Low pressure liquid is injected into the cooler via a capillary tube - very small bore diameter pipe, as the high pressure liquid passes through it then becomes low pressure / temperature liquid - it uses it's own energy to do this.
This low pressure liquid goes into the cpu cooler were the refrigerant absorbs the heat and the liquid refrigerant will boil off and become a super heated vapor. This then goes down the suction line back to the compressor were the refrigerant is compressed to a high pressure / temperature vapor this passes through the condenser were heat is rejected via the air or water depending on system and you left with a high pressure, medium temperature sub cooled liquid this then goes into the cap tube as described above.
So the 2 pipes are liquid inlet and Suction back to the compressor.
Basically it's same as whats happens in your fridge and car A/C.
