A cascade refrigeration system is designed to supply 9 tons of refrigeration at an evaporator temperature of -55OC and a condenser temperature of 20OC. The load at -55OC is absorbed by a unit using R-22 as the refrigerant and is rejected to a condenser at -15OC. The cascade condenser is cooled by a unit using R-12 as the refrigerant and operating between -25OC and 20OC condenser temperature. The refrigerant leaving the R-12 condenser is subcooled to 15OC while there is no subcooling of the R-22 refrigerant. The gas leaving both the evaporators is dry and saturated and the compressions are isentropic. (a) Draw the cycle schematic diagram and (b) draw the corresponding p-h diagram. Neglecting losses, determine the following: (c) the quantity of refrigerant circulated per minute in the R-22 unit and (d) in the R-12 unit, (e) the COP for each unit, (f) the COP of the whole system and (g) the theoretical power to run the whole system
. A cascade refrigeration system is designed to supply 9 tons of refrigeration at an
evaporator temperature of -55OC and a condenser temperature of 20OC. The load at
-55OC is absorbed by a unit using R-22 as the refrigerant and is rejected to a condenser
at -15OC. The cascade condenser is cooled by a unit using R-12 as the refrigerant and
operating between -25OC and 20OC condenser temperature. The refrigerant leaving the
R-12 condenser is subcooled to 15OC while there is no subcooling of the R-22 refrigerant.
The gas leaving both the evaporators is dry and saturated and the compressions are
isentropic. (a) Draw the cycle schematic diagram and (b) draw the corresponding p-h
diagram. Neglecting losses, determine the following: (c) the quantity of refrigerant
circulated per minute in the R-22 unit and (d) in the R-12 unit, (e) the COP for each
unit, (f) the COP of the whole system and (g) the theoretical power to run the whole
system
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