Experimental Study And Numerical Simulation On Heat And Mass Transfer Performance Of Elliptic Finned Tube Evaporative Condenser

Energy plays a very important role in the development of national economy.With the improvement of people’s living standards,people’s production and daily life need to consume a lot of energy,and the air conditioning field occupies about 50%to 60%of the proportion,so it is necessary to pay enough attention to the energy saving problem of air conditioning.In air conditioning refrigeration system,condenser is one of the important equipment of refrigeration system,the energy consumption in the total energy consumption of refrigeration system is larger,condenser is mainly divided into air cooling condenser,water cooling condenser and evaporative condenser,evaporative condenser using water film evaporation to transfer heat,can greatly save energy.This paper studies an annular elliptic finned tube evaporative condenser.This heat exchanger uses the oval outer tube embeds with the circular inner tube,and the refrigerant flows between the outer tube and the inner tube.Meanwhile,the oval outer tube is equipped with corrugated fin,which can effectively increase the heat transfer area and enhance the heat transfer performance.According to the structural characteristics of the annular elliptic finned tube heat exchanger,the experimental test system of the annular elliptic finned tube evaporative condenser is set up,and according to the actual size of the heat exchanger,the physical model of the heat exchanger is established by Ansys ICEM software.Using the heat exchanger experimental test system,choosing the control variable method,study and analyze the influence of faced air velocity,inlet air wet bulb temperature,circulating water temperature and cooling water flow rate on the heat exchanger,and get the best operating parameters of the heat exchanger in the"evaporative condensation"mode and"water condensation"modes.By numerical simulation of the heat transfer and flow characteristics inside and outside the heat exchanger tube using Ansys Fluent software,the results were verified with the experimental data in good agreement with the maximum relative error of 8%.The specific conclusions are drawn are as follows:(1)In the"evaporative condensation"mode,the increase of faced air velocity leads to the rapid increase of the external pressure loss of the heat exchanger.When the oncoming wind speed increases from 2.5 m/s to 3.7 m/s,the pressure drop of the air outside the heat exchanger increases by 6.07 times,the external heat flow density of the heat exchanger increases by 22.3%,the mass transfer coefficient of the water film outside the tube increases by 19.1%,the maximum value is 0.187 kg/(m~2·s),and when the wind speed is less than 3.1m/s,the external heat flow density increases rapidly by 16.8%,and when the wind speed is greater than 3.1 m/s,the growth trend is flat.So 3.1 m/s is the best faced air velocity.Through numerical simulation under the same working conditions,the maximum relative error between the experimental value and the simulated value is 4%.(2)According to the cold drying climate characteristics of low in Xi’an,in the mode of"evaporative condensation",as the inlet air wet bulb temperature increases from 9.6°C to11.6°C,the external heat flow density of the heat exchanger rapidly decreases by 92.2%.It can be seen that the increase of the wet ball temperature of the inlet air will sharply deteriorate the heat transfer performance of the heat exchanger.Through numerical simulation under the same working conditions,the maximum relative error between the experimental value and the simulated value is 4%.(3)In the"water condensation"modes,the temperature of circulating water temperature increases from 17°C to 33°C,the heat flow density in the heat exchanger is reduced by47.8%;the cooling water flow increases from 0.066 m~3/h to 0.162 m~3/h,the heat flow density in the heat exchanger increases by 83.4%.Reducing the temperature of cooling water and increasing the flow rate of cooling water can strengthen the heat transfer performance of the heat exchanger.Under the same working condition,the maximum relative error between the experimental value and the simulated value are 8%and 5%.The theoretical analysis of heat and mass transfer and the numerical simulation and experimental study of the evaporative condenser are helpful to realize the energy saving and consumption reduction of the evaporative condensing air conditioning system,and provide a theoretical basis for the engineering application of the evaporative condenser.