What is a cooling tower? How do cooling towers work? What is an adiabatic cooling tower?

Heat Transfer

What is a cooling tower? How do cooling towers work? What is an adiabatic cooling tower?

A cooling tower extracts heat out of process cooling water and pushes it into another medium, usually air, so that the process cooling water is cooled and ready to be recirculated.

In plastics processing, cool process water is pumped out from the base of the cooling tower and through one or more cooling circuits in various pieces of equipment (i.e., processing machines, molds, desiccant dryers, water-cooled chillers, etc.). The process water absorbs and carries heat away from the equipment so that operating temperatures stay in a range needed for optimal processing.

This warm “returning” water needs to be cooled and, as its name implies, that’s what a cooling tower does.

“Open Loop” Cooling Towers

  1. Evaporative Cooling Towers. The oldest and simplest cooling towers cool water effectively using evaporation. Warm returning water is pumped into the top of the tower, then it flows or is sprayed over a series of baffles that break up the water stream to maximize its surface area. A relatively small amount the water evaporates into the air, taking with it a large amount of process heat in the form of latent heat energy. As a result, the remaining water is cooled and left free to flow down into the bottom of the tower, ready for recirculation.
  1. Induced-draft or “counterflow” cooling towers. To accelerate the evaporation and cooling process, many evaporative cooling towers are equipped with top-mounted fans that draw air from the base of the tower, pulling it up through the baffles and the water stream. Cooling towers like this are called induced-draft or “counterflow” cooling towers, since the air is moving in the opposite direction of the water.  Virtually all of Conair’s evaporative cooling towers use a counterflow design, including:

Because evaporative cooling towers like these spray the cooling water into open air, they are called “Open Loop” systems.  And, while there’s no doubt that evaporative and counterflow cooling towers like these do an excellent job, they do have several significant operating costs.  First, evaporation costs water, since the process water lost to evaporation must be continually replenished, and this can be undesirable in areas where water is in limited supply or where utility costs (water and sewer) are high.  Second, counterflow fans consume electricity—another utility for which processors may pay relatively high prices. And third, chemical treatment of process water is usually needed to prevent the buildup of mineral deposits in piping and process equipment that is exposed to cooling water.

“Closed Loop” Cooling Towers

To avoid these issues, plastics processors can turn to cooling tower technologies that do the job with little or no water loss.  These cooling tower designs are “Closed Loop” because the cooling water (or, in some cases, process fluid such as ethylene glycol coolant) are never exposed to the ambient environment.

  1. Fluid coolers. The simplest of these is a basic fluid cooler. These coolers pump warm “returning” water through a large heat exchanger– a system of tubes held within finned panels that resembles a large radiator. One or more fans draw air up and through the panels, absorbing heat.  While fluid coolers provide some cooling capacity, they cannot generate “leaving” water temperatures as low as evaporative cooling towers can.  So, their use may be limited unless supplemental cooling equipment, such as portable chillers, are used to lower process water temperature further.
  2. Adiabatic Towers. These tower coolers offer processors several choices for managing their process water cooling needs and utility costs.

Like a fluid cooler, an adiabiatic tower cooler uses a closed circuit, cycling process fluid through a finned heat exchanger where fans draw ambient air in to absorb heat and cool the fluid for recirculation. In cool climates or when relatively high process temperatures are acceptable, fan-forced air may provide sufficient cooling capacity.

When greater cooling capacity is required, adiabiatic tower coolers can provide it by spraying a small amount of water onto special evaporative panels located in front of the finned radiator panels.  As air flows through these wetted panels it evaporates, significantly reducing the temperature of the air so it can carry away more process heat. In this way, adiabiatic cooling towers achieve leaving water temperatures that are nearly as low as those of evaporative cooling towers with little water loss to evaporation. Controls actively monitor process water temperatures and automatically adjusts fan speeds and water flow to the wetted panels to balance water- and energy-use against process cooling requirements.

Conair provides a range of adiabiatic cooling towers in its EarthSmart ESTW Series , with capacities from 17 to 195 tons of cooling capacity.

If you’ve got questions about process fluid cooling tower systems, Conair has answers.  Just drop us a note or give us a call.