Understanding Irreversible Processes in a Desiccant Wheel via Direct Entropy Generation Modeling

This work presents for the first time a direct calculation of entropy generation mechanisms in a desiccant wheel (DW). A previously validated model is used to compute the entropy generated by various irreversible mechanisms. In addition, a clearly defined, idealized dehumidification process is proposed. The results show that irreversible heat transfer is the dominant source of entropy generation, accounting for about 40 % in the reference case. Mass transfer is the second-largest contributor, followed by dissipation and mixing. Comparison with the ideal process reveals that a large share of the system’s exergy demand originates from irreversibilities within the DW itself, rather than from losses in the exhaust air streams. Parametric analysis of regeneration temperature and wheel rotational speed identifies operating conditions that minimize entropy generation. In addition, the temperature spread at the wheel outlet is found to be a reliable indicator of entropy generation. Local entropy generation analysis shows that optimal operating points exhibit a more dispersed distribution of entropy generation, whereas non-optimal points feature smaller dominant active zones at the boundary surfaces. These findings clarify the dominant loss mechanisms and provide practical guidance for improving the design and operation of desiccant wheels. • Entropy generation mechanisms in a desiccant wheel are analyzed via the direct method. • Differentiation of entropy generation by source and location. • A clearly defined idealized dehumidification process is proposed. • Real dehumidification is compared to the ideal process. • A strategy to minimize entropy generation is shown.