Ies conventional-mechanical-engineering-2010

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~..,~ .. q{~. ... ?.d.LQ.;: ID&ineertni S~rvice ExaminatioD. •

Sl. No. 22782 A-GUG-K-NFA

MECHANICAL ENGINEERING

Paper-I

( Conventional )

( Time Allowed : Three Hours I

INSTRUCTIONS

Candidates should attempt anY.

Each question carrie 4

The number of marks carr"e ti e eh subdivision of a question is indicated a lie en of the subdivision.

Answers must b

f necessary, and indicate ... ~-ame clearly.

For air, R - kJ/kg-K, Cp ;:; 1·005 kJ/kg-K,

/14

• f I ,

,.._ , M = 28 · 966 kg/kg-mole.

rwise indicated, symbols and notations have their usual meanings.

10 kg of pure ice at -10 oc is separated from 6 kg of pure water at + 10 oc in an adiabatic chamber using a thin adiabatic membrane. Upon rupture of the membrane, ice and water mix uniformly at constant pressure. At this pressure, the melting temperature of ice is 0 oc and

[ P.T.O.

the latent heat of melting is 335 kJ /kg. The mean specific heat at constant pressure for ice and water are respectively 2·1 kJ/kg-K and 4·2 kJ/kg-K.

(i) Sketch the systems before and after mixing.

What is the final

(iv) Is the fmal phase of solid ice, liquid wate mixture?

{b) eveloped a transfer by

heat or work, x~ a e to produce hot and cold stre s o$ air from a single stream of ~ t an intermediate tempera ' '~eady-state test data provi~11 e inventor indicate that the ~:lt'~fl!iers the device at a pressure ~"'"""'T""'~erature, respectively of 5 bars

J!t13 oc and leaves the device as cold aicltream at -21 oc and as hot air~tream at 79 oc each at a pressure of 1 bar. Further, it is also noted that 40°/o of the mass of air is entering the device as cold stream. Neglecting any changes in kinetic and potential energies of the streams at inlet and exit sections and using ideal gas model with C P and R for air, respectively at 1·005 kJ /kg-K and 0·287 kJ /kg-K, evaluate the claim using energy and entropy balances.

10

Sketch the device as a control volume. 10

A-GUG-K-NFA/14 2

{c) Using Maxwell's relations and the thermodynamic definitions for C P and Cv in terms of gradients, show the following :

(d)

2. (a)

(i) Tds = CvdT + T ( ~~ t dv

=Cpdr-r(av) dp ar P

(ii) Joule-Thomson coefficient

calorimeter: the calo_;·;,.......v;;~F

A f~ · ~y der engine of an automobile is «:9 v rrted to run on propane (C 3H 8 )

el. "P<. dry analysis of engine exhaust ~..A.~~.·v,e~ volumetric percentage of CO, C02

a:Hd 0 2 , respectively at 9·79%, 4·90% and 2·45%. Write the resulting chemical

10

10

reaction and find the equivalence ratio. 10

The spark plug is fixed at 18° before top dead centre (TDC) in an SI engine running at 1800 r.p.m. It takes 8° of rotation to start combustion and get into flame propagation mode. Flame termination occurs at 12° after TDC.

A-GUG-K-NFA/14 3 [ P.T.O.

(c)

(d)

Flame front can be approximated as a sphere moving out from the spark plug which is offset 8 mm from the centre line of the cylinder whose bore diameter is 8·4 em. Calculate the effective flame front speed during flame propagation. The engine speed is increased to 3000 r.p.m. and ·subsequently as a result of which the effective flame fro speed increases at a rate such tha i . s directly proportional to 0·85 ti s c:f: engine speed. Flame development er spark plug firing still takes ;o f e~ne rotation. Calculate how rotation must be adv the flame terminati 12° after TDC.

roperties that a possess to meet the

equirement of internal

10

gmes. 10

describe the

Explain Reynolds analogy and derive the expression to evaluate the heattransfer coefficient using it. Give

10

physical meaning of the expression. 5

(b) Differentiate between fm efficiency and fin effectiveness. 5

A-GUG-K-NFA/14 4

(c) Show that the differential equation governing conduction heat transfer in a solid sphere with heat generation is

. d 2 T 2 dT q"' . given by--+--+-= 0, where T lS

dr 2 r dr k the temperature at any radius r, qm is the heat generated per unit volume and k is the thermal conductivity of the solid sphere. Show the general nature of the tempe.rature distribution in this cas .

