Principles of Ammonia Refrigeration Systems
- Ammonia is an effective refrigerant.refrigerating equipment image by Alexey Kuznetsov from Fotolia.com
Ammonia refrigeration systems are a classic example of gas absorption refrigeration. The absorption refrigerator was invented by Baltzar von Platen and Carl Munters in 1922. The absorption refrigerator utilizes a heat source that provides the necessary energy to drive the cooling system instead of depending on electricity to energize a compressor. These refrigerators are ideal where waste heat is available or electricity is scarce. An example of waste process heat is the exhaust from a steam boiler. Often, this valuable heat is simply exhausted into the atmosphere. - Evaporative cooling is how sweat cools people's skin.back of man running image by jimcox40 from Fotolia.com
The thermodynamic process utilized in ammonia refrigeration is based on evaporative cooling. When a liquid evaporates, it carries heat away. Absorptive refrigerators use a coolant (in this case, ammonia) that is regenerated in a closed cycle. As molecules evaporate, they move faster. Heat moves from slower moving molecules to faster moving ones and the faster ones absorb heat. This process is similar to human sweating where the water from sweat evaporates, cooling the surface of the skin. - Hydrogen helps to lower ammonia's boiling point.Different size and shaped pipes at a power plant image by Andrei Merkulov from Fotolia.com
Liquefied ammonia enters the evaporator in the presence of hydrogen. Hydrogen gas lowers the partial pressure of ammonia, allowing it to evaporate quicker. This changes ammonia's boiling point and converts it into a gas mixed with hydrogen. This lowering of the boiling point is responsible for the cooling. The ammonia must now be separated from the hydrogen. The absorber is a series of tubes where water is dripped down from the top. Ammonia is absorbed in the water while hydrogen gas flows back to the evaporator. - As ammonia evaporates, it takes heat from the water.I'm Just Venting! image by waynocook from Fotolia.com
Ammonia is now mixed with water and heat is applied. This heat is usually waste heat from another system. The heat boils the ammonia out of the water which takes heat out of the water mixture, thus cooling it. This phase is called the generator. The chilled water can be used for refrigeration applications and the ammonia is sent to a condenser. A condenser is a heat sink that removes the heat from the vaporized ammonia and condenses it back into a liquid. The ammonia then flows back to the evaporator and the cycle begins again.
