And also why can’t we use nitrogen instead of coolants ?
In: Chemistry
Coolant is just something which can be pumped onto or through some equipment to prevent it overheating.
In a car engine, heat needs to be removed from the engine and transferred to the air. A coolant is used to transfer heat from the engine to a radiator, which then transfers the heat to air. In a car engine the coolant is water, with some additives to prevent corrosion and prevent the liquid freezing in cold temperatures.
Coolants can be used in other machines, as long as they are suitabke for the process. Gases can be used as coolant, but don’t transfer heat as effectively as liquids like water.
Aircraft engines used cold air as a coolant. Cold air is pumped into very hot parts, like turbine blades, in order to prevent them overheating.
Air conditioning is a completely different process. This is refrigeration which typically uses a process called phase change cooling. This uses the principle that when a liquid evaporates it absorbs a ton of heat, and that when a gas is compressed it may liquify and release that heat.
Phase change cooling requires that the substance used liquifies or evaporates at suitable temperatures and pressures. These substances are called refrigerants. Different refrigerants are needs for air conditioning, refrigerators and freezers because of the different temperatures needed.
Nitrogen is not suitable for phase change refrigeration as it does not change phase at useful temperatures and pressures. Car in dioxide can be used, but the pressures needed are extremely high making systems difficult to build compared to synthetic refrigerants like hydrofluoroolefins or hydrofluorocarbons.
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