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DOI: 10.1615/ICHMT.2012.CHT-12.410
pages 663-680

Jingchun Min
2Department of Engineering Mechanics, Tsinghua University, No. 1, Qinghua Yuan, Haidian District, Beijing 100084, China

Xiaomin Wu
Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Beijing Key Laboratory for CO2 Utilization and Reduction Technology, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China

Ming Su
Energy Research Inst., National Development and Reform Commission, Beijing 100038, China


A mathematical model was presented to predict the performance of a total heat exchanger with a vapour-permeable membrane core. The model considers combined heat and mass transfer as well as pressure drop in the core. The model provides analytical expressions for the heat and moisture transfer resistances through the membranes, both of which are operating condition dependent. Numerical calculations are carried out to investigate the effects of the membrane core geometry, the membrane physical property and the outdoor air state on the exchanger performance. The core geometry includes the membrane spacing (channel height) and thickness, the membrane property includes the membrane transport and adsorption parameters, and the outdoor air state includes the outdoor air temperature and humidity. The calculation results show that under equal fan power condition, as the channel height increases, the total heat transfer rate initially increases, after attaining to a maximum, turns to decrease, whereas the enthalpy effectiveness monotonously decreases. As the moisture diffusivity in membrane increases, the total heat transfer rate increases; as the membrane adsorption constant increases, the total heat transfer rate initially increases, after reaching a maximum, turns to decrease. Similar changes are observed for the enthalpy effectiveness. As the outdoor air temperature or humidity increases, the total heat transfer rate increases. For fixed outdoor temperature, as the outdoor humidity increases, the enthalpy effectiveness initially decreases to a minimum and then increases. The enthalpy effectiveness decreases with increasing outdoor temperature for low outdoor humidities but shows little change with the outdoor temperature for higher humidities.

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