冷却塔讲义.ppt

* Psychrometric process for cooling tower at ARI conditions Assume 1 lb of water is cooled by 1 lb air Water cools from 95F to 85F and releases 10 Btu heat to Air The 10 BTUs raises the enthalpy of the air from 42.4 Btu/lb to 52.4 Btu/lb and saturates the air The leaving condition is 87.5F and 100% RH The moisture content went from 0.018 lb to 0.028 lb = 0.011 lb water evaporated This is why cooling towers lose about 1% of their water flow to evaporation The latent heat of evaporation is 1045 Btu/lb 1045 x 0.011 lb = 11.45 Btus cooling effect 10 Btus was used to cool the water The rest was used to cool the air from 95F to 87.5F There are two main types of natural draft towers: (Click once) Cross flow tower (left figure): air is drawn across the falling water and the fill is located outside the tower (Click once) Counter flow tower (right figure): air is drawn up through the falling water and the fill is therefore located inside the tower, although design depends on specific site conditions * Now we can talk about cooling towers Induced draft and forced draft towers, how they operate, and how they can be controlled. * * Now we can talk about cooling towers Induced draft and forced draft towers, how they operate, and how they can be controlled. Assessment of Cooling Towers Measured Parameters 应测量的参数 Wet bulb temperature of air 空气湿球温度 Dry bulb temperature of air 空气干球温度 Cooling tower inlet water temperature 冷却塔进水温度 Cooling tower outlet water temperature 冷却塔出水温度 Electrical readings of pump and fan motors 水泵和电机运行参数 Water flow rate 水流速度 Air flow rate 空气流速 Performance Parameters 运行参数 Range 冷却水温差 Approach 冷幅 Effectiveness 效率 Cooling capacity 冷却塔容量 Evaporation loss 蒸发损失 Cycles of concentration 浓缩倍数 Blow down losses 排污损失 Liquid / Gas ratio 液体/气体比 Assessment of Cooling Towers 1. Range 冷却水温差 Difference between cooling water inlet and outlet temperature: 冷却水进出水温差： Range (°C) = CW inlet temp – CW outlet temp High range = good perfo