1.Easy
A heat engine takes in 2600 kJ of heat from a hot reservoir and rejects 1430 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 2600 kJQL = 1430 kJ
W = kJ
Heat engines & refrigerators worksheet with answers
2.Easy
A refrigerator removes heat from its cold space at a rate of 9 kW while its compressor uses 3 kW of power. Find the rate Q̇H at which it rejects heat to the kitchen.
Q̇L = 9 kWẆ = 3 kW
Q̇H = kW
3.Medium
A reversible refrigerator keeps a cold room at 4 °C by removing 8 kW of heat, and rejects heat to the surroundings at 28 °C. Find the rate Q̇H at which it rejects heat.
TL = 4 °CTH = 28 °CQ̇L = 8 kW
Q̇H = kW
4.Medium
A reversible (Carnot) heat engine takes in 500 kJ of heat from a reservoir at 600 °C and rejects 174 kJ per cycle. Find the temperature TL of the cold reservoir in °C.
TH = 600 °CQH = 500 kJQL = 174 kJ
TL = °C
5.Hard
A heat engine takes in 4600 kJ of heat from a reservoir at 550 °C, produces 2024 kJ of work and rejects the rest to a reservoir at 30 °C, per cycle. Find the total entropy generated Sgen per cycle.
TH = 550 °CTL = 30 °CQH = 4600 kJW = 2024 kJ
Sgen = kJ/K
6.Hard
A Carnot heat engine receives 120 kW of heat from a source at 500 °C and rejects heat to the surroundings at 30 °C. All of its work drives a Carnot refrigerator that removes heat from a freezer at -10 °C and also rejects heat to the surroundings at 30 °C. Find the rate Q̇L at which heat is removed from the freezer.
TH = 500 °CT0 = 30 °CTL = -10 °CQ̇H = 120 kW
Q̇L = kW
Answer key
- 1. W = 1170 kJ
- 2. Q̇H = 12 kW
- 3. Q̇H = 8.693 kW
- 4. TL = 30.71 °C
- 5. Sgen = 2.909 kJ/K
- 6. Q̇L = 479.9 kW
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