Origin of Surface-Driven Passive Liquid Flows

Passive liquid flow occurs in nature in the transport of water up tall trees and is desired for high-heat flux removal in thermal management devices. Typically, liquid-vapor surface tension is used to generate passive flows (e.g., capillary and Marangoni flows). In this work, we perform a fundamental molecular study on passive liquid flow driven by the solid liquid surface tension force. Such surface tension values are first estimated by placing a liquid film over the surface and simulating various surface temperatures, followed by which simulations are performed by differential heating of the liquid film over the surface. Very strong passive liquid flows are obtained that lead to steady-state, continuous, and high heat flux removal close to the maximum theoretical limit, as predicted by the kinetic theory of evaporation. Nondimensional empirical relations are developed for surface tension gradient, flow velocity, and evaporation rate.