Multi-phase, non-thermal transfer of water in a simple geometry by P. Lidon, CSI member Abe Stroock, and colleagues; email: ads10@cornell.edu
It has long been acknowledged that heat and water transport of in soils and plants are intimately coupled. Pioneering work by Philip and de Vries proposed the physical basis and governing equations to describe these processes; their theory has since been refined many times. However, the lack of appropriate sensors for in situ monitoring of water status has impeded clear interpretation of field experiments and no general consensus has emerged on a precise description of water transport in non-isothermal porous media. In this paper, we use a new microfluidic tool called the microtensiometer that measures water potential to study a simple model situation: we measure the evolution of water potential in a vapor gap across which a controlled temperature gradient is applied and report a decrease of water potential with temperature difference by −7.9±0.4MPa.K-1, in agreement with previous experiments using other techniques. Based on a thermodynamic analysis of our system, we derive a theoretical prediction for this effect. Our model differs from Philip and de Vries equations by an additional water flux, negligible in our experiment but which should become significant in the case of unsaturated, nanoporous media. Both predictions by our model and by Philip and de Vries are close to the experimental value but with a discrepancy significant when compared with experimental uncertainties.
Abraham Stroock, Chemical and Biomolecular Eng.
