Solid propellant gas generators that have high gas capacity are used for fast pressurization of inflatable devices or elastic shells. However, many applications such as control surface actuation, air bottle pressurization in rocket engines and safety systems of automobiles (airbags) require exit gases at near ambient temperature. A scheme suitable for short duration applications is passive cooling of gas generator gases by using a packed bed as compact heat exchanger. A study indicated that the mass flow rates of solid propellant gas generators for applications such as air bottle pressurization and control system actuators were of the order of 1 kg/s. Since pressure and enthalpy drop correlations for packed beds with mass flow rates (~1 kg/s) and packing sphere based Reynolds number (Red) ~ 9X104 were unavailable in open literature, an experimental investigation was deemed necessary. The objectives of the present study were (a) characterization of packed beds for pressure and enthalpy drop, (b) develop Euler and Nusselt number correlations at Red~105 and (c) evolve an engineering procedure for estimation of packed bed pressure and enthalpy drop. An experimental test facility with a hydrogen-air combustor was designed and fabricated for this purpose to characterize a variety of packed beds for pressure drop and heat transfer. Flow through separate packed beds consisting of 9.5mm and 5mm steel spheres and lengths ~200mm and ~300mm were studied in the sphere based Reynolds numbers (Red) range of 0.4X104 to 8.5X104. The average porosity (є) of the randomly packed beds was ~0.4. The ratios of packed bed diameter to packing diameter for 9.5mm and 5mm sphere packing were ~ 9.5 and 18 respectively. The inlet flow temperature was unsteady and a suitable arrangement using mesh of spheres was used at either ends to eliminate flow entrance and exit effects. Stagnation pressures were measured at entry and exit of the packed beds. The pressure drop factor fpd, (ratio of Euler number (Eu) to packed bed dimensions) for packed bed with 9.5mm spheres exhibited an asymptotically decreasing trend with increasing Reynolds number, and a correlation for the pressure drop factor is proposed as, fpd=Eu/ [6(1-є) (L/dp)] =125.3 Red-0.4; 0.8X104 < Red < 8.5X104 (9.5mm sphere packing). However, for packed beds with 5mm spheres the pressure drop factor fpd, was observed to increase in the investigated Reynolds number range. The correlation based for pressure drop factor is proposed as, fpd= Eu/ [6(1-є) (L/dp)] =0.0479 Red0.37; 0.4X104 < Red < 3.9X104 (5mm sphere packing). The pressure drop factor was observed to be independent of the inlet flow temperature. Gas temperatures were measured at the entry, exit and at three axial locations along centerline in the packed beds. The solid packing temperature was measured at three axial locations in the packed bed. At Red~104, the influence of gas phase and solid phase thermal conductivity on heat transfer coefficient was found to be negligible based on order of magnitude analysis and solid packing temperature data obtained from the experiments. Evaluation of sphere based Nusselt number (Nud) at axial locations in the packed bed indicated a length effect on the heat transfer coefficient, which was a function of Reynolds number and size of spheres used in packing. The arithmetic average of Nusselt numbers at different axial locations in the packed bed were correlated as Nud=3.85 Red0.5; 0.5X104 < Red < 8.5X104. The Nusselt numbers obtained in the experiments were consistent with corresponding literature data available at lower Reynolds numbers. In this experimental study Euler number correlations for pressure drop and Nusselt number correlations for heat transfer were obtained for packed beds at Red~105. An engineering model for estimation of packed bed pressure and enthalpy drop was evolved, which is useful for sizing of packed bed heat exchanger in solid propellant gas generation systems.

