Why do they use radiators, and why is water the liquid of choice? As you might expect, it is the physical and chemical properties of water that dictate its use. What properties?
Fluid ChoiceCommon fluids include free moving solid-particles, liquids, and gases. As an example of fluid solids, black molybdenum sulfide is a solid lubricant used on certain moving automotive parts.
That gases can cool should be intuitive. One blows on a forkful of hot food to keep from scalding his tongue. On a hot summer day, one uses either a fan or an air conditioner (which also uses a fan) to cool himself.
However, it is liquids, in most instances that are the fluids of choice, since a liquid is better suited to remove more heat than air can. It can be piped in where it absorbs heat by contact and then carries it away. Yes, the coolant absorbs enough of the heat that the system, the motor, can function optimally.
Water Coolant RulesWater is not only free-flowing, it is plentiful and inexpensive. But most importantly, it is has a very high heat capacity. This means it takes a lot of heat to raise the temperature of water 1º C. A high heat capacity, cheap, and abundant liquid makes water the obvious choice for cooling most internal combustion engines. In fact, it is unwise to add too much antifreeze to the coolant, since this can prevent effective cooling.
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