology has potential in many applications in metallurgical industries.
This thesis describes how the McGill heat pipe was developed, tested, modeled and applied in high heat flux situations. Until the development of the McGill Heat Pipe, three main issues had prevented the successful use of heat pipe technology in high heat flux applications. These relate to limitations imposed by film boiling, dry-out, and the structure of the flow. The McGill Heat Pipe has successfully addressed and overcome these limitations.
To overcome film boiling and dry-out, a flow modifier was developed. The structure of the flow was changed by introducing a reservoir and a return line. This thesis describes some of the work that is being carried out to develop and evaluate families of flow modifiers, or spiral springs. Results from a number of high flux experiments will be detailed and the effects of the flow modifiers for each case will be described. In addition, the velocity of the return water was visualized with magnesium alloy chips and was measured with a video camera. Comparisons of the operation of the heat pipe both with and without a flow modifier are presented. This is the first study of its kind in which a transparent glass return line and particles were used to visualize the liquid flow in the return line of the heat pipe.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 94-96).
Introduction: Rotorcraft engines can lose up to 70% of the potential chemical energy of their fuel as waste heat. Harvesting this waste heat and converting it to useful work would improve the efficiency and power output of the engine. Figure 1 shows two possible engine systems in which a secondary engine could be used to harvest waste heat. For the gas turbine engine in Figure 1A, the main source of waste heat is the enthalpy of the engine's exhaust gases. In the case of the spark ignition engine in Figure 1B, there are three sources of waste heat: the enthalpy available in the exhaust gases, the heat rejected by the coolant loop, and the heat rejected by the oil loop. For each engine system, the heat from waste heat engine is rejected to the ambient air. Possible candidate systems for waste heat recovery include closed cycle systems such as the Rankine and Brayton engines. Rankine engines typical use water as a working fluid. The performance of water-based Rankine engines suffer from low pressures in the working fluid at the temperatures of the ambient and, therefore, require large low pressure expanders and condensers to operate efficiently. Organic working fluids have higher vapor pressures and can be used in Rankine engines instead of water. The higher vapor pressures of these fluids allow the use of smaller expanders. However, organic working fluids are limited to temperatures below 250 C, which is substantially lower than the typical temperatures available in the waste streams. Brayton engines can operate at higher temperatures using inert gases such as helium and argon as working fluids. In either of these engines, the turbomachinery and heat exchangers must remain leak tight as the working fluid is cycled through at high temperatures and high pressures. As a consequence of this requirement, these cycles will not be considered further in this work. Thermoelectric devices, on the other hand, do not require leak tight passages or turbomachinery. These are compacted and are expected to have a higher reliability since they have no moving parts. These advantages have motivated this study on thermoelectrically-based waste heat engine. For a thermoelectrically-based waste heat engine to be feasible, it must be capable of absorbing and rejecting large amounts of heat in part to compensate for the low efficiencies of thermoelectric materials. It must also be light weight and compact to address concerns of power to weight ratios and space constraints in rotorcraft. Therefore, the waste heat engine must be designed to minimize thermal resistance while also minimizing the mass and volume of the heat exchangers.
by Victoria D. Lee.
S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 69-74).
