Universal direction in thermoosmosis of a near-critical binary fluid mixture

TL;DR

This paper investigates thermoosmosis in near-critical binary fluid mixtures, revealing a universal flow direction determined by the mixture's proximity to the consolute point, regardless of component adsorption.

Contribution

It introduces a universal property of thermoosmosis flow direction in near-critical mixtures, independent of component adsorption, using a coarse-grained theoretical approach.

Findings

Flow direction aligns with temperature gradient near upper consolute point

Flow direction opposes temperature gradient near lower consolute point

Flow behavior is universal across different component adsorption scenarios

Abstract

We consider thermoosmosis of a near-critical binary fluid mixture, lying in the one-phase region, through a capillary tube in the presence of preferential adsorption of one component. The critical composition is assumed in the two reservoirs linked by the tube. With coarse-grained approach, we evaluate the flow field induced by the thermal force density. We predict a universal property; if the mixture is near the upper (lower) consolute point, the flow direction is the same as (opposite to) the direction of the temperature gradient, irrespective of which component is adsorbed onto the wall.