A Study On Performance Of Counter-flow Hollow Fiber Membrane Modules Used For Humidity Control

With the continuous improvement of people’s comfort requirement,humidity control has become an important part of the heating,ventilation and air conditioning system.The indoor air quality will reduce at the too high or too low air humidity environment,and then affect people’s living and production level.In addition,indoor greenhouse gas emissions and energy shortages increase the energy consumption of air-conditioning systems,dehumidification energy consumption accounts for about 20% of air conditioning energy consumption,it is urgent to reduce the energy consumption of dehumidification.Therefore,it is of great significance to adopt appropriate air conditioning methods to improve human comfort and reduce energy consumption.Among many humidity control methods,membrane-based liquid desiccant air dehumidification has attracted the attention of researchers due to its advantages of low energy consumption,environmental protection and performance.This chapter studied the hollow fiber membrane module under the condition of air and solution flow counter current,the experimental test and numerical simulation analysis of hollow fiber membrane module under humidification and dehumidification modes were carried out respectively.The main contents of this paper are as follows:Firstly,a counter flow hollow fiber membrane humidification module was assembled with polypropylene(PP)membrane material,and air humidification experiments were carried out in the laboratory to explore the effects of different air and solution inlet flow rates on air outlet temperature and humidity and humidification solution outlet temperature.The experimental results show that the counter flow hollow fiber membrane module has higher humidification capacity and humidification efficiency under the conditions of low air flow and high humidification solution flow,,the maximum humidification capacity can reach 0.0863kg/h.Secondly,the influence of membrane material porosity on the module humidification performance was studied,and the heat and mass transfer mechanism in the module was analyzed.By establishing the numerical model of the module,the distribution of temperature and humidity flow field under different porosity was obtained.The simulation results show that when the porosity changes from 0.35 to 0.8,the humidification capacity and humidification efficiency of the membrane module increase with the increase of porosity.When the porosity is greater than 0.8,the increase of porosity has little effect on the humidification performance of the membrane module.Considering that the increase of porosity will reduce the support strength of the membrane material,it is suggested to design the porosity of the membrane material between 0.65 and 0.8.Then,through the analysis of Sherwood number and Nusselt number,the correlation between porosity and heat and mass transfer coefficient was fitted,which laid a theoretical foundation for the design of membrane materials for membrane-based liquid humidity control module.During the dehumidification process of adiabatic countercurrent hollow fiber membrane module,the latent heat of condensation will be released,resulting in the temperature rise of liquid desiccant,thus reducing the mass transfer driving force of the module.To avoid this,this paper proposed a kind of internal cooling counter flow hollow fiber membrane dehumidification module,a cooling water device was introduced to limit the temperature rise of liquid desiccant.The mathematical models of the adiabatic and internal cooling reverse flow hollow fiber membrane dehumidification components were established respectively.And the distribution law of the internal fluid flow field of the two devices is obtained.This paper discussed influence of inlet parameters such as air flow,air moisture content,air temperature,liquid desiccant flow rate,liquid desiccant temperature and liquid desiccant concentration on dehumidification and dehumidification efficiency of the two devices.The results show that the dehumidification capacity and dehumidification efficiency of the two devices increase with the decrease of air inlet moisture content,the decrease of liquid desiccant temperature and the increase of liquid desiccant flow,the increase of liquid desiccant concentration.The dehumidification capacity and dehumidification efficiency of the two devices increase with the increase of air flow.And the dehumidification effect of the internal cooling dehumidification membrane module is better than that of the adiabatic dehumidification membrane module,under the same working condition,the dehumidification capacity of inner cooling dehumidification membrane module can be increased by 0.031 kg / h.The maximum dehumidification efficiency can be increased by 18.3%.