Dual-Module humidity pump with hollow fiber membranes for isothermal dehumidification in industrial drying

Abstract

Traditional dehumidification and drying processes are energy-intensive as they involve cooling the air below the dew point to condense and remove water vapor. Vacuum membrane dehumidification offers energy-saving opportunities, but its full potential remains undeveloped due to the presence of water vapor within the vacuum pump and excessively high pressure ratios. Recent studies proposed a dual-module humidity pump (DMHP) to address this, but the increased air permeation into the system requires strategies to prevent air pressure buildup and diffusion barrier formation. This study investigates a DMHP, specifically designed to address these issues by incorporating hollow fiber membranes for isothermal dehumidification in industrial heat pump dryers (HPDs). Membrane geometry and properties are coupled with a partial pressure-driven ε-NTU method, and a discretized model is used to identify water vapor transport under sub-ambient conditions. Thermodynamic models of the components are developed, and membrane-integrated HPDs are compared to a conventional HPD. The proposed system’s specific moisture extraction rate ($\mathrm{SMER}$) exceeds conventional HPDs by 69%. Global sensitivity analysis reveals that $\mathrm{SMER}$ is 7.2 times more responsive to ambient conditions than dryer inlet conditions, with membrane geometry and properties’ interactions exerting greater influence than their individual effects. The optimum pressure ratio for the water vapor compressor, ranging from 1.2 to 3.8 and adjustable via synchronized control of rotational speeds with the vacuum pump, enhances $\mathrm{SMER}$ by up to 33.7% with a vapor balance ratio of 0.84–0.89. The results suggest that future work should investigate further optimization of membrane modules and variable built-in volume ratio compressors to unlock the full potential of DMHP technology.