Download PTU (Punjab Technical University) B.Tech (Bachelor of Technology) / BE (Bachelor of Engineering) 2021 January Agriculture-Engineering 3rd Sem 78589 Thermodynamics And Heat Engine Previous Question Paper
Total No. of Pages : 02
Total No. of Questions : 18
B.Tech. (Agriculture Engineering) (Sem.?3)
THERMODYNAMICS AND HEAT ENGINE
Subject Code : BTAG-303-19
M.Code : 78589
Time : 3 Hrs. Max. Marks : 60
INST RUCT IONS T O CANDIDAT ES :
1 .
SECT ION-A is COMPULSORY cons is ting of TEN questions carrying TWO marks
each.
2 .
SECT ION-B c ontains F IVE questions c arrying FIVE marks eac h and s tud ents
have to atte mpt any FOUR q ues tions.
3 .
SECT ION-C contains THREE questions carrying T EN marks e ach and s tudents
have to atte mpt any T WO questio ns.
SECTION-A
Write briefly :
1.
Show that the internal energy is a property of the system.
2.
What is a non-flow process?
3.
What is a polytropic process? How it is different from adiabatic process?
4.
What main conclusion can be drawn with respect to the efficiency of a Carnot engine?
5.
State the importance of second law of thermodynamics.
6.
What does the principle of entropy increase signify?
7.
Why does entropy remains constant in a reversible adiabatic process?
8.
What is an air standard efficiency?
9.
List the assumptions made in the analysis of air standard cycles?
10. What do you understand by mean effective pressure?
SECTION-B
11. A fluid at pressure of 3bar and with specific volume of 0.18 m3/kg contained in a cylinder
behind a piston expands reversibly to a pressure of 0.6 bar according to law :
C
p
2
V
Where C is a constant? Calculate the work done by the fluid on the piston.
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12. A steam turbine operates under steady flow conditions. It receives 7500 kg/h of steam from
the boiler. The steam enters the turbine at 2800 kJ/kg enthalpy, 70m/s velocity, and an
elevation of 4m. The steam leaves the turbine at 2000 kJ/kg enthalpy, 140 m/s velocity, and
an elevation of 1.5m. Heat losses from the turbine to surroundings amount to 1600 kJ/h.
Calculate the output of the turbine.
13. Prove that all reversible engines operating between the same two heat reservoirs have the
same efficiency.
14. In a certain heat exchanger, 60 kg of water is heated per minute from 225 K to 285 K by
hot gases which enters in the heat exchanger at 425 K. If the flow rate of gases is 120
kg/min, estimate the net change in entropy. Take cp(water) = 4.186 kJ/kg ? K and
cp (gas) = 1 kJ/kg ? K.
15. Derive an expression for air standard efficiency for an Otto cycle.
SECTION-C
16. A Diesel engine has a compression ratio of 14. The fuel is cut off at 0.08 of stroke. The
relative efficiency is 52%. Find the massof fuel of calorific value 42000/kJ/kg which would
be required per kWh.
17. A gas at 1 bar and 300 K is compressed adiabatically upto 10 bar and then expanded
isothermally upto initial specific volume and then cooled at constant volume to initial
conditions. Find work, heat and change in internal energy per kg of gas for each process
and for the entire processes. Take R=297 J/kg-K and y = 1.4.
18. a) Prove that the heat absorbed or rejected during a polytropic process is
n ? Polytropic work done and
1
polytropic specific heat is given by the expression.
n
cn c
1 n
b) A Diesel engine has a compression ratio of 14. The fuel is cut off at 0.08 of stroke. The
relative efficiency is 52%. Find the mass of fuel of calorific value 42000 kJ/kg which
would be required per kWh.
NOTE : Disclosure of Identity by writing Mobile No. or Making of passing request on any
page of Answer Sheet will lead to UMC against the Student.
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This post was last modified on 26 June 2021