As the cost of variable renewable energy resources like wind and solar decline rapidly the major barrier to decarbonization of the electrical grid becomes that of energy storage. Current storage technologies are much too expensive to justify widespread adoption and it is unclear what type of technology is even capable of fulfilling this role. Flow batteries are an often proposed technological solution to this problem but they are plagued by high cost and reliability issues due to the expensive and complex balance of plant included in the system design. In this work a new design for a gravity driven flow battery is explored which is capable of drastically lowering the cost of flow batteries by removing the pumps and membranes and replacing their function with density stratification and flow driven by the density change of the electrode reactions. A design for a zinc-bromine battery which makes use of this free convection during operation is explored. The system is studied through construction of prototype cells, exploration of key design variables, and a techno-economic analysis of the technology is performed showing cost viability. The free convection phenomenon which underlies the battery operation is expanded upon by connecting non-dimensional correlations in heat transfer with electrochemical transport equations in order to create predictive understanding of flow behavior based on system composition. This correlative understanding is used to construct a model of a zinc-bromine gravity driven flow battery. This model shows results which align with experimental data and gives insight into the complex transport dynamics of the system.

No description available.

The purpose of this study is to build, test, validate, and implement two heat transfer models, and couple them to an existing fluid flow solver, which can then be used for simulating multi-disciplinary problems. The first model is for heat conduction computations, the other one is a quasi-one-dimensional cooling channel model for water-cooled jacket structural analysis. The first model employs the integral, conservative form of the thermal energy equation, which is discretized by means of a finite-volume numerical scheme. A special algorithm is developed at the interface between the solid and fluid regions, in order to keep the heat flux consistent. The properties of the solid region materials can be temperature dependent, and different materials can be used in different parts of the domains, thanks to a multi-block gridding strategy. The cooling channel flow model is developed by using uasi-one-dimensional conservation laws of mass, momentum, and energy, taking into account the effects of heat transfer and friction. It is possible to have phase changes in the channel, and a mixture model is applied, which allows two phases to be present, as long as they move at the same bulk velocity and vapor quality does not exceed relatively small values. The coupling process of both models (with the fluid solver and with each other) is handled within the Loci system, and is detailed in this study. A hot-air nozzle wall problem is simulated, and the computed results are validated with available experimental data. Finally, a more complex case involving the water-cooled nozzle of a Rocket Based Combined Cycle(RBCC) gaseous oxygen/gaseous hydrogen thruster is simulated, which involves all three models, fully coupled. The calculated temperatures in the nozzle wall and at the cooling channel outlet compare favorably with experimental data.

The electric field-induced reduction of heat transfer from a rod-stabilized diffusion flame and a step-stabilized premixed flame was investigated. The fuel examined was propane. Inlet velocity for the diffusion mode was a nominal value of 3.4 m/s with nominal air/fuel ratios of 420, 320, and 270. Inlet velocities ranged from 4.5 to 9.9 m/s for the premixed mode with equivalence ratios of 0.65 to 1.03. Maximum applied voltages for the diffusion and premixed modes were 8.0 and 6.6 kVDC, respectively. The field was applied in a direction perpendicular to the flow. Heat transfer amelioration was quantified using records of temperature versus downstream distance from the stabilizer acquired for the external surface of the heatloaded electrode which was exposed to the ambient environment. In addition, shadowgraphs and photographs were used to observe any alteration of flame position or of the bulk flowfield. These observations were used to investigate mechanisms potentially responsible for heat transfer reduction. The rod-stabilized diffusion mode displayed some field-induced reduction in heat transfer. Both bulk flow alteration and reduction in radiation (associated with soot) were concluded to be responsible. Flame impingement on the heat-loaded electrode was reduced by a field-induced increase in flow along the surface. Flame luminosity was reduced by the electric field (presumably due to a field-induced modification of soot production and/or destruction). This caused a reduction in radiative heat transfer. No heat-transfer amelioration was noted for the premixed step-stabilized mode. This was attributed primarily to a geometry not accommodating to field-induced heat transfer reduction. Higher velocities and a lower presence of soot than the diffusion mode and problems associated with flame impingement on both electrodes (reduces maximum voltages and distorts field), also contributed to the negative result. Limited displacement of the luminous portion of the reaction zone was noted. / Master of Science

