Question

Air enters the evaporator section of a window air conditioner at 14.7 psia and 90°F with a volume flow rate of 200 ft3 /min. Refrigerant-134a at 20 psia with a quality of 30 percent enters the evaporator at a rate of 4 lbm/min and leaves as saturated vapor at the same pressure. Determine (a) the exit temperature of the air and (b) the rate of heat transfer from the air.

Answer #1

An air conditioner using refrigerant-134a as the working fluid
and operating on the ideal vapor-compression refrigeration cycle is
to maintain a space at 36°C while operating its condenser at 1600
kPa. Determine the COP of the system when a temperature difference
of 4°C is allowed for the transfer of heat in the evaporator. (Take
the required values from saturated refrigerant-134a tables.)

Atmosphric air at 40 F and 50% relative humidity enters the heating
section of an airconditioning device at a volumetric flow rate of
100ft^3/min. Water vapor is added to the heated air to increase the
relative humidity to 55%. The temperature after the heating section
is 72F and the temperature at the exit is 74F. Using the
appropriate fomulas:
a) determine the rate of the heat transfer in Btu/min.
b) determine the mass flow of water vapor in lbm/min.

Refrigerant 134a is the working fluid in a vapor-compression
heat pump system with a heating capacity of 60,000 Btu/h. The
condenser operates at 240 lbf/in.2, and the evaporator temperature
is 0°F. The refrigerant is a saturated vapor at the evaporator exit
and a liquid at 110°F at the condenser exit. Pressure drops in the
flows through the evaporator and condenser are negligible. The
compression process is adiabatic, and the temperature at the
compressor exit is 180°F. Determine (a) the mass...

Air is heated as it flows through a constant diameter
tube. The air enters the tube at 50 psia and 80 F with an average
velocity of 10 ft/s at the entrance. The air leaves at 45 psia and
255 F.
a) Sketch the control volume
b) Determine the average velocity of the air (ft/s) at the
exit
c) If 23 lbm/min of air is to be heated, what diameter (in.) tube
is required?

4.58 Air enters a compressor operating at
steady state with a pressure of 14.7 lbf/in^2, a temperature of 808
F, and a volumetric flow rate of 18 ft /s. The air exits the
compressor at a pressure of 90 lbf/in^2 Heat transfer from the
compressor to its surroundings occurs at a rate of 9.7 Btu per lb
of air flowing. The compressor power input is 90 hp. Neglecting
kinetic and potential energy effects and modeling air as an ideal
gas,...

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...

Air enters a counterflow heat exchanger operating at steady
state at 22°C, 0.1 MPa and exits at 7°C. Refrigerant 134a enters at
0.2 MPa, a quality of 0.21, and a mass flow rate of 30 kg/h.
Refrigerant exits at 0°C. There is no significant change in
pressure for either stream. (a) For the Refrigerant 134a stream,
determine the rate of heat transfer, in kJ/h (b) For the
refrigerant stream evaluate the change in flow exergy rate, in
kJ/h. (c) For...

Air at 95°F, 1 atm, and 10% relative humidity enters an
evaporative cooler operating at steady state. The volumetric flow
rate of the incoming air is 1765 ft3/min. Liquid water
at 68°F enters the cooler and fully evaporates. Moist air exits the
cooler at 70°F, 1 atm. There is no significant heat transfer
between the device and its surroundings and kinetic and potential
energy effects can be neglected.
a)Determine the mass flow rate of the dry air in lb(dry
air)/min....

Liquid propane enters a combustion chamber at 77⁰F and at a rate
of 0.75 lbm/min where it is mixed and burned with 150% excess air
that enters the combustion chamber at 40⁰F. If the combustion is
complete and the exit temperature of the combustion gases is 1800
R, determine (a) the mass flow rate of the air and (b) the rate of
heat transfer from the combustion chamber.

Consider an air-cooled condenser in which a stream of R-134a
enters at 12 bar and 60degC, and leaves as a saturated liquid at 12
bar, and air enters as a separate stream at 1 bar, 35degC and
leaves at 1 bar, 45degC. The two streams do not mix but heat
transfer from one stream to the other stream occurs at the rate of
6.94 kW.
Determine
(a) the mass flow rates for the R-134a and the air (kg/s),
and
(b)...

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