And also why can’t we use nitrogen instead of coolants ?
In: Chemistry
so, the short answer to the second question is we could, and do: its called air cooling (given that the atmosphere is 70% nitrogen by volume). pure nitrogen gas would be a significant increase in expense but limited additional capability. liquid nitrogen would come with massive weight penalties related to the extensive refrigeration required to keep the nitrogen down at -200c, and deal with the state change of the nitrogen turning back to gas….at which point you might as well use that refrigeration capacity to just directly cool the engine and stop mucking about with liquid nitrogen.
as to how of liquid coolants: they work by running a liquid, which is usually but not always water* through the hot parts to the engine. this heats up the coolant, and takes heat out of the engine block itself. the hot coolant is then moved to a radiator system of some sort, with a lot of small diameter pipes that maximise the effective surface area of the coolant, and then the heat is transferred out of the system into the air. the cooled coolant is then fed back into the engine block.
why? its smaller, which is vital in cars and such where space is at a premium, and while water is heavy, a liquid cooled system can often be lighter than a air cooled system for a given heat load, as side effect of that reduced size.
*most cars run on water with some additives like anti-freeze, but you can get systems that run on more exotic working fluids if the specific engine requires it. Their are some nuclear reactors that have a molten salt working fluid, for example.
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