Flow And Heat Transfer Characteristics And Air-side Flow Field Optimization Of Air-cooled Condenser Cell

Dry cooling technology receives rapid development in the power plant condenser heat rejection in north China that is short of water resources but rich of coal due to its remarkable water saving advantage. The air-cooled condenser generally consists of tens of condenser cells. For each condenser cell, the finned tube bundles are arranged in the A-frame form fitted with an axial flow fan below. As a result of the specific A-frame chamber of the condenser cell and the complicated aerodynamic behavior at the outlet of the axial flow fan, the ascending of the cooling air in the A-frame chamber is rotational, and the flow field presents central symmetric, resulting in a serious non-uniformity of air flow rate through the fin-tube bundles of the condenser cell. The heat rejection capability of the fin-tube bundles at different zones varies widely and the heat transfer surfaces of the fin-tube bundles are badly utilized. The flow and heat transfer characteristics of the air-cooled condenser are deteriorated.The commercial software Fluent is used to investigate the aerodynamic characteristics inside the A-frame chamber of air-cooled condenser cell by means of CFD methods. It is observed that the immobile zones and vortices appear at the bottom of the condenser cell and the serious reversed flows are formed at the center of the chamber, resulting in the increased flow resistance. The flow towards the fin-tube bundle of the cooling air from the outlet of the axial flow fan is blocked and the flow and heat transfer performances of the condenser cell are affected.On the basis of the aerodynamic behavior in the condenser cell, seven flow field leading measures are proposed in this study. The thermo-hydraulic performances of the condenser cells with flow field leading measures are studied by means of CFD simulation. The optimized measure is taken as the final resolution for the air-cooled condenser. The change of the thermo-hydraulic performances of one column of condenser cells with the flow field leading measure is analyzed at ambient winds. The flow velocity and temperature at the outlet of the fin-tube bundle are obtained, and the mass flow rate and heat rejection for each condenser cell are calculated. The results show that the flow distortion gets serious at the inlet of the windward axial flow fan and the operation of the axial flow fan becomes abnormal, resulting in the deteriorated thermo-hydraulic performances. The reversed flows can be found in the windward condenser cell for some serious cases. The leeward condenser cell is less affected by ambient winds, but the hot plume is driven to the fan inlet of the leeward condenser cell due to the reversed flows of the windward condenser cell, resulting in the increased inlet air temperature of the leeward fan. The thermo-hydraulic performances will be deteriorated. By means of the flow field optimization due to the flow leading for the condenser cell, the flow rate and heat rejection of the leeward condenser cells increase and the performances are improved.The flow field leading measure of cooling air in the A-frame condenser cell is applied to one300MW direct dry cooling power plant. The spot thermo-hydraulic performances test is carried out for one column condenser cells before and after the flow field leading. The flow velocity distribution at the outlet of fin-tube bundle of each condenser cell is measured and the back pressure of the turbine is obtained. The measured outlet air velocity of the fin-tube bundle agree well with the calculated data by means of CFD simulation, showing that the flow field optimization project obtained from the CFD method is exact and reliable. The air-side flow field optimization can improve the flow and heat transfer characteristics of the direct dry cooling system and reduce the back pressure of the turbine.