Conjugate heat and mass transfer in a desiccant-airflow system: A numerical solution method

An effective numerical method was developed for analyzing, as a conjugate problem, transient two-dimensional heat and mass transfer between a solid desiccant and a humid laminar airstream. The method is also more generally applicable to conjugate problems of heat and mass transfer between solids and flowing fluids. The alternating direction implicit (ADI) procedure with an upwind scheme is used for solving both the energy and mass transfer equations. The secant method is applied to solve the local equilibrium relationship between the water content and the water vapor concentration in the silica gel bed. Comparison with conventional, nonconjugate problem solutions has shown that such solutions produce unacceptably large errors in thick-bed (of the order of 2 cm) desiccant systems; for example, they overpredict the water absorption rates by 53%.