Download GTU BE/B.Tech 2019 Winter 7th Sem New 2171914 Gas Dynamics Question Paper

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GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER- VII (New) EXAMINATION — WINTER 2019

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Subject Code: 2171914 Date: 23/11/2019
Subject Name: Gas Dynamics
Time: 10:30 AM TO 01:00 PM Total Marks: 70

Instructions:

1. Attempt all questions.

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2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Use of Gas Table is permitted.

MARKS

Q.1 (a) Define the following terms: 03

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1. Stagnation pressure
2. Critical and maximum velocity
3. Stagnation velocity of sound.

(b) Write a short on reference velocities. 04

(c) In a supersonic diffuser, the air flows at the rate of 100 kg/s at 07

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0.7 bar and 260 K static conditions, enters at Mach number 2.6
and at exit its Mach number is 1.3.
Determine: 1) stagnation pressure and temperature at inlet, 2)
velocity of air at inlet, 3) area at throat and exit, 4) static
pressure and temperature at exit, 5) velocity of air exit.

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M	T/ To	P/Po	A/A*	p/po
1.3	0.7474	0.3609	1.066	0.4829
2.6	0.4252	0.0501	2.896	0.1179

Q.2 (a) Explain the expansion and compression adiabatically with help 03
of T-S and P-V diagrams.

(b) Derive the following relationship for an isentropic flow. 04

^A/_A* = f(M, y)

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(c) Explain how does a shock wave develop in the diverging 07
section of a supersonic nozzle? How does this wave move
towards the exit?

OR

(c) Prove that the mass flow parameter is given by following 07

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expressions.

mvTo / APo = f(y, R, Po)

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Q.3 (a) Write a short on Supersonic Diffusers. 03

(b) Derive the equation of static pressure ratio across the normal 04

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shock:

P₂/P₁ = f(y)

(c) Starting from the energy equation for flow through a normal 07
shock, obtain the Prandtl Mayer relation in terms of mach
number.

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OR

Q.3 (a) Write a short on Supersonic pitot tube. 03

(b) Derive the following relations for flow through a normal shock: 04

M₂² = f(M₁, y)

(c) Derive the expression for the pressure ratio across normal shock 07

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in terms of density ratio.

Q.4 (a) Draw the Fanno curve on h-s diagram and discuss the effect of 03
friction in case of supersonic flow.

(b) Air flows at a pressure of 101 kPa and temperature of 27 °C into
a 462 cm long tube of 4 cm diameter. The tube is perfectly 04

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insulated. Determine the maximum mass flow rate and exit
pressure to produce this flow. Take f= 0.005.

M	P/P*	T/T*	4fLmax/D
0.3	3.619	1.178	5.299
0.35	3.0922	1.1713	3.4691
0.4	2.696	1.163	2.31
0.5	2.1381	1.11429	1.06908

(c) Derive an expression for change in entropy as a function of 07
stagnation pressure ratio for Fanno flow process. Hence show
that stagnation pressure always decreases in the process.

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OR

Q.4 (a) Define Fanno flow process and state its governing equations. 03

(b) Derive the following equation for one dimensional isentropic 04
flow.

dA/A = dP/P (1-M²)

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(c) Air at the rate of 33.68 m³/s leaves at 150 kPa and 293 K while 07
flowing in pipe of 0.5 m dia. The length of pipe is 60 m. Take f
=0.005.
Determine the following:
1) Mach number at exit.

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2) The inlet pressure and temperature.
3) Maximum length of pipe that can be used.

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Q.5 (a) What is Rayleigh flow? Give two practical examples. 03

(b) Explain the mechanism of energy conversion when a subsonic 04

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flow is heated in Rayleigh flow.

(c) Air enters a constant area duct at pressure, temperature and 07
Mach number 100 kPa, 280 K, and 2.5 respectively. Heat is
transferred to the duct such that exit Mach number equal to 1.2.
Find: 1) Heat transferred per kg of air. 2) Pressure and

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temperature at the exit. 3) Maximum amount of heat that can be
transferred.

M	P/p*	T/T*	To/To*
1.2	0.79576	0.91185	0.97872
2.5	0.24616	0.3787	0.71005

OR

Q.5 (a) Write the conditions Under which the assumption of Rayleigh 03
flow is not valid in a heat exchanger?

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(b) Derive the following expressions in Rayleigh line flow. 04

T₁/T₂ = f(M₁, M₂, y)

(c) Prove that Mach number at the. maximum enthalpy and 07
maximum entropy point on Rayleigh line are 1/vy and 1.0
respectively.

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