Heat and mass transfer analysis in laser drying

In laser drying, a continuous or pulsed laser beam irradiates the surface of a water-containing porous medium. The high power of the laser beam leads to quick heating of the surface and therefore fast evaporation of water at the surface. As the water at the surface evaporates away, the water inside the medium diffuses towards the surface driven by the water concentration gradient. Traditional treatment of such a diffusion process is based on classical diffusion theories, Fourier's law for heat conduction and Fick's law for mass diffusion. In the case of laser drying, however, a small time scale would lead to diffusion under non-equilibrium conditions. A generalized diffusion theory that takes into account fast transient behavior is therefore needed. This paper presents a numerical analysis of the laser drying process by employing a generalized, Maxwell-Cattaneo equation to treat both heat and mass transfer. Calculations are performed to illustrate the non-classical transport of moisture. The effect of the heat flux density and the initial moisture content on water removal is also investigated.