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West Bengal Institute of Technology (WBIT) 2009-2nd Sem B.Tech Electronics and Communications Engineering Electronics & Comm ( - ) Engineering Thermodynamics & Fluid Mechanics - Question Paper

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ENGINEERING & MANAGEMENT EXAMINATIONS, JUNE - 200b MECHANICAL SCIENCE SEMESTER - 2

3

cs/u.'i-Ecvi/JSM-ti/Miv-syi/oa

Tiii.j ; G Houra ]

; Full Marks : 70

GROUP - A ( Multiple Choice Type Questions )

1. C:i0O,;e the correct alternatives for any ten of the following

lOx 1 = 10

I) A perpetual motion machine is

a) a thermodynamic machine

o) a non thermodynamic machine

:> u reel xuachlne

d) a h}'pothetical machine whose operation would violate the laws cf

thermodynamics.

U) Thennodytuonic system may be defined as a quantity of matier upon whica ictea-.iOi. in focused for study If

a) it Is only bounded by real surface

b) the boundary surface is constant in shape and volume

0) it Is not bounded by an imaginary surface

1) it is bounded by either real surface or imaginary surface, irrespective cl

shape or volume.

Li} The expression JPdv may be applied for obtaining woric of

a) uon-ilow revcrsibk process

0

o) steady iiow reversible process

teady flow non-reversible process

d) steady iiow adiabatic reversible process.

las'

iv) The gas constant ( R ) is equal to the i

y} aum of two specific heats b) difference oi i-jvo specific heats 1 c> product cl two specific heats d) none of these. [_._______

v) Carnot cycle operates between the temperature of 100C K and 500 K Then th.: efficiency of the cycle is

a) 50% b) more than 50% v

c) less than 50% d) none of these,

vi) In a reversible cycle, the entropy of the system u) increases h'j decreases

c) uoes not chuage

d) ilrst Increases then decreases

- * s) depends on the properties of working substance, vi'i) Th.' t. -ent heat of vaporisation at critical point is

C

a) i'jsa than zero b) greater than zero

c) vqual to zero d) all of these,

viii) T.ae work output of theoretical Otto cycle

increases with increase in compression ratio

b) increases with increase in pressure ratio

c) increases wiih increase in adiabatic index V

d) follows all of these. .

ix) Atmospheric pressure is

a) Gauge Pr. - Absolute Pr. b) Absolute Pr. - Gauge Pr.

c] Absolute Pr. - Vacuum Pr. d) Gauge Pr. + Vacuum Pr.

V¹ D P

V² D²

VD

v

b)

d)

c:

x) A differential manometer is used for measuring the a) pressure at a point b} velocity at a point

c) GuiWsi t. :e of pressure at two points

d) discharge,

xt) Reynolds number is expressed as a) p-

Vp* D

c)

xii) During the throttling process

a) irntm&i energy does not change

b) pies does not change

c) entropy does not change

_r-

i

d) enthalpy does not change.

GROUP-B (Short Answer Type Questions }

Answer any three of the following questions.

3x5= II

b) What is the difference between a refrigerator and a heat pump ?

Establish the relation ; COP_HP = COP_R + 1.

* v O

3, Prove that entropy change for an ideal gas

l D \

! f-

\^Fi )

J

+ mC_p In

(is = m C_u In

C3,6.1*a:/S!sai* i:MB.301/0J 6 | Jliilil

<i. A C-025m* vessel contains 0-3 kg of steam at 2 MPg. Determine the quality aiU enthaijjliy of steam. Given t, = 212-2 C, Vj = 0-0011*7 m^u/eg, V₃ = 009t5 i.i /kg, hj- = 90S*5 kJ/kg, h_Jg = 1888-7 kJ/kg, S_/ = 2-447 kJ/kg.K, S_/9 =3 590 kJ/kg.K

L* t

- %-

i

k

i

Staic anti . ove Pascal's Law of Pressure at a point of a fluid boiy. j

i) Stale Newton laws of viscosity.

