Numerical Study Of Finned Serpentine Tubes' Flow And Heat Transfer Performance In Direct Air Cooling Power Plant

Today, water resource is growing more and more scarce, direct air cooling system for its remarkable performance has been widely used in various water-saving air-cooled power plants, especially in the "rich coal-water" areas. Direct air cooling system consists of a number of Direct Air Cooling units, each unit includes the condenser tubes bundle showed a "chevron" arrangement and a large axial flow fan at the bottom of unit, Turbine exhaust steam flows in the finned tubes, ambient air is pressured by the fan and go through the condenser tubes, so turbine exhaust heat is taken away by the ambient air and the exhaust steam condenses into water. Therefore, finned tubes are the core component in a direct air cooling system, their thermal dissipation performance determines the air cooled condenser's heat transfer performance directly.The development of fin tube bundles comes through several rows of tubes, two rows of tubes and the commonly used single-row tubes, and flat tubes brazing with snake-like fins are the mainly form of single-row tube flat tubes. So far, many scholars have been studied the flat tubes brazing with snake-like fins, got certain results and obtained the relational formulas of heat transfer coefficient and pressure loss with the head-wind speed relation. The air inlet velocity has a 60°angle with the horizontal plane because of the finned tubes presented in the "chevron" arrangement, but previous studies almost have not taken the angle into account. Considering the angle could affect the heat transfer coefficient and pressure drop, this paper makes numerical simulations of the finned tubes with horizontal arrangement and "chevron" arrangement on the basis of the previous studies. We know the difference and connection between the two arrangements by analyzing the difference of the velocity field and the temperature field, and have the corresponding mathematical relational formulas by comparing the variety trends of the average heat transfer coefficient and pressure loss with different face velocities.In addition, this article also optimized the design of the finned tubes by seeking a simple, little effect on the original production process technology and methods, in order to achieve the purposes of improving heat transfer coefficient and reducing the area of air cooling system. The method is making several holes on the fin to improve the disturbance of the air flow, then makes several numerical simulations of different hole pitches, at last studies the change of the heat transfer coefficient and flow loss in order to find an optimal solution.