Yes / The ever-increasing demand for high performance electronic and computer systems has unequivocally called for increased microprocessor performance. However, increasing microprocessor performance requires increasing the power and on-chip power density of the microprocessor, both of which are associated with increased heat dissipation. In recent times, thermal management of electronic systems has gained intense research attention due to increased miniaturization trend in the electronics industry. In the paper, we present a numerical study on the performance of a convective-radiative porous heat sink with functionally graded material for improved cooling of various consumer electronics. For the theoretical investigation, the thermal property of the functionally graded material is assumed as a linear and power-law function. We solved the developed thermal models using the Chebyshev spectral collocation method. The effects of inhomogeneity index of FGM, convective and radiative parameters on the thermal behaviour of the porous heat sink are investigated. The present study shows that increase in the inhomogeneity index of FGM, convective and radiative parameter improves the thermal efficiency of the porous fin heat sink. Moreover, for all values of Nc and Rd, the temperature gradient along the fin of FGM is negligible compared to HM fin in both linear and power-law functions. For comparison, the thermal predictions made in the present study using Chebyshev spectral collocation method agrees excellently with the established results of Runge-Kutta with shooting and homotopy analytical method. / Supported in part from PhD sponsorship of the first author by the Tertiary Education Trust Fund of the Federal Government of Nigeria.

<p>  </p> <p>As consumer adoption and total energy consumption of electric vehicles continues to rapidly increase, it is important to develop comprehensive system modeling frameworks that consider the complex interactions of their mechanical, electrical, and thermal subsystems to guide component technology development. This thesis studies the influence of cabin glass properties on the performance of an electric vehicle thermal system and overall cabin design considerations. The work first builds a generic long-range electric vehicle dynamic thermal system model while considering the system architecture, component sizing, control scheme, and glass properties. This comprehensive system model is used to assess the influence of cabin glass radiative properties on vehicle performance. The system model incorporates simplified models for all salient components in the electric traction drive, cabin HVAC, and battery subsystems, and uses a higher fidelity cabin thermal model that is able to capture the individual properties of the cabin glass used in the vehicle. To study the cabin model in isolation, a heat-up scenario is used to find that a cabin air temperature reduction of 8 °C through the use of different glass properties alone. Additionally, the cabin model is run repeatedly to produce a large data set that is trained using a machine learning regression model. This surrogate regression model that is used to reduce the computational time allowing for fast studies of glass properties and build an application engineering tool. The overall system performance is then evaluated under a dynamic NEDC drive cycle which is repeated until battery depletion to determine a vehicle range. A system validation is done on the HVAC subsystem by using steady-state thermodynamic analysis and comparing to the dynamic system model. This results in good agreement between four different subsystem modeling approaches. The system model is used to study five different glazing design cases, each corresponding to different transmission and reflection properties of the glass, by predicting their impact on the vehicle range. The cases span all theoretically possible glass properties while also enabling inspection of practical glass technologies that are available or under development to be adopted in modern electric vehicles. The influence of glass on vehicle range is then further compared at various locations across the United States to understand and illustrate the effects of ambient conditions and solar load. The system model predicts a vehicle range of 188.5 miles under a high solar loading scenario typical for Phoenix, AZ using traditional glass properties, which increases to a range of 221.6 miles using high-performance glass properties, representing a significant potential gain of 33.1 miles using technologies available on the market today. Under this same loading scenario, the glass properties at their extreme physical limits could theoretically affect the vehicle range by up to 92.5 miles. The influence of the glass properties is location-specific, and the model predicts that using the same glass at different locations can affect the range of vehicle by up to 100.8 miles for traditional glass properties and 73.4 miles for high-performance glass properties. </p>

