SUMMARY

Cryogenic/sub-ambient operation of microprocessors offers a viable means of extracting greater computational performance out of current generation microprocessors. To achieve the promised performance, compact, low cost, sub-ambient cooling solutions need be made available, which can remove high heat fluxes (~100 W/cm2) at temperatures below ambient (80 K – 290 K). Adsorption based thermal compressors offer notable advantages over mechanically driven compressors for use in Joule-Thompson expansion based refrigeration systems owing to their ability to be powered using waste heat (instead of electricity), absence of noise and vibration and no use of lubricants in the refrigerant circuit. Main technical challenges in practical implementation of these systems include: low uptake of nitrogen by activated carbon at above ambient temperatures and large compressor size and low coefficient of performance (COP). Proposed research is aimed at addressing these technical challenges and understanding the minimum size and maximum efficiency limits of adsorption refrigeration systems. Multi-stage compression of nitrogen is adopted to reach the high pressure required by the refrigeration cycle in a step-wise manner. Flat bed compressor topology is implemented to increase the surface area to volume ratio of the compressor to enable faster thermal cycling (leading to reduction in compressor size). Recovery and reuse of heat stored in the inert thermal mass of compressor beds is proposed using a regenerative fluid loop linking several flat beds (leading to an improvement in COP and reduction in heat rejection requirements from the compressor). The unique contributions of the work include: first demonstration of adsorption compression of nitrogen under terrestrial conditions, compact compressor concept and an improvement in the COP of adsorption refrigeration system for cryocooler applications (~100 K evaporator load temperature) using miniature compressor beds.