(d) A counterflow heat exchanger is to designed to cool 900 kg/ hr of · from 60 oc to 32 oc using a fluid 't sp. heat 1·0 kJ /kg-K at 15 °C. lle . eat of the oil is 0· 5 kJ ~~~~ d the maximum allowable e.x~~ }e~erature of the cooling fluid is oC\:..)Vork out the following :

(i) Sketch t e templo'o'_....~,... ............. -

(ii) F. tl li' .

If the ~~ter of the tube is 2 em th g which the cooling fluid passes an overall heat-transfer coefficient s 200 W fm 2 -K, find the number of

bes required and the tube length. Assume density of the cooling fluid is 250 kgjm3 . If the. maximum velocity through the tube cannot exceed 2 m/s and the maximum length of the exchanger is limited to 12 m due to space restriction, find the configuration of the exchanger and sketch the fmal design. 15


-----------------------------~·~· ~·----~

(e) Find the average film coefficient heat transfer on the water side of a singlepass steam condenser. The inner diameter of the tube is 23 mm and cooling water enters at 15 oc and leaves at 25 oc. The average water velocity is 2·1 m/ s. Sketch the system and show the temperature distribution. Properties of water are given below. Find the he t transfer per metre length of the for the above case : 10

• Temp. Density Sp. heat Thermal

(0 C) {kg/m3) {kJjkg-K)

10

20 30

1000

1000

1000

469 9·52 1·306 361·892 7·02 1·006 288·650 5·42 0·805

4. (a) jf ed ammorua vapour enters a 1 dia x 14 em stroke twin-cylinder

......_\ sia gle-acting compressor at 0·2~65 MPa ~~whose volumetric efficiency is 79% and

speed _420 r.p.m. The delivery pressure is 1·1672 MPa. Liquid NH3 at 21 oc enters the expansion valve. For ideal cycle, find (i) the ammonia circulated in kg/min, (ii) the refrigeration in tons and (iii) COP of the cycle. Assume sp. heat

A-GUG-K-NFA/14 6

------~~---------------------------- ·

Pressure {MPa)

0·2365 1·1672

(b)

of NH3 as 2·19 kJ/kg-K and density 0 ·77 kg/m 3 . Properties ofNH3 are given

below :

Sat. Sp. Enthalpy Enlropy temp. volume (kJ/kg) (kJ/kg-K) (OC) of vap.

Sat. . Sat. Sat. Sat. at sat.

(m3 /kg) liq. vap. liq.

-15 0·5106 -831-46 481·52 5·4387

+30 0·11084 -620·70 523·42

A Bell-Coleman refrigeration used to produce 10 tons of

air at the inle -20 oc. For COP, rna s circulated/min, theore~ tston displacement of co, · SOJ" and power required per ton of r i ration. Assume C P for air as ·00~ kJfkg-K. Find the cylinder

ens1ons if the compressor IS

ingle-acting single-cylinder with L/D

10

ratio of 1·2 and runs at 600 r.p .m . 10

(c) With a neat sketch, explain the winter air-conditioning system. Why a single psychrometric process cannot be applied in winter air-conditioning? 10

A- GUG- K-NFA/14 7 ( P.T.O.

(d) Calculate all the psychrometric properties of air at 1 bar and 25 oc dbt and 15 oc wbt. The following properties of water may be as$umed :

25 lS

Sat. pressure

(bar)

0·03166

0·01703

Sp. volume of vapour

(m 3 /kg}

43·40

77·98

Enthalpy (kJ /kg)

Sat. liq.

62·94

10 0·01078

0 0·01002

5. (a)

The following expression ma necessary :

on equations and property ~~,_..,._,_ show that the (i) Mach

m e is unity at the point of ~urn entropy and (ii) Mach number

i }r at the point of maximum

temperature.

Air at 1 MPa and 600 oc enters a conserving nozzle with a velocity of 150 mfs. Determine the mass flow rate through the nozzle for a nozzle throat area of 50 em 2 when the back pressure is (i) 0·7 MPa and (ii) 0·4 MPa.

A-GUG-K-NFA/14 8

10

15

(c)

Assume that the flow through the nozzle is steady) one-dimensional and isentropic.