Many critical applications today, in electronics, optics and aerospace fields, among others, demand advanced thermal management solutions for the acquisition of high heat loads they generate in order to operate reliably and efficiently. Current competing technologies for this challenging task include several single and two phase cooling options. When these cooling schemes are compared based on the high heat flux removal (100-1000 W/cm2) and isothermal operation (within several oC across the cooled device) aspects, as well as system mass, volume and power consumption, spray cooling appears to be the best choice. The current study focused on high heat flux spray cooling with ammonia on enhanced surfaces. Compared to some other commonly used coolants, ammonia possesses important advantages such as low saturation temperature, and high heat absorbing capability. Moreover, enhanced surfaces offer potential to greatly improve heat transfer performance. The main objectives of the study were to investigate the effect of surface enhancement on spray cooling performance, and contribute to the current understanding of spray cooling heat transfer mechanisms. These objectives were pursued through a two stage experimental study. While the first stage investigated enhanced surfaces for the highest heat transfer coefficient at heat fluxes of up to 500 W/cm2, the second stage investigated the optimized enhanced surfaces for critical heat flux (CHF). Surface modification techniques were utilized to obtain micro scale indentations and protrusions, and macro (mm) scale pyramidal, triangular, rectangular, and square pin fins. A third group, multi-scale structured surfaces, combined macro and micro scale structures. Experimental results indicated that micro- and macrostructured surfaces can provide heat transfer coefficients of up to 534,000 and 426,000 W/m2oC at 500 W/cm2, respectively. Multi-scale structured surfaces offered even a better performance, with heat transfer coefficients of up to 772,000 W/m2oC at 500 W/cm2, corresponding to a 161% increase over the reference smooth surface. In CHF tests, the optimized multi-scale structured surface helped increase maximum heat flux limit by 18%, to 910 W/cm2 at nominal liquid flow rate. During the additional CHF testing at higher flow rates, most heaters experienced failures before reaching CHF at heat fluxes above 950 W/cm2. However, the effect of flow rate was still characterized, suggesting that enhanced surfaces can achieve CHF values of up to 1,100 W/cm2 with 67% spray cooling efficiency. The results also helped shed some light on the current understanding of the spray cooling heat transfer mechanisms. Data clearly proved that in addition to fairly well established mechanisms of forced convection in the single phase regime, and free surface evaporation and boiling through secondary nucleation in the two phase regime, enhanced surfaces can substantially improve boiling through surface nucleation, which can also be supported by the concept of three phase contact lines, the regions where solid, liquid and vapor phases meet. Furthermore, enhanced surfaces are capable of retaining more liquid compared to a smooth surface, and efficiently spread the liquid film via capillary force within the structures. This unique advantage delays the occurrence of dry patches at high heat fluxes, and leads to higher CHF.

No description available.

No description available.

Due to climate change, the energy system needs to change from traditional fossil fuels to be dominated by renewable energy sources. Not only the energy system, but the increasing number of vehicles and emissions from the transport sector are a problem for climate change and that need to be solved. Both can be solved with batteries, to handle climate change issue. The lithium-ion batteries (LIBs) have a high energy density which is important due to the less needed materials for the batteries. LIBs can be used in a battery energy storage system (BESS) to store the excess energy for later usage, and as an electric vehicle (EV) battery. For these high energy density batteries, there comes drawbacks such as safety issues by deviating temperatures which have effects on the capacity, lifetime, performance, and in worst case a thermal runaway can occur which may lead to fire and explosions. These temperature issues can be solved with a battery thermal management system (BTMS), which can manage temperature deviation. Cylindrical battery cells with the dimension 18650 with the cell chemistry Lithium-Nickel-Cobalt-Aluminum-Oxide (NCA) will be investigated with different discharge rates, how the heat generation increases, and how it can be handled by cooling systems. A battery pack will be built up in computational fluid dynamics (CFD) software called Ansys Fluent, to be simulated and see how the influence of cooling methods affect the energy density of the 18650 batteries. Air-cooling and liquid-cooling with fan as air-cooling and plate cooling as liquid cooling will be used in this work. 20 cells were investigated with air and liquid cooling, with two different cases with air-cooling. 100 cells with just liquid cooling during 0,5C was investigated on how the number of cells impacted on the energy density. It was seen that the different discharge rates (C-rate) had an impact on the amount of cooling, with air cooling being not as good as liquid cooling for cooling the battery pack and more flow was needed. The energy density in relation to weight showed that 20 cells with less spacing using air-cooling had the best energy density at 196,68 Wh/kg. It was also seen that the number of cells had an impact on the energy density in relation to volume. With the best energy density with 100 cells using liquid cooling at 279,96 Wh/L.

The deployment of electric vehicles has speeded up during the past ten years. As heavy-duty trucks are a significant source of GHG emissions, electrification is an encouraging way to lead to sustainability beyond doubt. However, some constraints regarding electric vehicles have emerged. Range extension is a primary challenge of the development of electric vehicles, where thermal conditioning systems can have a considerable impact. Some researches have been done on electric passenger vehicles. However, studies regarding the energy consumption for the thermal conditioning system of heavy-duty electric vehicles are scarcely provided.This study therefore focuses on estimating the energy consumption for the auxiliary heating/cooling and studying the influence of the ambient temperature, vehicle velocity, payload, and driving cycles. A designed integrated thermal conditioning system model was constructed in GT-SUITE, with three subsystems to provide thermal comfort for the truck cabin, meet the operative temperature for battery packs and condition the power electronics and the electric machine. Calibrations were done and yielded acceptable relative errors less than 10%, regarding the cabin and battery heaters.The study shows that the thermal conditioning system consumes the most energy during extremely cold weather, reaching up to 10 kW when the ambient temperature is lower than -20℃. Moreover, the energy consumption during heating/cooling will increase if the vehicle velocity increases. However, it remains stable during mild weather. Payload has different impacts on the energy consumption for heating and cooling. As higher payload results in higher waste heat from the electric machine and batteries, it alleviates the heating while burdens the cooling. Four different driving cycles were simulated, and the result reveals that despite the cycle with the lowest average speed has the highest energy consumption/km, however has the lowest average power.

