1.Easy
A heat engine takes in 2700 kJ of heat from a hot reservoir and rejects 1620 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.
QH = 2700 kJQL = 1620 kJ
η = %
Heat engines & refrigerators worksheet with answers
2.Easy
A refrigerator removes heat from its cold space at a rate of 6.38 kW while its compressor uses 2.2 kW of power. Find the rate Q̇H at which it rejects heat to the kitchen.
Q̇L = 6.38 kWẆ = 2.2 kW
Q̇H = kW
3.Medium
A heat engine works between a hot reservoir at 450 °C and a cold reservoir at 40 °C. It takes in 1100 kJ of heat. Find the most work Wmax it could possibly produce.
TH = 450 °CTL = 40 °CQH = 1100 kJ
Wmax = kJ
4.Medium
A heat engine works between a hot reservoir at 325 °C and a cold reservoir at 40 °C. It takes in 2700 kJ of heat. Find the most work Wmax it could possibly produce.
TH = 325 °CTL = 40 °CQH = 2700 kJ
Wmax = kJ
5.Hard
Two Carnot engines work in series. Engine A receives heat from a reservoir at 800 °C and rejects heat to an intermediate reservoir at temperature Tm. Engine B takes all that heat and rejects heat to a reservoir at 35 °C. Both engines produce the same work. Find Tm in °C.
TH = 800 °CTL = 35 °C
Tm = °C
6.Hard
A refrigerator keeps its cold space at -20 °C in a kitchen at 25 °C, removing heat from the cold space at 3 kW. Find the minimum power input Ẇmin.
TH = 25 °CTL = -20 °CQ̇L = 3 kW
Ẇmin = kW
Answer key
- 1. η = 40 %
- 2. Q̇H = 8.58 kW
- 3. Wmax = 623.7 kJ
- 4. Wmax = 1286 kJ
- 5. Tm = 417.5 °C
- 6. Ẇmin = 0.5333 kW
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