1.Easy
A heat engine takes in 4500 kJ of heat from a hot reservoir and rejects 2475 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 4500 kJQL = 2475 kJ
W = kJ
Heat engines & refrigerators worksheet with answers
2.Easy
A heat engine takes in 3700 kJ of heat from a hot reservoir and rejects 2220 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.
QH = 3700 kJQL = 2220 kJ
η = %
3.Medium
A heat engine works between a hot reservoir at 500 °C and a cold reservoir at 5 °C. It takes in 1800 kJ of heat. Find the most work Wmax it could possibly produce.
TH = 500 °CTL = 5 °CQH = 1800 kJ
Wmax = kJ
4.Medium
A reversible refrigerator keeps a cold room at -30 °C by removing 1 kW of heat, and rejects heat to the surroundings at 35 °C. Find the rate Q̇H at which it rejects heat.
TL = -30 °CTH = 35 °CQ̇L = 1 kW
Q̇H = kW
5.Hard
A heat pump delivers 8 kW of heat to a heating system at 22 °C, taking heat from a source at 7 °C. Its actual COP is 35% of the Carnot COP between these temperatures. Find the electrical power Ẇ it uses.
TH = 22 °CTL = 7 °CηII = 35%Q̇H = 8 kW
Ẇ = kW
6.Hard
Two Carnot engines work in series. Engine A receives heat from a reservoir at 650 °C and rejects heat to an intermediate reservoir at temperature Tm. Engine B takes all that heat and rejects heat to a reservoir at 30 °C. Both engines have the same thermal efficiency. Find Tm in °C.
TH = 650 °CTL = 30 °C
Tm = °C
Answer key
- 1. W = 2025 kJ
- 2. η = 40 %
- 3. Wmax = 1152 kJ
- 4. Q̇H = 1.267 kW
- 5. Ẇ = 1.162 kW
- 6. Tm = 255.9 °C
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