Currently used refrigerant has reached 70~80 species, and is growing more and more. But only more than more than 10 kinds of refrigeration are used in food industry and air-conditioning. It is widely used only in the following:
1. Ammonia (code: R717)
Ammonia is the most widely used medium-pressure medium temperature refrigerant. The solidification temperature of ammonia is-77.7 ℃, the standard evaporation temperature is-33.3 ℃, at ambient temperature condensation pressure is generally 1.1~1.3MPa, even when the summer cooling water temperature up to 30 ℃, may not exceed 1.5MPa. The unit standard volume refrigeration capacity of ammonia is approximately 520kcal/m3.
Ammonia has a very good absorbent, even in the low temperature water will not precipitate from the ammonia liquid, so the system will not have "ice plug" phenomenon. Ammonia is not corrosive to steel, but the ammonia liquid contains moisture, copper and copper alloys have corrosive action, and the evaporation temperature slightly increased. Therefore, copper and copper alloys cannot be used in ammonia refrigeration units, and the moisture content of ammonia should not exceed 0.2%.
The critical temperature of ammonia is higher (tkr=132 ℃), the latent heat of vaporization is large, under the atmospheric pressure is 1164KJ/Kg, the unit volume refrigeration capacity is also large, the size of ammonia compressor can be smaller.
Pure ammonia has no adverse effect on lubricating oil, but it decreases the lubricating effect of frozen oil when there is moisture. Ammonia is not easy to dissolve in lubricating oil, so it is necessary to set up oil separator in the device, reduce the lubricating oil into the condenser and evaporator, and prevent the heat transfer from oil contamination after the surface is reduced.