Effect of nozzle orientation on electrospray cooling

Abstract

• The performance of electrospray cooling is similar for all spray angles from 90° (normal to target surface) down to 30°. • A sharp drop in cooling performance occurs at a spray angle of 25°due to incomplete jet-to-droplet breakup, droplet rebound from the target surface, and a reduction in the electrohydrodynamically-induced convective air flow. • Electrospray cooling is ideal for constrained environments or hard-to-reach surfaces. Two-phase cooling is an efficient method for heat removal from electronic systems. One implementation of this approach is based on electrospray atomization, where droplets of the cooling fluid are produced using high electric potentials. Electrospray cooling has several unique advantages, including low power consumption, precise delivery of coolant, and compact design. Past work has mostly focused on spray orientations where the nozzle is directed normal to the high-temperature surface. In this short communication, we examine electrospray cooling at varying spray angles, which can provide easier integration for constrained environments or hard-to-reach surfaces. Water is used as the working fluid at four different flow rates from 60 to 120 mL/hr. The nozzle orientation was varied from normal to the surface (90°) down to an acute spray angle of 25°. We found that any angle larger than 30° achieved an evaporation efficiency exceeding 100% at the critical heat flux. The efficiency dropped to 90% at an angle of 25° for all flow rates. Surface temperatures increased and the critical heat flux decreased with spray angle, with the sharpest change occurring at a spray angle of 25°. This was due to droplet rebound, incomplete droplet breakup at high flow rates, and a reduction in electrohydrodynamically-induced convective cooling. The work reported here will assist in the integration of electrospray atomization for cooling applications.