Experimental study on heat transfer enhancement in subcooled flow boiling under pressurized conditions

抄録

In this study, the cooling capabilities of flow boiling heat transfer aided by electrohydrodynamic (EHD) force and diamond-electrodeposited boiling surface is investigated in a micro-slit channel (MSC). The MSC uses a two-phase flow cooling system, in which an electric field is applied to a dielectric liquid using a slit electrode. To reduce the wall temperature below 60 °C and promote cooling in electronic devices, a dielectric liquid with a saturation temperature of 15 °C HCFO-1224yd (AGC, AMOLEA, CF₃CF = CHCI) was selected as a working fluid. Moreover, the entire system was pressurized using nitrogen gas to suppress liquid flow instabilities due to the generation of cavitation at the saturated system pressure. To enhance boiling heat transfer, the surface was electrically deposited with fine diamond particles (mixture of particles with diameters 20 and 1.5 μm), and an electric field of −5 kV/mm was applied between the surface and slit electrode. The experiments were conducted under various system pressures (75-230 kPa), mass flow rates (1.67-5.00 g/s), and degrees of subcooling (5-15 K) to evaluate the heat transfer performance. The electric field was effective in increasing both the critical heat flux (CHF) and heat transfer coefficient (HTC). The high electric field enhanced the boiling heat transfer until the inflow liquid entirely evaporated. Increasing the mass flow rate was also effective in increasing the CHF and HTC at lower wall temperatures, resulting in a maximum of 101 W/cm² at 64 °C and 37 kW/m²·K at 52 °C, respectively. Increasing the system pressure improved the HTC but elevated the wall temperature. Subcooling was effective in increasing HTC. Increase in either pressure or subcooling did not change the CHF because the entire inflow liquid evaporated in the MSC chamber due to the electric field effect.