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The ionic liquid butylmethylimidazolium hexafluorophosphate (bmim)(PF6) and five different hydrofluorocarbon refrigerants were investigated as the working fluid pairs for a waste-heat driven absorption heat pump system for possible applications in electronics thermal management. A significant amount of the energy consumed in large electronic systems is used for cooling, resulting in low grade waste heat, which can be used to drive an absorption refrigeration system if a suitable working fluids can be identified. The Redlich–Kwong-type equation of state was used to model the thermodynamic conditions and the binary mixture properties at the corresponding states. The effects of desorber and absorber temperatures, waste-heat quality, and system design on the heat pump performance were investigated. Supporting experiments using R134a/(bmim)(PF6) as the working fluid pair were performed. Desorber and absorber outlet temperatures were varied by adjusting the desorber supply power and the coolant temperature at the evaporator inlet, respectively. For an evaporator temperature of 41 °C, which is relevant to electronics cooling applications, the maximum cooling-to-total-energy input was 0.35 with the evaporator cooling capability of 36 W and the desorber outlet temperature in the range of 50 to 110 °C.

It is now widely recognized that the three-dimensional (3D) system integration is a key enabling technology to achieve the performance needs of future microprocessor integrated circuits (ICs). To provide modular thermal management in 3D-stacked ICs, the interlayer microfluidic cooling scheme is adopted and analyzed in this study focusing on a single cooling layer performance. The effects of cooling mode (single-phase versus phase-change) and stack/layer geometry on thermal management performance are quantitatively analyzed, and implications on the through-silicon-via scaling and electrical interconnect congestion are discussed. Also, the thermal and hydraulic performance of several two-phase refrigerants is discussed in comparison with single-phase cooling. The results show that the large internal pressure and the pumping pressure drop are significant limiting factors, along with significant mass flow rate maldistribution due to the presence of hot-spots. Nevertheless, two-phase cooling using R123 and R245ca refrigerants yields superior performance to single-phase cooling for the hot-spot fluxes approaching ∼300 W/cm2. In general, a hybrid cooling scheme with a dedicated approach to the hot-spot thermal management should greatly improve the two-phase cooling system performance and reliability by enabling a cooling-load-matched thermal design and by suppressing the mass flow rate maldistribution within the cooling layer.

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