Investigation of packing type of dehumidifier/regenerator in liquid desiccant air-conditioning system

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Investigation of packing type of dehumidifier/regenerator in liquid desiccant air-conditioning system


Author: Wang, Yalin
Title: Investigation of packing type of dehumidifier/regenerator in liquid desiccant air-conditioning system
Degree: M.Eng.
Year: 2015
Subject: Air conditioning.
Refrigeration and refrigerating machinery.
Humidity -- Control.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xii, 59 pages : color illustrations
Language: English
Abstract: This thesis is intended to compare the performance of different dehumidifier packing types for Liquid Desiccant Air-conditioning system. Three packing types were investigated in this study, which named corrugated structured packing, S-shaped polyvinyl chloride packing, and Globular-shaped polypropylene packing. This research includes theoretical and experimental parts. Theoretically, the two key parameters ---the packing's surface area and void ratio were obtained by using measuring instruments. Then, an experimental setup was established to test the system performance of the liquid desiccant system. The literature review demonstrated that the liquid desiccant dehumidification method was the most efficient and energy-saving dehumidification method. There were essentially five kinds of packing materials for liquid desiccant dehumidifier, including the plate type filling material, structured packing, falling film material, fin type material and packed bed material. Each type of material has a different shape and size, which may significantly influence its dehumidification performance. In this dissertation, an experimental table was set up to compare three common types of materials in the market. Different experimental conditions were set to find out which environment parameter influenced the materials largely. The relationship between the material's surface area and dehumidification performance has also been obtained. Previous researches just simulated the performance and operation processes of liquid desiccant dehumidification system. The comparison between different dehumidification methods and different influencing factors was also got. Up to now, each type of filling material has previously been investigated penetratingly and scrutinizingly. Many professors discussed their heat transfer performance by doing experiments and simulations. However, there is still a blank for researchers to compare different types of filling materials under the same environmental condition. In this research, three typical packing types were chosen to investigate the influence of different dehumidifier materials on the system performance. Two main performance indicators were applied including the mass transfer rate and heat transfer value. The total surface area and void ratio were got by using measuring tools and the conjecture was assumed before the experiment that there was a relationship between the surface area and dehumidification performance. The results demonstrated that with the increase of the inlet air temperature, the mass transfer rate of the air would decrease. The main cause of this phenomenon was the vapor pressure difference between the liquid desiccant and the air. The vapor pressure of air was decreased with the increase of the inlet air temperature, which made the mass transfer driving force drop. The experiment results also showed that the heat transfer value increased with the increase of the inlet air temperature. The molecular heat movement theory could be utilized to explain this phenomenon, which the higher the inlet air temperature, the quicker the motion of the molecules. These two parameters would both be increased by the increase of desiccant solution mass flow rate. With the increase in the liquid flow rate, the molecular driving force increase would lead ultimately. The experiment results also proved the relationship between the packing's surface area and the packing's dehumidification performance. The larger the surface area, the better the packing{174}s dehumidification performance. From this experiment, the regular packing had the best dehumidification performance which may because of its regular arrangement. The results may help the engineers choose materials in air-conditioning area.

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