| Indirect evaporative cooling technology is a residual cooling recovery technology that absorbs the heat of the outdoor fresh air(primary air)through the heat and mass exchange between the indoor exhaust air(secondary air)and water.It can significantly reduce the fresh air treatment energy consumption of the air conditioning system.However,in the process of the practical application,because the wall surface of the indirect evaporative cooling heat exchanger is hydrophobic,the gas-liquid contact area is small,which reduces the effect of heat and mass transfer between secondary air and water film;At present,the research on water vapor condensation heat transfer in the primary air mostly focuses on the impact of the latent heat release on the performance of the heat exchanger,but there are few studies on strengthening the heat and mass transfer performance of the indirect evaporative cooling heat exchanger.Therefore,this paper takes the indirect evaporative cooling heat exchanger as the research object,and uses the methods of the theoretical analysis,experimental research and numerical simulation to carry out the following research on strengthening its heat and mass transfer performance.(1)Based on the law of conservation of energy and mass,a heat and mass transfer model of the indirect evaporative cooling heat exchanger with parallel flow(cocurrent,countercurrent)and cross current considering the water film coverage of the secondary channel and the primary air condensation is established.The effects of the air flow mode,the water film coverage and the primary air condensation on the heat flux of the heat exchanger are analyzed.It is found that the heat flux of countercurrent and cross flow heat exchangers is large.The heat and mass transfer effect of the indirect evaporative cooling heat exchanger can be enhanced by increasing the water film coverage of the secondary channel and promoting the condensation heat transfer of water vapor in the primary air.(2)A counter current porous foam copper indirect evaporative cooling heat exchanger is designed.The effects of the primary and secondary air temperature and moisture content on the heat flux and wet bulb efficiency are analyzed.The results show that the indirect evaporative cooling heat exchanger with porous foam copper can significantly improve the water film coverage of the secondary channel.Under different conditions,the heat flux of the indirect evaporative cooling heat exchanger with porous foam copper is between 48.6 W and 151.7 W,and the wet bulb efficiency is between41.4%and 73.2%.Compared with the traditional indirect evaporative cooling heat exchanger,the heat flux of the indirect evaporative cooling heat exchanger with porous foam copper is increased by 55.6%.(3)An indirect evaporative cooling-dehumidification integrated test system is established.The effects of the primary and secondary air temperature and moisture content,the air flow rate and the solution concentration on the system performance are studied.It is found that the integrated operation mode can make the water vapor in the primary air change continuously and stably,and strengthen the heat and mass transfer performance of the indirect evaporative cooling heat exchanger.Under the test conditions,the dehumidification capacity of the integrated operation mode is between0.92 g/s and 1.58 g/s,and the heat flux density is between 1.08 W/m~2 and 2.42 W/m~2.Compared with the traditional indirect evaporative cooling heat exchanger,the dehumidification capacity is increased by 197.1%and the heat flux density is increased by 37.9%.(4)Based on the second law of thermodynamics,the utilization and loss of the useful energy in the system under integrated and traditional operation modes are compared and studied by exergy analysis method.The results show that the loss rate of the integrated operation mode is between 16.3–27.5%,and the efficiency ratio is between 2.01–4.98.Compared with the traditional operation mode,the efficiency ratio can be increased by 23.5%.At the same time,the economic and environmental analysis results show that the integrated operation mode has good economic and environmental benefits.(5)Based on the law of energy and mass conservation,the heat and mass transfer model of the indirect evaporative cooling-dehumidification integrated heat exchanger is established,and the accuracy of the mathematical model is verified by experimental data.The effects of channel gap and length on pressure drop,total energy consumption,heat flux and energy efficiency ratio are analyzed,the optimal structural parameters of the heat exchanger are obtained.The heat and mass transfer performance of the optimized heat exchanger is predicted.The simulation results show that the channel gap of the heat exchanger has a great influence on the resistance.When the channel gap and length are 5 mm and 600 mm,respectively,the energy efficiency ratio of the system reaches the maximum.The performance prediction results show that the dehumidification efficiency of the indirect evaporative cooling-dehumidification integrated heat exchanger is between 62.5%and 76%,and the wet bulb efficiency is between 21%and 60%. |
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