Consider a two-stage compression refrigeration system operating between the pressure limits of 0.8 and 0.14 MPa (see Fig. Q 2). The working fluid is refrigerant -134a . The refrigerant leaves the condenser as a saturated liquid and is throttled to a flash chamber operating at 0.4 MPa. Part of the refrigerant evaporates during this flashing process, and this vapour is mixed with the refrigerant leaving the low-pressure compressor. The mixture is then compressed to the condenser pressure by the high-pressure compressor. The liquid in the flash chamber is throttled to the evaporator pressure, and it cools the refrigerated space as it vaporizes in the evaporator. Assuming the refrigerant leaves the evaporator as saturated vapor and both compressors are isentropic, determine (a) the fraction of the refrigerant that evaporates as it is throttled to the flash chamber, (b) the amount of heat removed from the refrigerated space and the compressor work per unit mass of refrigerant flowing through the condenser, and (c) the coefficient of performance (COP). Re-draw the schematic diagram and sketch the cycle accurately on a T-s diagram with the property values labelled at all state points.
Consider a two-stage compression refrigeration system operating between the pressure limits of 0.8 and 0.14 MPa
(see Fig. Q 2). The working fluid is refrigerant -134a . The refrigerant leaves the condenser as a saturated liquid and is throttled to a flash chamber operating at 0.4 MPa. Part of the refrigerant evaporates during this flashing process, and this vapour is mixed with the refrigerant leaving the low-pressure compressor. The mixture is then compressed to the condenser pressure by the high-pressure compressor. The liquid in the flash chamber is throttled to the evaporator pressure,
and it cools the refrigerated space as it vaporizes in the evaporator. Assuming the refrigerant leaves
the evaporator as saturated vapor and both compressors are isentropic, determine
(a) the fraction of the refrigerant that evaporates as it is throttled to the flash chamber,
(b) the amount of heat removed from the refrigerated space and the compressor work per unit mass
of refrigerant flowing through the condenser, and
(c) the coefficient of performance (COP).
Re-draw the schematic diagram and sketch the cycle accurately on a T-s diagram with the property
values labelled at all state points.
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