Selection Principles of Refrigerants

In steam compression refrigerators, the choice of refrigerants should not only have good thermodynamic and physical and chemical properties, but also have good environmental characteristics. Specific requirements are as follows:

(1) It has no destructive effect on human ecological environment. It does not destroy the ozone layer of the atmosphere, and does not produce greenhouse effect.

(2) Higher critical temperature. It can liquefy at room temperature or ordinary low temperature. It is hoped that the critical temperature is much higher than the ambient temperature in order to reduce the throttling loss of refrigerants and improve the circular economy.

(3) Within the working temperature range, with appropriate saturated vapor pressure, the minimum evaporation pressure should not be lower than the atmospheric pressure, so as to prevent the external air from infiltrating into the system; condensation pressure should not be too high, otherwise it will cause the increase of compressor power consumption, and require the system to have a higher pressure bearing capacity and increase equipment costs.

(4) Large refrigeration capacity per unit volume. It can reduce the compressor gas flow.

(5) Low viscosity and density. Reduce the loss of flow resistance in the system.

(6) High thermal conductivity. It can improve the heat transfer coefficient of heat exchanger, reduce the heat transfer area of heat exchanger and reduce material consumption.

(7) Non-combustion, non-explosion, non-toxic. It is not corrosive to metal materials, chemical action to lubricating oil and decomposition at high temperature.

(8) The isentropic index is small. It can reduce the exhaust temperature, reduce the power consumption in the compression process, and is conducive to safe operation and increase the service life.

(9) Low solidification temperature. Avoid solidification at evaporation temperature.

(10) It has good insulation performance.

(11) The price is low and easy to obtain.

(12) Small compression work per unit volume.

At the time of publication, refrigerants that fully meet the above twelve requirements have not been found. But when choosing, it can be considered comprehensively according to the conditions of use and so on.

For example, fluorine refrigerant is often used in small closed compressor household devices. Ammonia is often used in large-scale industrial refrigeration and hydrocarbons are used in petrochemical industry.

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