The overarching goal of this work is to address the design of next-generation, high torque density electrical machines through numerical optimization using an integrated thermal-electromagnetic design tool that accounts for advanced cooling technology. A parametric thermal model of electric machines was constructed and implemented using a finite difference approach incorporating an automated, self segmenting mesh generation. A novel advanced cooling technology is proposed to improve thermal transport in the machine by removing heat directly from the windings via heat exchangers located between the winding bundles. Direct winding heat exchange (DWHX) requires high convective transport and low pressure loss. The heat transfer to pressure drop tradeoff was addressed by developing empirically derived Nusselt number and friction factor correlations for micro-hydrofoil enhanced meso-channels. The parametric thermal model, advanced cooling technique, Nusselt number and friction factor correlations were combined with a parametric electromagnetic model for electric machines. The integrated thermal-electromagnetic model was then used in conjunction with particle swarm optimization to determine optimal conceptual designs. The Nusselt number correlation achieves an R² value of 0.99 with 95% of the data falling within ± 2.5% similarly the friction factor correlation achieves an R² value of 0.92 with 95% of the data falling within ± 10.2%. The integrated thermal-electromagnetic design tool, incorporating DWHX, generated an optimized 20 kW permanent magnet electric machine design achieving a torque density of 23.2 N-m/L based on total system volume.

Le phénomène de Rayleigh-Bénard correspond à l'état instable dans lequel se trouve une couche horizontale d'un fluide dilatable, soumise à un gradient de température DT. Si ce dernier dépasse une valeur critique DTc, des mouvements convectifs naissent à l'intérieur du fluide. Concernant les fluides à seuil, le phénomène devient plus complexe. Le seuil s'ajoute aux forces stabilisatrices au sein du fluide et modifie de manière fondamentale le transfert de matière et le transfert thermique. Au départ, le fluide est au repos ; le gradient de vitesse est alors nul et la viscosité efficace infinie partout. L'approche de stabilité linéaire est incapable de fournir une solution aux équations d'écoulement car on doit perturber, par les forces d'Archimède, un fluide d'une viscosité infinie. Dans ce travail de thèse, des expériences de Rayleigh-Bénard ont été effectuées sur des solutions à base de Carbopol 940 présentant un seuil de contrainte. Le dispositif expérimental nous a permis d'avoir des résultats quantitatifs et qualitatifs intéressants. Les mouvements thermoconvectifs ont ensuite été filmés par la technique d'ombroscopie. L'effet non-linéaire au début de la convection a été observé.

All heat pump cycles have one common feature that connects them to one another; this feature is the presence of a heat exchanger. There are even some heat–driven cycles that are completely composed of heat exchangers, every heat exchanger fulfilling a different, though critical role. The need therefore exists to optimize heat exchangers, more specifically Compact Heat Exchangers (CHE). This study deals with the optimization of such a CHE by determining an optimal hydraulic diameter of the micro–channels in a CHE, for minimal hydraulic losses. Two Computational Fluid Dynamics (CFD) models were developed for a single micro–channel that is present in a CHE. The first model had a semi–circular cross–section, the second a triangular cross–section. The results were verified by comparing it with existing experimental data. Following the verification of the results, the micro–channel was optimized by implementing an optimum diameter for the lowest pressure drop over the micro–channel. This was done for both the semi–circular and triangular micro–channel cross–sections. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.

All heat pump cycles have one common feature that connects them to one another; this feature is the presence of a heat exchanger. There are even some heat–driven cycles that are completely composed of heat exchangers, every heat exchanger fulfilling a different, though critical role. The need therefore exists to optimize heat exchangers, more specifically Compact Heat Exchangers (CHE). This study deals with the optimization of such a CHE by determining an optimal hydraulic diameter of the micro–channels in a CHE, for minimal hydraulic losses. Two Computational Fluid Dynamics (CFD) models were developed for a single micro–channel that is present in a CHE. The first model had a semi–circular cross–section, the second a triangular cross–section. The results were verified by comparing it with existing experimental data. Following the verification of the results, the micro–channel was optimized by implementing an optimum diameter for the lowest pressure drop over the micro–channel. This was done for both the semi–circular and triangular micro–channel cross–sections. