Steam jet refrigeration system.pptx

steam jet refrigeration system full working and a simple way to understand it covering the aspects of heat and refrigeration systems.

1. Steam jet refrigeration system SANIA BAISOYA A2399819028

2. INTRODUCTION The steam jet refrigeration system (also known as ejector refrigeration system ) is one of the oldest methods of producing refrigeration effect. It is a cooling technique which involves usage of steam and water for cooling purposes. This system utilizes mostly low-grade energy and relatively small amounts of shaft work. In this system, water is used as the refrigerant. Not used when temperatures below 5°C are required. Temperatures attained using water as a refrigerant are in the range which may satisfy air conditioning, cooling, or chilling requirements. Thus, it is widely used in food processing plants and in some chemical industries for several purposes.

3. WHY IS THIS UNCONVENTIONAL TECHNIQUE PREFERRED ? Steam jet cooling system is preferable over conventional cooling system because: Employs a steam injector or booster instead of mechanical compressor to compress the refrigerant to the required condenser pressure level. Water is used as the refrigerant; environment is free of CFC's and other refrigerants which produce harmful gases leading to depletion of ozone layer.

4. Principle of steam jet refrigeration system : – PRINCIPLE - "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. Basically , boiling the water under 100°C by the process of reducing the pressure on the water surface below atmospheric pressure.

5. SCHEMATIC DIAGRAM

6. COMPONENTS OF STEAM JET REFRIGERATION SYSTEM There are various components in this system. Evaporator: The evaporator or flash chamber is a large vessel and is heavily insulated to avoid the rise in temperature of water due to highly ambient temperature. Condenser: Chills the LP, HT air coming from the thermo-compressor using chilled water as the refrigerating medium. Ejector: (replacing compressor) Used to compress the water vapours coming out of the flash chamber Nozzle: It is used to increase the velocity of the steam.

7. WORKING OF A STEAM JET COOLING SYSTEM High pressure steam flows to the nozzle from the boiler which is expanded. The flash chamber is heavily insulated and is fitted with perforated pipes which spray warm water coming out of refrigerated space. Some of this water is converted into vapours after absorbing latent heat from the rest of the water, thereby cooling it. Water vapours from the flash chamber drawn along with the high velocity steam jet from the boiler and it is further compressed in the thermo compressor. This leads to rise in temperature and pressure of the mixture. T hen it is fed to the water cooled condenser. The condensate is again fed to boiler as feed water. Generally, 1% evaporation of water in the flash chamber is sufficient to decrease the temperature of chilled water to 6°C. Chilled water is circulated by a pump to the point of application. The warm water from the load is returned to the flash chamber. The water is sprayed through the nozzles to provide maximum surface area for cooling. The water, which is splashed in the chamber and any loss of cold water at the application, must be replaced by makeup water added to the cold water circulating system.      

8. NOW WHAT IS IT’S COP ? The COP may be defined as the ratio of evaporator refrigeration load to heat input to the boiler as follows:                                   

9. WHAT STEAM JET EJECTORS ACTUALLY DO? High pressure steam from the boiler(generally called primary fluid or motive steam) is admitted to the steam chest and expanded in convergent -divergent nozzle to a very low pressure and attains supersonic velocities in the range of 1000m/s to 1350m/s. The flash chamber is connected to the region of low pressure of the ejector. The water vapour from the flash chamber is entrained in the high velocity jet of steam and both are mixed in the mixing section at the constant pressure. The velocity of mixture will be super sonic after the completion of the mixing process. This supersonic steam get a normal shock in constant area throat of diffuser, resulting in rise of pressure and subsonic flow. The diverting portion of the diffuser velocity head is recovered as pressure head and finally high pressure steam is condensed in condenser.

10. Advantages Simple construction Vibration free system Highly reliable Low production cost Water is used as a refrigerant which is perfectly safe. Low running cost Load variation quickly adjusted It is suitable for places where steam is available such as process industry, steel plant, petroleum plants, thermal power plants etc.

11. Disadvantages Not suitable for water temperature below 5C. The maintenance of high vacuum in the evaporator is necessary for proper functioning of the system. COP is very low. Eff iciency of ejector is not good.

12. APPLICATION Food processing plant for precooling of vegetables and concentrating fruit etc. the removal of paraffin wax from lubricating oils Gas plants Breweries Rubber and vulcanizing industries Paper and pulp industries.

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