I'm reading the Wikipedia article on vapor-compression refrigeration.
In the cycle, first the refrigerant absorbs heat from the source to be cooled, which causes it to be vaporized. Then this vapor goes through a compressor, which increases the pressure and temperature of the vapor. From Wikipedia:
Circulating refrigerant enters the compressor in the thermodynamic state known as a saturated vapor2 and is compressed to a higher pressure, resulting in a higher temperature as well. The hot, compressed vapor is then in the thermodynamic state known as a superheated vapor and it is at a temperature and pressure at which it can be condensed with either cooling water or cooling air flowing across the coil or tubes.
I'm slightly confused about this stage. Why do we compress the vapor to increase its temperature, only to cool it down again in the condenser? The refrigerant has first absorbed heat from the heat source. Why don't we just conduct this vapor into the condenser, causing it to reject heat to cool down? It seems strange that we are artificially adding heat to the vapor, when removing heat from the heat source to be cooled is our goal.
In this part it is said:
From point 1 to point 2, the vapor is isentropically compressed (compressed at constant entropy) and exits the compressor as a superheated vapor. Superheat is the amount of heat added above the boiling point.
From point 2 to point 3, the vapor travels through part of the condenser which removes the superheat by cooling the vapor.
So we are adding superheat, only to remove it in the next step? The diagram from the section also confuses me:
The text explains that the compression at 1-2 is isentropic, which can also be seen from the T-S diagram. But the text also says that superheat is added at this point. But doesn't isentropic mean that no heat is added or removed from the system?
So to summarize: are we adding heat to the refrigerant during the compression stage or not? And if we are, why are doing it only to remove it in the next step, rather than just conducting the saturated vapor through the condenser to give up heat?