Consider a two$-$stage compression refrigeration

system operating between the pressure limits of $0\mathrm{.}8$ and

$0\mathrm{.}14$ MPa $.$ The working fluid is refrigerant$-134$a$.$ The refrig$-$

erant leaves the condenser as a saturated liquid and is throt$-$

tled to a flash chamber operating at $0\mathrm{.}4$ 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 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 coeffi$-$

cient of performance. Answers: $($a$)0\mathrm{.}165,($b$)146\mathrm{.}4k\frac{J}{k}g,$

$32\mathrm{.}6k\frac{J}{k}g,($c$)4\mathrm{.}49$