Heat and mass transfer between a porous medium and a parallel external flow. Application to drying of capillary porous materials

Abstract

A numerical method allowing heat and mass transfer between an unsaturated porous medium and an external air flow to be predetermined is presented. Various numerical simulations are carried out in order to study the behaviour of the heat and mass convective transfer coefficients at the interface during drying. The simulations show that leading edge effects give rise to a space non-uniformity of the variables at the interface. It follows that the interfacial transfer coefficients differ from the standard values corresponding to boundary layer flows on the flat plate with uniform temperature or concentration at the wall. Furthermore, it is shown that one-dimensional simulation of the phenomena inevitably leads to incorrect results when the leading edge effects concern a sufficiently large part of the porous body. Lastly, the effect of the occurrence of large-scale heterogeneities of water content at the interface during drying is also studied.