Thermo-flow Characteristic Research On Indirect Air-cooled Heat Exchangers And Dry Cooling Towers In Power Plants

With the increasing demand to energy utilization, it is essential to build an economic, efficient and stable energy supply system for the development of national economy. The large coal-fired power units are dominant in the whole power and energy supply. In recent years, indirect air coolin system has been widely used in power plants in north China with distinct superiority in water conservation, as well as high energy efficiency.Several factors, namely the ambient temperature, air flow rate and direction, the size and scale of air cooling tower, finned tube bundles, have significant influences on the characteristics of air flow and heat dissipation performance. The introduction of four incorporate towers, including dry cooling tower, desulfidation tower and exhaust flue gas chimney and dust collecting equipment, increases the complexity of interior structure of air cooling tower in further, as well as the air flow field and temperature field. It is of great significance for enhancing the heat transfer, safe and economic operation, to specify the flow characteristics inside the indirect air cooling tower and flow field optimization.Based on the hot state wind tunnel experiment, the heat transfer performance of four slotted tube bundles with different parameters were tested to get the dimensionless correlation between air side Nusselt number, Nu, friction factor of fins, f, with air flow Reynold number, Re. The precise physical models were established to find the optimal design of finned tube bundles. Based on the results obtained on fin bundle level, the ambient air conditions, typically the air velocity and air direction were studied to quantify their effects on the flow field and heat dissipation features inside air cooling tower by means of numerical simulation. The influences of ambient air velocity, equipments in tower were investigated on the flow heat transfer characteristics for four incorporated towers. The gas concentration field is analysed to guarantee flue gas corrosion.To diminish the adverse affect of environmental natural wind on air cooling tower, air flow guiding devices were introduced and installed inside and outside air cooling tower. Numerical simulation was introduced to evaluate the effects of flow guiding devices under different wind directions and velocities. Different styles were studied and compared to reveal their influences on the air flow and heat transfer performances of air cooling tower. 2 Sideward windbreaks are recommended to modify the air flow field, inner guideance also help to improve the inner air flow if possible. The investigations may take a theoretical basis for the optimization of air flow field inside dry cooling tower.Cooling columns are taken as counterflow heat exchangers. Two irreversible heat transfer processes including the heat transfer process between circulating water and cooling air and the mixing process of circulating water from different sectors, were taken into account by analyzing the heat transfer process of heat exchangers in indirect dry-cooling cooling system. A typical indirect dry-cooling tower was optimized based on the entransy dissipation optimization method to obtain the optimal circulating water distribution, the optimization result showed that the indirect dry-cooling system got greater heat transfer rate compared with the traditional method. It showed that the entransy dissipation based optimization method had obvious advantages in the optimization of complicated heat exchanger network.