Optimization Study Of Thermo-flow Performances For Forced Draft Direct Dry Cooling System

In the new period,new requirements are put forward for energy saving and environmental protection of power plants in China.Because of its remarkable advantages of water saving and low pollution,the air cooling system of power plants has been widely used in coal-rich and water-deficient areas in China.Among them.forced draft direct air cooling system is widely used because of its low investment and high cooling efficiency.However,the heat transfer performances of forced draft direct air cooling system are affected by many factors,among which the structure and layout of heat transfer surface and the influence of variable environmental and meteorological conditions are the main reasons for the poor performance of air cooling system.Based on the current researching status of heat transfer in forced draft direct air cooling system at home and abroad,in this paper,with the help of commercial software Fluent as well as the experimental verification,and aiming at a better heat transfer performance,the air cooling system is optimized from two aspects including the arrangement of finned tube bundles and the array of air-cooled condensers.Considering the inherent defects of the structure of air-cooled condenser cell,a new type of oblique finned tube bundle is proposed,and its flow and heat transfer characteristics are obtained with numerical simulation.On this basis,the new type of oblique finned tube bundles is applied to the condenser cell to obtain the heat transfer performance of the new condenser cell.Compared with the traditional condenser,it is found that the flow and heat transfer performance of the new condenser unit has been greatly improved.Especially when the inclined angle reaches to 45°.the area of low-speed and high-temperature in the lower part of the condenser disappears completely.and the growth rate of mass flow rate and heat transfer rate reaches up to 12.81%and 8.96%respectively,compared with the traditional condenser cell.Through multi-scale numerical simulation of forced draft direct air cooling system.the spatial distribution of heat transfer performances for large-scale air cooling system are revealed in this paper,and a detailed study of heat transfer under adverse environmental windy conditions is also carried out.Considering the adverse effect of ambient wind on the traditional rectangular air cooling system,a square array of air-cooled condenser is proposed to weaken the influence of ambient wind.The results show that the reverse flow in the upwind condenser cells and hot plume recirculation of the peripheral condenser cells are both weakened for the proposed square array under windy conditions.Accordingly,the mass flow rate and total heat rejection increase a lot especially in the wind direction of-90°with a heat rejection improvement of 25.21%at the wind speed of 16 m/s,which leads to an improved thermo-flow performance of air-cooled condensers.In the absence of ambient winds,the total heat rejection of air-cooled condensers in the square array is almost the same as the conventional one.