Numerical Simulation Of Direct Air-cooled Condenser In Power Plant

Because of its properties of water-saving and environmental protection, and the recycle of water resources, the direct air-cooled system in power plant has broad prospect in the northern of China, which has lots of coals but little water resources. Because of the air as the cooling medium and the temperature of air is varying diurnal and seasonal, so the backpressure of the air-cooled turbine changes according with the changing of air temperature. The characteristic of the direct air-cooled condenser's air side's flow-field will affect the heat transfer of the heat exchanger and the efficiency of the condenser directly, so seize the particularities and rules of the flow-field is very important to the design and optimize of condensers.At present, the methods of separate computation and Lumped Parameter Method treated on air-cooled fan are widely used in the computation of direct air-cooled condenser's flow field analysis. But both methods have notable shortages, the former approach's boundary conditions were difficult to given, and the second's computational error is rather big. Use this as a foundation, this thesis put forward the coupled computation between rotational fan and stock-still components.The major works of this thesis are as follow:1) Design process of direct air-cooled fan using fifth power type line is introduced, and simulates the inner flow-field of the fan by CFD software: NUMECA.2) Couple computation of fan and A-frame was applied by the usage of frozen rotor.3) Analyze the distribution of velocity, temperature and pressure in A-frame under different rotating speed of the fan. And the compare between coupled computation and brief computation was presented.The result indicates that during the design of fan, the fifth power type line method's efficiency of fan is much higher than theα-equal method, about 10 percentages, so the former has significant energy saving effect.The coupled computation is direct simulation to the cooling cell of condenser. The advantageous of this method is that there's no inaccurate boundary condition between the rotational and stock-still, and the inlet and outlet boundary condition is sufficient. The distribution of velocity, temperature and pressure in A-frame and heat transfer coefficient and quantity of heat transfer of the airside were gained under different rotate speed of the fan by couple computation. The compare between coupled computation and brief calculation indicated that brief calculation can't embody the infection of fan's outlet's radial and azimuthal velocity upon flow-field; but the coupled computation not only could give boundary conditions conveniently, but also could reflect many important flow phenomena, such as sink flow, the flow field of air in the chamber is rather chaos, so the flow field is more logical.This thesis provides basis for the optimum design of condenser through the simulation of condenser's cooling cell.