Numerical study on the effects of regeneration temperature on dehumidification performance of desiccant materials

Abstract

Desiccant is a material that can adsorb water vapor in the air and is widely used in the solid desiccant dehumidifier (SDD). Properties of desiccant material would affect the dehumidification performance of the SDD system. Research and development of desiccant materials have continued to gain attention by researchers. The material should have high adsorption capacity and can be easily-regenerated at a low regeneration temperature. This is as a result of the global quest to solve energy and environmental issues. Despite the development of many new desiccant materials, few studies were reported on the performance assessment of various desiccant materials in the SDD system. Such an assessment can be done through experimental work, but this requires repetitive testing, which can be expensive and time-consuming. Several researchers have used numerical simulations. However, the studies were carried out only on a two-dimensional (2D) simplified model of a single air channel for predicting the performance criteria. These models reduce the reliability of the findings because of the oversimplification from a real condition. Therefore, this study aims to determine the effects of regeneration temperature on the moisture removal capacity (MRC), dehumidification effectiveness (DE), and coefficient of performance (COP) of desiccant materials using a three-dimensional (3D) model. A 3D model of the single air channel enclosed with desiccant material was developed. The incompressible flow simulations were carried out using transient solver. The model was validated by comparing the time-variation of average moisture content and temperature of process air and regeneration air at the channel exit using experimental data obtained from the literature. It was found that the difference between the measured and predicted moisture content and temperature during adsorption process is 5.4 % and 1.0 %, respectively. For the desorption process, the difference between the measured and predicted moisture content and temperature is 3.0 % and 0.3 %, respectively. These figures show that the 3D single-channel model is well-validated and reliable for predicting the desiccant material performance. Four types of desiccant materials were considered, and six values of regeneration temperature were selected to evaluate their effects on the performance. Among all four materials, silica gel/CaCl2 has the highest MRC, DE, and COP. MRC increases from 0.3 g/s at 40°C to 0.57 g/s at 90°C. DE of silica gel/CaCl2 rises from about 22 % at 40°C to 43 % at 90°C. This is because at a higher regeneration temperature, more moisture can be desorbed from the desiccant material. This condition increases the ability to adsorb moisture for the next adsorption process and it leads to a higher MRC and DE. The COP values decrease from 0.9 at 40°C to 0.7 at 90°C. This is because, at a higher regeneration temperature, the regeneration heat consumption increases and lead to a lower COP. It is also observed that zeolite 13X has the lowest performance compared to other desiccant materials. The average value of MRC, DE, and COP for zeolite 13X are 0.27 g/s, 20.3 %, and 0.46, respectively. This research contributes to an economical and accurate way for determining the performance criteria of solid desiccant materials. With the established 3D model, the most suitable desiccant materials that give the highest performance can be identified accurately.