This thesis presents a series of three related studies with the aim of developing a surface that promotes robust dropwise condensation. Due to their remarkably low droplet adhesion, superhydrophobic surfaces were investigated for application to dropwise condensation. Although precise model superhydrophobic surfaces were necessary to gain insight into these phenomena, it was recognized that wide-scale implementation necessitates a surface that can be mass-produced at an industrial scale. To this end, anodized metal oxide surfaces were pursued as candidate condenser materials. First, a study was performed to determine the precise conditions leading to the transition between wetting and non-wetting states. By depositing pendant drops of various sizes on a superhydrophobic surface and observing their wetting behavior, a hitherto unknown mechanism for wetting transition is reported. A new phase diagram was developed which shows that both large and small droplet can transition to wetted states due to the new deceleration-driven and the previously-known Laplace mechanisms. It is shown that the attainment of a non-wetted superhydrophobic state is more restrictive than previously thought. Second, we investigate the large-scale fabrication of superhydrophobic surfaces via two different methods: solvent-induced crystallization of a thermoplastic polymer, and anodic oxidation of aluminum. Although the polymer surface as not able to withstand the high temperatures seen during condensation, the applicability of the anodized metal surface to dropwise condensation was further investigated. Third, to replicate the conditions of a typical power plant or desalination plant, an apparatus was constructed that condenses steam at pressures below 1 atm. It employs a vacuum chamber in which a surface is exposed to saturated steam at various pressures. The rig design and operating principles are explained, and the results of condensation tests on superhydrophobic anodized metal oxide surfaces are presented. It was found that although the metal oxide surfaces were able to resist wetting of macroscale droplets, they suffered from non-preferential nucleation and droplet growth. This led to the eventual growth of a macroscale Wenzel droplet, which proved to be difficult to shed from the surface.
by Adam Paxson.
S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, September, 2020
Cataloged from student-submitted PDF of thesis.
Includes bibliographical references (pages 25-26).
Environmental concerns and economic incentives have created a push for a reduction in emissions and an increase in efficiency. The U.S. Department of Energy estimates that 20 to 50% of the energy consumed in manufacturing processes is lost in some form to waste heat. The purpose of this study is to review the waste heat recovery technologies currently available in both commercial and research applications to determine how thermoacoustics may serve a role in furthering the use of waste heat recovery units. A literary review of the most common waste heat recovery units was compiled to determine the advantages and disadvantages of the different technologies by comparing components and their governing processes. An existing model of a thermoacoustic converter (TAC) was reviewed and a conceptual analysis written to suggest improvements for future experimental designs.
by Alex Aguilar.
S.B.
S.B. Massachusetts Institute of Technology, Department of Mechanical Engineering

External stresses surrounding bone can stimulate heat shock proteins (HSPs), which are involved in anti-apoptosis, cell proliferation, and differentiation. In vitro stress modulation and HSP induction may be critical factors for enhancing bone regeneration. We investigated whether applying individual or combinatorial stress conditioning (thermal, tensile, and biochemical) and effective HSP modulation could induce in vitro responses in preosteoblasts indicating mitogenic/osteogenic/angiogenic/anti-osteoclastic effects. A preosteoblast cell line (MC3T3-E1) was exposed to conditioning protocols utilizing thermal stress applied with a water bath, tensile stress using a Flexcellâ„¢ bioreactor, and biochemical stress with the addition of growth factors (GFs) (i.e. transforming growth factor-beta 1 (TGF-β1) and bone morphogenetic protein-2 (BMP-2)). Furthermore, the role of HSP70 in osteogenesis under normal conditions and in response to heat was investigated by transfecting preosteoblasts with HSP70 small interfering RNA alone or in combination with thermal stress and measuring cellular response. Heating at 44°C (for 8 minutes) rapidly induced osteocalcin (OCN), osteopontin (OPN), osteoprotegerin (OPG), vascular endothelial growth factors (VEGF), and cyclooxygenase 2 (COX-2) mRNA at 8 hour post-heating (PH). The addition of GFs with heating induced OPG and VEGF genes more than heating or GF addition alone. OPN, OCN, and OPG secretions increased with the addition of GFs. However, matrix metalloproteinase-9 (MMP-9) secretion was inhibited by heating, with more significant declines associates with GF inclusion. Equibiaxial tension (5%, 0.2 Hz, 10 seconds tension/10 seconds rest, 6 days) with GFs enhanced proliferation than tension or GF addition alone. MMP-9 secretion decreased in response to tension alone or more with GFs. Tension (1-5%, 24 hours) with GFs induced prostaglandin E synthase 2 (PGES-2), OPG, and VEGF genes more than tension or GFs alone. Combinatorial conditioning with thermal stress (44°C, 8 minutes) and tension (3%, 0.2 Hz, 10 seconds tension/10 seconds rest, 4 hours for HSP gene and 24 hours for VEGF secretion and MMP-9 gene) induced HSP27 and HSP70, secretion of VEGF (protein), and suppression of MMP-9 (gene) more than heating or tension alone. HSP70 silencing followed by heating (44°C, 8 minutes) enhanced expression of HSP27. Mitogenic activity was inhibited by heating with more significant decrease occurring by heating and HSP70 silencing. At 10 hours PH, TGF-β1, MMP-9, and ALP mRNA decreased in response to heating and HSP70 silencing. At 48 hours PH, heating following HSP70-silencing induced VEGF secretion significantly. In conclusion, effective application of individual or combinatorial conditioning utilizing heating, tension, and GFs could be beneficial as a bone healing-strategy by rapidly inducing stress proteins (HSPs), angiogenic factor (e.g. VEGF), anti-osteoclastogenic cytokines (e.g. OPG), and bone matrix proteins (e.g. OPN and OCN) with anti-resorptive activity by inhibiting MMP-9.
