1.Easy
A heat engine takes in 3800 kJ of heat from a hot reservoir and rejects 2280 kJ to a cold reservoir in each cycle. Find its thermal efficiency η.
QH = 3800 kJQL = 2280 kJ
η = %
Heat engines & refrigerators worksheet with answers
2.Easy
A heat engine takes in 1700 kJ of heat from a hot reservoir and rejects 1020 kJ to a cold reservoir in each cycle. Find the net work W it produces per cycle.
QH = 1700 kJQL = 1020 kJ
W = kJ
3.Medium
A heat engine works between a hot reservoir at 450 °C and a cold reservoir at 35 °C. It takes in 2300 kJ of heat. Find the most work Wmax it could possibly produce.
TH = 450 °CTL = 35 °CQH = 2300 kJ
Wmax = kJ
4.Medium
A reversible refrigerator keeps a cold room at -20 °C by removing 2.5 kW of heat, and rejects heat to the surroundings at 30 °C. Find the rate Q̇H at which it rejects heat.
TL = -20 °CTH = 30 °CQ̇L = 2.5 kW
Q̇H = kW
5.Hard
A refrigerator keeps its cold space at 2 °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 = 2 °CQ̇L = 4 kW
Ẇmin = kW
6.Hard
A heat pump keeps a house at 20 °C while it is 2 °C outside, delivering 15 kW of heat to the house. Find the minimum power input Ẇmin.
TH = 20 °CTL = 2 °CQ̇H = 15 kW
Ẇmin = kW
Answer key
- 1. η = 40 %
- 2. W = 680 kJ
- 3. Wmax = 1320 kJ
- 4. Q̇H = 2.994 kW
- 5. Ẇmin = 0.3344 kW
- 6. Ẇmin = 0.921 kW
Full step-by-step solutions: practise this topic on examproblems.com.