Isolated moving charged droplet evaporation characteristics in electrostatic field with highly volatile R134a

Abstract

The evaporation characteristics of a charged moving droplet with high volatility are the key during electrostatic spray cooling, which determines cooling capability. Fundamental investigations of the charged droplet evaporation are helpful in enhancing the cooling capability and advancing the electrostatic spray model, whereas the corresponding data with the highly volatile R134a are very scarce. In this work, an improved evaporation model that accounted for the effects of the corona wind, Coulombic fission, and electric force under the electric field was developed and validated to evaluate the importance of the electric field on the moving charged R134a droplet evaporation for the first time. Results demonstrated that the electrostatic field can improve the charged droplet evaporation through heat and mass transfer enhancement by the corona wind and counteracting the drag force from air. The droplet lifetime was shortened by 20.8% (i.e., from 105.6 ms to 83.6 ms) when the applied voltage increased from 0 kV to 10 kV. The increase in the ambient pressure has a damping effect on the charged droplet evaporation because of the decreasing driving force for the heat and mass transfer, which should be avoided in electrostatic spray cooling. Exponential decay in the charged droplet lifetime when the applied voltage increased was observed, and the corresponding results with different initial droplet diameters and velocities provide the first-hand fundamental data for the modeling and simulation of electrostatic spray cooling with the highly volatile R134a.