Research On Heat And Moisture Transfer And Energy Recovery Of Membrane-based Enthalpy Heat Exchanger

Abstract:With the improvement of request to indoor air quality and comfortable indoor environment, the increasing fresh air usually lead to high energy consumption in air-conditioning. Although the application of air heat recovery technology can ease the contradictory of fresh air quality and the increasing energy consumption, but the technical weaknesses of low heat transfer efficiency and large resistance loss for traditional air heat exchanger restrict its development and application. Therefore, the development of air heat exchanger with low resistance and high efficiency has become an urgent demand of the moment.A new type of membrane based enthalpy heat exchanger was designed and simulated by the method of numerical simulation, and the feasibility and effectiveness in subway environmental control system was been analyzed. During the studying, distribution of the heat exchange channel internel velocity field, temperature field and vapor mass fraction filed, and main structural factors and external factors which influent heat and moisture transfer properties are compared and analyzed. Establish a theoretical model of energy recovery for membrane based enthalpy heat exchanger and put forward an energy efficiency evaluation which is relative benefit ratio. Through making membrane based enthalpy heat exchanger introduced into the energy saving area of subway environmental control system, and it is been calculated and analyzed of energy saving effects for typical subway environmental control system with the heat recovery application in different thermal partitions.The results show that the heat transfer efficiency of membrane based enthalpy heat exchanger decrease with different degrees with the increase of cross flow point of view, film thickness or channel height increase, while aspect ratio’s increasing was able to significantly enhance the heat and moisture transfer performance. For a given exchanger, the larger the air volume, the smaller the heat transfer efficiency and the greater the resistance loss and the lower the efficiency coefficient. With the difference between indoor and outdoor temperature and humidity increases, the heat transfer efficiency tended to increase, but the increase is’t exceed2%, which indicate the the new type membrane based enthalpy heat exchanger has stable capability of strong heat and moisture transfer. It is unfavorable that heat recovery unit applied to subway environment control system with large fan total pressure. When the energy efficiency of air conditioning is low, using heat recovery unit can recover more heat, while having greater energy saving potential. Enthalpy efficiency directly affects the heat recovery capacity of the heat exchanger, and large enthalpy efficiency cause significant heat recovery performance. The resulets of this paper provides theoretical basis for further optimization and widely engineering applications of membrane based enthalpy heat exchanger.