With increased focus on miniaturization and high performance in electronics, thermal management is a very important area of research today. In multiple applications such as portable electronics, consumer electronics, military applications, automobile, power electronics, high performance computing, etc. innovative thermal management strategies are necessary. In this work, two novel approaches to dissipate redundant heat better- first by novel carbonaceous-nanoparticle additives to develop thermal interface materials with superior performance and the second by using advanced metal additive manufacturing techniques to design and analyze metal-lattice based heat sinks are presented. Thermal Interface Materials with multiple carbon-based nanoparticle fillers such as coal-derived Multi Layered Graphene (MLG), standard reduced Graphene Oxide (rGO), Multi-Walled Carbon Nano Tubes (MWCNTs), and Graphene Nano-Platelets (GNPs) in thermal paste were synthesized and seen to have superior heat dissipation properties. Also, graphene was synthesized from coal through an in-house, facile, scalable and cost-effective process. The enhancement in thermal conductance varies from ~70% in the coal-MLG to ~14% in MWCNTs-based TIMs. Noteworthy is ~3.5 times larger enhancement in thermal performance with the in-house coal-derived-MLG as compared to the commercially available g-MLG. At a 3% wt. fraction of coal-MLG, enhancement in thermal conductance was almost 120% higher compared to the base thermal grease. In the second part, metal lattice-based heat sinks are designed for additive manufacturing for use in passive cooling of high-flux thermal management. A parametric optimization based on the lattice geometry, thickness, and height subject to additive manufacturing constraints is conducted. Intricate metal lattices with low mass based on the Simple Cubic, Octet, and Voronoi structures were generated by implicit modelling in nTopology® and their thermal performance was analyzed through numerical analysis using commercial CFD packages. The Voronoi lattice performed best with a significant improvement in thermal performance (~18% reduction in junction temperature difference with respect to ambient) as compared to a standard baseline Longitudinal heat Sink (LHS), while reducing the mass of the heat sink by ~2.1 times. Such optimized metal lattice-based heat sinks can lead to significant downsizing, reduction in overall mass and cost in applications where thermal management is critical with a need for low mass. We believe that such novel scalable materials and processes suited for mass production could be critical in meeting the material, design and product development needs to tackle the thermal management challenges of the future. / Master of Science / With increase in demand of high power and performance in electronics, there is a concurrent increase in redundant heat that needs to be dissipated. With enhanced focus and push towards electric vehicles, defense, consumer electronics, datacenter and supercomputing applications, electronics cooling is a critical area of research today. There are two primary resistances to heat- as it is removed from electronics package to the surrounding atmosphere – due to the thin layer of a material called Thermal Interface Material (TIM) at the interface between the heat sink and the package, and the resistance offered by the heat sink itself. In this work, a two-pronged approach for better cooling in electronics is presented. Firstly, carbon-based nano-sized particles are used to synthesize novel TIMs that provide superior heat transport capabilities as compared to a standard baseline. In the second approach, complex metal-lattice based heat sinks are designed for manufacturing with advanced techniques such as metal 3D printing. Multiple carbon-based nano-particle additives such as Multi Layered Graphene synthesized from coal (MLG), standard commercially available reduced Graphene Oxide (rGO), Multi-Walled Carbon Nano Tubes (MWCNTs), and Graphene Nano-Platelets (GNPs) are dispersed in thermal paste and all of the resulting composites were found to remove heat better from electronics packages. The improvement in this ability varies from ~70% in the coal-MLG to ~14% in MWCNTs-based TIMs. Noteworthy is ~3.5 times larger enhancement in the heat transport ability with the use of in-house coal-derived-MLG as compared to the commercially available g-MLG. At an 3% wt. fraction of coal-MLG, there was a 1.2x increase in thermal performance as compared to the base thermal grease. Also, it is significant to mention that MLG was synthesized from coal through an in-house, facile scalable and cost-effective process. In the second part, metal lattice-based heat sinks designed for metal 3D printing for use in passive cooling of electronics was investigated. Multiple geometric parameters such as the lattice type, thickness, and height subject to additive manufacturing constraints were studied. Intricate metal lattices with low mass based on three structures- Simple Cubic, Octet, and Voronoi were generated by implicit modelling, and their thermal performance was predicted by computer based-simulations using commercial CFD packages. The Voronoi lattice performed best with a significant reduction (~18%) in junction temperature difference with the surrounding atmosphere- as compared to a standard baseline rectangular heat sink design, while simultaneously reducing the mass of the heat sink by ~2.1 times. Such optimized metal lattice-based heat sinks can lead to significant reduction in overall mass, size, and cost in weight sensitive applications. We believe that such novel scalable materials, designs, and processes suited for mass production could be critical in meeting the material, design and product development needs to tackle the thermal management challenges of the near future.

