Dynamic thermal management of flashing spray cooling by the frequency conversion of compressor

Dynamic thermal management of electronic equipment is of practical importance to adapt to the quickly changed heat load at local spot. A closed-loop experimental system was constructed to study the heat transfer mechanism and cooling performance of flashing spray cooling by R410A on a smooth flat copper surface in steady-state and varying operating conditions, especially the effect of frequency conversion of compressor. The results indicated that the superheat of 4 ℃ and 22 ℃ can be regarded as the transition points between three heat transfer stages of steady R410A flashing spray cooling: single-phase heat transfer, nucleate boiling, and transition boiling. To achieve the best cooling performance, superheat should be between 4 ℃ and 22 ℃ to keep heat transfer in stage II. The increase of compressor frequency can improve the cooling performance of spray system effectively. When the compressor frequencies are 10 Hz, 15 Hz and 20 Hz, CHF can reach 162.9, 168.3 and 175.0 W/cm², and the maximum heat transfer coefficient is around 60.5, 80.6, and 90.4 kW/(m²·K), separately, with surface temperature below 35 ℃, 30 ℃ and 25 ℃. At the same heat flux, the power consumptions for the system to reach steady-state at 15 Hz and 20 Hz are 12.2% lower but 5.9% higher than that at 10 Hz, which provides a feasible energy-saving strategy for spray cooling system in the practical thermal management of electronic equipment.