1.Easy
A heat engine takes in 900 kJ of heat from a hot reservoir and rejects 495 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 900 kJQL = 495 kJ
W = kJ
Heat engines & refrigerators worksheet with answers
2.Easy
A refrigerator removes heat from its cold space at a rate of 4.81 kW while its compressor uses 1.3 kW of power. Find the rate Q̇H at which it rejects heat to the kitchen.
Q̇L = 4.81 kWẆ = 1.3 kW
Q̇H = kW
3.Medium
A reversible (Carnot) heat engine takes in 4200 kJ of heat from a reservoir at 300 °C and rejects 2148 kJ per cycle. Find the temperature TL of the cold reservoir in °C.
TH = 300 °CQH = 4200 kJQL = 2148 kJ
TL = °C
4.Medium
A heat engine works between a hot reservoir at 550 °C and a cold reservoir at 20 °C. Find the highest possible thermal efficiency ηmax.
TH = 550 °CTL = 20 °C
ηmax = %
5.Hard
A refrigerator keeps its cold space at 5 °C in a kitchen at 25 °C, removing heat from the cold space at 4 kW. Find the minimum power input Ẇmin.
TH = 25 °CTL = 5 °CQ̇L = 4 kW
Ẇmin = kW
6.Hard
A heat engine takes in 2200 kJ of heat from a reservoir at 750 °C, produces 1078 kJ of work and rejects the rest to a reservoir at 40 °C, per cycle. Find the total entropy generated Sgen per cycle.
TH = 750 °CTL = 40 °CQH = 2200 kJW = 1078 kJ
Sgen = kJ/K
Answer key
- 1. W = 405 kJ
- 2. Q̇H = 6.11 kW
- 3. TL = 19.98 °C
- 4. ηmax = 64.39 %
- 5. Ẇmin = 0.2876 kW
- 6. Sgen = 1.433 kJ/K
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