New insights into intermittent spray cooling for high-power electronics applications

Intermittent spray cooling is an active flow control technique that enhances the overall spray efficiency. However, it often leads to a sudden high temperature due to liquid deficiency on the target surface during the intermittent periods. This paper proposed an intermittent spray technology with small flow rates to address high heat flux, based on integrated liquid wicking-reservoir surfaces with cotton, porous foamed copper(PFC), and copper mesh(CM) as porous media layers. It explored the effects of pulse duration and duty cycle(DC) on the cooling performance and clarified the enhanced heat transfer mechanism in both single-channel and multi-channel vapor separation. The unique properties of porous media allow them to use capillary action to spontaneously supply liquid to the target surface during the spray period, delaying the critical heat flux. During the intermittent period, the liquid storage characteristics of these porous media address the issue of liquid deficiency and promote liquid film boiling and evaporation by the micro-nano scale effect, further reducing the demand for cooling liquid. Compared to conventional intermittent spray cooling, the heat transfer performance on CM surface was improved by up to 129.2 % at a DC = 3:1. And the spray efficiency of the intermittent spray system reached up to 38.0 %, an improvement of 104.3 % compared to continuous spray. Additionally, using computational fluid dynamics, the paper visually analyzed the temporal changes in the percentage of liquid-to-vapor phase transition on the integrated liquid wicking-reservoir surfaces and the temperature distribution characteristics. Combining the heat transfer performance with spray efficiency, a pulse duration of 3 s with a DC = 3:1 is recommended for the intermittent spray cooling. Since the integrated liquid wicking-reservoir surfaces proposed in this paper can achieve higher spray efficiency, better temperature uniformity, and lower coolant demand, opening up new possibilities for intermittent spray cooling of electronic devices.