1.

A simple saturated refrigeration cycle for R-12 system

operates at an evaporating temperature of minus 5oC and
condensing temperature of 40°C. For a refrigerating
capacity of 1 kW, determine the volume flow rate of
refrigerant in m3/hr. At 40°C, hf = 238.5 kJ/kg: -5°C, hg =
349.30 kJ/kg; vg = 6.496 x10-2 m3/kg; the enthalpy the
entrance to the condenser is 372 KJ/kg.
Wednesday, 14 April 2021 9:25 AM

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2. A refrigeration system operates on the reversed Carnot
cycle. The maximum and minimum temperatures are
161.6°F and minus 13oF, respectively. If the heat rejected
to the condenser is 94.79 BTU/s, find the cooling capacity
in kW.
Wednesday, 14 April 2021 9:27 AM

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3. A refrigeration system is to be used to cool 45 metric
tons of water from 29°C to 18°C in 5 hours. The
refrigerant is ammonia and the operation conditions are
0.616 MPa evaporating pressure and 1.737 MPa
liquefaction pressure. Determine the quantity of cooling
water in the condenser for an Increase temperature of 7°
C, hf @ 1.737 MPa = 410.4 kJ/kg, hg @ 0.616 MPa =
1,471.6 kJ/kg, h at compressor exit = 1,620 kJ/kg.
Wednesday, 14 April 2021 9:27 AM

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4. An air conditioning system of a high-rise building has a
capacity of 0.35 MW of refrigeration. The evaporating and
condensing temperatures are 0°C and 35°C, respectively.
Determine work of compression in kW. Hf @ 35°C = 233.5
kJ/kg, hg @ 0°C = 351.48 kJ/kg. Enthalpy leaving the
compressor is 368 kJ/kg.
Wednesday, 14 April 2021 9:27 AM

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5. A refrigeration system operates on an ideal
compression using R-12 with an evaporator temperature
of - 30 °C and condenser exit temperature of 49.30°C and
requires 74.6 kW motor to drive the compressor. What is
the capacity of the refrigerator in tons of refrigeration?
Enthalpy at condenser entrance = 382 kJ/kg, condenser
exit = 248.15 kJ/kg, evaporator entrance = 248.15 kJ/kg
and evaporator exit = 338.14 kJ/kg.
Wednesday, 14 April 2021 9:27 AM

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6. Nestle dairy products plant must cool 4000 gallons of
fresh milk received from the farm per day from the initial
temperature of 80°F to a temperature of 38°F in 5 hours.
If the density of milk is 8.6 pounds per gallon, specific
heat of milk is 0.935 btu/lb.-°R, what must be the capacity
of the refrigerating machine in tons?
Wednesday, 14 April 2021 9:27 AM

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7. An air-conditioned room is being held at 24°C dry bulb
and 60% relative humidity. A flow rate of 4 m3/s of supply
air at 18°C dry bulb and 80% relative humidity is being
delivered to the room to maintain that steady condition,
what is the sensible heat absorbed from the room air?
Use standard atmospheric pressure.
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8. Calculate the amount of energy that must be removed
to cool the air at standard pressure in a house 20m x 30m
x 25m from 100°F to 40°F for a period of 4 hours. The
specific heat at constant pressure 0.24 BTU/lb.-°F. Use the
average mass of air based on the two temperature
readings.
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9. A refrigeration cycle having 0.2 MPa (hg = 190.8 kJ/kg)
and 0.95 MPa (h = 220 kJ/kg). The mass flow rate in the
cycle is 0.1 kg/sec with 12 kW rate of heat addition.
Determine the heat rejected per power.
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10. A reverse Carnot cycle requires 5 kW and extracts
energy from a lake to heat a house. If the house is kept at
25°C and the heat added is 1,800 kJ/minute, what is the
temperature of the lake?
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11. Fish weighing 11,000 kg with a temperature of 20°C is
brought to a cold storage and which shall be cooled
to -10°C in 11 hours. Find the required plant refrigerating
capacity in tons of refrigeration if the specific heat of fish
is 0.7 kcal/kg-K above freezing and 0.30 kcal/kg-K below
freezing point, which is -3°C. The latent heat of freezing is
55.5 kCal/kg.
Saturday, 17 April 2021 8:27 PM

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12. To cool farm products, 300 kg of Ice at -4.4°C are
placed in a bunker. Twenty-four hours later, the ice have
melted into water at 7.2°C. What is the average rate of
cooling provided by the ice in kJ/hr.?
Saturday, 17 April 2021 8:27 PM

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13. Fresh fish with a total load of 5,550 pounds with a
temperature of 15.55°C is brought to a cold storage and
will be cooled to -15.55°C in 5.55 hours. Calculate the
required plant refrigerating capacity in TOR If the specific
heat of fish is 5.55 KJ/kg-°K above freezing and 0.555
kcal/kg-°K below freezing point at - 5.55°C. The latent
heat of freezing is 55.5 Kcal/kg. Consider a heat loss of
15.55% during the cooling process above freezing point.
Saturday, 17 April 2021 8:29 PM

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14. How much is the capacity of refrigerating machine in
KW if it is required to cool 17,000 liters of evaporated
milk from an initial temperature of 70 degrees F to 37
degrees F in a period of 1.7 hours? The machine loss
accounted to 17% of the cooling load. The specific heat of
milk used is 1.7 BTU/lb-°R with a specific gravity of 1.17.
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Compute the heat to be removed from 110 kg of lean
beef if it were to be cooled from 20°C to 4°C. After which
it is frozen and cooled to -18°C. Specific heat of lean beef
above freezing is given as 3.23 kJ/kg-°C and below
freezing is 1.68 kJ/kg-°C, freezing point is -2.2°C, and
latent heat of fusion is 233 kJ/kg.
Sunday, 11 April 2021 10:08 PM

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Determine the approximate load on a cooling tower if the
entering and leaving temperatures are 96°F and 88°F,
respectively and the flow rate of the water over the tower
is 30 gpm. ANS: 2002 BTU/min
Tuesday, 14 December 2021 1:46 PM

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The natural draft-cooling tower has a 400-ton heat
rejection 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: 7°F, 8°F,
53.33%
Tuesday, 14 December 2021 1:47 PM

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A cooling tower receives 6 kg/s of water of 60℃. Air
enters the tower at 32℃ dry-bulb and 27℃ wet-bulb (SH
= 0.0206) and leaves at 50℃ and 90% RH (SH = 0.0766).
The cooling efficiency is 60.6%. Determine the mass flow
rate of air entering and the quantity of make-up water
required. ANS: 3.244 kg/s, 0.1817 kg/s
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