1.Easy
A refrigerator removes heat from its cold space at a rate of 5.76 kW while its compressor uses 2.4 kW of power. Find the rate Q̇H at which it rejects heat to the kitchen.
Q̇L = 5.76 kWẆ = 2.4 kW
Q̇H = kW
Heat engines & refrigerators worksheet with answers
2.Easy
A power plant delivers a net power output of 750 MW with a thermal efficiency of 25%. Find the rate of heat input Q̇H from the fuel.
Ẇ = 750 MWη = 25%
Q̇H = MW
3.Medium
A reversible refrigerator keeps a cold room at -20 °C by removing 4.5 kW of heat, and rejects heat to the surroundings at 25 °C. Find the rate Q̇H at which it rejects heat.
TL = -20 °CTH = 25 °CQ̇L = 4.5 kW
Q̇H = kW
4.Medium
A reversible refrigerator keeps a cold room at -5 °C by removing 8 kW of heat, and rejects heat to the surroundings at 35 °C. Find the rate Q̇H at which it rejects heat.
TL = -5 °CTH = 35 °CQ̇L = 8 kW
Q̇H = kW
5.Hard
A Carnot heat engine receives 10 kW of heat from a source at 650 °C and rejects heat to the surroundings at 20 °C. All of its work drives a Carnot refrigerator that removes heat from a freezer at -5 °C and also rejects heat to the surroundings at 20 °C. Find the rate Q̇L at which heat is removed from the freezer.
TH = 650 °CT0 = 20 °CTL = -5 °CQ̇H = 10 kW
Q̇L = kW
6.Hard
A heat pump keeps a house at 21 °C while it is 2 °C outside, delivering 9 kW of heat to the house. Find the minimum power input Ẇmin.
TH = 21 °CTL = 2 °CQ̇H = 9 kW
Ẇmin = kW
Answer key
- 1. Q̇H = 8.16 kW
- 2. Q̇H = 3000 MW
- 3. Q̇H = 5.3 kW
- 4. Q̇H = 9.193 kW
- 5. Q̇L = 73.2 kW
- 6. Ẇmin = 0.5813 kW
Full step-by-step solutions: practise this topic on examproblems.com.