Principles of Ammonia Refrigeration Systems
There are two general principles of ammonia refrigeration systems. Vapor compression systems use anhydrous ammonia, an ammonia (NH3) that does not contain water. The other system, absorption cooling uses a generator in combination with aqua ammonia, an ammonia that contains water.
Nearly all industrial food production and chemical industries use ammonia to cool their refrigerators and freezers. Vapor compression is the most popular method of refrigeration used in industrial processes due to its capacity to maintain highly precise temperatures necessary for specific cooling.
An important component of the vapor pressure process involves the chemical and physical property called Dalton's Law of Partial Pressures. This law states that the total pressure that is exerted by a gas is equal to the sum of all individual pressures of each component pressure of the absorption system.
There are five general components to the mechanical vapor compression system.
- Compressor: Increases the vapor pressure of the anhydrous ammonia in order to condense the vapor from the gaseous state into a liquid.
- Evaporator: Absorbs the heat of the vapor from the anhydrous NH3.
- Expansion-throttling: Allows the liquid to exand from a state of high pressure to a state of lower pressure in a two-phase mixture process.
- Condenser: Rejects the heat from the cycle by cooling the mixture through removing the heat. Water or air is circulated around the piping coils of the condenser in order to de-pressurize the mixture.
- Piping: This is a crucial part of the entire system which connects the four mechanical components of the vapor pressure coolant system.
It is important to note that ammonia refrigeration systems are mainly used in industrial and commercial processes, no longer in residential homes or RV's, because of the danger associated with anhydrous ammonia's propensity to cause an explosion due to pressure and heat given off by the compressor.