Lithium ion (Li-ion) batteries have been identified as a promising solution to meet the increasing demands for alternative energy in electric vehicles (EVs) and hybrid electric vehicle (HEVs). This work describes experimental and numerical study of thermal management of battery module consisting of cylindrical Li-ion cells, with an emphasis on the use of active control to achieve optimal cooling performance with minimal parasitic power consumption. The major contribution from this work is the first experimental demonstration (based on our review of archival journal and conference literature) and the corresponding analysis of active thermal control of battery modules. The results suggest that the active control strategy, when combined with reciprocating cooling flow, can reduce the parasitic energy consumption and cooling flow amount substantially. Compared with results using passive control with unidirectional cooling flow, the parasitic energy consumption was reduced by about 80%. This contribution was achieved in three steps, which was detailed in this dissertation in chapters 2, 3, and 4, respectively. In the first step, an experimental facility and a corresponding CFD model were developed to capture the thermal behavior of multiple battery cells. Based on the experimental and CFD results, a reduced-order model (ROM) was then developed for active monitoring and control purposes. In the second step, the ROM was parameterized and an observer-based control strategy was developed to control the core temperature of battery cells. Finally, based on the experimental facility and the ROM model, the active control of a battery module was demonstrated. Each of these steps represents an important facet of the thermal management problem, and it is expected that the results and specifics documented in this dissertation lay the groundwork to facilitate further study. / Ph. D.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / The project aimed at numerically modeling the flow and thermal processes occurring in a Volkswagen Citi Golf Chico underhood using computational fluid dynamics (CFD). The motivation for this investigation was to develop and demonstrate the capability of CFD as an automotive analysis tool. This would allow local automobile analysts and designers enhanced analyses of the thermal and flow conditions occurring in this com-pact environment, leading to improved local vehicles. A review of relevant literature indicated that the CFD community in South Africa is small with comparison to the international sector. The application of CFD to analyse automo-biles in South Africa is limited and practised by few. This experience requires develop-ment and refinement, such that South Africa may improve vehicles manufacture in the country. The review also indicated that CFD used in the international communities pro-vides good results, promoting simulation-based engineering. The experimental investigation involved parking a vehicle in the subsonic wind tunnel intake at the Mechanical Engineering Department in Stellenbosch. This tunnel is 3.7 m wide, 4 m long and 2.8 m tall, capable of wind speeds up to 90 m/s. Various equipment including thermocouples, a thermal imager and a hand held hot-wire anemometer pro-vided temperature and velocity measurements within the underhood. A pitot-static probe connected to a pressure transducer measured the wind tunnel velocities. The numerical investigation started with the creation of a three-dimensional geometry of the underhood from measurements taken of the vehicle. This geometry, created with Solid Edge version 14, formed the domain for automatically generating discretised grids using STAR-Design version 3.2. Subsequently, boundary conditions and numerical models were applied to the grids, which included simplified fan and radiator models. The analysis concluded with results obtained from the numerical CFD simulations, per-formed with STAR-CD version 3.24. The validity and accuracy of the numerical solutions was verified and quantified with the numerical results. The evaluation consisted of two test cases (wind tunnel speeds of 0 m/s and 5 m/s), each simulated at three different grid resolutions. Each simulation con-tinued until they fully converged to a single solution. The comparison of the three simu-lations from each case indicated that the results were grid independent. The final in-spection of the results in terms of y+ values and boundary conditions indicated that the models implemented were valid. The comparison of the numerical results for temperatures and fan inlet velocities with the experimentally measured data served as a measure to quantify the applicability of CFD for underhood investigations. The comparison between the two sets of results proved acceptable, with a maximum difference of 10%, indicating that CFD is capable of predicting temperatures and flow fields with reasonable accuracy. The numerical results indicated that while the vehicle travels at higher velocities, the underhood remains well ventilated. The underhood tends to trap the hot air from the radiator and other heat sources when the vehicle remains stationary, causing the air to heat further. This can be addressed by the installation of vents in the side panels near the top of the underhood environment. This should allow the hot air to escape, possibly resulting in a significant reduction of the underhood temperatures. Momentum and energy source terms modelled the effects from the fan and radiator. These models worked well for both cases, but improvement is necessary. Special at-tention should be given to the condition where the radiator fan obstructs the flow through the radiator. A further result of the project was the establishment of a flexible foundation for conduct-ing numerical simulations on automobiles. It allows for the inclusion of additional com-ponents and the implementation of more advanced models for representing effects from various engine components.