Research On Dynamic Regulation Mechanism Of Packed Liquid Desiccant Dehumidifier

Dehumidification technology has been widely applied in people’s productive lives.To meet requirements for human comfort and indoor air quality,the indoor air relative humidity should be maintained at 30% ～ 60%.To keep the nutrition,shape and other characteristics of food,air with different low humidity ratio is often used to dry food in stages to achieve rapid drying and long-term storage.Therefore,the creation of air with low humidity ratio is crucial.However,considering the dehumidification requirements or air temperature and humidity ratio would vary continuously,making it difficult to obtain stable and reliable air with low humidity ratio,and then leading to long drying time and poor quality of foodstuffs,which would damage the improvement of quality in production life.To obtain stable and reliable air with low humidity ratio,the liquid desiccant dehumidification process needs to be dynamically regulated.Liquid dehumidification,as a type of dehumidification technology,is favored due to its high energy saving potential and operational flexibility.However,the driving heat sources often use renewable heat sources such as solar energy,and the demands of users also change constantly when the system is running,making operating parameters of the system fluctuate greatly and difficult to operate stably.Therefore,this paper conducts a study on the liquid dehumidification,focusing on the dynamic characteristics and regulation mechanisms of the liquid dehumidification.The study is divided into three parts:1)During the dynamic liquid desiccant dehumidification process,the variation law of the air outlet humidity ratio with time,when the inlet parameters suddenly change,was revealed.The experimental setup of the liquid desiccant dehumidifier was designed and built,and the experimental study of dynamic liquid desiccant dehumidification process was carried out,to obtain dynamic characteristics of the dehumidifier when different inlet parameters changed.This reveals the differences and their causes in dynamic characteristics of the dehumidifier when each inlet parameter changes,and determines the regulation strategy in the control of liquid desiccant dehumidification process,indicating the direction for the development of control algorithms in the future.In addition,the change of the air outlet humidity ratio with time in the dynamic liquid desiccant dehumidification process can be described by an exponential function through theoretical derivation,which provides convenience for in-depth analysis of the heat and mass transfer law in the dynamic liquid desiccant dehumidification process.2)A dynamic model of the liquid desiccant dehumidifier was built up.Since the distribution and flow conditions of desiccant and air inside the dehumidifier,as well as the evolution law of local heat and mass transfer coefficients with time are difficult to be obtained,making the physical model difficult to be established.Therefore,this paper uses the time-delayed neural network(TDNN)model,originating from the neural network modeling method of the dehumidification process under steady-state conditions.Due to many factors affecting the liquid desiccant dehumidification process,it makes the model inputs complex and difficult.Therefore in this paper,we changed the determining method of model inputs,and took the already known air outlet humidity ratio to predict its values in the future moment,so as to establish an improved time-delay neural network(i TDNN)model to simplify the model input,and complete the establishment of the dynamic liquid desiccant dehumidification model.3)Dynamic control algorithm for the liquid desiccant dehumidification process was developed.The PID and a novel fuzzy logic control algorithm were used to dynamically control the liquid desiccant dehumidification process,and to explore the feasibility and shortcomings of various control algorithms,respectively.Then we proposed a new dynamic control algorithm to improve the shortcomings of the above algorithms,and verified the feasibility and superiority of the new dynamic control algorithm through control experiments.The research in this paper will provide theoretical support and methodological guidance for the liquid desiccant dehumidifier to achieve accurate control of air humidity ratio,and lay the foundation for intelligent operation of the liquid desiccant dehumidifier at the same time.