Electrospray cooling dynamics: Impact of spray mode transitions and flow rates on heat transfer regimes

This study investigates the electrohydrodynamic (EHD) spray cooling performance of eco-friendly solvents, specifically distilled water and ethanol, across a wide flow rate range of 50–500 ml/h. We demonstrate that the transition from dripping to electro-dripping and stable cone-jet regimes imparts sufficient momentum to charged droplets to penetrate the insulating vapor layer, which effectively suppresses the Leidenfrost effect at high temperatures. To evaluate cooling performance, we systematically compare the heat flux (q), convective heat transfer coefficient (h), enhancement ratio, Nusselt number (Nu), and cooling efficiency (η) as functions of the fluid properties and spray modes. Our results indicate that the EHD-induced droplet acceleration disrupts the thermal boundary layer, significantly increasing both h and Nu compared with gravity-driven cooling. While distilled water exhibits a higher peak q due to its superior latent heat, ethanol achieves enhanced system-level efficiency and more uniform dispersion due to its lower surface tension. These findings provide essential physical insights and optimal design guidelines for next-generation thermal management systems tailored to high-power, high-density electronic devices.