WorksheetsPart 4 Thermo
Total questions: 10
Worksheet time: 5mins
Heat is transferred to a heat engine from a furnace at a rate of 80 MW. If the rate of waste heat rejection to a nearby river is 50 MW, determine the net power output and thermal efficiency for this heat engine:
30 MW & 37.5 %
40 MW & 0.375 %
50 MW & 35.7 %
60 MW & 0.357 %
A car engine with a power output of 50 kW has a thermal efficiency of 24 percent. Determine the fuel consumption rate of this car if the fuel has a heating value of 44,000 kJ/kg
0.00273 kg/s
0.00373 kg/s
0.00473 kg/s
0.00573 kg/s
A machine which can do work by making use of heat that flows out spontaneously from a high temperature source to a low temperature sink is called:
Carnot engine
Cyclic machine
Heat engine
Heat machine
What is true about entropy?
if it increases in one place, it must decrease elsewhere
If it decreases in one place, it must increase elsewhere
It must decrease in the universe
Efficiency of a heat engine is the ratio of:
Heat taken from the high temperature reservoir (Q) to the work obtained in a cyclic process (W)
Work obtained in a cyclic process (W) to the heat taken from the high temperature reservoir (QH)
Work obtained in a cyclic process (W) to the heat taken from the low temperature sink (QL)
Heat taken from the low temperature sink (QL) to the work obtained in a cyclic process (W)
In a heat engine, what is the relationship between QH, QL and W?
W = QH + QL
W = QL - QH
W = QH - QL
W + QH + QL = 0
An air conditioner provides 1 kg/s of air at 15 oC cooled from outside atmospheric air at 35 oC. Estimate the amount of power needed to operate the air-conditioner:
(Cp of air = 1.005 kJ/kgK)
1.09 kW
1.19 kW
1.29 kW
1.39 kW
A car engine operates with a thermal efficiency of 35 %. Assuming the air-conditioner has a coefficient of performance (COP) of 3 working as a refrigerator cooling the inside using engine shaft work to drive it. How much extra fuel needed to remove 1 kJ from the inside of the car?
0.752 kJ
0.952 kJ
0.852 kJ
None of the above
A cyclic machine receives 325 kJ from a 1000 K energy reservoir. It rejects 125 kJ to a 400 K reservoir and the cycle produces 200 kJ of work as output. This cycle is
reversible
irreversible
impossible
None of the above
The increase in entropy when one mole of ice melts to form water is: (Latent heat of fusion of ice is 80 cal/g)
0.293 Cal/molK
0.65 Cal/molK
5.275 Cal/molK
3.41 Cal/molK
