Temperature polarization effects in thermo-osmosis

Abstract

Water transport induced by heat flow across cellophane and cellulose acetate membranes has been extensively studied in recent years. In comparing the results obtained by the various authors, remarkable differences emerge among the apparent behaviour of otherwise similar membranes. Discrepancies are so large that in some cases the very existence of this transport phenomenon has been questioned. In this paper, an effect is discussed which appears significantly to affect heat-and-mass-transfer-coupled phenomena. A temperature polarization concept is used as an analogy to concentration polarization in reverse osmosis. This appears to account for most of the discrepancies in the published data. However, there remain differences in the experimental results which cannot be explained solely on the basis of “temperature polarization”. Thus, it appears necessary to perform further experimental investigations on thermo-osmosis through these membranes under well controlled thermal conditions. In this regard, a standard procedure is suggested which should allow determination of true thermo-osmotic transport coefficients, by accounting for thermal polarization effects. A physical interpretation of mass transfer across membranes induced by heat flow is also introduced. This will be further developed in subsequent papers.