You may use the following table for one-dimensional isentropic flow (for an ideal gas with y = 1· 4} : 15

M p p .T A M* Po Po To A*

0·74 0·695 0·771 0·901 1·068

0·76 0·682 0·761 0·896

0·78 0·669 0·750 0·892

0·80 0·656 0·740

0·82 0·643 0·843

~l~n what you mean by the specific speed of a turbine. Using Buckingham-1t theorem and variables such as power (P}, speed (N), head (H), diameter of turbine (D), density of fluid (o) and acceleration due to gravity (g}, obtain the expression for the specific speed for a

10

turbine. 15


{b) Explain what you mean by momentum correction factor. The velocity distribution in a pipe is given by

where, U = maximum velocity at the centre of the pipe

u = local velocity along r

R = radius of the pipe

Find the momentum correction if n = 0 ·20. • 15

(c) {i) Deflne degree of tur

(d)

(ii)

the help of neat e een a hydrodynamically

~==-~'"'"...!.~ e and a hydrodynamically

5

..,., .. "-'~~ttl surface. 5

G1v a neat sketch of practical feed heating arrangement of a 660 MW unit · f steam turbine. Write the salient features of this system with reasonings for selecting its main parts. 10

Discuss the need of governing of steam turbine. With the help of a neat sketch, discuss the working principle of hydro-mechanical speed-governing loop of a steam turbine by showing the characteristics on torque and frequency versus time and torque or load versus frequency. 1 0

A-GUG-K-NFA/14 10

-------------------------------------------------------

(c) A steam power plant generating 500 MW of electrical power employs a natural circulation boiler which supplies steam at a pressure of 150 bars and temperature of 550 oc. The condenser pressure is 0·05 bar. The turbine, mechanical and generator efficiencies are 87%, 98% and 99°/o respectively. The boiler uses pulverized coal having a calorific value of 26 MJ /kg and yields 92% efficiency. The feedwater passing through the fee heaters enters the boiler at 160 °C. T e risers of the furnace are 55 in high while the downcomers are placed out tJ::~ furnace for producing natural · · n. The quality of steam at the ~ptof the riser is 12% and a minim ~elocity of mixture leaving the · e oct entering the drum is 1·4 m r..s. 'l'he aimensions of the riser tubes e 65 mm OD and 3 mm ~clfuess while the dimensions downcomers are 185 mm 0 !f!1:1 8 mm thick. Assume no pres u lit-.0p and heat loss to the

or :{-Out the following :

(i} ch the layout of natural crrculation boiler unit showing ~mace, drum, risers, downcomers,

mizers, and show the process on T-s diagram

(ii) The generation of rate of steam ignoring the amount of steam bled off to feed heaters in kg/ s

(iii) The rate of fuel flow required in kg/s


L-------------~---------------------------------- --

....

(iv) The evaporation factor

(v) The circulation ratio

(vi) The number of riser tubes

(vii) The number of downcomers

(viii) State reasons for selecting fewer in number and bigger in diameter as downcomers while number and smaller in as riser tubes m circulation boiler

hf3 = 137·8 kJ/kg,

Pnser. top = 396 Y

p downcomer , i le - 603 kg/ m 3

(d) e help of a neat sketch, discuss

15

"'"' _.. ,.ief the working principle of steam 41ressure control system used in modem steam boilers. 5

. (a) What do you mean by cavitation phenomena associated with hydraulic turbomachines? Discuss the causes of cavitation and its prevention with reference to hydraulic turbines. Mention the location of cavitation in hydraulic turbopumps and turbines, and give reasons for this. 10

A-GUG-K-NFA/14 12

-·- ~

(b) An axial-flow compressor employed in gas turbine plant delivers air at the rate of 300 kg/ s and develops a total pressure ratio of 20. The inlet stagnation conditions are 300 K and 1 bar. The isentropic efficiency of the compressor is 87%. The compressor is having 18 stages and the blade speed is kept at 200 mf s to minimize noise generation. The stage degree of reaction at the mean bla e height is 50%. The axial velocity of flo

is 160 m/ s. The work done ~en l'S

0·88. The hub-tip diameter a: i~0·8.

(i)

(ii) fluid angles of the first +stage

The hub and tip diameters including blade height

(iu) State the reasons why the pressure rise per stage in axial-flow compressor is less than that of centrifugal com pressor 10 ·


(c) A gas turbine power plant developing 250 MW of electrical power employs a single-shaft gas turbine reheat cycle having the following data :

Total compressor pressure ratio = 30 Total ambient conditions = 1 bar

and 300 K Polytropic efficiencies for both

compressor and turbine = 0·9 ea Total turbine inlet temperature

both turbines = 1600 K ac Pressure loss in both co

= 2% of entry p e e each Total turbine exhaust

assembly = 0·98

-~w r calorific value of fuel = 42 MJ/kg

kJjkg-K and ...... \ ~ e, CPa =1·005 ~~ CPg =1·16 kJ/kg-K.

