A cascade refrigeration system is required to supply 20 tonnes of refrigeration at an evaporator temperature of -50°C and a condenser temperature of 40°C. The load at -50°C is absorbed by a unit using R-22 refrigerant and is rejected to a cascade condenser at -10°C. This cascade condenser is cooled by a unit using R-12, as the refrigerant and operating between -25°C evaporating temperature and 40°C condensing temperature. The refrigerant leaving the R12 condenser is subcooled by 5°C and there is no subcooling of R22 refrigerant. The gas leaving both the evaporator is dry and saturated and the compressions are isentropic. Neglecting losses, find a) compression ratio of each unit b) quantity of refrigerant circulated per minute for each unit c) COP of the whole system & theoretical power required to drive the system.
Give an illustration on Primary and Secondary refrigerant. What are the desirable proportions of an ideal refrigerant?
Define "Cryogenics". Mention its application. Why dry ice, despite its high manufacturing cost. is used as a refrigerant?
Write short notes on the following: