Consider a two-stage cascade refrigeration system operating between the
pressure limits of \(1.2 \mathrm{MPa}\) and \(200 \mathrm{kPa}\) with
refrigerant-134a as the working fluid. The refrigerant leaves the condenser as
a saturated liquid and is throttled to a flash chamber operating at 0.45 MPa.
Part of the refrigerant evaporates during this flashing process, and this
vapor 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 cools the refrigerated space as it vaporizes in the evaporator.
The mass flow rate of the refrigerant through the lowpressure compressor is
\(0.15 \mathrm{kg} / \mathrm{s}\). Assuming the refrigerant leaves the
evaporator as a saturated vapor and the isentropic efficiency is 80 percent
for both compressors, determine \((a)\) the mass flow rate of the refrigerant
through the high-pressure compressor, \((b)\) the rate of heat removal from the
refrigerated space, and \((c)\) the COP of this refrigerator. Also, determine
\((d)\) the rate of heat removal and the COP if this refrigerator operated on a
single-stage cycle between the same pressure limits with the same compressor
efficiency and the same flow rate as in part ( \(a\) ).
