Experiments were conducted to study the effects of enhanced surface structures on heat flux using spray cooling. The surface enhancements consisted of cubic pin fins machined on the top surface of copper heater blocks. The structure height, pitch, and width were parametrically varied. Each copper block had a projected cross-sectional area of 2.0 cm2. Measurements were also obtained on a heater block with a flat surface for baseline comparison purposes. A 2×2 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) and gassy conditions (chamber with N2 gas at 101 kPa) with a bulk fluid temperature of 20.5°C. Results for both the degassed and gassy cases show that structure width and separation distance have a dominant effect upon the heat transfer for the size ranges used. Cubic pin fin height had little impact upon heat flux. The highest critical heat flux (CHF) attained for any of the surfaces was 121 W/cm2, giving an enhancement of 51% relative to the flat surface case under nominally degassed conditions. The highest CHF in the gassy case was 149 W/cm2, giving an enhancement of 38% relative to the flat surface case.

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