Study of dynamic performance of liquid desiccant dehumidification process

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Study of dynamic performance of liquid desiccant dehumidification process

 

Author: Lin, Jing
Title: Study of dynamic performance of liquid desiccant dehumidification process
Degree: M.Eng.
Year: 2015
Subject: Air conditioning -- Control -- Mathematical models.
Humidity -- Control -- Mathematical models.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xiv, 79 pages : illustrations (some color)
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2826151
URI: http://theses.lib.polyu.edu.hk/handle/200/8239
Abstract: Liquid desiccant dehumidification, as an alternative to conventional dehumidification, has attracted increasing interests in recent years. It can achieve dehumidification purpose by reducing the water vapor content of moist air with liquid desiccants, and there is no need to reheat supply air. Besides, low grade thermal energy can be utilized in this system. Therefore, it can improve the indoor thermal comfort, indoor air quality as well as energy saving. However, the potential drawbacks in big dimension and unstable operation hinder the widespread applications of liquid desiccant air conditioning system. In order to solve this problem, the dynamic performance of liquid desiccant dehumidification process is studied in the research.The main works of this research are shown as follows. Firstly, based on the dynamic mathematical model reported by Wang et.al (2014), a system simulation about the dynamic dehumidification process has been developed with FORTRAN programing. The model has been validated by experiments results. Secondly, a dynamic liquid desiccant experimental test rig has been built up and the dynamic experiments results have been obtained. Thirdly, the steady-state and dynamic characteristics of dehumidification process have been predicted based on the validated model. Finally, a series of experimental results under changing operation condition are obtained and discussed.The steady-state simulation results show that the outlet air humidity and temperature is affected by inlet parameters such as air humidity ratio, air flow rate, solution temperature as well as solution concentration. From the case study of dynamic performance simulation, it seems that the transient time before achieving steady state for the air humidity ratio and air temperature is about 250 seconds.The experimental results show that inlet air temperature is major influent factor of outlet air temperature, and the inlet air humidity ratio has significant effect on outlet air humidity ratio. Both of the time constant of outlet air humidity ratio and outlet air temperature are about 30 seconds, which can be used for the design of controller. Results also shows that dynamic dehumidification process can achieve steady state faster under high temperature and humidity ratio inlet condition. A negative step change of inlet air humidity ratio and inlet solution flow rate lead to the outlet air temperature, air humidity ratio and outlet solution temperature rapid and gradual decrease. Besides, when the inlet air temperature and inlet solution temperature gradual change, the outlet air temperature,air humidity ratio and outlet solution temperature change accordingly. The above analysis results can be used for optimal design of liquid desiccant based hybrid system.

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