Experimental study on effect of enhanced surfaces and inclined mode on spray cooling heat transfer performance using HFE-649 coolant

Experiments have been performed to study the effect of enhanced surfaces including micro-finned, micro-/nano-coated (coating thickness of 100 mu m and 200 mu m) and hybrid surface on heat transfer coefficient and critical heat flux using spray cooling. Commercial HFE-649 coolant obtained from 3 M Corporation has been used to spray over copper heater of 10 mm(2) cross-sectional area using a full cone pressure swirl nozzle with 0.51-mm orifice diameter. The pressure swirl nozzle squeezed the incoming fluid and dispersed into spray droplets in the volumetric flux range between 1.0 and 4.5 cm(3)/cm(2)s. Results have been obtained for various surfaces at optimum distance of nozzle-to-surface and comparison is done with the plain surface. Findings revealed that heat transfer performance improved considerably with hybrid surface, which showed at least 360% enhancement in heat transfer coefficient and 72.9% in critical heat flux in contrast to the plain surface. An improvement of 7.1% in critical heat flux is observed for hybrid surface in comparison with other enhanced surfaces. Furthermore, experiments were conducted to examine the effect of inclination angle (0 degrees, 15 degrees, 30 degrees, and 45 degrees) on heat transfer performance. The heat transfer coefficient, critical heat flux, and cooling efficiency all improved dramatically at 15 degrees C inclination angle. In comparison with horizontal spray, an improvement of 18.9% and 20.1% in heat transfer coefficient and critical heat flux, respectively, have been observed. However, heat transfer performance degraded with the further increase of inclination angle. Other experimental parameters remain constant, such as the volumetric flux, spray height, and spray pressure.