Question

A cooling plant adopted a two-stage cascade refrigeration system
to meet the required cooling load. In both upper and lower cycles,
the refrigerant leaves condenser as saturated liquid and enters
compressor as saturated vapor. The isentropic efficiency of the
upper cycle compressor is 80 %, while the lower cycle compressor is
70% efficient. The pressure limits of the upper and lower cycles
are 1 MPa and 0.2 MPa with refrigerant-134a, respectively. Heat
rejection from the lower cycle to the upper cycle takes place in an
adiabatic counterflow heat exchanger where the lower cycle enters
about at 0.5 MPa and the upper cycle enter about at 0.32MPa. If the
mass flow rate of the refrigerant in the upper cycle is 0.28 kg/s,
determine

1)the mass flow rate of the refrigerant in the lower cycle

2)the rate of heat removal from the refrigerated space and the
power input into the compressors

3)the COP of the refrigerator,

Answer #1

A two-stage cascade refrigeration system is shown below. The
refrigerant is R134a. It consists of two ideal vapor-compression
cycles with heat exchange between the condenser of the
lowertemperature cycle and the evaporator of the higher-temperature
cycle. The hotter cycle operates between 0.7 MPa and 0.35 MPa,
while the cooler cycle operates between 0.35 MPa and 0.12 MPa. If
the ﬂow rate in the hotter cycle is 0.5 mol/s, determine the
following:
What is the ﬂow rate in the cooler cycle?...

Consider a single-stage refrigeration system operating between the pressure limits of 1.4 MPa and 160 kPa
with refrigerant R134a as the working fluid. The refrigerant is a saturated liquid at the condenser exit and a
saturated vapor at the compressor inlet. The isentropic efficiency for the compressor is 80 percent. If the
mass flow rate of the refrigerant through the cycle is 0.11 kg/s determine (a) the rate of heat removal from the
refrigerated space, and (b) the coefficient of...

Consider a commercial refrigerator which operates on the
refrigeration cycle. R-
134a is used as the working
uid and the refrigerated space is kept at -25oC by rejecting
its
waste heat to cooling water that enters the condenser at room
temperature, that is 20oC, at a
rate of 0.1 kg/s and leaves at 40oC. The refrigerant enters the
condenser at 1.2 MPa and 70oC
and leaves at 40oC. The inlet state of the compressor is saturated
vapor at 100 kPa...

A commercial refrigerator with refrigerant-134a as the working
fluid is used to keep the refrigerated space at −30°C by rejecting
its waste heat to cooling water that enters the condenser at 18°C
at a rate of 0.32 kg/s and leaves at 26°C. The refrigerant enters
the condenser at 1.2 MPa and 65°C and leaves at 42°C. The inlet
state of the compressor is 60 kPa and −34°C and the compressor is
estimated to gain a net heat of 460 W...

A condenser is essentially a type of heat exchanger that is used
to remove heat from a vapor and convert it to liquid. The picture
below shows a condenser that is used in a commercial refrigerator
with refrigerant-134a as the working fluid. Water enters the
condenser at 18ºC at a rate of 0.25 kg/s and leaves at 26ºC. The
refrigerant enters the condenser at 1.2 MPa and 50ºC and leaves at
the same pressure but at T=41.3ºC. a) Find the...

A commercial refrigerator with refrigerant R-134a as the working
fluid is used to keep the refrigerated space at -30 C by rejecting
its waste heat to cooling water that enters the condenser at 18 C
at a rate of 0.25 kg/s and leaves at 26 C. The refrigerant enters
the condenser at 1.2 MPa and 65 C and leaves at 42 C. The inlet
state of the compressor is 60 kPa and -34 C and the compressor is
estimated to...

R-134a enters the compressor of a refrigerator as superheated
vapour at 0.14 MPa, -10 °C at a rate of 0.12 kg/s, and it leaves at
0.7 MPa and 50 °C.
The refrigerant is cooled in the condenser to 24 °C and 0.65 MPa,
and it is throttled to 0.15 MPa.
Disregard any heat transfer and pressure drops in the connecting
lines between the components.
Show the cycle on a T-s diagram with respect to saturation
lines, and determine
(a) the...

A vapor-compression refrigeration cycle operates at steady state
with Refrigerant 134a as the working fluid. Saturated vapor enters
the compressor at 2 bar, and saturated liquid exits the condenser
at 8 bar. The isentropic compressor efficiency is 80%. The mass
flow rate of refrigerant is 7 kg/min. Determine: (a) the compressor
power, in kW, (b) the refrigeration capacity, in tons, (1 ton =
3.5168 kW) and, (c) the coefficient of performance, (d) rate of
entropy production in kW/K, for the...

An ideal vapor-compression refrigeration cycle operates at
steady state with Refrigerant 134a as the working fluid. Saturated
vapor enters the compressor at 1 bar, and saturated liquid exits
the condenser at 4 bar. The mass flow rate of refrigerant is 8.5
kg/min.
Determine the compressor power, in kW.

Regarding a Vapor-Compression cycle: A refrigerant (HCFC-22)
enters the compressor of a refrigerator as a superheated vapor at
.14MPa and -20 degrees Celsius at a rate of .05 kg/s and leaves at
.8 MPa and 50 degrees Celsius. The refrigerant is cooled in the
condenser to 26 degrees Celsius and .72MPa and is then throttled
down to .15 MPa. Determine the rate of heat removal from the
refrigerated space and the power input to the compressor and the
Coefficient of...

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