Numerical Simulation Optimizing Study On The Forced Draft Mechanical Cooling Tower Layout

Electric power industry is the foundation of the national economic development. In recent years, with the rapid development of social economy, power shortage situation is exacerbating, electricity power demand is constantly increasing. In the power system, the natural draft cooling tower is widely applied, but in order to adapt to the rapid development of the demand of electric power, there is the case that 200 MW unit using mechanical ventilation and cooling tower for cooling, and this trend is more and more obvious, this is mainly due to the low investment and short construction period of mechanical draft cooling tower. Mechanical ventilation cooling tower has been widely used in chemical, metallurgical, pharmaceutical, brewing and other industries. For natural ventilation cooling tower, due to the large cooling water quantity, one or several can meet the requirements, and the body of the natural draft cooling tower is higher, under the influence of momentum and buoyancy of the hot air outlet, hot and humid air is difficult to sank to the ground to cause heat recirculation, so the natural ventilation cooling tower reflux and disturbance has less influence on the cooling effect. While for mechanical draft cooling tower, due to the smaller single-tower cooling water quantity, they often need to be arranged in rows together. Especially in recent years, the build scale significantly increased. Drenching density and ventilation has been enhanced. They must be pumped in a lot of air. When the spacing of cooling tower is too small or is close to other buildings, it will worsen the air distribution of inlet and water spray device and reduce the amount of ventilation. Meanwhile, the hot and humid air from the tower outlet may be sucked by itself or adjacent tower to reduce their cooling effect. In the calculation of cooling tower, the temperature and humidity of the air are usually from the nearest weather station data. While in the actual runtime, affected by ambient wind, the area of cooling towers will become hotter and more humid. If the inlet conditions are not to be amended will lead to that the calculation water temperature is low and cause improper design. Although the relevant specifications for cooling tower have given the requirements about the layout of cooling tower, but they did not consider the affection by ambient wind. Some of the staff has done related research, but these research is aimed at specific projects and not have a systemic. So, it is necessary to do some research about the ambient wind speed and direction, the layout of cooling tower for tower group’s influence on reflux of the tower. In order to reduce the adverse effect due to improper arrangement.This paper establishes a 3-D numerical model of single tower and tower group to study the air flow field with FLUENT software. Mass/heat source is added to the fill. The ambient wind is added by UDF. By calculating, it is concluded that in the conditions of without ambient wind, the changes about reflux of different type of single tower; under conditions of ambient wind, different wind speed and direction’s influence on reflux; when arranged in a single row of cooling tower, different wind speed and direction、length of tower group’s influence on reflux; multi-row arrangement of the cooling tower, different wind speed and direction、row spacing of tower group’s influence on reflux. The results show that:(1) In the conditions of no ambient wind, different ratio of the outlet and inlet velocity have no influence on reflux; when there is ambient wind, reflux rate gradually decreases with the increase of v1/v2; under the conditions of same tower type, reflux becomes larger with the increase of velocity.(2) In the case of several cooling towers single row layout, when direction is 90°,the average reflux rate increases first, then decreased with the increase of velocity. When the ratio of the length and width of tower row is greater than 5, the variation of reflux rate decreases; when direction is 0°, the reflux rate of the last tower of the tower row is highest, but it is smaller. So, it’s better to make the tower long axis parallel to the dominant wind direction with enough room.(3) Multi-tower and single-row layout. when direction is 0°, the reflux of leeward tower is greater, and it increases with the increase of row spacing.90° direction, reflux rate decreases with the increase of L1/B, when L1/B is greater than 1, it remains unchanged.(4) Multi-tower and multi-row layout.0° direction, the average reflux rate decreases rapidly with the increase of tower line spacing, when L2/B is greater than 1, reflux rate is very small and it is basic not influenced by tower line spacing.90° direction, When wind speed is small, average reflux rate decreases with increasing row spacing. When wind speed is more than 9 m/s, with the increase of row spacing, the average reflux increases first then decreases. The bigger the row spacing is, the interference is smaller. In contrast, the interference is bigger in the leeward towers.Comprehensive considering the above calculation results, this paper obtains various factors’s influence on reflux and interference and put forward the reasonable tower row spacing for engineering.