Model development of heat/mass transfer for internally cooled dehumidifier concerning liquid film shrinkage shape and contact angles

Abstract

Moisture affects building materials, the thermal comfort of building occupants and the work performed by them. The plate liquid desiccant air-conditioning system (LDACS) is a promising dehumidification alternative to traditional air-conditioning system for lower energy consumption and less pollution. The shrinkage of the falling film on working plates critically influences the dehumidification performance by affecting the wetting area and film thickness. This paper developed a new model of plate dehumidifier concerning the shrinkage shape and the variable film thickness of falling film. The new model was validated by experiments and compared with existing models. The results indicated that the effect of contact angles on dehumidification performance can be accurately predicted. The moisture removal rates increased rapidly from 2.0 g/kg to 2.56 g/kg as the contact angles decreased from 85° to 5°, while the wetting area increased from 0.145 m2 to 0.176 m2. The distribution of the humidity ratio of process air along flow direction with different contact angles was also simulated. Besides, the average film thickness decreased from 0.952 mm to 0.889 mm as the contact angles decreased from 85° to 5°. The annual electricity consumption of plate LDACS with different contact angles for a typical building in Hong Kong was estimated and analysed by using the newly developed model. The new model can achieve a better predictive accuracy by considering the exact shrinkage shape of falling film and the findings can provide a new insights improving the performance of plate dehumidifiers and other industrial applications, such as vertical condensers, evaporators and absorption towers.