| In recent years, the direct dry cooling system is widely adopted by the power plants in "three-north areas" of China, in which coal is abundant, but water is poor. More emphases are thus placed on the performance of air-cooled condensers (ACC). As a widely used element of air-cooled condensers, the thermo-flow characteristics of the wave-finned flat tube bundle are key issues to the ACC performance. On the basis of the uneven flow and heat transfer of the cooling air through the finned tube bundles, a new wave-finned tube is proposed in the present studies, for which an60°angle is existed between the fin and the base tube, so the fin surface is parallel to axial direction of the axial flow fan. A three-dimensional model of this new wave-finned flat tube bundle is established and calculated by using numerical simulations. The flow and temperature fields are presented. The influences of air inlet velocity, fin height and fin pitch, and the buoyancy force on the air side flow and heat transfer performances are analyzed. The correlations of friction factor and convection heat transfer coefficient are suggested, which can be used to the optimal design of the new wave-finned flat tube.This new finned tube is applied to the air-cooled condenser cell. The fin pitch is optimized along the whole base tube by introducing the principle of "flow field uniformity", in which the sparse fin pitch is set to the area with a large air flow rate, but small fin pitch is adopted in the area with a low air flow rate. An optimal fin pitch configuration along the tube is recommended, in which the velocity and temperature fields of cooling air through the finned tube bundle become more uniform, and the heat rejection increases by5.7%. The thermo-flow performances of the air-cooled condenser cell are conspicuously improved and the back pressure of the turbine is thus reduced by using the proposed optimal method in this research. |
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