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-08-01T12:12:38Z No. of bitstreams: 1 GuilhermeKeitiAoyama_DISSERT.pdf: 15234104 bytes, checksum: 840b7a842bd5ddf42c7ae593a0b9117a (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-08-03T19:57:19Z (GMT) No. of bitstreams: 1 GuilhermeKeitiAoyama_DISSERT.pdf: 15234104 bytes, checksum: 840b7a842bd5ddf42c7ae593a0b9117a (MD5) / Made available in DSpace on 2017-08-03T19:57:19Z (GMT). No. of bitstreams: 1 GuilhermeKeitiAoyama_DISSERT.pdf: 15234104 bytes, checksum: 840b7a842bd5ddf42c7ae593a0b9117a (MD5) Previous issue date: 2017-03-27 / Canais compostos s?o caracterizados por possu?rem canais principais, regi?es mais largas onde o fluido escoa axialmente com maior facilidade, e canais secund?rios (fendas) que s?o regi?es mais estreitas onde o fluido ? desacelerado devido aos efeitos viscosos. Para determinar os coeficientes de transfer?ncia de calor e de atrito nos canais compostos ? necess?rio entender o comportamento dos escoamentos turbulentos que ocorrem neles, por?m isto continua sendo um desafio para a engenharia. Estes canais apresentam, al?m do fluxo axial paralelo ao canal, flutua??es na velocidade transversal que est?o associadas a estruturas de grande escala denominadas de estruturas coerentes. Assim, neste trabalho buscou-se analisar os efeitos do aparecimento dessas estruturas e as suas consequ?ncias para o escoamento, tanto na parte din?mica como na t?rmica. Para isto foi utilizado uma geometria empregada em trabalhos experimentais, que ? composta por um canal retangular com um tubo interno, de di?metro D, que est? a uma dist?ncia W/D da parede inferior do canal. O fluido escoa axialmente apenas na parte externa do tubo. No total foram analisados cinco casos, modificando apenas a rela??o W/D (espa?amento da fenda). Para examinar as caracter?sticas do escoamento turbulento no interior deste canal, empregou-se o pacote ANSYS CFX 13 com o modelo de turbul?ncia SAS-SST. Os resultados mostraram que quanto maior a rela??o W/D, mais elevados foram os valores do Fator de Desempenho T?rmico. Este fator ? uma rela??o entre o n?mero de Nusselt e o fator de atrito e, quanto maior seu valor, melhor ? o desempenho t?rmico do canal. Em rela??o as estruturas coerentes, nos canais em que surgiram, elas t?m uma grande influ?ncia sobre os escoamentos, j? que essas estruturas acabam elevando os valores locais dos coeficientes de transfer?ncia de calor e de atrito superficial, o que torna esse fen?meno indispens?vel nos projetos e an?lises de seguran?a de equipamentos que possuem fendas. / Compound channels are characterized by having main channels, wider regions where the fluid flows axially more easily, and narrower regions (gaps) where the fluid is decelerated due to the viscous effects. In order to determine the heat transfer coefficients in these channels it is necessary to understand the behavior of the turbulent flows in them, but this remains a challenge for engineering. These channels have, in addition to axial flow parallel to the channel, a cross flow velocity in the gap region that are associated with large scale structures called coherent structures. Thus, the goal of this work is to compare the effects on the appearance of coherent structures of large scale and its consequences for the flow in dynamic and thermal characteristics. To accomplish this, the same geometry used in the experimental works was applied, which is composed of a rectangular channel with an internal tube of diameter D and it is located at a distance W/D from the lower wall of the channel. The fluid flows axially only on the outside of the tube. In total, five different cases were analyzed, modifying only the W/D ratio (gap distance). To examine the characteristics of the turbulent flow inside this channel, ANSYS CFX13 with SASSST turbulence model was applied. The results showed that the W/D ratio increase also caused an increase in the values of the Thermal Performance Factor. This factor is a relationship between the Nusselt number and the friction factor, and the higher its value, better is the thermal performance of the channel. In relation to the coherent structures, in the channels in which they arise, they have a great influence on the flows, since these structures end up raising the local values of heat transfer and friction coefficients, making this phenomenon indispensable in projects and safety analyzes of equipment with gap.

