Effect of Disjoining Pressure and Working Fluid on Multi-Scale Modeling for Evaporative Liquid Metal Capillary

This research presents a new multiscale model of an evaporating liquid metal capillary meniscus under nonequilibrium evaporation sustaining a nonisothermal interface.

The primary investigation is elaborated on to examine the critical role of the disjoining pressure, which consists of both the traditional van der Waals component and a new electronic pressure component, for the case of liquid metals. The fully extended dispersion force is modeled along with an electronic disjoining pressure component that is unique to liquid metals attributing to their abundant free electrons. For liquid alkali metals (sodium and lithium), as a favorable coolant for high temperature two-phase devices, the extended meniscus thin film model (sub-microscale) is coupled to a CFD model of the evaporating bulk meniscus (sub-millimeter scale).

Two extreme cases of sodium are compared, i.e. with or without incorporation of the electronic disjoining pressure component. It is shown that the existence of electronic component of the disjoining pressure leads towards larger total capillary meniscus surface areas and larger net evaporative mass flow rates. Furthermore, the net evaporative mass flux in the bulk meniscus region is needed to accounted for to obtain a true picture of the total capillary evaporation transport.

Comparative study of sodium(Na) and lithium(Li) coolants with existence of the electronic disjoining pressure is performed. The heat pipe with lithium coolant shows enhanced thin film area and higher heat transfer capability with less evaporative mass flux than one with sodium coolant does under the same overheating condition.