# WBUT Previous Years Question Papers EE

### Engineering Thermodynamics And Fluid Mechanics B Tech 2^{nd} Sem 2012

Time Allotted : 3 Hours

_{Fu}u Marks : 1

The figures in the margin indicate full marks.

Candidates are required to give their answers in their own word

as far as practicable.

GROUP – A

( Multiple Choice Type Questions ) \ ,

^{1} • Choose the correct alternatives for any ten of the following:

10 x l = ;

i) During throttling process

a) internal energy remains constant

b) entropy remains constant

#

c) enthalpy remains constant

d) pressure remains constant.

n) Which of the following is an intensive thermodynami property ?

a) Volume b) Energy

c) Mass ■ d) Temperature.

iii) Newton’s law of viscosity relates to

a) pressure velocity and viscosity

b) shear stress and rate of angular deformation in a fluidc) shear stress, temperature, viscosity and velocity

d) pressure, viscosity and rate of angular deformation.

iv) Stoke is the unit of

a) surface tension b) viscosity

c) kinematic viscosity d) none of these.

v) The first law of thermodynamics furnishes the relationship between

a) heat, work and properties of the system

b) heat and internal energy

c) various thermodynamic properties of the system

d) heat and properties of the system.

vi) Entropy change depends on

a) change of temperature b) mass transfer

c) thermodynamic state d) heat transfer.

vii) The increase in temperature

a) increase the viscosity of the liquid

b) decrease the viscosity of the liquid

c) increase the viscosity of the gas

d) both (b) and (c).

viii) A stream line is a line

a) which is along the path of a particle

b) which is always parallel to the main direction of flow

c) across which there is no flow

d) on which tangent drawn on any point gives the direction of velocity.

ix) For the same compression ratio and heat rejection, the efficiency of Otto cycle is

a) greater than diesel cycle

b) less than diesel cycle

c) equal to diesel cycle

d) none of these.

x) A refrigerator and a heat pump operate between the same temperature limits. If the COP of the refrigerator is

4, the C.O.P. of the heat pump would be

a) 3 ; b) 4 .

^{5} d) none of these.

xi) Work done in a free expansion process is

a) positive b) negative

^{c) }^{zero} d) maximum,

xn) A stagnation point is a point in a fluid flow where

a) pressure is zero

b) velocity of flow is zero

c) total energy is zero

d) total energy is maximum.

xiii) An inventor claims that his heat engine has the following specifications. Power developed 50 kW, Fuel burned per hour 3 kg, heating value of fuel 75000 kJ per kg. Temperature limits 627°C. His engine is

a) reality b) impossible

c) costly d) none of these.

xiv) A flow of viscous fluid with ^i= 10 Ns/m^{2} has a velocity distribution given bv u = 0-90t/ – y“. The shear stress at y = 0-45 m is

a) 0-90 Ns/m^{2} b) zero

c) infinity d) none of these.

xv) For irrotational flow

a) V = constant b) V *V = f(t)

c) V x V = 0 d) V x V = V (x, y, t)

xvi) Reynold’s number is expressed as

a) p VD/fi b) V^{2} D/p

c) Vp^{2}S/y d) V^{2}D^{2}/ y

. GROUP -B

( Short Answer Type Questions )

Answer any three of the following. 3×5= 15

- a) Draw the rheological diagram for Newtonian and non-
- Newtonian fluids. 2

b) Show the pressure decreases exponentially with elevation for an isothermal compressible fluid at rest.

- a) What is the basic difference between a process and a
- cycle ? 2

b) Show that the work done in isothermal process from the state 1 to state 2 is given by

** ^{W}l-2** =

**Pi**(

^{v}\^{lo}8e Pi –

^{lQ}ge

**Pw**)

^{3}

2123

- Show that the two dimensional flow described by the equation y = x + 2x
^{2}– 2y^{2}is irrotational. - a) State Newton’s law of viscosity.
- b) What are the causes of viscosity ?
- c) What is no-slip condition ? 1

- A 150 mm diameter shaft rotates at 1500 r.p.m in a 200 mm long journal bearing with an internal diameter 150-5 mm. The uniform annular space between the shaft and the

bearing is filled with oil of dynamic viscosity 0-8 poise. Calculate the power required to rotate the shaft.

**GROUP -C **( Long Answer Type Questions )

Answer any three of the following. 3 x 15 = 45

- a) What is PMM2 ? Why is it impossible ? What is its

difference from PMM1 ? 5

b) Show that the COP of a heat pump is greater than the COP of a refrigerator by unity. 4

c) A carnot heat engine draws heat from a reservoir at temperature T_{A} and rejects heat to another reservoir at

temperature T_{B}. The carnot forward cycle again drives a

carnot reversed cycle engine or carnot refrigerator, which absorbs heat from reservoir at temperature T_{c}

and rejects heat to reservoir at temperature T_{A}. Derive

an expression for the ratio of heat absorbed from reservoir at temperature T_{B}, such that heat supplied to

engine Q_{A} is equal to heat absorbed by refrigerator Q_{c}.

Determine efficiency and cop (Co-efficient of performance) of carnot refrigerator. 6

- a) A simple U-tube manometer containing mercury is

connected to a pipe in which a fluid of specific gravity

0-9 and having vacuum pressure is flowing. The other

end of the manometer is open to atmosphere. Find the

vacuum pressure in pipe, if the difference in mercury

level in the two limbs is 50 cm and the height of fluid in

the left limb from the centre of pipe is 10 cm below.

Assume any other data required. 5

b) The velocity vector in a fluid flow is give by V = 2x^{3}i – 5a:^{2}yj + 2tk

Find the velocity and acceleration of a fluid particle at (2, 1, 3) at time t = 1. 10

- a) Derive the expression for continuity equation for a

three-dimensional steady incompressible flow. 5

b) Describe the steady flow and unsteady flow. 2

c) A jet of water from a 25 mm dia nozzle is directed vertically upwards, assuming that jet remains steady and neglecting any loss of energy. What will be the dia at a poinf 4-5 m above the nozzle, if the velocity with which jet leaves the nozzle is 12m/s? 8

- a) An engine working on Otto cycle has an air standard cycle efficiency of 56% and rejects 544 kJ/kg of air. The pressure and temperature of air at the beginning of compression are 0-1 Mpa and 60°C respectively. Calculate

i) the compression ratio of the cycle

ii) Work done/kg of air

iii) the pressure and temperature at the end of compression

iv) maximum pressure oi the cycle. 8

b) Find the pressure at an elevation of 3000 m above the

sea level by assuming

i) an isothermal condition of air

ii) an isentropic condition of air.

Pressure and temperature at sea level are 101*32 kN/m^{2} and 293-15 K. Consider air to be an ideal gas with R = 287J/kgK and y = 1-4. 7

11. a) Determine die quantity of heat required to produce 1 kg of steam at a pressure of 6 bar at a temperature of 25°C under the following conditions.

i) when the steam is wet having a dryness fractions 0-9

ii) when the steam is dry saturated

iii) when it is superheated at a constant pressure at 250°C.

Assume the mean specific heat of superheated steam to be 2-3 kJ/kg. 7

b) Two bodies, each of equal mass m and heat capacity

are at temperature T1 and T2 respectively (T1>T2). The

first body is used as a source of heat for reversible

engine and the second body as the sink. Show that the

maximum work obtainable from such an arrangement is mC _{8}