Ph. D.

This study is carried out at Scania’s production centre in Södertälje. The heat treatment process fora crown wheel is subject to a significant amount of parameters which are complex to model. Theaim of this study is to investigate the feasibility of improving process predictability for the casehardening depth of crown wheels by using advanced analytics.The project is initiated by studying in depth the steps involved in the case hardening process and theproperties of the raw material for the crown wheel. The field of machine learning is also studied andexplored to know its applications and the resources it requires. For the prediction of the output, dataanalysis is conducted to find the parameters affecting the process after which data is gathered fromdifferent databases and is cleaned and synthesised to be used for machine learning in Python. Aregression and classification analysis is made by using pre-existing algorithms for prediction fromthe Scikit-learn library. The models obtained are evaluated by using metrics and a classificationmodel is found to have the greatest prediction ability. A technical and business value evaluation ismade to judge its performance.This study resulted in the development of a basic tool which can make predictions on the casehardening depth, with certain limitations. Additionally, conclusions in regards to the differentparameters affecting the output were derived.
Föreliggande rapport är resultatet av ett examensarbete utfört på uppdrag av Produktionscenter vidScania CV AB i Södertälje. Värmebehandlingsprocessen för kronhjul är beroende av en betydandemängd parametrar som är komplexa att modellera. Syftet med detta examensarbetet är att genomanvändning av avancerad analys undersöka möjligheten att förbättra förutsägbarheten för härddjupetvid sätthärdning av kronhjul.Arbetet inleds genom att studera de steg som är involverade i sätthärdningsprocessen ochråmaterialets egenskaper. Området maskininlärning studeras och utforskas för att känna till desstillämpningar och vilka resurser som krävs för dess användning. För prognos av utdata utförsdataanalys för att hitta parametrar som påverkar processen. Dessa data samlas från olika databaser,sorteras och syntetiseras för att kunna användas för maskininlärning i Python. En regressions- ochklassificeringsanalys görs genom att använda redan existerande algoritmer för förutsägelse frånScikit-learn. Modellerna som erhållits utvärderas med hjälp av metrik och en klassificeringsmodellbefinns ha den bästa förutsägelsesförmågan. En utvärdering av teknik- och affärsvärde utförs för attbedöma modellernas prestanda.Denna studie resulterade i utvecklingen av ett grundläggande verktyg som kan göra förutsägelserom härddjupet vid sätthärdning, med vissa begränsningar. Dessutom drogs slutsatser med avseendepå olika parametrar som påverkar processens resultat.

Effective cooling of electronic components arranged in vertically oriented parallel boards is considered. The objective of the present investigation is to examine the effects of global flow in a channel upon the local heat transfer from a flush mounted source. The concept of adiabatic heat transfer coefficient and its application is clarified by reviewing its origins and examining a series of numerical experiments on a well-defined model problem. Simulations are conducted in the regions of laminar forced flow, mixed forced and local buoyant convection and buoyancy-induced flow. Local buoyancy effects cause a departure of adiabatic heat transfer coefficient from its value for pure forced convection. Calculations cover the range 10-3 at Pr = 0.7. The superposition principle for temperature fields is validated for forced convection. The effects of mixed convection upon this phenomenon is subsequently examined.

