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科技视界
Science &Technology Vision
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委托协议Science &Technology Vision 科技视
托业满分界0Introduction Air source heat pump systems are ud for heating and cooling buildings all year around.They are energy efficient ,compact and have low installation cost.The fin -tube heat exchanger has been widely ud as condenr and evaporator in the heat pump system.When moist air flows across cold heat exchanger surfaces who temperatures are lower than the freezing temperature ,condensation and frost formation easy occur on the heat exchanger surfaces.The frost layer increas the heat transfer resistance between the heat exchanger and air ,further ,degrades the performance of the heat exchanger and even results in the shutdown of the heat pump.Therefore ,exploring frosting behaviors of a fin -tube heat exchanger are focud on by rearchers worldwide.The frost accumulation on the surface of evaporator was a complex unsteady heat and mass transfer process.V
萌发菌arious studies had been conducted experimentally and numerically on frost formation.An experimental investigation was undertaken to characterize the effect of inlet air temperature ,inlet air humidity ,air velocity and cooling surface temperature on the frost growth by Lee [1].The experimental result showed with higher air temperatures ,the frost layer incread in mass amount and density ,while decreasing in thickness.However ,Lee [2]put out the higher air temperatures lead to faster frost growth through experimentally investigating frost formation and growth in a spirally -coiled circular fin -tube heat exchanger.Seker et al.[3]got the same result that frost growth faster with air temperature increa.Yan [4]showed the effects of temperature and relative humidity of air ,flow rate of air ,refrigerant temperature ,fin pitch ,and row number on heat transfer performance.Ye [5]defined the value of the air -side heat transfer coefficient at the maximum mass transfer rate as the critical air -side heat transfer coefficient.The frost growth was significantly retarded when the heat exchanger was operated under conditions that avoided the critical air -side heat transfer coefficient.In order to protect the heat pump from the harm of frost formation ,the effects of different inlet air temperature ,relative humidity and air velocity on evaporator cooling capacity ,air pressure drop and total heat transfer coefficient during frosting were studied.The performance of the finned tube heat exchanger under frosting process was experimentally studied with inlet air temperature 0~10℃、relative humidity 80%~90%and face velocity 2~2.5m /s.The prent study predicted and ve
rified the total heat transfer rates ,the airside pressure drop and the heat transfer coefficient by applying the a news model that considered the reduction of face velocity and the incread air flow rates through each ction due to frost formation.1Experimental system 1.1Experimental methods and instruments The experimental system consisted of four parts ,including the air duct system ,refrigeration cycle system ,data acquisition system and measurement system.The schematic diagram of the experimental system was shown in Fig.1.There were two refrigeration cycle circuits in the experimental system ,which was compod of inverter compressor ,evaporator ,thermal expansion valve and air -cooled condenr.One of refrigeration cycle circuits provided cold energy for the test heat exchanger.Another circuit cooperated with electric heater and humidifier to adjust airside inlet parameter.The refrigerant flow rate that was located between test evaporator and condensate was measured by a Coriolis -type mass flow meter with an accuracy of ±0.3%of reading.The inlet and outlet temperatures of the refrigerant ,and the inlet and outlet (dry -bulb and wet -bulb )temperatures of air were measured by pre -calibrated RTDs (Pt -1000)which have an accuracy of 0.2℃.The pressure difference before and after the heat exchanger was measured by the differential pressure transducer with an accuracy of ±0.23%of reading.The air flow rate was controlled by a frequency conversion fan ,and the airflow rate was measured by the
Experimental study on the frost characteristics of fin tube heat exchanger
越吃越饿
建队日手抄报Ma Teng-fei ZHANG Di -di LIU Yu-qing TIAN Xiao-liang*(Institute of Energy Engineering,Qingdao University,308Ningxia Road,Qingdao 266071,China)
【Abstract 】The heat and mass transfer characteristics under frosting on surface of heat exchanger were experimentally investigated in different conditions of air temperature ,relative humidity ,and face velocity.The heat transfer and heat transfer coefficient decread faster with the high relative humidity ,low air temperature and initial face velocity.The air pressure drop ro faster with the high relative humidity and low air velocity.【Key words 】Heat and mass transfer ;Mathematical modeling ;Pha transition
中图分类号:TK172文献标识码:A 文章编号:2095-2457
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