Experimental study on optimal spray parameters of piezoelectric atomizer based spray cooling

Piezoelectric atomizer could enhance heat transfer of spray cooling at low flow rate through improved atomization of liquid droplets. To optimize the heat transfer performance of piezoelectric atomizer based spray cooling, a novel piezoelectric atomizer was designed in this paper. The piezoelectric atomizer was composed of two piezoelectric ceramic films (110 kHz) and a stainless steel micropore disk with different outlet diameters of 5 μm, 7 μm, 9 μm, 20 μm and 25 μm (corresponding flow rates of 0.5 mL/min, 1.0 mL/min, 3.8-5.0 mL/min, 11.0-16.0 mL/min and 20.0-29.0 mL/min, respectively). The effects of micropore outlet diameter, volumetric flow rate and spray height on surface temperature distribution, heat flux and the spray cooling efficiency were studied. It was found that the volumetric flow rate increased with the increase of micropore outlet diameter. As the flow rate increased, the heat flux increased but the spray cooling efficiency decreased as a sacrifice. The correlation between spray cooling efficiency/heat flux and flow rate (range from 0.5 mL/min to 29.0 mL/min) of all atomizers could be generalized into one exponential decay/growth curve. An optimal diameter of 9 μm could achieve high heat flux of 123.8 W/cm2 at a relatively low volumetric flow rate of 5.0 mL/min, and the corresponding spray cooling efficiency was as high as 53.8%. For each atomizer, there was an optimal spray height which differs with the micropore outlet diameter.