| Along the MTR lines are the city's most prosperous regions, the land prices nearby the subway station are more expensive. if the cooling tower is installed on the ground of the MTR station, not only the cost is very high, but also lead to the noise pollution, health problems, and impact the urban landscape. it is urgent need an efficient heat exchanger to alternative the currently used cooling tower, move the cooling tower into the MTR station and solve the problem that there is no place fo installing the cooling tower of the underground building, such as the subway station. This paper developed a new heat exchanger by researching the air parameters of the subway station's exhaust channel, Comparing the heat and mass transfer mechanism of the existing heat exchangers, and optimizing the cooling methods, and making use of the computational fluid dynamics, Engineering Thermodynamics and the heat transfer theory to study heat and mass transfer mechanism and the performance of the heat exchanger.The air parameters of the exhaust channel where the new heat exchanger that we developed is installed in the station, directly determine whether the heat exchanger is high efficiency. Several significant station's air parameter of the Guangzhou Metro has been measured, it is find that moving the cooling tower into the MTR station from the ground is theoretically possible, because the air temperature and the humidity are not significantly higher on new wind operating conditions, some one even develop to the direction that benefit heat exchange, the heat and wet sourse in the exhaust channel has little effect on the air temperature and humidity.A new type of spiral heat exchanger (patent application number: 200910300390.3) was put forward through comparison of the existing indirect evaporative cooler, the secondary flow phenomenon in the spiral heat exchanger and the coiled tube heat exchanger is simulated using CFD, and identified the R/r critical value by comparing the secondary flow at different R/r value and mass flow rate. And found that the secondary flow phenomenon only exists at the entrance of the semi-annulus reentry pipe of the coiled tube heat exchanger, and disappeared rapidly 100～200mm away from the exit of straight tube, but always exists in the spiral heat exchanger, thus leads to the disturbance of the boundary layer always exists, compared to the coiled heat exchanger, the performance of the spiral heat exchanger improved about 40% .Experimental studied the performance of the heat exchangers by fixed spray cooling, spray cooling (fluorescent tubes and coated water-absorbent material), rotary spray cooling, and established the rotary spray cooling is the best cooling method. Compared to the fixed spray cooling and the spray cooling, the rotary spray cooling has improved the heat flux, respectively, 32% and 80%。Initially, coated water-absorbent material on the surface of the heat exchanger can enhance the performance of the heat exchanger, after running a week, the water-absorbent material fouled foamed seriously which lead to the thermal resistance increased and deteriorated the uniformity of the water film,so,coated water-absorbent material weak the performance of the heat exchanger.Because of the uniformity and integrity of the water film has an important impact on the performance of the heat exchanger, in this paper, a novel conception is put forward that rotating spray cooling on both sides of the special heat exchanger to form uniform, complete water film, and developed a new rotating water distribution installation(patent application number: 200910300391.8,200910300388.6) and a new type gas-water atomization(patent application number:200820303833.5),thus constituted a new indirect evaporative cooler(patent application number: 200910300389.0) with the former installations, obtained the required quantity of the nozzle, identified fitting function of the rotate speed that influenced by the frictional resistance, the angle between the spray direction and the direction vertical to the heat exchanger surface, the mass flow rate of the water and the compressed air,analysised the droplets distribution in the air, experimental studied its frictional resistance and the spray angle that influenced by the parameters that the mass flow rate of the spray medium ,the angle between the spray direction and the direction vertical to the heat exchanger surface and the nozzle exit diameter, acquired fitting function of the rotate speed , the spray angle and the leakage coefficient, determined the key parameters of the spray system, to provide the basic data for the research of the heat exchanger.The droplet size has important impact on the air temperature, humidity and the state of the water film, the quantity of the nozzle and the compressed air are determined by the spray angle and the droplet distribution, acquired the initial structures parameters of the nozzle through theoretical calculation, and make use of the CFD to analysis the influence of the ratio between the mass flow rate of the compressed air and the spray water , the nozzle exit diameter on the performance of the nozzle, when the nozzle exit diameter d= 0.6mm, the compressed air mass flow rate of the optimum ratio is 8 m3/h,and its atomization is best, the spray angle is 100°.Set up the heat transfer model of the rotary spray indirect evaporative cooler for the MTR, studied the heat and mass transfer mechanism of the heat exchanger, analysised the heat and mass transfer process between the spray water and the droplet, and the process between the water film and air, obtained the cooled water film temperature by first cooling ,the float rate of the spray water and the best tube length of the Spiral heat exchangers,rasearched the performance with different parameters that the mass flow rate of the spray water and the cooling water, air temperature, humidity and the structural parameters of the heat exchanger. and solved it using Matlab software, acquired the temperature of the cooling water and the water film along the tube, and the air enthalpy, entropy, resistance and the optimum tube length of the heat exchanger which is short for Lopt, and found that the Lopt is only concerned with the spiral pitch and the diameter of the heat exchanger, the air speed and spray water exist the best values.The influence on the performance of the tube diameter, mass flow rate of the spray water, air velocity, air temperature and humidity is studied by orthogonal test. Experimentally researched the performance and found that the heat flux is maximum when the air velocity is 3m/s, the volume flow rate of the compressed air and the spray water are, respectively, 8 m3/h and 20L/h; when two heat exchangers operating in parallel, the difference between the heat flux of one exchanger and a single one running independent is very small, and the compressed air volume will be halved; if the surface has oil ,the heat flux will reduce by 20%.Through simple economic analysis of the rotary spray indirect evaporative cooler and the closed cooling tower that current commonly used, found that without considering the land costs of the cooling tower that installed on the ground of MTR station, the costs of the heat exchanger nearly the same when the tube length reach to the Lopt value, and operating in parallel, and come true the dream that moving the cooling tower into the station from the ground floor, and solved the problem that there is no place for installing the cooling tower in the MTR station, is of great economic significance.
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