Download GTU (Gujarat Technological University Ahmedabad) B.Tech/BE (Bachelor of Technology/ Bachelor of Engineering) 2020 Summer 8th Sem 2171914 Gas Dynamics Previous Question Paper

Enrolment No.___________

**GUJARAT TECHNOLOGICAL UNIVERSITY**

**BE - SEMESTER? VIII EXAMINATION ? SUMMER 2020**

**Subject Code: 2171914**

**Date:26/10/2020**

**Subject Name: GAS DYNAMICS**

**Time: 10:30 AM TO 01:00 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 Gas Table is permitted.**

**MARKS**

**Q.1 (a)**Define following :

**03**

1) Maximum fluid velocity

2) Critical velocity of sound

3) Hypersonic flow

**(b)**"Bulk moduluas of elasticity of ideal gas is directly

**04**

proportional to the pressure of the ideal gas in

reversible adiabatic process" prove the above

statement.

**(c)**Define M*. Derive following relation:

**07**

2

{

}M2

pr

oportiona

2 = +1

-1

l to

1-{

}M2

+1

Calculate maximum value of M* for diatomic gas.

**Q.2 (a)**Compare adiabatic expansion and isentropic

**03**

expansion processes on TS diagram.

**(b)**Air flowing in a duct has a velocity of 300m/s,

**04**

pressure 1 bar and temperature 290K. Determine

stagnation temperature and velocity of sound

corresponds to stagnation condition.

**(c)**From the continuity equation, derive the equation for

**07**

non-dimensional mass flow rate in terms of pressure

ratio of static and stagnation pressure.

*m T*

*R*

Non-dimensional mass flow rate =

0

*A**

*P*

0

**OR**

**(c)**From the continuity equation derive the relation :

**07**

( 1

/ 2( -1))

1 2

*A p*

*M*1

*

*A p*0

-1 2

1

*M*

2

**Q.3 (a)**What is shock strength?.Write the equation which

**03**

represents shock strength in terms of upstream Mach

number.

**(b)**Upstream gas properties are Mach number 2.5,

**04**

Pressure 2 bar and temperature 275K.

1

What is Mach number, pressure and velocity of gas in

downstream side of shock.

**(c)**Starting from energy equation prove that,

**07**

Mx* * M*y = 1.

Where upstream and downstream reference Mach

numbers for normal shock are represented by Mx* and

M*y respectively.

**OR**

**Q.3 (a)**What is shock? Represent normal shock on hs

**03**

diagram along with Rayleigh and Fanno curve.

**(b)**A gas at a Mach number of 1.8, pressure 0.8 bar and

**04**

temperature 373 K encounter shock. Determine

density after shock and compare it with isentropic

density.

**(c)**From the energy equation, derive the following

**07**

relation for the normal shock

2/( 1)

2

*M*

2

*x*

*M*

*y*

2 /( 1) 2

*M*1

*x*

Where upstream and downstream reference Mach

numbers for normal shock are represented by Mx* and

M*y respectively.

**Q.4 (a)**What is Fanno flow? Give examples of Fanno flow in

**03**

thermal systems.

**(b)**Prove that at maximum entropy point on Fanno curve

**04**

is where Mach number is unity and all processes

approach this point.

**(c)**A circular duct passes 8.25 kg/s of air at an exit Mach

**07**

number of 0.5. The entry condition of air is 3.45 bar

and 380C. Co-efficient of friction of duct is 0.005. If

entry Mach number is 0.15 determine:

1) Length of duct

2) Diameter of duct

3) Exit pressure and temperature of air.

**OR**

**Q.4 (a)**Differentiate : Fanno flow and Isothermal flow.

**03**

**(b)**Write governing describing Fanno curve. Draw three

**04**

different Fanno curve on TS diagram for three

different mass densities.

**(c)**Air enters a long circular at 3 bar, 312 K and Mach

**07**

number 0.5. If the flow is isothermal throughout the

duct Calculate:

1) Length of the duct require to get Mach number 0.7

at exit.

2) Pressure and temperature at exit where M = 0.7.

3) Limiting Mach number.

Take : Duct diameter 0.125m and friction factor

0.0045.

**Q.5 (a)**What is critical state? Calculate the ratio of stagnation

**03**

pressure to the critical pressure for monoatomic gas.

**(b)**State the four assumptions of Rayleigh flow as well as

**04**

write two applications where Rayleigh flow analysis is

applicable.

2

**(c)**The Mach number at the exit of combustion chamber

**07**

is 0.9. The ratio of stagnation temperature at exit and

entry is 3.74. if the exit condition is 2.5 bar at 1273K,

determine :

1) Pressure, temperature and Mach number at

entry.

2) Heat supplied per kg of the gas.

Take : = 1.3 and Cp = 1.218 kJ/kg-K

**OR**

**Q.5 (a)**Write the equation of A/A* and draw the graph of

**03**

(A/A* ) M.

**(b)**Write momentum equation for Rayleigh flow. Plot

**04**

*dp*

Rayleigh curve on pv diagram and find :

for

*dv*

*R*

Rayleigh line.

**(c)**The conditions of a gas in a combuster at entry are :

**07**

0.343 bar, 310 K and 60 m/s. If the stagnation enthalpy

is increased by 1172.5 kJ/kg between entry to exit,

Calculate

1) Pressure at exit.

2)Temperature at exit and

3) Mach number at exit.

*****************

3

This post was last modified on 04 March 2021