to reduce the temperature of the water. Tey are effective when air temperature is cool but might not function prop- erly during the summer months in warm climates. In those cases, trim coolers, essentially added heat exchangers using city water supplies, might be needed to supplement the dry air cooling units. Dry air cooling installations require a relatively larger footprint than comparable evaporative cooling systems because air flow is less efficient for cooling than evaporation. Hybrid units operate as dry air coolers during the
cooler months and incorporate a water spray used only as needed during the hottest summer months. Essentially, evaporative cooling support is built into the hybrid unit. So hybrid cooling towers operate with equal effectiveness in hot weather and cold weather, offer a simplified design and reduce city water consumption. Because of the large cooling capacity needed, the warm summers typical in southern Georgia and the limited space available for installation, Chassix required an evaporative cooling tower for its new system. Te selected unit is a ver- tical cross flow cooling tower with two 75 HP fans, able to cool 5,500 gallons per minute (GPM) from 115F to 85F. While the cooling tower’s job is to reduce the tempera-
ture of the heated water coming from the furnace, water returning to the furnace that is too cold will cause its own problems. Tat’s because water that is close to or below the prevailing wet bulb temperature, typically about 75F or less, will produce condensation on the furnace coil that can lead to electrical arcing. Such arcing can result in serious coil damage. To address this problem, most induction furnace cooling systems incorporate automatic cold water diver- sion valves. When the automatic controls detect that the temperature of the water leaving the furnace is too cold, the water is diverted from the cooling tower and flows directly back into the furnace. Tis continues until the desired out-
能需要从根本上增加使用自来水的热交换器以补充的 干式空气冷却单元的不足。因为空气冷却比蒸发冷却 效率低，对比相同冷却能力的蒸发式冷却塔，干式空 气冷却塔需要相对较大的占地面积。 混合型冷却塔在寒冷月份时以干式空气冷却模式 运行，仅在最热的夏季需要配合使用喷淋水冷却。本 质上，蒸发式冷却单元可以内置在混合型冷却塔中。 因此，混合型冷却塔可以在炎热的天气和寒冷的天气 同样有效的运行，这种简明的设计减少了自来水的消 耗。
由于需要冷却能力很大，格鲁吉亚南部典型的温暖 的夏天和可用于安装的空间有限，Chassix公司选择 蒸发式冷却塔作为新系统。选定的产品是垂直布置盘 管的冷却塔，配有2台75 HP的风扇，每分钟能够把 5500加仑水从115F冷却至85F。
虽然冷却塔的工作是降低从炉体流出的热水温度， 但是如果返回到炉体的水温过低将会导致问题。这是 因为水接近或低于当时环境的湿球温度，通常约为 75°F或更低时，会在炉体线圈上引起结露，可导致匝 间电弧产生，电弧会导致严重的线圈损坏。为解决此 问题，感应炉冷却系统应包括自动冷水导流阀。当自 动监控装置检测到炉体的出水温度过低，循环水将不 经过冷却塔而直接返回到炉体中。这种情况会持续到 达到所需的出水温度为止。嵌入加热器还可以把水加 热到所需温度。
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FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION September 2014
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