Application of Electrohydrodynamic Atomization to Two-Phase Impingement Heat Transfer

Abstract

The effect of electric fields applied to two-phase impingement heat transfer is explored for the first time. The electric field applied between a capillary tube and heated surface enhances the heat transfer by controlling the free boundary flow modes from discreet drops to jets, to sprays. Through an experimental study, the impingement heat transfer was evaluated over a range of operating conditions and geometrical parameters with subcooled ethanol used as the working fluid. The ability to change the mode of impinging mass did change the surface heat transfer. The characteristics of the impinging mass on heat transfer were dependent on flow rate, applied voltage, capillary tube to heated surface spacing, capillary tube geometry, heat flux, heater surface geometry, and capillary tube array configuration. Enhancement occurred primarily at low heat fluxes (below 30W∕cm2) under ramified spray conditions where the droplet momentum promoted thin films on the heated surface resulting in 1.7 times enhancement under certain conditions. Higher heat fluxes resulted in greater vapor momentum from the surface, minimizing the effect of different impingement modes. The use of capillary tube array allowed for electrohydrodynamics atomization enhancement and higher liquid flow rates, but electrostatic repulsive forces diverted the spray from the heater surface. This reduced the mass flux to the surface, leading to premature dryout under certain conditions.