Heat transfer characteristics of dielectric fluid spray cooling targeting high heat flux and high evaporation efficiency

Due to its electrical insulation and suitable boiling temperature range, dielectric fluid spray cooling has great potential in electronic device cooling. We conducted an experimental study on a spray cooling system with adjustable operating parameters. The HFE-7100 dielectric fluid is used to obtain the effects of nozzle pressure difference, fluid subcooling and chamber pressure on spray and heat transfer characteristics. The results show that high nozzle pressure difference and high chamber pressure lead to production of droplets with small size, high velocity and high density. In respect to heat transfer, increasing nozzle pressure difference enhances heat flux whereas mitigates evaporation efficiency. Compared to saturated fluid, the one with subcooling at 27 degree celsius enables an increase of critical heat flux (CHF) by 29.2 %, while heat transfer coefficient and evaporation efficiency are both reduced. Reducing chamber pressure has been found to enhance both heat flux and evaporation efficiency. Increasing the chamber pressure to 120 kPa enables the spray cooling to achieve a CHF of 143.2 W<middle dot>cm(-2) and evaporation efficiency of 93.4 %. These findings enable different control strategies for dielectric fluid spray cooling aiming at high heat flux and high evaporation efficiency respectively. As compact design of a spray cooling system is the main target, the strategy of low nozzle pressure difference, high subcooling and low chamber pressure is suggested to be adopted to enhance the utilization of working fluid. An empirical correlation of CHF for dielectric fluid spray cooling with a wide evaporation efficiency has been improved and its maximum deviation is less than 6.7 %.