Multidimensional numerical analysis of coupled heat and mass transfer for energy-efficient desiccant bed regeneration

초록

This work implements a multi-dimensional numerical scheme to capture the time-dependent thermal and moisture migration occurring inside zeolite 13X packed columns over cyclic sorption and desorption stages. By integrating implicitly coupled user-defined functions with linear driving force (LDF) kinetics and the Sips equilibrium isotherm, a two-dimensional axisymmetric computational fluid dynamics (CFD) model ensures stable numerical convergence for both capture and release steps. Unlike traditional one-dimensional formulations that overlook spatial variations, the present model effectively captures radial gradients in temperature, gas-phase concentration, and solid loading arising from external heat transfer and column wall thermal inertia. A comparison with the one-dimensional model showed that cross-sectional averaging underestimates the required regeneration time by 12.0-15.3% for 50% moisture removal and by 21.3-30.4% for 75% moisture removal. To avoid the inefficient tailing regime near equilibrium, a practical regeneration criterion of 90% moisture removal was adopted. The desorption driving force is significantly amplified by elevating the regeneration thermal input, which subsequently curtails the required purge-gas flow rate. In the high-efficiency regime where the mass-flow-rate ratio was below unity, increasing the regeneration temperature from 453K to 463K and 473K reduced the total regeneration power consumption by approximately 8% and 15%, respectively. The lowest power consumption was achieved at 473K. These results demonstrate the importance of multidimensional transport analysis for accurate regeneration prediction and energy-efficient desiccant bed operation.

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