Study On Air Flow Characteristics And Optimization For Large Scale Dry Cooling Tower

With distinct superiority in water conservation, as well as higher energy-saving effect and safer operation over direct air cooling, the indirect air-cooling, also named as dry cooling technology, has been widely used in the thermal power units of northern China, characterized as abundance in coal and lacking in water.The indirect air cooling is a typical transfer process between the ambient air and the radiators surrounding or inside air cooling tower. Several factors, namely the ambient temperature, air flow rate, the size and scale of air cooling tower, radiator and fins, have significant influences on the characteristics of air flow and heat dissipation performance. The introduction of three incorporate towers, including that of dry cooling tower, desulfidation tower and exhaust flue gas chimney, 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 commonly-used Forgo-type tube bundles was studied to get the dimensionless correlation between air side Nusselt number, Nu, friction factor of fins,f,with air flow Reynold number, Re. Typical factors were analyzed in terms of affecting the low-temperature operation and freezing inside fin tubes. The freezing rules were derived under different operation conditions such as ambient air temperature, air velocity and power load. The results can provide reference for the safe operation of dry cooling power generating units under low-temperature environment in winter.With numerical simulation method, the effect of air velocity on flow and heat transfer characteristics were quantified with different air intake angle. Based on the results, the influence of radiator fin angle was investigated on flow and heat transfer of radiators, air flow field and temperature field inside the air cooling tower, for the optimized design of indirect air-cooling radiator fin 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 temperature, chimney height and ambient temperature were also investigated on the flow heat transfer characteristics for three incorporate towers.To overcome the harmful affect of environmental natural wind on dry cooling tower, air flow guiding devices were designed and installed inside air cooling tower. Numerical simulation was introduced to quantify the effects of flow guiding devices. The layer number and diversion of guiding plates were studied and compared to reveal their influences on the air flow and heat transfer performances of air cooling tower. The investigations may take a theoretical basis for the optimization of air flow field inside dry cooling tower.