Citric acid is used in calico printing, also in the preparation of effervescing draughts, as a refrigerant and sialogogue, and occasionally as an antiscorbutic, instead of fresh lemon juice.
The dilute acid, or vinegar, may be used to bathe the skin in fever, acting as a pleasant refrigerant.
You would need considerable experience to determine the correct refrigerant charge by using the pressure gage readings.
Here, the heat from the water is conducted to a sealed circuit containing refrigerant, warming it up.
This heat is subsequently transferred to an evaporating refrigerant in a heat exchanger.