Work out the following :

process on T-s diagram

{ii) The plant specific work in kJ /kg

(iii) The mass flow rate of air required in kg/s

A-GUG-K-NFA/14 14

(iv) The specific fuel consumption m kg/kWh

(v) The actual thermal efficiency 15

(d) With the help of a simple sketch, discuss in brief the working principle of hydrornechar.Ucal speed-governing system (prime control} of a water reaction turbine.

***

A-GUG-K-NFA/14 15 88-38*

-. '

~Arofftr ~ ai tfr,~ ;· :-· '~4:~:.=~-... -· . P n t.? · . • . • • • '-' S · "i ~ - · fh ·~ m~ .. : .;.....~; ,;...;.;; ";..;...;"~·-------..

·3 6 t'J 4 9 . ' . I A-GUG-K-NFB I Sl. No.

MECHANiCAL ENGINEERING · Paper II

(Conventional)

Time Allowed ·: Three Hours

Candidates . should attem

Queslimi ·. o/ short answer type .

. ' The 1 ll f · of ~tarks i:'!-rried by .each . subdiv · ion ~a questioll is indicated at the e11d

d;l the subdivision/ ques_tion.

ers Tnust be wr~rtell only in. ENG!---lS/1. ·

um.e suitable data, if ne_cessary and indicate the same clearly.

Unless otherwise indicated, symbols and notations used ilal-'e their usual "wauiugs.

Neat sketches to be. drawn, wherever_ required.

(Cont~.)

. 1. (a)

Section 'A'

c

AB=AD=l

uitable reverted gear train using four gear heels is to be. used for a clock. the minute

hm1d of which 'is fixed to the driving spindle and the hour hand to a driven s1eeve rotating freely on the same drivii1g spindle axis. The tnodular pitch is to be kept san1e for all the wheels and each wheel should have least.nun1ber of teeth but not 11 or Jess. Determine number of teeth on· each wheel of the gear train·.

A-GUG-K-NFB 2 (Contd.)

..

..

•

(d)

A rotating disc of 1·0 m diameter has two eccentric masses of 0·5 kg each ~t radii of 5{f mm and 60 nun with an angular interval .... between them as f50° on the pl~ne of the d.isc. A bulandng mass o~ 0·1 kg is to be attached in order to balance the disc. What should be the~ radial distance Of the balancing J11«.1SS fron1 lhe · centre of the ~isc and its angular position fnt, the eccentric mass which is at. 50 mm radll{~ ?

ystem paran1eters ·as given.

Q'he 11st~n rod of di~n1ete: 20 n:m an.d length ~0 mn1 1n a hydrauhc cyhnder JS subJected to · compressive force of J 0 ~N due to internal pressure. The· piston end of the rod is guided along the cylinder and the other end of the rod is him!ed at the cross-head. The modulus of ......

elasticity for piston rod n1atcrial is 200 GPa. Estimate the factor of safety taken for the

. piston rod design.


. .

----------------------------------~-------~-

I .

(1)

.. '0 kN is applied to a rigid bar

suspelfd~tiy 3 wires as shown in the above fi m, ~hat force will be resisted by each W1 C ?

• he outside wires are of AI, cross·sectional area 300 .1ntn2 and length 4 m. The central wire is steel with area 200 mm2 \lnd Jength 8 m.

Initially tl~ere is no· slack in the wires

E = 2 x 105 N!Jnm2 for Steel

= 0·667 x 105 N/mm2 for Aluminium

' A-GUG-K-NFB 4 (Contd.)

•

•

(g)

(h)

(i)

(1)

2 . 3

' For th~ planar structure shown in ·figure d~termine the reactions .or , · reaction components. +

similarities and differences

·hat are effects of adding ·Silicon and· Mans:wnese to cast iron ? Write· in short about ..... . Zn-base die cast aJJoys.

What is meant by interchangeable manufacture ? Discuss a 'Go' gauge .

.(m) What are the advantages and disadvantages of a-c welding machine ?

A-GUG-K-NFB . 5 (Contd.)

..

(n) SIZe

(o)

(p)

(q)

(r) What is float or slack and when subcritical path becomes critical ?

(s) What is an ideal operating tt ristics curve?

(t) Distinguish between p1anning and manufa

requirements source planning.