A common technique to improve the performance of shell and tube heat exchangers (STHE) is by redirecting the flow in the shell side with a series of baffles. A key aspect in this technique is to understand the interaction of the fluid dynamics and heat transfer. Computational fluid dynamics simulations and experiments were performed to analysis the 3-dimensional flow and heat transfer on the shell side of an STHE with and without baffles. Although, it was found that there was a small difference in the average exit temperature between the two cases, the heat transfer coefficient was locally enhanced in the baffled case due to flow structures. The flow in the unbaffled case was highly streamed, while for the baffled case the flow was a highly complex flow with vortex structures formed by the tip of the baffles, the tubes, and the interaction of flow with the shell wall.

This study is aimed to evaluate the techno-economic feasibility of implementing heat driven cooling technologies in buildings connected to Tafjord Kraftvarme’s district heating network in Aalesund, Norway. Heating and cooling demands were found by projecting two 4000 𝑚2 office buildings according to Passive House and Low Energy Building criteria, within the frame of the energy requirements in the TEK17 building regulations (Standard Norge, 2012) (Norwegian Building Authority, 2017). Suitable cooling and heating equipment, both electrical and heat driven, were dimensioned based on the peak cooling load of the projected buildings, and technical and economic information obtained from the distributors of the equipment. LCOE analysis shows that the heat driven cooling solutions could be able to compete economically, in variable extent, with the electrically driven solutions given relatively low heating demand or by applying investment subsidies or price reduction on district heat for cooling purpose. The desiccant cooling solution could even compete with the electrical driven solution even without subsidies or price reduction on DH for cooling. This is mainly because of its enhanced heat recovery reducing the heating demand. The absorption cooler on the other hand, has both a higher consumption and higher power input of district heat while running, and is therefore less competitive without subsidy or price reduction on DH for cooling. In the building cases explored, the absorption cooling solution requires either subsidy or price reduction on DH for cooling to compete with the electric chiller and district heat solution, while it require both to come close to compete economically with the heat pump solutions. With increasing heating demand the heat driven solutions, which use district heat as their heat source, become less competitive compared to the heat pump solutions. This is because, with the mild winters in Aalesund, the heat pumps can run with a COP of 2-3 while the COP of district heat it is considered to be 1. Other important factors that is not covered by the LCOE analysis is the reliability and environmental aspect. None of the heat driven cooling solutions use any environmentally unfriendly refrigerants, and the maintenance of the cooling machines are minor. The lifetimes of the machines are estimated to be 20 years for the desiccant and 40 years for the absorption cooler, compared to 15 years for the heat pumps and electric chiller. The heat driven cooling solutions can therefore be considered more reliable both in terms of regulations on refrigerants and on maintenance and lifetime. An additional important factor is that compared to the heat pump solutions, the heat driven cooling solutions with district heat to cover the heating demand can replace large quantities of electricity consumption with low-grade thermal energy. Considering both the economic, environmental and reliability factors, the heat driven cooling solutions could be a viable option and should be considered when implementing heating and cooling equipment in buildings connected to the district heating network in Aalesund or other locations with similar climate.
