Numerical Study On The Aerodynamic Characteristics Of The Forced Draft Mechanical Cooling Tower

With the rise and development of inland nuclear power industry in China, the forced draft mechanical cooling tower will be used more and more in its important water system to satisfy the requirements of equipment security and earthquake resistance. The forced draft mechanical cooling tower is not only different from the conventional induced draft mechanical cooling tower in ventilation way, but also has distinct difference in tower shape and structure layout. If the tower shape is different, the aerodynamic characteristics will be different which is closely related to the heat transfer performance. There are a large number of simulation and experimental studies on the flow, the tower shape and the resistance of the natural draft cooling tower and induced draft mechanical cooling tower at home and abroad, but few studies have done on the aerodynamic characteristics of the forced draft mechanical cooling tower, so it is of great theoretical significance and engineering value to study the aerodynamic characteristics of the forced draft mechanical cooling tower.Take the forced draft mechanical cooling tower as the research object, the paper establishes a3-D model to study its aerodynamic characteristics with Fluent software. The porous model is used to simulate the fill and the fan model is used to simulate the fan of the tower. By simulating, the velocity and pressure distribution of the tower are known at the condition of different tower shape and fill resistance, and then aerodynamic characteristics are studied based on these. Main achievements are as followings:(1) The convergent section height position of the outlet affects the resistance characteristic, as the position heightens the resistance decreases, and keeps stable at the end. It only influences the wind velocity distribution uniformity on the fill section but the uniformity below the fill section, which the higher the position is, the more uniform the wind velocity distribution on the fill section is.When the relative height position (HC/HCO) is between0.96and1.05, the aerodynamic characteristics can be optimized which can guarantee not only the resistance is smaller, but also the wind velocity distribution is relatively uniform.(2) The convergent section angle of the outlet only has effects on the resistance characteristic and the wind velocity distribution uniformity on the fill section. The larger the angle is, the smaller the resistance is and the more unevenly the wind velocity distributes. The aerodynamic characteristics is the most optimal when the relative convergent section angle (HCO/HG) is between0.93and1.05. (3) The bottom height of the fill doesn’t have effects on the resistance characteristic and the wind velocity distribution uniformity on the fill section. But it influences the wind velocity distribution uniformity below the fill section, the higher the position is, the more uniform the wind velocity distribution is, and the higher the water pump head at the same time. Take all this into account, the bottom height of the fill of1.50m above the air inlet is more appropriate.(4) The influence on the resistance characteristic and wind velocity distribution uniformity by different fill resistance is in the same regular pattern, but the less the fill resistance is, the less the total resistance is and the worse the wind velocity distribution uniformity is.Based on the calculation results, this paper obtains the resistance formulas of each part of the tower and the total resistance formula which is in the preparation for thermodynamic calculation of the forced draft mechanical cooling tower.In a word, the aerodynamic characteristics of the forced draft mechanical cooling tower are intensively studied through simulation. The change characteristics of the resistance and the wind velocity distribution uniformity with the tower shape and the fill resistance are clearly stated, at last calculation formulas of the resistance of the tower are obtained, which will provide effective technical support for the forced draft mechanical cooling tower used in the important water system.