Study On Enhanced Heat Transfer Performance And Field Measurement Of The New Evaporative Condenser

With the development of economy,people have more demands for the subway in the process of traveling.However,the subway station is mostly located in the downtown area of the city,the layout of cooling towers on the ground affects the urban landscape,and the noise generated during its operation affects the life of the surrounding residents.Thus the application of air conditioning system with a water-cooled condenser is limited.The air conditioning system with an evaporative condenser eliminates the load of the metro station by means of sensible heat exchange and latent heat exchange,which improves the heat exchange capacity and replaces the cooling tower in the water-cooled system.However,most of the air conditioning system with an evaporative condenser in the practical projects adopts the method of circulating spray water.After the heat exchange between the spray water and the refrigerant,the spray water is recycled without cooling.The temperature of the spry water gradually increases with the operation of the system which resulting in a decrease in the heat exchange efficiency of the refrigerant.Based on the above problems,a new evaporative condenser with an annular elliptic finned tube heat exchanger was designed in this paper.The new evaporative condenser included a round inner tube and elliptical outer tube.The refrigerant flows between the round inner tube and the elliptic outer tube,and it simultaneously exchanges heat with the cooling water in the inner tube,the spray water,and the cooling air flowing past the outer tube.The new annular elliptic finned tube heat exchanger leaded to an increase in its heat transfer performance.The experimental system of the annular elliptic finned tube heat exchanger was set up in this paper,the system could handle the inlet air of the evaporative condenser,and it provided the guidance for the study of the heat and mass transfer performance of the annular elliptic finned tube heat exchanger under different conditions.The measurement and analysis of the experimental data will be studied in the follow-up research.According to the theoretical analysis of the heat and mass transfer process of the evaporative condenser,the affecting parameters of the heat and mass transfer process were determined.This paper built up the simulation model of the annular elliptic finned tube heat exchanger and the round finned tube heat exchanger,and the models were based on the structure of the field measurement system.The parameters(such as pressure drop outside the tube,the heat exchange capacity and the heat transfer coefficient)were simulated and compared with the field measured value.The power consumption of the fan in the air conditioning system with the annular elliptic finned tube was 11.18% to 14.65% lower than that of the round finned tube under the conditions that the inlet air temperature was 27 °C and the air flow velocity ranged from 3 m/s to 4 m/s,which proved that the energy-saving performance of the annular elliptic finned tube heat exchanger was higher than that of the round finned tube heat exchanger.The outlet refrigerant temperature of the annular elliptic finned tube was 2.66 °C to 10.21 °C lower than that of the round finned tube when the temperature of the spray water was ranged from 27.5 °C to 33.5 °C and the spray water flow rate was 0.2 kg/s.The refrigerant enthalpy difference of the annular elliptic finned tube increased by 3.91 k J/kg to 15.18 k J/kg compared with the round finned tube.The heat exchange capacity of the annular elliptic finned tube increased by 2.34% to 9.28%,and the heat transfer coefficient of the annular elliptic finned tube was 47.42% higher than that of the round finned tube under the same conditions.In this paper,the field measured data were compared with the simulated value of the annular elliptic finned tube and the round finned tube.The result showed that the heat exchange capacity of the annular elliptic finned tube increased by 2.92% to 4.80% compared with the measured value of the round finned tube when the inlet temperature of the refrigerant was 42 °C and the spray water temperature was in the range of 27.5 °C to 33.5 °C.The heat exchange capacity of the annular elliptic finned tube increased by 4.46% to 10.18% compared with the measured value of the round finned tube when the spray water temperature was 27.5 °C and the inlet temperature of the refrigerant was from 42 °C to 57 °C.Therefore,the annular elliptic finned tube heat exchanger had better heat transfer performance compared with the round finned tube heat exchanger when the spray water temperature and the refrigerant temperature were in a high value,and it had a better application prospect in the practical engineering.