Studiens syfte är att utvärdera den tekno-ekonomiska genomförbarheten av att implementera värmedrivna kylelösningar i byggnader knytna till Tafjord Kraftvarme’s fjärrvärmenetvärk i Aalesund, Norge. Uppvärmnings- och nerkylningskrav hittades vid at projictera två 4000 𝑚2 kontorsbyggnader enligt “Passive House and Low Energy Building” kriterier, inom ramen av energikrav i TEK 17 byggnadsförordningar (Standard Norge, 2012) (Norwegian Building Authority, 2017). Passande nerkylnings- och uppvärmingsutrustning, både elektrisk och värmedriven, blev dimensionerande baserad på toppbelastning till de projicerade byggnader, och den tekniska och ekonomiska information tagen från utrustningsdistributörerna. LCOE-analysen visar att den värmedrivna nerkylningslösningen kan vara konkurrenskraftig ekonomisk sett, i variabel utstreckning, med de elektriska drivna lösningarna om varmebehovet är lågt eller vid at använda subventioner eller prisnedsättning på fjärrvarme som används för kylning. Nerkylningslösningen med torkmedel kan även vara konkurrenskraftig med den elektrisk drivna även utan subventioner eller prisnedsättning på fjärrvarme. Det är huvudsakligen på grund av dens förbättrade värmeåterhämtning som reducerar uppvärmningskraven. Absorptionskylaren å andra sidan, har både högre ströminmatning av fjärrvarme medan den är i gång och är därför mindre konkurrenskraftig utan subventioner eller prisnedsättning på fjärrvarme som används för kylning. I de utforskade byggnadsfallen kräver absorptionskylaren antigen subventioner eller prisnedsättning på fjärvarme för att kunna konkurrera med den elektriska kylmaren, medan det krävs både för att kunna konkurrera med värmepumpelösningen. Med ökande uppvärmingskrav blir de värmedrivna lösningarna som använder fjärrvarme som värmekälla mindre konkurrenskraftiga jämfört med värmepumpelösningarna. Detta på grund av de milda vintrar i Aalesund som leder till att värmepumparna kan köra med en COP på 2-3 medan den anses vara 1 for lösningarna som brukar fjärrvarme. Andra viktiga faktorer som inte ingår i LCOE-analysen är pålitlighet och miljöaspekten. Ingen av de värmedrivna nerkylningslösningarna andvänder något miljöovänligt köldmedium och underhållet av nerkyningsmaskiner är minimalt. Maskinernas livsläng är beräknad till 20 år för torkmedelkylaren och 40 år för absorptionskylaren, jämfört med 15 år för värmepumparna och den elektriska kylaren. De värmedrivna nerkylningslösningarna kan därför  anses vara mer pålitliga både beträffande reglering av köldmedium och underhåll samt livslängd. Ytterligare en viktig faktor är att de värmedrivna nerkylningslösningarna, jämfört med värmepumplösningarna, kan vara et livskraftig alternativ, både med hänsyn til den ekonomiska faktoren, miljöfaktoren och pålitligheten och borde därför tas hänsyn till vid implementering av uppvärmings- og nerkylningsutrustning i byggnader knytna till fjärrvärmenätet.

The use of Combined Heat and Power (CHP) units, heat pumps and electric boilers increases the linkages between electricity and heat networks. In this thesis, a combined analysis was developed to investigate the performance of electricity and heat networks as an integrated whole. This was based on a model of electrical power flow and hydraulic and thermal circuits together with their coupling components (CHP units, heat pumps, electric boilers and circulation pumps). The flows of energy between the electricity and heat networks through the coupling components were taken into account. In the combined analysis, two calculation techniques were developed. These were the decomposed and integrated electrical-hydraulic-thermal calculation techniques in the forms of the power flow and simple optimal dispatch. Using the combined analysis, the variables of the electrical and heat networks were calculated. The results of the decomposed and integrated calculations were very close. The comparison showed that the integrated calculation requires fewer iterations than the decomposed calculation. A case study of Barry Island electricity and district heating networks was conducted. The case study examined how both electrical and heat demands in a self-sufficient system (no interconnection with external systems) were met using CHP units. A solution was demonstrated to deliver the electrical and heat energy from the CHP units to the consumers through electrical and heat networks. The combined analysis can be used for the design and operation of integrated heat and electricity systems for energy supply to buildings. This will increase the flexibility of the electricity and heat supply systems for facilitating the integration of intermittent renewable energy.