Os sistemas de proteção contra gelo são comumente utilizados na aviação. O piccolo tubo, que é um dispositivo com vários furos por onde passam os jatos de ar quente que aquecem as superfícies a serem protegidas, é o mais utilizado. Dependendo do processo de manufatura, os furos podem variar desde um formato cilíndrico até um formato cônico. O objetivo deste trabalho foi analisar a influência da conicidade destes furos na transferência de calor com o lábio da entrada de ar. Os resultados mostraram que o impacto é mínimo. Para tal análise, foram utilizados tanto programas de geração de malha (ICEM), quanto de mecânica de fluidos computacional - (FLUENT). O modelo térmico foi validado com a vasta literatura disponível, que inclui tanto dados experimentais, quanto simulações que também utilizaram mecânica dos fluidos computacional.

A literatura corrente possui informações limitadas sobre o projeto da área de troca térmica de tanques com jaqueta, serpentina helicoidal, serpentina espiral e chicana tubular vertical, em operação com fluidos não-Newtonianos. A presente tese teve por objetivo principal analisar a transferência de calor, potência consumida e ampliação de escala em tanques com impulsores mecânicos na agitação de fluidos não-Newtonianos com duas superfícies de transmissão de calor, chicana tubular vertical e serpentina em espiral. O trabalho também visou fornecer métodos de ampliação de escala de tanques com agitação para fluidos não-Newtonianos que sigam o modelo reológico da lei das potências. A unidade experimental contemplou dois tanques de acrílico, com volume de 10 litros e 50 litros, respectivamente, chicanas tubulares verticais e serpentina em espiral. Os impulsores mecânicos utilizados foram o axial com 4 pás inclinadas a 45° e o radial turbina com 6 pás planas. Como fluidos utilizaram-se soluções aquosas de carboximetilcelulose (0,5%, 1,0% e 1,5%), solução aquosa de carbopol 940 (1,5%), solução aquosa de sacarose (50%) e água. Todos os experimentos foram conduzidos em batelada. Com os dados obtidos, empregou-se o uso de regressões para a obtenção da Equação de Nusselt, as quais forneceram valores de coeficiente de determinação ajustados entre 0,83 e 0,89 com Reynolds no intervalo de 20 a 405000, Prandtl na faixa de 4 a 6400 e índice reológico do modelo da lei das potências entre 0,45 e 1,00. Observou-se que no aquecimento realizado com a chicana tubular vertical, o impulsor radial forneceu coeficientes de convecção 20% acima quando comparado com o impulsor axial, entretanto o consumo de potência foi cerca de 66% maior em relação ao impulsor axial. No caso da serpentina espiral, o impulsor axial promoveu coeficientes de convecção por volta de 15% superiores em relação ao impulsor radial com um consumo de potência 65% menor. Desse modo, em processos em que não é necessária uma elevada turbulência, recomenda-se o uso do impulsor axial com a serpentina espiral, porém, se o processo demandar uma turbulência significativa, deve-se usar o impulsor radial com a chicana tubular vertical. Em uma última análise, os modelos não-lineares obtidos para ampliação de escala forneceram erros entre 11% e 20% na predição da rotação no tanque industrial, os quais são válidos para Reynolds modificados de Metzner e Otto (1957) na faixa de 20 a 4000 e para fluidos não-Newtonianos pseudoplásticos com índices reológicos entre 0,45 e 1,00. / Current literature has limited information on the design of the thermal exchange area of tanks with jacket, helical coil, spiral coil and vertical tuber baffle, in operation with non-Newtonian fluids. The main purpose of this thesis was to analyze heat transfer, power consumption and scale-up in tanks with mechanical impellers in the agitation of non-Newtonian fluids with two heat transfer surfaces, vertical tube baffle and spiral coil. The work also aimed to provide methods of scale-up tank scale with agitation for non-Newtonian fluids that follow the rheology model of the law of powers. The experimental unit included two acrylic tanks, with a volume of 10 liters and 50 liters, respectively, vertical tube baffles and spiral coil. The mechanical impellers used were the 45° pitched blade turbine (PBT) and the Rushton turbine (RT). Aqueous solutions of carboxymethylcellulose (0.5%, 1.0% and 1.5%), aqueous solution of carbopol 940 (1.5%), aqueous solution of sucrose (50%) and water were used as fluids. All the experiments were conducted in batch. With the obtained data, we used the regressions to obtain the Nusselt Equation, which provided coefficient of determination values adjusted between 0.83 and 0.89 with Reynolds in the range of 20 to 405000, Prandtl in the range of 4 to 6400 and rheological index of the power law model between 0.45 and 1.00. It was observed that in the heating performed with the vertical tube baffle, the RT provided convection coefficients 20% higher when compared to the axial impeller, however the power consumption was about 66% higher in relation to the PBT. In the case of the spiral coil, the PBT promoted convection coefficients around 15% higher than the RT with 65% lower power consumption. Thus, in processes where high turbulence is not required, it is recommended to use the PBT with the spiral coil, but if the process requires significant turbulence, the RT must be used with the vertical tubular chassis. In a final analysis, the nonlinear models obtained for scaling provided errors between 11% and 20% in the prediction of rotation in the industrial tank, which are valid for Metzner and Otto (1957) modified Reynolds in the range of 20 to 4000 and for non-Newtonian pseudoplastic fluids with rheological indexes between 0.45 and 1.00.

