| When the air source heat pump is heating in low temperature and high humidity areas,serious frosting often occurs on the surface of the finned tube heat exchanger,which not only leads to the decline of the heat exchange performance of the finned tube heat exchanger but also the unit will consume additional energy to defrost,to increase the operational energy consumption of the unit.Therefore,it is of great theoretical and practical significance to study the frosting and to defrost on the surface of the finned tube heat exchanger.Firstly,the formation process of droplets on the fin surface is analyzed.A heat and mass exchange model based on the droplet impact theory is established by combining various interphase forces as the source term.The enthalpy porosity method is used to track the solidliquid film interface.The enthalpy difference experimental results verify the accuracy of the numerical model.The calculation model considering the formation of droplets is determined through comparative calculation,which can more comprehensively and accurately calculate the frost growth process.The effects of mass transfer rate,air temperature,humidity,inlet velocity,and fin surface temperature on the average frost thickness and density are analyzed.The results show that there is a positive correlation between the growth of the frost layer and the rate of water vapor impacting the fin surface;Under the working conditions of this paper,the thickness of the frost layer is the highest when the temperature range of wet air is 1 ℃ ～3 ℃.The frosting density is the same when the wet air temperature exceeds 0 ℃.The frosting density is the same.Under the action of head-on wind speed,the changing trend of frost layer density and frost layer thickness is opposite.Then,in order to analyze the cycle of the whole process of frosting and defrosting on the surface of the air source heat pump,the unsteady defrosting model of the finned tube heat exchanger is established,and the accuracy of the defrosting model is verified by the cold bench defrosting experiment in the literature.The average thickness and density of the frost layer obtained in the frost layer growth stage are substituted into the defrosting calculation,the frost layer distribution in each defrosting stage is studied,the relationship between the frost layer melting rate and various factors is revealed,and the time consumed in the whole process of frosting and defrosting is summarized.The results show that when adjusting the indoor hot and humid environment in winter,the energy-saving control should be carried out by increasing the outdoor unit’s wind speed and the fins’ surface temperature.Finally,high-speed railway stations in typical areas with high humidity and cold winter are investigated.A scheme of frost suppression machine room is proposed for substations and buildings requiring heating and refrigeration.Based on the theoretical frosting environmental parameter curve in the literature,the ambient temperature around the fins of the air source heat pump under investigation is numerically calculated.The most appropriate structural parameters of the frost suppression machine room are obtained.The position of the airflow vortex in the machine room is obtained,which can be used as a sign to judge the temperature uniformity of the machine room.Then,the hot air parameters required by many standard units in engineering are studied,and the difference in heat distribution between a double row and a single row is analyzed.The results show that: Taking the central axis of the machine room as the boundary,the larger the total air volume on the right will reduce the heat required by the frost suppression machine room;When arranging the units,the arrangement mode that the number of columns is greater than the number of rows can be adopted to reduce the energy consumption required by the frost suppression machine room. |
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