ii) A large plate moves with speed u₀ over a stationary plate on a layer of oil. 11 t:i velocity profile is that of a parabola { as shown in figure* i ) with oil at the pl.ue? having the velocity as the plates, what is the shear str-ss on ths movi.ig pi; t? from the cil ? ¹ * 4

f

GROUP -C ( Long Answer Type Questions )

\

*

I

Answer any three of the following questions.

a) Prove that P_v - rnRT where '

P = .pressure

V = volume of m mass of gas T a u.aperature = characteristic gas constant.

rafiifc

b) Write down the significant of universal gas constant ( R_m ) and prove that

Rwhere, M mtlccuLir weight of the substance,

M

c) When 01421 leg of a gas is heated from 27' C to 127 C and it u observed that the gas requires 202 kg of heat at constant pressure and 142 kJ of heat at

onstant volume, jind me adiabatic characteristic of gas constant and moiecuiat weight of the gas, 4 + 2 : 4 + 5

o. a) What is a steady How process ? Write the steady flow energy equation for a single steam entering and a stogie steam leaving a control volume and explain the various terns in it. Calculate work done from SFEE for turbine,

b) A turbine operates under steady flow condition and receiving steam at the following conditions :

. Pressure 1-2 MPa, Temperature - 188 C, Eathalphy 2785 kJ/kg,

velocity 33 3 m/see and elevation 3 m.

Steam leave-; the iurbine eu the following state :

P = 20 kPa, V = 100 m/sec, enthalphy - 2512 k; kg and heat lost to the surrounding at the rate = 0-29 kJ/sec and the rate of steam flow through the turbine is 0 42 Kg/sec. What is the power output of the turbine in kW ?

2 + 3 + 2 f B

a) Derive an expression for continuity equation for a three dimensional steady

incompressible flow,

b) A jet of water from a '25 uuu diameter nozzle is directed vertically upwards, assuming that jet remains steady and neglecting any loss of energy. What will be the diameter ac a point 4-5 m above nozzle, if the velocity with which jet leaves the nozzle is 12 m/sec ? i

Jet of Water

4.5 m

Dia = 25 mm

ll
Nozzle

t -

!.ic velocity vector for a 2D incompressible ilow Cel-:! is givea

c)

}. State whether the flow is contuiuous

discontinuous.

10. a) ' Draw the nature of p-v and T-s plots of a Rankine cycle (with saturated sieam -

turbine inlet},

b) A lump of steel of mass 15 kg at 557 C is dropped in i 20 kg of oil ai ;a J. . : specific heats of steel and oil are 0-5 kJ/kg-K arid 3-5 kJ/kg-K respective;_v. Calculate the entropy change of the steel, oil and the universe.

e} Itfc bodies euoli of equal mass m and heat capacity C are of te-np&'rda e t\ end T_z (Z\ > T_a j respectively. The first body is used as a source of i ever s..<

en#.e and the second as .the sink. Show that the maximum work ohtxiinEb:-:-from such an -i.a..agement is m_c (pjT\ - ) 4 + 5 r

11. a) Prove that 'W' constant in .adiabatic process and ai-.-o xi:r

b) Wliat is cyclic heat engine ? Find the efficiency of heat engine in terms of sourc-.; iad sink temperature. .

Which change is more effective to increase the efficiency of the engine.

' 5 + 3 + 1 > 3 :

a) Derive aa expicton of actual discharge through a venturimeter tube.

b] Write Bernoulli's equation and describe the various terms in it.

What are the assumptions involved in derivation of Bernoullis equation ?

cs/iS.ve-vii/Jtfc'-s/Ms-aoi/Ov . 9

c) a. the figure, the fluid uowing in (W-12N/m³) aad the manoinetric fluid Is MerJaiji Rc i oil { wpeciflo vlty = 0-827 }. Assuming no l03S, compute the flew r-te.