food grade product line by Water Services Ltd

why use Water for cooling?

The efficient removal of heat from industrial processes is an important requirement in the design and operation of cooling systems. We have to ask why is water the medium of choice for heat rejection? Basically, there are two primary reasons. First, water is cheap and available in abundance. Second and more important, water has the ability to accept more heat than any other practically available cooling fluid. Simply put, water has a high heat acceptance capacity (specific heat). The specific heat of a substance is the number of British Thermal Units (BTU) required to raise the temperature of one pound (weight) of that substance one degree Fahrenheit. Since one BTU will raise the temperature of one pound of water from 45° to 46°F, the specific heat of water is one (BTU/lb. °F). This is almost twice the specific heat of some organic liquids such as methanol or ethanol, or put another way, almost twice the volume of these organics is required to accept the same amount of heat as water.

Water has another property that makes it useful as a coolant. That is called its "heat of vaporization", which is the amount of heat that must be added to water to convert it from a liquid to a gas. The vaporization of water occurs at 212°F (at atmospheric pressure) with water's heat of vaporization equal to 970 BTU/lb. The specific heat of vaporization for water changes with water temperature. Specifically, colder waters have higher heats of vaporization than warmer waters. Therefore, as water evaporates in a cooling pond or cooling tower, it extracts the heat of vaporization from the surrounding bulk water.

Therefore, in summary, water has a high specific heat (the ability to accept heat from another source) and a high heat of vaporization as it changes from a liquid to a vapor. It is a relatively cheap, available, transportable liquid that can accept heat at one point and be pumped some distance to reject this heat at another location.