Shang Xiandong. / "September 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (p. 141-146). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Heat removal technologies are among the most critical needs for three-dimensional (3D) stacking of high-performance microprocessors. This research reports a 3D integration platform that can support the heat removal requirements for 3D integrated circuits that contain high-performance microprocessors in the 3D stack. This work shows the use of wafer-level batch fabrication to develop advanced electrical and fluidic three-dimensional interconnect networks in a 3D stack. Fabrication results are shown for the integration of microchannels and electrical through-silicon vias (TSVs). A compact physical model is developed to determine the design trade-offs for microchannel heat sink and electrical TSV integration. An experimental thermal measurement test-bed for evaluating a 3D inter-layer liquid cooling platform is developed. Experimental thermal testing results for an air-cooled chip and a liquid-cooled chip are compared. Microchannel heat sink cooling shows a significant junction temperature and heat sink thermal resistance reduction compared to air-cooling. The on-chip integrated microchannel heat sink, which has a thermal resistance of 0.229 °C/W, enables cooling of >100W/cm² of each high-power density chip, while maintaining an average junction temperature of less than 50°C. Cooling liquid is circulated through the 3D stack (two layers) at flow rates of up to 100 ml/min. The ability to assemble chips with integrated electrical and fluidic I/Os and seal fluidic interconnections at each strata interface is demonstrated using three assembly and fluidic sealing techniques. Assembly results show the stacking of up to four chips that contain integrated electrical and fluidic I/O interconnects, with an electrical I/O density of ~1600/cm².

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1982 / Includes bibliographical references. / by Paul Douglas Symolon. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Mechanical Engineering

Comme le groupe de symétries de Lie des équations aux dérivées partielles représentent les propriétés physiques intrinsèques contenues dans les équations, il offre un outil efficace pour étudier et modéliser les phénomènes physiques. Ainsi, dans cette thèse, on se propose d’appliquer la théorie du groupe de symétries de Lie à la modélisation des écoulements anisothermes.On calcule alors des lois de paroi, et, plus généralement des lois d’échelle, pour la vitesse et la température dans le cas d’un écoulement parallèle. En fait, ces lois d’échelle se révèlent être simplement des solutions auto-similaires des équations de Navier-Stokes moyennées par rapport aux symétries des équations.Ensuite, par l’approche de la théorie des groupes de Lie, on construit une classe de modèles de sous-maille qui sont invariants par les symétries des équations de Navier-Stokes anisothermes.Ces modèles ont l’avantage de respecter les propriétés physiques des équations qui sont contenues dans les symétries. De plus, par cette approche, le modèle de flux de chaleur apparaît naturellement,sans qu’on ait besoin de faire appel à la notion de nombre de Prandtl de sous-maille,ce qui augmente la portée de ces modèles par rapport à la plupart des modèles existants. Par ailleurs, le comportement proche de la paroi de certains des modèles proposés est étudié. Enfin,des tests numériques en convection naturelle et en convection mixtes sont effectués. / Since the Lie group of a given partial differential equation, represent the intrinsic physical propertiesof the equation, it gives a strong tool for modeling its physical phenomenas. The mainpurpose of this thesis, is to apply the Lie group theory, in modeling non-isothermal flows. Therefore,we calculate wall laws and more generally scaling laws for the velocity and the temperatureof a parallel flow. In fact, these scaling laws are simply self-similar solutions of the Navier-Stokesequations averaged with respect to their symmetry.The approach of the Lie group theory, leads to a class of sub-grade models which are invariantvia the symmetries of the non-isothermal Navier-Stokes equations. These models respectthe physical properties contained in these symmetries. Moreover, via this approach the heat flowmodel appears naturally in this class, without introducing the notion of the Prandlt number,which is not the case for any other existing model. From the other side, the behavior near thewall of particular models in this class, is studied. Finally, numerical tests are done in both casesof the natural convection and the mixed one.

