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In automobiles, Why we need to implement latent heat concept (phase change) in evaporator?
Why not sensible heat?
Many heat exchangers are having higher heat removal rate. Say intercooler!! Radiator!! etc without any latent heat involved.
Can anyone guide me with this??
I also know latent heat of say R134a is very high compared to sensible heating.
2 bar --> 206 kJ/kg vaporization
20 bar --> 128 kJ/kg condensation
But is there any other specific reason for going towards phase change concept?
I probably did not fully understand your question.Quote:
Originally Posted by AastroGuru
But my answer is, because there is phase change of refrigerant in heat exchanger.
http://en.wikipedia.org/wiki/Latent_heat
A simply answer perhaps?
Due to short pipe runs phase change is required to protect compressor from liquid pumping.
Second thought, why not ?
Quote:
Originally Posted by AastroGuru
The reason we use latent heat is because it requires more heat energy to change the state of a
substance than it does to just add heat.
So the evaporator can do more work for its limited size.
The other reason is if we just used sensible heat exchange, the coldest we would be able to get
the fluid to, would be ambient tempreture. If the ambient temp outside the car is warmer than
20 degC then you would not have much heat exchange.
By altering the pressure of the refrigerant we can make it a higher temp than the outside ambient
to get heat exchange and we can make it lower than the inside of the car to get heat exchange.
Cheers taz.
.
Dear, Latent heat transfer is 70% of the total heat transfer, if you only want sensible then you have to increase your heat exchanger size by more than 5 times.
thanks
amit