Drying gels

An analysis is presented for the stresses and strains produced during drying of a rigid elastic porous body, such as commercial porous glass, or a dense gel. The pressure distribution in the liquid during drying is shown to obey the diffusion equation, so solutions can be found in the literature for cases of interest. Results are presented for a flat plate drying from both sides, a plate that warps as a result of drying from one side, a cylinder drying from the lateral surface, and a sphere. The tensile stress that develops at the drying surface is proportional to the evaporation rate, and increases as the permeability of the body decreases. The maximum stress depends on the shape of the body and decreases in the order flat plate > cylinder > sphere > warping plate.