Numerical study of the evaporation in laminar humid air flow of a liquid film flowing over an inclined plate.

By using an implicit centered finite differences method with a non-uniform grid, the authors study numerically the evaporation of a thin liquid film f lowing over an inclined plate in a forced hu mid-air flow. They consider th e existence of two-dimensional laminar boundary-layers with variable physic al properties and show that the term of enthalpy diffusion is always neglig ible, whether the plate is adiabatic, isothermal or heated by a constant he at flux density. By using in the liquid film transfer equations which are o ne-dimensional, partially two-dimensional and two-dimensional, the authors additionally show the following features. If the plate is adiabatic, the li quid mass flow rate is without influence on the transfers and the gas-liqui d interface behaves like an isotherm surface at rest. In this case, one may use a one-dimensional model in the film whatever liquid mass flow rare is. If the wall is isotherm or heated by a constant heat flux and when the liq uid mass flow rate is less than 10(-3) kg.m(-1).s(-1), the one-dimensional model is sufficient; if it is included in the interval [10(-3) kg.m(-1).s(- 1), 10(-2) kg.m(-1).s(-1)[, the partially two-dimensional model is useful; if it is superior to 10(-2) kg.m(-1).s(-1), it is necessary to use the two- dimensional model. Generally, whatever the thermal conditions on the plate are, heat transfer is dominated by the liquid-vapor transition. (C) 2000 Ed itions scientifiques et medicates Elsevier SAS.