Sublimation from a porous solid of high thermal conductivity

Theory is developed for sublimation from a porous solid of high thermal conductivity.The porous solid, which contains the material to be sublimed, is initially at a temperature T₀ and is submerged in a gas stream at temperature T_∞. The theory includes realistic expressions for the vapour pressure and the heat and mass transfer coefficients and assumes that the transfer occurs in a quasi-steady state.Numerical integration of the system of equations yields simultaneously the temperature of the solid and the fraction sublimed as a function of time. The predictions show good agreement with experimental results for the sublimation of D-camphor from a porous bronze bar.The experimental study includes the independent measurement of the coefficients for external heat transfer, the binary diffusion coefficient of D-camphor in air and of the tortuosity factor of the plate, thus not having any adjustable parameters. The error in the prediction of the time for sublimation is better than 10 per cent.A new unsteady method is proposed and employed for the determination of effective diffusivities (or tortuosity factors) taking into account open and closed pores.