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图为英国一座自然抽风式(Natural draft)双曲面结构的冷却塔近底部位置。
图为英国一座自然抽风式(Natural draft)双曲面结构的冷却塔近底部位置。

冷却塔(Cooling tower),火力发电厂核能发电厂、大型空调设备制冷设备的循环水冷却装置。根据其通风方式,可以分为自然通风冷却塔和机力通风冷却塔。


大多数发电厂的冷却塔结构都是单叶双曲面形状。由于单叶双曲面是一种双重直纹曲面(Ruled surface),它可以用直的建造。这样既可减少阻力,又可以用最少的材料来维持结构的完整。


若以其热传导方式分类,冷却塔大致有 :

  • 湿式冷却塔(Wet cooling towers) (or open circuit cooling towers) operate on the principle of evaporative cooling. The working fluid and the evaporated fluid (usually water) are one and the same.
  • 闭合回路冷却塔(Closed circuit cooling towers) (or fluid coolers) pass the working fluid through a tube bundle, upon which clean water is sprayed and a fan-induced draft applied. The resulting heat transfer performance is close to that of a wet cooling tower, with the advantage of protecting the working fluid from environmental exposure and contamination.
  • 干燥式冷却塔(Dry cooling towers) are closed circuit cooling towers which operate by heat transfer through a surface that separates the working fluid from ambient air, such as in a tube to air heat exchanger, utilizing convective heat transfer. They do not use evaporation.
  • 混合式冷却塔(Hybrid cooling towers) are closed circuit cooling towers that can switch between wet and dry operation. This helps balance water and energy savings across a variety of weather conditions.

In a wet cooling tower (or open circuit cooling tower), the warm water can be cooled to a temperature lower than the ambient air dry-bulb temperature, if the air is relatively dry (see dew point and psychrometrics). As ambient air is drawn past a flow of water, a small portion of the water evaporates, and the energy required to evaporate that portion of the water is taken from the remaining mass of water, thus reducing its temperature. Approximately 970 BTU of heat energy is absorbed for each pound of evaporated water (2 MJ/kg). Evaporation results in saturated air conditions, lowering the temperature of the water processed by the tower to a value close to wet-bulb temperature, which is lower than the ambient dry-bulb temperature, the difference determined by the initial humidity of the ambient air.

To achieve better performance (more cooling), a medium called fill is used to increase the surface area and the time of contact between the air and water flows. Splash fill consists of material placed to interrupt the water flow causing splashing. Film fill is composed of thin sheets of material (usually PVC) upon which the water flows. Both methods create increased surface area and time of contact between the fluid (water) and the gas (air), to improve heat transfer.


把空气流动通过冷却塔的方法大致有三种 :

  • 自然抽风(Natural draft) — 通过烟囱产生的上扬力。由于在相等的压力中,大气中的空气相对较为干燥及低温并与排放气体产生密度上的差距,造成冷却塔内温暖而潮湿的空气“自然地”向上流动。
  • 机械式抽风(Mechanical draft) — 利用大型风扇制造气流并把冷却塔内的潮湿蒸发气体抽走。
    • 引风(Induced draft) — 在烟囱的排气口位置(大部分位于上方)装设大型风扇并把空气向上抽。风扇会把冷却塔内的潮湿空气导出排气口。此方式会产生较低的进入空气流动速度及较高的排出空气流动速度,并减低已排走气体回流至进气口处的可能性。
    • 鼓风(Forced draft) — 在烟囱的引风 / 吸风口位置装设大型风扇或鼓风机(Blower)。风扇强制把外在空气“推入”冷却塔内,并营造较高的进入空气流动速度及较低的排出空气流动速度。 低排出空气流动速度较容易受回流空气易受影响。 With the fan on the air intake, the fan is more susceptible to complications due to freezing conditions. Another disadvantage is that a forced draft design typically requires more motor horsepower than an equivalent induced draft design. The benefit of the forced draft design is its ability to work with high static pressure. Such setups can be installed in more-confined spaces and even in some indoor situations. This fan/fin geometry is also known as blow-through.
  • 机力辅助式自然通风(Fan assisted natural draft) — 一种混合式构型,以自然抽风式为基础,辅以风扇引导气流

由于有良好的结构强度及可以节省较多建造物料,双曲面结构(Hyperboloid structure)冷却塔所有自然抽风形式冷却塔的标准设计。双曲面亦可以增加向上对流空气的流动速度并增加冷却效率。此种设计的冷却塔亦特别广为不靠近海边或大量水源的核能发电厂燃煤发电厂所用。而混合型冷却塔的热处理效能则可高达92%。[1]

  1. ^ Gul, S. Optimizing the performance of Hybrid: Induced-Forced Draft Cooling Tower. Journal of the Pakistan Institute of Chemical Engineers. 2015-06-18, 43 (2). ISSN 1813-4092 (英语). 
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