Principle of steam jet refrigeration system: -
The boiling point of a liquid changes with change in external pressure. In normal conditions, pressure exerted on the surface of a liquid is the atmospheric pressure. If this atmospheric pressure is reduced on the surface of a liquid, by some means, then the liquid will start boiling at lower temperature, because of reduced pressure. This basic principal of boiling of liquid at lower temperature by reducing the pressure on its surface is used in steam jet refrigeration system. The boiling point of pure water at standard atmospheric pressure of 760 mm of Hg is 1 00°C. It may be noted that water boils at 12′C if the pressure on the surface of water is kept at 0.014 bar and at 7′C if the pressure on the surface of water is 0.01 bar. The reduced pressure on the surface of water is maintained by throttling the steam through the jets or nozzles. Working of steam jet refrigeration system: -
The flash chamber or evaporator is a large vessel and is heavily insulated to avoid the rise in temperature of water due to high ambient temp. It is fitted with perforated pipes for spraying water. The warm water coming out of the refrigerated space is sprayed into the flash water chamber where some of which is converted into vapours after absorbing the latent heat, thereby cooling the rest of water. The high pressure steam from the boiler is passed through the steam nozzle thereby increase its velocity. The high velocity steam in the ejector would entrain the water vapours from the flash chamber which would result in further information of vapour. The mixture of steam and water vapour passes through the ventilate-tube of the ejector and gets compressed. The temperature and pressure rises considerably and fed to the water cooled condenser where it gets condensed. Analysis of Steam Jet Refrigeration System: -
The temperature – entropy (T– s) and enthalpy-entropy (h – s) diagrams for a steam jet refrigeration system are shown in fig....
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