What are the characteristics of common refrigerants?

What are the characteristics of common refrigerants?

Currently, commonly used refrigerants include water, ammonia, and Freon.

Water

Water's advantages as a refrigerant are its non-toxicity, odorlessness, non-flammability, and ease of availability. However, its vapor has a larger volume per unit of mass, resulting in lower refrigeration capacity per unit volume. Water also has a high freezing point, limiting its ability to achieve low temperatures, making it suitable only for applications above 0°C. Therefore, water is commonly used as a refrigerant in steam喷射 refrigeration systems and lithium bromide absorption refrigeration units.

2. Ammonia

Ammonia is the most widely used refrigerant, primarily employed in ice-making and refrigeration. The advantages of ammonia as a refrigerant include its high refrigeration capacity per unit volume, moderate evaporation and condensation pressures. Even at a cooling water temperature of up to 30 degrees Celsius, the condensation pressure does not exceed 1.52 MPa. As long as the evaporation temperature is not lower than -33.4 degrees Celsius, the evaporation pressure is always greater than one atmosphere, preventing vacuum formation in the evaporator. Ammonia has low viscosity and low flow resistance, excellent heat transfer properties, and does not corrode steel. It is easily soluble in water, reducing the likelihood of "ice plug" occurrences in the system. Additionally, ammonia is affordable and readily available.

Ammonia's primary drawbacks include its strong, pungent odor, high toxicity, and harmful effects on the human body. When the volume fraction of ammonia in the air reaches 0.5% to 0.6%, exposure for half an hour can cause intoxication. Ammonia is highly flammable and explosive; it can ignite at a volume fraction of 11% to 14% in the air and cause an explosion when mixed with a flame at a volume fraction of 16% to 25%. Therefore, ammonia refrigeration rooms must ensure proper ventilation.

Chlorofluorocarbons

Freon refrigerants come in various types with diverse performance characteristics, yet they share common features. The advantages of Freon refrigerants include their non-toxicity, odorlessness, resistance to combustion, non-corrosiveness to metals, low thermal conductivity, resulting in lower exhaust temperatures. They also have a high molecular weight, making them suitable for centrifugal refrigerant compressors. However, their drawbacks include lower refrigeration capacity per unit volume for some refrigerants, larger circulation volumes, high density, high flow resistance, and the release of toxic gases when chlorofluorocarbons are exposed to open flames. Additionally, they have low heat transfer coefficients, are expensive, and are prone to leakage that is difficult to detect.