T0006-P Electric Field Effects on Pool Boiling Heat Transfer in Low-G Environments

Pool boiling is a highly effective mode of heat transfer allowing high heat flux levels driven by relatively small temperature differences between the heated wall and the liquid. The high heat transfer coefficients associated with boiling have made the use of these processes increasingly attractive to aerospace engineering. Applications of this type include compact evaporators in the thermal control of aircraft avionics and spacecraft environments, heat pipes, and use of boiling to cool electronic equipment. In spite of its efficiency, cooling based on liquid-vapor phase change processes has not yet found wide application in aerospace engineering due to specific process uncertainties and related reliability problems associated with the low gravity environment.

Even less is known about the impact of electric fields on heat transfer in boiling in microgravity and their potential for heat transfer enhancement under such conditions and the mechanisms for responsible for the enhancement. Previous measurements have shown that heat transfer in boiling in microgravity can be higher than that in earth gravity at low wall superheats due to an increase in the number of nucleation sites on the surface, with a corresponding decrease in the critical heat flux. The measurements to date indicate that critical heat flux in microgravity under saturated conditions decreases from normal earth gravity. Based on the remarkable improvements accomplished under terrestrial conditions, the use of electric fields to replace the gravitational body force shows great potential to increase the amount of heat that can be transferred from a surface in microgravity.

The objective of the proposed research is to determine the mechanisms by which nucleate boiling heat transfer occurs in microgravity with and without the influence of electric fields. This proposal describes work where local heat transfer is measured simultaneously at many points on the heater surface in an effort to determine how boiling heat transfer is affected by the missing gravity and as an additional parameter by the electric field. Experiments will be carried out from the nucleate boiling regime through critical heat flux into the transition boiling regime.