Download GTU B.Tech 2020 Summer 3rd Sem 3131905 Engineering Thermodynamics Question Paper

Download GTU (Gujarat Technological University Ahmedabad) B.Tech/BE (Bachelor of Technology/ Bachelor of Engineering) 2020 Summer 3rd Sem 3131905 Engineering Thermodynamics Previous Question Paper

Seat No.: ________
Enrolment No.___________

GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER? III EXAMINATION ? SUMMER 2020
Subject Code: 3131905 Date:02/11/2020
Subject Name: Engineering Thermodynamics
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.

2. Make suitable assumptions wherever necessary.

3. Figures to the right indicate full marks.
4. Use of Steam table and refrigeration property table is permissible.

Marks
Q.1 (a) State and define different thermodynamic systems
03

(b) Describe quasi-static process.
04

(c) A reversible heat engine operates between two reservoirs
07
at temperature of 600?C and 40?C. The engine drives a
reversible refrigerator which operates between reservoirs
at temperatures of 40?C and -20?C. The heat transfer to the
heat engine is 2000 kJ and the net work output of
combined engine refrigerator plant is 360 kJ. Evaluate the
heat transfer to the refrigerant and net heat transfer to the
reservoir at 40?C.

Q.2 (a) State first law for a closed system undergoing (i) cycle and
03
(ii) a change of state.

(b) Show that the COP of a heat pump is greater than the COP
04
of refrigerator by unity.

(c) The mass rate of flow into a steam turbine is 1.5 kg/s, and
07
the heat loss from the turbine is 8.5 kW. The following
data are known for the steam entering and leaving the
turbine. Determine power output from turbine.

OR

(c) Nitrogen enters a diffuser at 100 kPa, 300 K, with a
07
velocity of 250 m/s and the exit velocity is 25 m/s. If
nitrogen can be considered as an ideal gas
with Cp=1.042 kJ/kg K, Find the exit temperature of
Diffuser.
Q.3 (a) State and prove Clausius theorem.
03

(b) Suppose that 1 kg of saturated water vapor at 100?C is
04
condensed to a saturated liquid at 100?C in a constant-
pressure process by heat transfer to the surrounding air,
which is at 25?C. What is the net increase in entropy of the
water plus surroundings?

(c) Explain principle of increase of entropy. Apply it for the
07
heat transfer through a finite temperature difference.
1

OR

Q.3 (a) Define following terms (i) Availability (ii) Irreversibility
03

(b) Explain Guoy-Stodola theorem.
04

(c) 5 kg of air at 550 K and 4 bar is enclosed in a closed
07
system.(i) Determine the availability of the system if the
surrounding pressure and temperature are 1 bar and 290 K
respectively. (ii) If the air is cooled at constant pressure to
the atmospheric temperature, determine the availability
and effectiveness. Assume specific heats remain constant
during process. For air consider Cp= 1.005 kJ/kgK and Cv=
0.718 kJ/kgK.
Q.4 (a) State the assumptions made for the analysis of air standard
03
cycle

(b) For the same compression ratio and heat rejection, which
04
cycle is most efficient: Otto, Diesel or Dual? Explain with
p-v and T-s diagram.

(c) In a steam power cycle, the dry saturated steam supplied
07
at 15 bar. The condenser pressure is 0.4 bar. Calculate the
Carnot and Rankine efficiencies of the cycle. Neglect
pump work.

OR

Q.4 (a) Draw the sketch of Rankine cycle p-V, T-s and h-s
03
diagram (consider Inlet and exit to turbine is superheated
and saturated steam respectively).

(b) Explain simple regenerative Rankine cycle.
04

(c) An air standard Diesel cycle has a compression ratio of 20,
07
with an inlet state of 95 kPa, 290 K, and a maximum cycle
temperature of 1800 K. If air can be assumed to be an ideal
gas with R= 0.287 kJ/kg.K and Cv= 0.717 kJ/kg.K,
Determine net specific work output of the cycle.
Q.5 (a) Draw open cycle gas turbine diagram and represent simple
03
Brayton cycle on T-s and p-V diaram.

(b) Explain Bomb calorimeter with neat sketch.
04

(c) An ice-making machine operates on ideal vapour
07
compression refrigeration cycle using refrigerant R-12.
The refrigerant enters the compressor as dry saturated
vapour at ? 15?C and leaves the condenser as saturated
liquid at 30?C. Water enters the machine at 15?C and
leaves as ice at ? 5?C. For an ice production rate of 2400
kg in a day, determine the power required to run the unit.
F
ind also the C.O.P. of the machine. Use refrigerant table
only to solve the problem. Take the latent heat of fusion
for water as 335 kJ/kg. Assume Cpice=2.0935 kJ/kgK and
Cpwater=4.187 kJ/kgK.

OR
Q.5 (a) Draw the T-s and P-h diagram of VCR cycle when inlet to
03
compressor is superheated vapour and condenser outlet is
sub-cooled liquid.
(b) Discuss factors affecting performance of VCR cycle.
04

(c) Calculate the amount of theoretical air required for the
07
combustion of 1 kg of acetylene (C2H2) to CO2 and H2O.

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