WBUT Question Papers CS Mechanical Science B Tech 2nd Sem June 2009

 

WBUT Question Papers CS Mechanical Science

B Tech 2nd Sem June 2009

 

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GROUP – A ( Multiple Choice Type Questions )

1. Cliooje the correct alternatives for any ten of the following

I) A perpetu&i motion machine is

a)          a thermodynamic machine D) a not; tnermodynamlc machine

o)  a reel machine

d) n hj’pothetical machine whose operation would violate the laws cf

thermodynamics.

u) Thermodymonic system may be defined as a quantity of matier upon whicn attention 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 c?

shape or volume.

Li) The expression JPdv may be applied for obtaining won; of

a)          non-ilow reversible process ij) steady iiow reversible process

teady flow non-reversible process

 

 

 

d)          steady iiow adiabatic reversible process.

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

v;} aum of two specific heats b) difference ox I wo specific heats                                   1

c> product cl two specific heats d) none of these.                                              L_.

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)          aoes not change

d)          tlrst Increases then decreases

• * .

s) depends on the properties of working substance, vt!) Th,; ,i.;.ent heat of vaporisation at critical point is

i’jsa than iierc        b) greater than zero

e)        v-qual to zero        d) all of these,

viii)    Toe work output of theoretical Otto cycle

increases with increase in compression ratio b! increases with increase in pressure ratio c) increases wiiL increase in adiabatic index V u) 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.

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x) A differcniiai manometer is used for measuring the

a)         pressure at a point

b)          velocity at a point

c)          dmti atice of pressure at two points

d)          discharge,

xt) Reynolds number is expressed as a) p-

Vp * D

VD

i*

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v

b)

d)

c:

c)

 

 

 

 

 

 

 

 

 

 

 

 

xii) During the throttling process

a)         imtru&i energy does not change

b)         pies does not change

c)          entropy does not change

d)          enthalpy does not change.

 

 

 

 

 

GROUP -B (Short Answer Type Questions }

Answer any three of the following questions.

 

 

 

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

Establish the relation ; COPHP = COPR + 1.

 

 

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<. A c-025’r.[2] vessel contains 0-3 kg of steam at 2 MPr. Determine ihe quality ai l enthalphy of steam. Given tt = 212*2* C, Vj — 0*001177 :n/.<g. Vg – 00995 i.i ,’kg, hf = 90&’5 kJ/kg, hJa = 1888-7 kJ/kg, Sj = 2-447 kJ/kg.K, S/8 =“3 590 k J/kg.ft

State and prove Pascal’s Law of Pressure at a point of a fluid body.

0           St.uc Newton laws of viscosity.

11)       A lcirge 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-1 ) with oil at the pUu’‘ havaig the velocity as the plates, what Is the shear stress on tY.z .novt.ig pk t from the ell ?              1 ■* 4

 

 

 

 

 

GROUP -C ( Long Answer Type Questions )

Answer any three of the following questions.

a)          Prove that Pv – tnRT where P = pressure

V * volume of m mass of gas

T = te.aperature

i< * characteristic gas constant.

 

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b)          Write dowa the significance of universal gas constant ( Rm ) and prove that

R- —s. where, M molecular weight of the substance,

M

c)          When 01421 kg 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 constant volume. j^ind me adiabatic characteristic of gas constant and moieculai weight of the gas,       4 f 2 : 4 + 5

c.. a; What is a steady How process ? Write the steady flew energy equation for a single steam entering and a single steam leaving a control volume and explain the various terms 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, Enthalphy 2785 kJ/kg,

velocity 33 3 m/sec and elevation 3 m.

Steam leave-; the turbine at the following state :

P = 20 kPa, 7 = 100 m/sec, enthalphy – 2512 kJ/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 r B

a)          Derive an expression for continuity equation for a three dimensional steady incompressible flow.

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

Jet of Water

Dia = 25 mm

Nozzle

 

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velocity vector for a 2D incompressible iiow £ei! is givea

■                                                   u       J. State whether the flow is eontuiuous

 

 

 

 

discontinuous.

10. a) Draw the nature of p-v and T-s plots of a Ranklne cycle (with saturated sie.-m – •

■                                       tarbine inlet}. •

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

‘ c) Two bodies each of equal mass m and heat capacity C are of tempe^ta e t\ aad Tz (7\ > T;») respectively. The first body is used as a source of revei .<

and the second as .the sink. Show that the maximum work obtainable

from such an umaigement is mc « – ^fr2 j .             4 + 5 r

is,, a) Prove ttoat >V”f » constant in .adiabatic process and ai-:r> ■r

 

b)          Wiiat is cyclic .neat engine ? Find the efficiency of heat engine in terms of sourc ami sink temperature. .

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

■                                                                                  5 + 3 + 1 > 3

i2.      a) Daiva m eaq^rc©-,vibn of actual discharge through a venturlraeter tube,

b)          WHie Bernoulli’s equation and describe the various terms in it.

What are the assumptions involved in derivation of Bernoulli’s equation ?

 

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0) in the ligurc, the fluid flowing In (W^-12N/m3) arid the manometric fluid is Mfriar.: Red oil ( specific gravity = 0-827 ). Assuming no lo.w. compute the flew r xte.

[Assuming Vx «*: P2]

 

 

5 + ( 3 + 2 ) -. 5

  1. 13.      a) Draw the rheokgical cur x for a class of Newtonian and non-Nt vto.iixui fluid

j) tcate aua prove hydrostatic iaw of fluid. What is the stagna ion pressure an a ] oint in a Juki flow ?

c)         

Determine ihe pressure difference between points A and 8. Specilc gravities cf

enzene, kevoacne and cur .ire 0-88, 0-82 and 1-2 x 10′3 res; tcivs’y.

 

Kerosine

 

9 cm

 

Water

 

 

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[1] j.) What is quality of wet steam ?

[2] Prove that entropy change for an ideal gas

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