Investigation of pore size effect on spray cooling heat transfer with porous tunnels

Previous studies have shown that spray cooling heat flux enhancement may be attained using enhanced surfaces (i.e., embedded surfaces). However, most enhanced surface spray cooling studies have been limited to extended surface structures. This study investigates the effect of porous tunnels (and pore size) on spray cooling heat flux. The pores were machined into the top of each heater block leading into the sub-surface tunnels. Pore diameters varied between 0.25 mm and 1.0 mm. Pore density was held constant for each of the enhanced surfaces tested. Each copper block had a projected cross- sectional area of 2.0 cm. Measurements were also obtained on a heater block with a flat surface for purposes of baseline comparison. A 2x2 nozzle array was used with PF-5060 as the working fluid. Thermal performance data was obtained under nominally degassed (chamber pressure of 41.4 kPa) conditions with a bulk fluid temperature of 20.5 degrees C. Results show that the highest critical heat flux (CHF) attained was 141 W/cm(2) using pores 1.0 mm in diameter. This gave an enhancement of 75% relative to the flat surface case.