Mechanical refrigeration system

 In mechanical refrigeration system, the vapours caused by a sudden change of liquid in metering device without gaining any heat is known as flash gas. Before entering the liquid into the evaporator, the formation of flash gas at the metering device is not useful at all. Because this flash gas does not gain any heat in the evaporator. Therefore, for avoiding flash gas in the liquid line, the vapours are condensed in the condenser below their condensing point by circulating more quantity of cold water than required or by using heat exchanger. Such type of liquid below its condensing point is called sub-cooled liquid. This sub-cooled liquid contains more heat gaining ability below its boiling point which helps in avoiding the flash gas. A few degrees of temperature of sub-cooled liquid• rise at the metering device, but this liquid does not take the form of flash gas. In this way flash gas is avoided by sub-cooling the liquid and good net refrigerating effect is obtained. In addition to it, for avoiding flash gas another method is adopted in which the formation of flash gas in the metering device is collected just after the metering device in a flash chamber. This flash gas is directly returned to the suction line through a bypass line without sending it to the evaporator.