The Reciprocating Mechanism Driven Heat Loop (RMDHL) is a novel heat transfer device that utilizes reciprocating flow, either single-phase or two-phase flow, to enhance the thermal management in high tech inventions. The device attains a high heat transfer rate through a reciprocating flow of the working fluid inside the heat transfer device. Although the concept of the device has been tested and validated experimentally, analytical or numerical studies have not been undertaken to understand its working mechanism and provide guidance for the device design. The objectives of this study are to understand the underlying physical mechanisms of heat transfer in internal reciprocating flow, formulate corresponding heat transfer correlations, conduct an experimental study for the heat transfer coefficient, and numerically model the single-phase and two-phase operations of the RMDHL to predict its performance under different working conditions. The two-phase flow boiling model was developed from the Rensselaer Polytechnic Institute (RPI) model, and a virtual loop written in C programming language was used to eliminate the need for fluid structure interaction (FSI) modelling. The accuracy of several turbulence formulations, including the Standard, RNG, and Realizable k-ɛ Models, Standard and SST k-ω Models, Transition k - - ω Model, and Transition SST Model, have been tested in conjunction with a CFD solver to select the most suitable turbulence modelling techniques. The numerical results obtained from the single-phase and two-phase models are compared with relevant experimental data with good agreement. Three-dimensional numerical results indicate that the RMDHL can meaningfully reduce the peak temperature of an electronic device and result in significantly more uniform temperature across the device. In addition to the numerical study, experimental studies in conjunction with analytical studies are undertaken. Experimental data and related heat transfer coefficient as well as practically useful semi-empirical correlations have been produced, all of which provide archival information for the design of heat transfer devices involving a reciprocating flow. In particular, this research will lead to the development of more powerful RMDHLs, achieve a heat flux goal of 600 W/cm2, and significantly advance the thermal management at various levels. Considering the other advantages of coolant leakage free and the absence of cavitation problems, the RMDHL could also be employed for aerospace and battery cooling applications.

Solid-fluid thermal interactions during unsteady flow in porous media play an important role in the regenerators of pulse tube cryocoolers. Pore-level thermal processes in porous media under unsteady flow conditions are poorly understood. The objective of this investigation is to study the pore-level thermal phenomena during pulsating flow through a generic, two-dimensional porous medium by numerical analysis. Furthermore, an examination of the effects of flow pulsations on the thermal dispersion and heat transfer coefficient that are encountered in the standard, volume-average energy equations for porous media are carried out. The investigated porous media are periodic arrays of square cylinders. Detailed numerical data for the porosity range of 0.64 to 0.84, with flow Reynold's numbers from 0-1000 are obtained. Based on these numerical data, the instantaneous as well as cycle-average thermal dispersion and heat transfer coefficients, to be used in the standard unsteady volume-average energy conservation equations for flow in porous media, are derived. Also, the adequacy of current applied cycle-average correlations for heat transfer coefficients and the inclusion of the thermal dispersion in the definition of an effective fluid thermal conductivity are investigated.