||Spray cooling has been proven to be efficient in managing high power thermal load. Due to the MEMS technology, the spray nozzle plate has been reduced to minute size or even microscale with low power consumption. However, several of the key heat transfer mechanisms are still not well understood.|
The main goal of this study is to observe the velocity characteristics of the spray field, droplets distribution along the downstream, the boiling/cooling curves and the cooling performance.
In this study, we use a commercial PZT nozzle plate with three different nozzle diameters of dj = 7 μm, 10 μm and 35 μm. The corresponding volumetric rate is 3.47 ml/min, 6.53 ml/min and 50 ml/min, respectively. The PZT atomizer is composed of Ni-Co alloy nozzle plate bounded to the PZT ring actuator. The approximate numbers of micro nozzles on a circular Ni-Co plate are 2288 and 1071 corresponding to dj = 7 μm and 35 μm, respectively.
We use DI water as working fluid spraying on a copper flat heater which the target surface area is 2x2 cm2 and with a 14.5 mm thickness. The main experimental parameters are the spray height, H (30, 40, 50, 70, 90 mm), the initial temperature of the heater surface, Ts (300, 200, 100 ºC), and nozzle diameter, dj (7, 10, 35 μm). Both a transient and steady boiling curve are obtained as well as the quenching cooling curve. The results show that the average heat transfer coefficient (HTC) and the associated critical heat flux(CHF) could be over 2W/cm-K(HTC) and 200W/cm2(CHF), respectively.
Furthermore, by using micro particle image velocimetry (μPIV) and Interferometric particle Imaging (IPI) systems, we could image and analyze the velocity and droplet size of the spray field. Besides, we also study the droplets dynamics to understand the droplet-surface interactions relevant to spray cooling.