Design And Performance Study Of The Small Diameter Tube-and-fin Heat Exchanger For Automotive Heat Pump System

In order to solve the shortage of traditional resources and the problem of urbanenvironment pollution, developing new energy vehicles became an important strategyin China. In support of relative national policies, the domestic vehicle companiescarried out a series of research and production of new energy vehicles. Because newenergy vehicles have no traditional engine and there is not enough waste heat, now thenew energy vehicles commonly use PTC heaters for heating in winter. But the PTCheater can consume50%of total energy in new energy vehicles, and severely reducethe continued driving mileage of new energy vehicles. The idea of heat pump systemused in new energy vehicles attracted the attention of researchers and vehiclemanufacturers all the world. But the Al parallel flow heat exchangers commonly usedin traditional fuel vehicles cannot deal with the problem of condensate and frost, soparallel flow heat exchangers are difficult to use in vehicle heat pump system. In thisbackground, this paper carried out the study of small diameter tube-and-fin heatexchanger used in vehicle heat pump system.First, according to the collection and analysis of relevant literature and patents,two different structure of heat pump system for new energy vehicle are chosen for thisstudy. Then small diameter tube-and-fin heat exchanger of different dimensions andstructure are designed and manufactured as the outer heat exchanger of heat pumpsystem. In order to optimize the design of small diameter tube-and-fin heat exchanger,the simulation of heat exchanger and heat pump system is carried out. Follow-upexperiment test results show that, the performances of sample#4are±5%differentfrom the parallel flow heat exchanger, in the condition of the same frontal area andweight only0.23kg more.Second, the frost and defrost test was carried out in order to deal with theproblem of defrost in new energy vehicle heat pump system. The result shows that,the air side pressure drop of the parallel flow heat exchanger raises during the frostingand defrosting process cycled several times, whereas the heat transfer capacitydecreases. For the fin-and-tube heat exchanger, when the frosting process and thedefrosting cycled, the air side pressure drop and heat transfer capacity could return tothe initial value after defrost.Third, test rigs of heat pump system are built up, and the performance of heat pump system with small diameter tube-and-fin heat exchanger are tested undercooling and heating test conditions. Results showed that, in cooling condition, thecooling capacity is about2500~3500W, and COP is about2.5~3.7; in heatingcondition, the heating capacity is about1500~3000W, and COP is about2.5~4.0.