A tomografia por sensoriamento térmico é muito utilizada em diferentes aplicações industriais, tais como a determinação de propriedades térmicas de novos materiais, o controle da produção de calor e a temperatura no processo de manufatura. Entretanto, o emprego de técnicas tomográficas em processos industriais envolvendo transferência de calor ainda carece de métodos robustos e computacionalmente eficientes. Nesse contexto, o principal objetivo deste trabalho é contribuir para o desenvolvimento de uma técnica não intrusiva de medição do coeficiente de convecção a partir de medidas externas de temperatura e fluxo de calor baseada na solução do problema térmico inverso. Para tanto é necessário resolver um problema de condução acoplado a um problema de convecção de calor. Este acoplamento ocorre através do coeficiente de convecção no interior do domínio do problema, cuja determinação pode ser feita através da aplicação de um fluxo de calor e medição das temperaturas resultantes na superfície externa. A tomografia térmica é tratada como um problema de minimização global, cuja função objetivo é um funcional de erro que quantifica a diferença entre as medidas externas não intrusivas (temperatura real) e as medidas calculadas no modelo numérico (temperatura aproximada). A natureza mal condicionada do problema assim formulado se manifesta na superfície de minimização por produzir topologias problemáticas tais como múltiplos mínimos locais, pontos de sela, vales ao redor da solução, platôs, etc. Desse modo, uma técnica bastante sofisticada, capaz de convergir para a solução correta mesmo na presença dessas patologias é necessária para obtenção da solução. Neste trabalho optou-se pelo método de Newton para a minimização deste funcional em que a inversa da matriz Hessiana é substituída por uma pseudo-inversa construída a partir da técnica de Decomposição em Valores Singulares Truncados. Os resultados mostram que a técnica proposta foi capaz de superar os problemas de convergência associados à natureza intrínseca mal condicionada do problema inverso e o coeficiente de convecção foi reconstruído com precisão razoável. / Tomography by thermal sensing is widely used in different industrial applications, such as the determination of thermal properties of new materials, the control of heat production and the temperature in manufacturing processes. However, the application of tomographic techniques in industrial processes involving heat transfer still lacks robust and computationally efficient methods. In this context, the main objective of this thesis is to contribute to the development of a non-intrusive technique for measuring of the convection coefficient from external temperature and heat flow measurements based on the solution of the inverse thermal problem. This requires solving a conduction problem coupled with a heat convection problem, which is coupled through an internal convection coefficient, determined by applying a heat flux and measuring the resulting temperatures on the external boundary. The thermal tomography is treated as a global minimization problem in which the fitness function is an error functional that quantifies the difference between non-intrusive external measurements (actual temperature) and measurements calculated in a numerical model (approximate temperature). The ill-conditioned nature of the problem manifests itself in the minimization problem for producing problematic topologies, such as multiple local minima, saddle points, valleys around the solution, plateaus, etc. Thus, a very sophisticated technique that can converge to the correct solution even in the presence of these pathologies is necessary to obtain the solution. In this thesis the Newton\'s method was used for the minimization of this functional in which the inverse Hessian matrix was replaced by a pseudo-inverse built from the truncated singular value decomposition technique. Results show that the proposed technique was capable of overcoming the convergence problems associated with the intrinsic ill-conditioned nature of the inverse problem and the convection coefficient was reconstructed within reasonable precision.

A stacked microchannel heat sink was developed to provide efficient cooling for microelectronics devices at a relatively low pressure drop while maintaining chip temperature uniformity. Microfabrication techniques were employed to fabricate the stacked microchannel structure, and experiments were conducted to study its thermal performance. A total thermal resistance of less than 0.1 K/W was demonstrated for both counter flow and parallel flow configurations. The effects of flow direction and interlayer flow rate ratio were investigated. It was found that for the low flow rate range the parallel flow arrangement results in a better overall thermal performance than the counter flow arrangement; whereas, for the large flow rate range, the total thermal resistances for both the counter flow and parallel flow configurations are indistinguishable. On the other hand, the counter flow arrangement provides better temperature uniformity for the entire flow rate range tested. The effects of localized heating on the overall thermal performance were examined by selectively applying electrical power to the heaters. Numerical simulations were conducted to study the conjugate heat transfer inside the stacked microchannels. Negative heat flux conditions were found near the outlets of the microchannels for the counter flow arrangement. This is particularly evident for small flow rates. The numerical results clearly explain why the total thermal resistance for counter flow arrangement is larger than that for the parallel flow at low flow rates. In addition, laminar flow inside the microchannels were characterized using Micro-PIV techniques. Microchannels of different width were fabricated in silicon, the smallest channel measuring 34 mm in width. Measurements were conducted at various channel depths. Measured velocity profiles at these depths were found to be in reasonable agreement with laminar flow theory. Micro-PIV measurement found that the maximum velocity is shifted significantly towards the top of the microchannels due to the sidewall slope, a common issue faced with DRIE etching. Numerical simulations were conducted to investigate the effects of the sidewall slope on the flow and heat transfer. The results show that the effects of large sidewall slope on heat transfer are significant; whereas, the effects on pressure drop are not as pronounced.