A Carnot cycle operates between −8 ℃ and 18 ℃ . Find the coefficient of performance.
Ans. 10.19
A refrigeration system operates on the reversed Carnot cycle. The minimum and maximum
temperatures are −25 ℃ and 72 ℃ , respectively. If the heat rejected at the condenser is
6000 kJ/min. Find the power input required.
Ans. 1686.96 kJ /min
An ice plant produces 20 tons of ice per day at -15 ℃ from water at 25 ℃. If miscellaneous
losses are 12% of the freezing and chilling load, calculate the refrigeration capacity of the
plant in tons of refrigeration.
Ans. 31.5 TOR
Fish weighing 11,000 kg with a temperature of 20 ℃ is brought to a cold storage and which
shall be cooled to -10 ℃ in 11 hours. Find the required plant refrigerating capacity in tons of
below freezing point which is -3 ℃. The latent heat of freezing is 55.5 kCal/kg.
refrigeration if the specific heat of fish is 0.7 kCal/kg∙℃ above freezing and 0.30 kCal/kg℃
Ans. 24.37 TOR
An ideal vapor compression cycle requires 2.5 kW to power the compressor. You have found
the following data for the cycle: the enthalpy at the condenser entrance = 203 kJ/kg; exit =
55 kJ/kg; evaporator entrance = 55 kJ/kg; exit = 178 kJ/kg. If the mass flow rate of the
refrigerant is 0.10 kg/s, then the coefficient of performance of this refrigeration cycle is most
nearly:
Ans. 4.92
An air-conditioning system of a high-rise building has a capacity of 350 kW of refrigeration,
uses R-12. The evaporating and condensing temperatures are 0 ℃ and 35 ℃ respectively.
Determine the mass of refrigerant 12 circulated per second.
Properties of R-12:
At 0 ℃ : vg = 0.05539 m3/kg , hf = 200 kJ/kg , hg = 351.48 kJ/kg
At 35 ℃ : hf = 233.5 kJ/kg
Ans. 2.97 kg /s
An ideal gas refrigeration cycle using air as the working medium is to maintain a refrigerated
space at 0 ℉ while rejecting heat to the surrounding medium at 80 ℉ . The pressure ratio of
the compressor is 4. Determine the COP.
Ans. 2.06
An ideal gas refrigeration cycle (Reverse Brayton) using air as the working medium is to
maintain refrigerated space at −5 ℃ while rejecting heat to the surrounding medium is
21 ℃. The pressure ratio of the compressor is 5. Determine the coefficient of performance.
Ans. 1.71
A sample of air has dry-bulb temperature of 30C and a wet-bulb temperature of 25C . The
barometric pressure is 101.325 kPa. Calculate the enthalpy of the air if it is adiabatically
saturated. At 25 deg C Pv=3.17 kPa, hg=2547.2 kJ/kg.
kJ
Ans. 76.13
kg
A coil has an inlet temperature of 60F and outlet of 90F. If the mean temperature of the coil
is 110F, find the bypass factor of the coil.
Ans. 0.40
The mass of an outside air at 50C in an air conditioning unit is 60 kg. Find the temperature
after mixing if the outside air mixed with 40 kg with recirculated air at 35C.
Ans. 44 ℃
If the latent and sensible heat loads are 20 kW and 80 kW respectively, what is the sensible
heat ratio?
Ans. 0.8
Determine the approximate load (Btu/min) on a cooling tower if the entering and leaving
temperatures of water are 96F and 88F, respectively and the flow rate of the water over the
tower is 30 gpm.
btu
Ans. 2002.14
min
The natural draft cooling tower has a 400-ton heat rejected load. The temperature of the
water entering the cooling tower is 90°F and leaving at 82°F. Compute the approach, range
and cooling tower efficiency when the outdoor wet bulb temperature is 75°F.
Ans. T R =8 ℉ ; T A=7 ℉ ; e=53.33 %
A duct 0.40 m high and 0.80 m wide suspended from the ceiling in a corridor, makes a right
angle turn in the horizontal plane. The inner radius is 0.2 m and the outer radius is 1.0 m
measured from the same center. The velocity of air in the duct is 10 m/s. Compute the
pressure drop in this elbow. Assuming ; f = 0.3, = 1.204 kg/m3 and L = 10 m.
Ans. 340 Pa
