Refrigerant, also known as refrigerant and snow seed, is a medium substance that completes energy conversion in various heat engines. These substances usually increase power through reversible phase change (such as gas-liquid phase change). Such as steam in a steam engine, snow in a refrigerator and so on. When a general steam engine works, it releases the heat energy of steam and converts it into mechanical energy to generate power. Snow seeds in the refrigerator are used to transfer low-temperature heat to high temperature.
Some halogenated hydrocarbons (especially chlorofluorocarbons) are common working fluids in traditional industry and life, but they are gradually eliminated because of ozone hole. Other widely used working media are ammonia, sulfur dioxide and non-halogenated hydrocarbons (such as methane).
In 1805, O.Evans first put forward the idea of freezing water into ice by using volatile fluid in closed cycle.
He described the system, which evaporates ether under vacuum, pumps steam into a water-cooled heat exchanger, and uses it again after condensation. Perkins developed the vapor compression refrigeration cycle for the first time in 1834, and obtained the patent. In the vapor compression refrigeration equipment he designed, ether was used as refrigerant.
Early refrigerants were mostly flammable or toxic, or both, some were corrosive and unstable, or some were too high pressure, which often caused accidents.
Mechanical refrigeration appeared in the middle of19th century. Jacob Perkins made the first practical machine in 1834. It uses ether as refrigerant and is a vapor compression system.
Carbon dioxide (CO2) and ammonia (NH3) were used as refrigerants for the first time in 1866 and 1873 respectively. Other chemicals, including chemical cyanide (petroleum ether and naphtha), sulfur dioxide (R-764) and methyl ether, have been used as refrigerants for vapor compression. Its application is limited to industrial processes. Most foods are still preserved with ice collected in winter or made in industry.