| In industry,the mechanical draft counterflow wet cooling towers(MDWCTs)performance has an important influence on the production efficiency,which is limited by many factors such as tower structure,air parameters,circulating water parameters and driving force of fan.Due to the limited area,the MDWCTs group is generally arranged in a back-to-back array,and there is only a one-side air inlet.In a one-side air inlet MDWCT,the nonuniformity of air distribution along the depth of the tower results in the local area low cooling efficiency.Under the crosswind condition,the wind speed and direction directly affect the inlet air performance of the cooling tower.But so far,there are few studies on the influence mechanism of crosswinds on MDWCTs,especially one-side air inlet MDWCTs.The effect of crosswinds on MDWCTs is unclear.In view of this,the thermal performance of one-side air inlet MDWCTs and action mechanism of different factors including the crosswinds on the tower efficiency were investigated by means of numerical simulation.The distribution of aerodynamic field,temperature field and pressure field in the tower under variable conditions were analyzed,and on this basis,the three-dimensional efficiency enhancement mechanism of the MDWCTs was discussed.In this paper,the three-dimensional computational model of the one-side air inlet MDWCT was established,and the built cooling tower model was verified by the tower measured data.Based on the numerical calculation,the thermal performance of the one-side air inlet MDWCT with or without crosswind condition was analyzed,and the three-dimensional distribution of aerodynamic field,pressure field and temperature field was reported.The tower cooling performance was evaluated by ventilation volume G,the tower outlet water temperature drop and cooling efficiency.Under no crosswind condition,the study on the water and gas parameters distribution found that the air flow rate gradually decreases along the depth of the tower,the air temperature and humidity continue to increase,the water temperature gradually increases,and the cooling efficiency in the inner area of the cooling tower is relatively low.Longitudinal vortex appears at the upper edge of the air inlet,which reduces the effective ventilation and local cooling efficiency.The backflow phenomenon of the air flow was shown out of the tower,rising the temperature and humidity level of the air flow in the air inlet.As for the heat transfer capacity between water and air,the fill zone efficiency is the strongest,and the rain zone is next to the fill zone.Compared with the fill zone and the rain zone,the spary zone efficiency is weaker.When the crosswind direction is 0°,the study on the cooling tower performance under variable conditions found that the cooling capacity of the cooling tower increases with the inlet water temperature increasement,and decreases with the increase of the circulating water volume and the ambient dry bulb temperature.When the crosswind velocity va is 2 m/s,the effective ventilation volume with different crosswind direction is reduced compared with the crosswind direction of 0°.Under the crosswind direction of 90°,135° and 180° condition,the air backflow phenomenon is shown out of the tower.The crosswind direction and crosswind velocity have an obvious effect on the performance of MDWCT.With crosswind condition,the cooling tower with 0°crosswind direction has the best performance,which is higher than the tower performance of 45° crosswind direction.The tower cooling performance increases with the increase of the crosswind velocity.The crosswind is beneficial to the operation of the cooling tower.The cooling tower with 90°,135° and 180° crosswind direction has low performance.The tower cooling performance decreases with the the crosswind velocity increasement.When the crosswind velocity va is less than 5m/s,the cooling tower with 900 crosswind direction has better performance than that with 135°crosswind direction,and the cooling tower with 1800 crosswind direction has the lowest cooling efficiency.When the crosswind velocity va is more than 5 m/s,the performance of the cooling tower with 135° and 180° crosswind direction is better than that with 90°crosswind direction.Based on the three-dimensional heat transfer characteristics of the tower,non equal height fill arrangement and air duct arrangement are adopted to optimize the tower thermal performance.The fill non equal height arrangement is to decrease the thickness of fill inner area,and to increase the thickness of fill outer area.Under the crosswind condition,the cooling tower performance with "123" fill arrangement is always better than that with "133" fill arrangement.However,the crosswind velocity is larger,this fill arrangement has the less obvious improvement effect on the cooling tower.For the MDWCT,the crosswind velocity va in the natural environment is generally lower than 8m/s,so it is recommended to adopt "123" fill arrangement to improve the cooling tower performance.When the air duct is arranged in the rain area,the cold air flows into the tower inner area through the air duct Because there is no water pouring resistance,the flow velocity is always higher than the air flow velocity outside the air duct,which improves the flow velocity distribution,reduces the air temperature and humidity level,and enhances the heat transfer process.Through the research on the tower performance with 3m2,4m2 and 6m2 cross-sectional area air duct,it can be seen that air duct has a negative impact on the tower performance at no crosswind condition.With the increase of crosswind velocity,the cooling tower efficiency all increases.The air duct of 4m2 cross-sectional area has the best improvement effect on the cooling tower,which is better than that with 3m2 cross-sectional area air duct.When the air duct cross-sectional area AP is 6m2,the tower performance is improved with va more than 5m/s.The bigger air duct is not good for the tower performance,which is determined by the tower flow field improvement due to the air duct,the air duct resistance and the space occupied in the rain.The suitable air duct will improve obviously the tower performance under the crosswind condition. |
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