An experimental investigation of vapor compression refrigeration cooling and energy performance for CPU thermal management

This case study experimentally investigates a R134a charged Vapor Compression Refrigeration (VCR) assisted liquid cooling of high-powered CPUs. In this hybrid system, water-based liquid cooling of the CPU is achieved in a pumped loop with a commercial cold plate affixed to the simulated CPU. The heat is then transferred to the evaporator heat exchanger of a miniature VCR system that rejects the energy to ambient air. Tests are performed at room temperature over a range of operating conditions, including CPU heat loads (12 W/cm2 - 75 W/cm2), liquid volumetric flow rates (0.5 Litre/min - 8 Litre/min), fan air speeds (2.1 m/s – 4.2 m/s), and compressor speeds (2540 rpm–6500 rpm). Both cooling performance and additional energy consumption implications are considered. Overall, it is shown that the miniature hybrid VCR system can cool the primary liquid to below ambient temperature, even at the highest tested heat load. As a result, cooling levels that far exceed both a conventional Fan-Fin Air Cooled heat exchanger and a Hybrid Liquid-Air Cooled system are achieved. Finally, optimal combinations of liquid flow rate and compressor speed are identified for minimum energy consumption of the cooling system to maintain a setpoint CPU die temperature. It is shown that management and control of pump, compressor and fan speeds can result in significant improvement in the overall system Coefficient of Performance (COP).