A comprehensive theoretical and numerical investigation of transient coupled heat and mass transfer in \(\mathrm {CaCl_2}\) -impregnated clay desiccant packed beds is presented. A one-dimensional axial dispersion model is developed to describe gas-phase moisture and energy transport, coupled with solid-phase moisture uptake and adsorption-induced heat generation under local thermal non-equilibrium conditions. Physically consistent Danckwerts boundary conditions are employed at the inlet and outlet to accurately account for the combined effects of convection and axial dispersion. An analytical benchmark solution is derived in the Laplace domain for the linearized transport equations and numerically inverted to obtain transient responses, providing a rigorous reference for model verification. A high order DQM method is employed to numerically solve the governing equations, in conjunction with a stiff time scheme. Validation yields outstanding results when comparing the predictions of the DQM to the Laplace-domain analytical solution of outlet humidity breakthrough, with spectral convergence achieved rapidly using only a few grid points. The short-term dynamics of moisture fronts, desiccant loading, and thermal effects resulting from adsorption are systematically examined through the spatial and temporal profiles of responses. The results highlight the intricate relationship between moisture dispersion and heat removal, underscoring the importance of accurately characterising axial dispersion and boundary effects in the modelling of desiccant packed beds. The proposed framework provides a robust and efficient tool for the study and design of desiccant-based thermal and dehumidification systems.
