Closed circuit cooling towers, also known as evaporative fluid coolers, keep the system clean and contaminant-free in a closed loop. This creates two separate fluid circuits: (1) an external circuit, in which spray water circulates over the coil and mixes with the outside air, and (2) an internal circuit, in which the process fluid to be cooled circulates inside the coil. During operation, heat is transferred from the warm fluid in the coil to the spray water, and then to the atmosphere as a portion of the water evaporates. In addition to chiller applications and industrial process cooling, closed circuit cooling towers are often used with heat pump systems, where closed loop cooling is required.
Principle of Operation
Closed circuit cooling towers operate in a manner similar to open cooling towers, except that the heat load to be rejected is transferred from the process fluid (the fluid being cooled) to the ambient air through a heat exchange coil. The coil serves to isolate the process fluid from the outside air, keeping it clean and contaminant-free in a closed loop. This creates two separate fluid circuits: (1) an external circuit, in which spray water circulates over the coil and mixes with the outside air, and (2) an internal circuit, in which the process fluid circulates inside the coil. During operation, heat is transferred from the internal circuit, through the coil to the spray water, and then to the atmosphere as a portion of the water evaporates.
Combined Flow Configuration
Combined flow is the use of both a heat exchange coil and fill for heat transfer in a closed circuit cooling tower. The addition of fill to the traditional closed circuit cooling tower design reduces evaporation in the coil section, reducing the potential for scaling and fouling. BAC’s combined flow closed circuit cooling towers utilize parallel flow of air and spray water over the coil, and crossflow air/water flow through the fill.
In parallel flow, air and water flow over the coil in the same direction. The process fluid travels from the bottom to the top of the coil, increasing efficiency by bringing the coldest spray water and air in contact with the process fluid at its coldest temperature.
In the fill air and water interact in a crossflow configuration: water flows vertically down the fill as air flows horizontally across it.