Abstract
Selective membrane dehumidification is a promising technology for energy efficient air dehumidification in buildings and has been ranked as a top alternative technology by the Department of Energy. One critical area that needs to be addressed is system modeling that incorporates device mass transfer characteristics and sizing. This work develops, validates, and applies a simple effectiveness-number of transfer units (πβπTU) modeling framework for dehumidification technologies that can be used to predict performance and determine required membrane area for a wide range of technologies, including energy recovery ventilators, vacuum membrane dehumidification, and desiccant dehumidifiers. Although the πβπTU method is a well-established framework for sizing and modeling heat exchangers, past attempts to create πL β πTπ L (meaning πβπTU for latent loads) models for dehumidification (referred to as latent cooling): (1) donβt agree on the definition of πTπ L, (2) are not fully analogous to the heat transfer definition of πTU, (3) cannot be easily applied across all technologies, (4) use humidity ratio, not vapor pressure, as the driving force, and (5) are often complex or lack a fundamental basis. In this work, we develop an effectiveness-NTU model for membrane humidity exchangers that is based on vapor pressure differences, employs a novel definition of the latent number of transfer units for dehumidification applications (πTπ L) and is fully analogous to the heat transfer effectiveness-NTU models employed for sensible heat exchangers. The resulting πLβπTπ L relationships are validated against experimental data with a maximum error of 1.2%. The overall methodology is applied in case studies for vacuum membrane dehumidification system sizing showing that the ratio of required membrane area per building floor area ranges between 0.1 to 3.5 depending on the building type and operating conditions. Finally, the framework is further generalized for applicability to any gas separation application.
Keywords
membrane, dehumidification, effectiveness, mass transfer, efficiency, gas separation
Date of this Version
9-5-2023
Recommended Citation
Fix, Andrew J.; Braun, James E.; and Warsinger, David M., "A general effectiveness-NTU modeling framework for membrane dehumidification systems" (2023). School of Mechanical Engineering Faculty Publications. Paper 70.
https://docs.lib.purdue.edu/mepubs/70
Comments
This is the author-accepted manuscript of Fix, AJ; Braun, JE; Warsinger, DM. (2023) "A general effectiveness-NTU modeling framework for membrane dehumidification systems." Applied Thermal Engineering, 236 Part B. Published by Elsevier, it's made available here CC-BY-NC-ND, and the version of record can be found at DOI: 10.1016/j.applthermaleng.2023.121514 .