Steam Jet Refrigeration System
The steam jet refrigeration system is the oldest way for delivering refrigerating impact. This system utilizes a steam ejector or promoter for compression of refrigerant to the condenser pressure level. In this system, we use water as a refrigerant. Therefore, freezing point water is 0C. Hence we use the steam jet refrigeration systems in food processing plants for precooling of vegetables and concentrating fruit juice, gas plants, paper mills, breweries, etc. The basic components of the steam jet refrigeration system are
- an evaporator,
- a compression device,
- a condenser
- and a refrigerant control device
Principle of Steam Jet Refrigeration System
The boiling point of water changes with external pressure. In normal conditions, the pressure exerted on the surface of any liquid is the atmospheric pressure. Suppose we reduce the pressure on the surface of the liquid by some external means then liquid also starts to boil at low temperature. We use this principle in a refrigeration system.
The boiling point of pure water at standard atmospheric pressure of 760mm of Hg is 100C. It may be noted that water boils at 12C if the pressure on the surface of the water is kept at 0.014 bar and 7C if the pressure on the surface of the water is 0.01bar. The reduced pressure on the surface of the water is maintained by throttling the steam through the jet or nozzles.
Working of Steam Jet Refrigeration System
The main components of the steam jet refrigeration system are the flash chambers or evaporators, steam nozzles, ejectors, and condenser.
- The flash chamber or evaporator is a large vessel. We insulate it to avoid a rise in temperature of water due to high ambient temperature. It is fitted with punctured funnels for splashing water.
- The warm water from the space sprays over the flash water chamber where some are converted into vapour after absorbing the latent heat, thereby cooling the rest of water.
- When the high-pressure steam passes through the steam nozzle, thereby its velocity increases. This high-speed steam in the ejector would entrain the water vapour from the flash chambers which would result in the further formation of vapours. The mixture of steam and water vapour passes through the venturi tube of the ejector and gets compressed.
- The temperature and pressure of the mixture rises and fed to the water-cooled condenser where it gets condensed. The condensate is again fed to the boiler as feedwater. A constant water level is maintained in the flash chamber and any loss of water due to evaporation is made up of the makeup water line.