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Title: On the importance of the heat and mass transfer resistances in internally-cooled liquid desiccant dehumidifiers and regenerators

Abstract

Liquid desiccant heat and mass exchangers are a promising technology for efficient humidity control in buildings. Many researchers have investigated these exchangers, often using numerical models to predict their performance. However, there is a lack of information in the literature on the magnitude of the heat and mass transfer resistances, both for the dehumidifier (which absorbs moisture from the air) and the regenerator (which heats the liquid desiccant to re-concentrate it). This article focuses on internally-cooled, 3-fluid exchangers in a parallel plate geometry. Water heats or cools a desiccant across a plate, and the desiccant absorbs or releases water into an airstream through a membrane. A sensitivity analysis was used to estimate the importance of each of the heat and mass transfer resistances (air, membrane, desiccant, plate, water), and how it changes with different design geometries. The results show that, for most designs, the latent and sensible heat transfer of the dehumidifier is dominated by the air mass transfer resistance and air heat transfer resistance, respectively. The air mass transfer resistance is also important for the regenerator, but much less so; the change in the desiccant equilibrium humidity ratio due to a change in either temperature or desiccant mass fractionmore » is much higher at the regenerator's higher temperatures. This increases the importance of (1) getting heat from the water to the desiccant/membrane interface, and (2) diffusing salt ions quickly away from the desiccant/membrane interface. The membrane heat transfer and water heat transfer resistances were found to be the least important. These results can help inform decisions about what simplifying assumptions to make in numerical models, and can also help in designing these exchangers by understanding which resistances are most important.« less

Authors:
 [1];  [1]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), NREL Laboratory Directed Research and Development (LDRD)
OSTI Identifier:
1421910
Report Number(s):
NREL/JA-5500-70557
Journal ID: ISSN 0017-9310
Grant/Contract Number:
AC36-08GO28308
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
International Journal of Heat and Mass Transfer
Additional Journal Information:
Journal Volume: 122; Journal Issue: C; Journal ID: ISSN 0017-9310
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; liquid desiccant; air conditioning; membrane; modeling; dehumidification; heat and mass transfer; heat and mass exchanger

Citation Formats

Woods, Jason, and Kozubal, Eric. On the importance of the heat and mass transfer resistances in internally-cooled liquid desiccant dehumidifiers and regenerators. United States: N. p., 2018. Web. doi:10.1016/j.ijheatmasstransfer.2018.01.111.
Woods, Jason, & Kozubal, Eric. On the importance of the heat and mass transfer resistances in internally-cooled liquid desiccant dehumidifiers and regenerators. United States. doi:10.1016/j.ijheatmasstransfer.2018.01.111.
Woods, Jason, and Kozubal, Eric. Tue . "On the importance of the heat and mass transfer resistances in internally-cooled liquid desiccant dehumidifiers and regenerators". United States. doi:10.1016/j.ijheatmasstransfer.2018.01.111.
@article{osti_1421910,
title = {On the importance of the heat and mass transfer resistances in internally-cooled liquid desiccant dehumidifiers and regenerators},
author = {Woods, Jason and Kozubal, Eric},
abstractNote = {Liquid desiccant heat and mass exchangers are a promising technology for efficient humidity control in buildings. Many researchers have investigated these exchangers, often using numerical models to predict their performance. However, there is a lack of information in the literature on the magnitude of the heat and mass transfer resistances, both for the dehumidifier (which absorbs moisture from the air) and the regenerator (which heats the liquid desiccant to re-concentrate it). This article focuses on internally-cooled, 3-fluid exchangers in a parallel plate geometry. Water heats or cools a desiccant across a plate, and the desiccant absorbs or releases water into an airstream through a membrane. A sensitivity analysis was used to estimate the importance of each of the heat and mass transfer resistances (air, membrane, desiccant, plate, water), and how it changes with different design geometries. The results show that, for most designs, the latent and sensible heat transfer of the dehumidifier is dominated by the air mass transfer resistance and air heat transfer resistance, respectively. The air mass transfer resistance is also important for the regenerator, but much less so; the change in the desiccant equilibrium humidity ratio due to a change in either temperature or desiccant mass fraction is much higher at the regenerator's higher temperatures. This increases the importance of (1) getting heat from the water to the desiccant/membrane interface, and (2) diffusing salt ions quickly away from the desiccant/membrane interface. The membrane heat transfer and water heat transfer resistances were found to be the least important. These results can help inform decisions about what simplifying assumptions to make in numerical models, and can also help in designing these exchangers by understanding which resistances are most important.},
doi = {10.1016/j.ijheatmasstransfer.2018.01.111},
journal = {International Journal of Heat and Mass Transfer},
number = C,
volume = 122,
place = {United States},
year = {Tue Feb 06 00:00:00 EST 2018},
month = {Tue Feb 06 00:00:00 EST 2018}
}

Journal Article:
Free Publicly Available Full Text
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