Multiscale modeling of electronics cooling and energy-conversion devices

It is noted that high density electronic devices have caused a sharp increase in heat-removal requirements and microchannel heat sinks applying forced convective boiling at the package level are developed to be very promising, as the attainable heat transfer rate is very favorable. In this work, numerical simulations are conducted to investigate flow boiling in microchannels. Since the boiling mechanisms are found to be strongly dependent on wall surface conditions, the validated two-phase flow boiling model is implemented to characterize nucleation sites on wall surfaces, addressing an optimal topology design which nucleates first under a given set of conditions from rather low superheating. Two cavity characteristic models are investigated to enable a compatible view. The stochastic model with randomly sized and located cavities has been proved to hinder the cooling capability by decreasing the critical heat flux, as compared to the deterministic model that comprises regular cavities. Additionally, the heat flux condition of the cooling target is studied to seek high-performing cooling schemes, considering seven different heating loads.;An attractive option for constructing Thermoelectric Generators (TEGs) is to incorporate a water-fed heat exchanger with commercially available thermoelectric modules. Two thermoelectric models are applied to predict the energy conversion performance of the TEGs. The thermal-based model employs a derivation of the Carnot efficiency, while the coupled-field model presents a more rigorous interfacial energy balance by capturing Joule heating, Seebeck, Peltier and Thomson effects. The model yielding better predictions of the conversion capability is then used to perform a computational examination of the TEGs embedded in 30 different configurations, which allows the identification and quantification of key design parameters including flow types, hot stream inlet temperatures, pressure drops, cross-sectional area, channel length and number of channels. Moreover, constrained by low thermodynamic efficiencies, TEGs require a comparatively large amount of heat to produce a given quantity of electricity. Further improvements in thermoelectric designs are thus needed. The feasibility of the two promising solutions to enhance power generation has been gauged. First, the patterned topography on wall surfaces is implemented and the improved performance has been observed by introducing stirred flows into the heat exchangers and equalizing the temperature across the channels. Second, the prospect of increasing the thermal transport capability of water by loading CuO nanoparticles in the TEGs with multi-scale heat exchangers is explored. The significant insight is gained to fabricate ideal TEGs having optimum power performance.