Principle of heat pump-the refrigerant-Ammonia

2. The refrigerant

     A working substance that continuously circulates in a refrigeration system and undergoes its own state change to achieve refrigeration.The refrigerant is vaporized in the evaporator by the heat of the cooling medium (water or air, etc.), and the heat is transferred to the surrounding air or water in the condenser for condensation.

 Currently, there are 70 to 80 kinds of refrigerants, and they are constantly growing.But there are only a dozen or more for the food industry and air conditioning refrigeration.

The following are widely used:

① Ammonia (code: R717)

    Ammonia is currently the most widely used medium-pressure medium temperature refrigerant.The solidification temperature of ammonia is -77.7 ° C, the standard evaporation temperature is -33.3 ° C, and the condensation pressure at normal temperature is generally 1.1 to 1.3 MPa.Even when the summer cooling water temperature is as high as 30 ° C, it is never possible to exceed 1.5 MPa.The unit standard volume capacity of ammonia is approximately 520 kcal/m3. 

    Ammonia has good water absorption. Even at low temperatures, water will not precipitate from the ammonia solution and freeze, so there will be no "ice plug" in the system.Ammonia does not corrode iron and steel, but in the case of ammonia containing water, it has corrosive effect on copper and copper alloy, and the evaporation temperature is slightly increased.Therefore, copper and copper alloy materials cannot be used in the ammonia refrigeration unit, and the water content in the ammonia should not exceed 0.2%.

 Ammonia has a small specific gravity and viscosity, a high heat release coefficient, and is inexpensive and easy to obtain.But ammonia has strong toxicity and flammability.According to the volume calculation, when the ammonia content in the air reaches 0.5%-0.6%, people will be poisoned when they stay in it; when they reach 11%~13%, they can ignite; when they reach 16%, they will explode when exposed to fire.Therefore, the ammonia refrigeration room must pay attention to ventilation and exhaust, and often need to exclude air and other non-condensable gases in the system.

 In general, the advantages of ammonia are: easy to obtain, low in price, moderate in pressure, large in unit cooling capacity, high in heat release coefficient, almost insoluble in oil, low in flow resistance, and easy to find when leaking.Disadvantages are: irritating odor, toxic, flammable and explosive, corrosive to copper and copper alloys.