Research On Heat And Moisture Transfer Enhancement Of Desiccant Coated Microchannel Heat Exchanger

The condensation and dehumidification process of traditional steam compression air conditioning will reduce the air conditioning performance coefficient.The desiccant cooling system based on a desiccant coated heat exchanger can separate the sensible heat load and latent heat load in hot and humid air to solve the above shortcomings.To realize the enhancement of heat and moisture transfer of the desiccant coated heat exchanger,the heat and moisture transfer performance of desiccant coated heat exchanger was studied from three aspects:the preparation of composite desiccant,the size optimization of microchannel structure,and the application of evaporative cooling.The main research contents and conclusions of this paper are as follows:(1)Experiments determined the best spraying and curing conditions to prepare dehumidifying heat exchanger by electrostatic spraying.The surface morphology,adsorption kinetics,and water vapor adsorption isotherm of the composite desiccant were studied.The results show that the composite desiccant’s thermal conductivity is almost 1.6 times that of silica gel.The density of the composite desiccant is 25.3%higher than that of pure activated carbon.The correlation coefficients of desiccant adsorption curves based on the LDF model and D-A equation fitting were all above 0.98.When the relative humidity is 60%,the composite desiccant’s water adsorption capacity reaches 1.1 kg/kg,which is 0.9 kg/kg higher than that of the pure activated carbon.(2)The heat and moisture transfer coefficients increase with the increase of airflow velocity.The smaller the fin spacing and the flat tube spacing,the larger the heat and moisture transfer coefficient.The thicker the desiccant coating,the larger the moisture transfer coefficient and the smaller the heat transfer coefficient.The lower the cooling water temperature,the faster the air flow rate,the better the dehumidification performance.(3)A mathematical model for transient heat and moisture transport of microchannel dehumidification heat exchanger is proposed.This paper built a dehumidification cooling system based on a desiccant coated microchannel heat exchanger to verify the mathematical model,and the error of verification results was less than 15%.Large fin spacing and flat tube spacing are beneficial to dehumidification.The system COP_e is about 2.0,and the highest dehumidification capacity is 1.57 kg/h.(4)This paper built an evaporative cooling air conditioning system with a desiccant coated microchannel heat exchanger.Under the typical weather conditions of Kunming in spring and summer,the theory of evaporative refrigeration efficiency can reach more than 86%.The average dehumidification capacity and thermal performance coefficient of microchannel dehumidification heat exchanger under mode III are 4.98 g/kg and 1.02,which are 2.34 g/kg and 0.2 higher than that of mode II,respectively.In all-day operation,the air-conditioning system’s maximum cooling capacity and power performance coefficient are 1.53 k W and 2.68.Dehumidification heat exchanger absorbs water vapor in wet air,improves the cooling capacity of the system,and reduces the humidity of supply air.