Numerical Simulation Of Gas-liquid Flow, Heat And Mass Transfer Process In Super-large Cooling Tower

As a cooling equipment of high efficiency, cooling tower is broadly used in industry and agriculture, especially in thermodynamic system of power stations and unclear plants. With the development of power industry and capacity of unit growing up in recent years, the requirement for cooling efficiency of cooling tower is increased gradually, and the research of cooling tower have developed and deepened. Based on National Nuclear Long-and-medium Term Development Planning (2011-2020), nuclear power construction is developing orderly, steadily and smoothly in premise of assuring the safety. The third-generation technology AP1000has been adopted by many nuclear power projects for its advantage of great capacity, advanced technology and high security. Cooling tower is one of the important components of AP1000and its thermal performance would directly influence steady operation of the unclear power station. The construction dimension of the cooling tower in AP1000unit is very large and much higher than the past cooling tower. In the super large cooling tower, the gas-liquid flow, heat transfer and mass transfer process are complex and have gone beyond the available domestic standard specifications, so the conventional one-dimensional and two-dimensional calculation method can not accurately calculate its performance. Moreover, model test can not satisfy the similar conditions in case of two-phase coupling and its cost is too high. In order to study the gas-liquid flow, heat transfer and mass transfer process and various influence factors, it is very necessary to develop a three-dimensional numerical computation model for thermal performance calculation of super large cooling tower.The three-dimensional numerical computation model for super large cooling tower was established here. The gas-liquid flow, heat transfer and mass transfer process were analyzed numerically under various conditions in super large cooling tower. The influences on thermal performance of cooling tower by the factors like fill distribution, water distribution, spray water rate, inlet water temperature and environment humidity were investigated. Further more, the effect of wind-control schemes under crosswind conditions were analyzed. The influence on flow field by the shape of tower outlet, and vapor diffusion around tower outlet were studied. These research results may provide forceful support to optimization design and scientific cooling performance evaluation of super large cooling tower. The major research works are as follow:(1) Establishment of the three-dimensional numerical computation model for cooling tower. Considering influence on heat and mass transfer and resistance characteristics by different fill distributions, the relationships of filler property by actual measurement was introduced, Lef factor was corrected, the models of gas-liquid flow, heat transfer and mass transfer in fill zone, spray zone and rain zone were established. Based on the Fluent software, a three-dimensional numerical simulation platform composed by lots of user defined functions (UDF) was developed to study the thermal performance in super large cooling tower.(2) Validation analysis to the three-dimensional numerical computation model. Two operating cooling towers were studied by this three-dimensional mathematical model. Through comparing with field experiment and simulated results, the accuracy and reliability of the above three-dimensional numerical computation model was tested and verified. It was found that the above3D numerical computation model can meet the requirement of the performance computation in super large cooling tower.(3) Research of influence on performance of cooling tower by different structure factors and operation parameters. Based on velocity, temperature and humidity distributions under different conditions, the influences of different fill distribution and water distribution were analyzed to select optimum distribution scheme. Moreover, the influences on tower performance by the factors like spray water rate, inlet water temperature and environment humidity were investigated.(4) Research of wind-control schemes under crosswind conditions. Flow distribution under crosswind condition was analyzed. The effects of crosswind-control schemes were analyzed and suggestions for crosswind-control schemes selecting under different weather conditions were proposed.(5) Research of the structure of tower outlet. The flow field with different shape of tower outlet, outlet area and diffusion angle were studied. The crosswind-control abilities of different tower outlet structure were analyzed, and then the selection scheme of tower outlet structure was obtained.(6) Research of vapor diffusion around tower outlet. Combining with the actual measurement data, the vapor diffusion and temperature diffusion in single tower and twin towers conditions were investigated. The vapor diffusion property under crosswind condition was analyzed, which may provide support to environmental affection appraisal and crosswind-control schemes selecting of the tower.Based on establishing and applying a three-dimensional numerical computation model for cooling tower, the influences of various cooling tower structures and operation parameters on cooling performance were analyzed. These conclusions may offer forceful support to optimization design, and also provide a good scientific cooling performance evaluation method of super large cooling tower.