2x20=40

2. (a) a ate mass 1noment of inertia of ·ad, the following observations

1a e during experimentation :

Mas of the connecting rod·= 50 kg. Pi~ance between big end bearing and · smaH

end bearing centres = 1000 rnn1.

Diameter of big end bearing = 100 mm. Diameter of sma11 end bearing = 50 mm. Time period of oscillation while connecting rod

'wa$ suspended fron1 big end= 1·75 second. Time period of oscillation while connecting rod

was suspended from s·mall end= 2·0 second.

6 · (Contd.)

--· ---- --

... ..•

..

(b) A machine

\Vhen tfqe m chine is actua11y tested for vibr:If n, ·t 1s found that the damping present in - e systeJn reduces the amplitude of suc&essive free .vibrations by 30%. Evaluate :

the actual force transmitted to foundation at ~he running speed 800 rpm.

· (ii) the force transmitted to foundation at resonance, and

(iii) the amplitude of vibration of the machine due to unbalance mass~ at resonance. 10

A~GUG-K-NFB 7 (Contd.)

----------------~~~---------

(c)

ring of n1ean radius

vertically with the top end fixcc ~shown in the above figure and

'Crtical load of 200 N nt the lowest

ralculate the vertical deflection of the lower t.

end if the ring is of rectangular cross-section 20 mm thick and 30 tnm· wide.

Value of Elostic tnodulus is 2xl05 N/rnn12 .

. Influence of circumferential and

forces may be neglec~ed.

A-GUG-K-NFB 8

shearing

10

(Contd.) ..

·.

,):

(d) A ·hollow .steel rod 200 mm )ong is to be .used as torsional spring. The ratio of inside t~ outside diameters is 1 : 2. The required stiff

ness of lhis spring is 100 N.m/degrec.

Determi11e the outside dian1etcr of the rod.

Value of G is 8xl04 Nhntn2:

• 3. (a) Det'ermine .the n1aximum and ffii. values .

of the primary and secondar)! ba · nee forces

pe · cylinder = 2·0 kg

. ·Com

·an · shaft speed = ;2000 rpm

lndicate the cnm~ positions con·esponding to

above maxinmm and minitnum values of

unbalance forces. Whether ·primary · and·

secondary unbalance forces can be bala·nced

completely or not? 10

A-GUG-Kt.NFB 9 · (Contd) ·

.·

(b) Two .railway coaches are coupled with the help of two tie rods of a tun1 buckle with right and left handed threads having single-start square threads. Pitch. and mean diameter of the threads are 8 rnn1 and 30 1nm respectively. HQw much energy will be spent in bringing two coaches ·closer through a distance o 320 mm against a steady load of 5·0 coefficient of friction in screw · thr ad 1

coupler nut as 0·12. Determine shear stress on the tie rod due to above torqu . + · 10

(c) The data obtained

t pherical shell of 150 mm internal diameter has to withstand an internal pressure of 30 Mega N/m2 . Ca1culate the thickness of the shell if the ·allowable stress is 80 MN/n12.

Assume the stress distribution in the shell to follow the law

• 2b b

ar =a-3 anda-o =a+3. r r

10


... ·- ·-----

~-

•

4. (a)

.. A st_iff bar of negligible weight tra s> r a load P to a combination of three 1cr ,t springs mrangcd in parallel as s 1 1 the above figure. The springs are of the sarne material and out of · ·o of equal diameters. They are of same.= ce c. gth befor~ loading. The number of those three· springs are 10, 12 and •. s ectively. while the 111ean

· c in ratio of. 1 : J ·2 : 1·4 respective yr:nd the distance 'x' as shown in figu ~ , rM that the stirr bar remains horizonta~f er the applicalioJ:l of load P. · 10 . . -

air of standard spur gears has 16 and 18 eth~ module 12·5 mm and pressure angle

14·5°. Examine whether the pair will have , interference. If so: what should be the number

of teeth in both the gears to ·avoid interference as we1l as the pair maintains the same speed ratio w~tliout modifying other parame.tcrs. Evaluate contact ratio for the new set. 10

A-GUG-K-NFB ·11 (Contd.)

(c) A flat belt drive is required to trans~ it- 10 k W

from a motor running at 1000 rpm. The belt

is 15 n1m thick and has a n1ass density of

0·001 gm/n1m3. Penllissible tensile stress for

the belt material is 2·5 N/mn12. Diameter of

the driving pulley is 250 mm·, whereas th

(d)

speed of the driven pulley is 367 q)m. Dr' 'tng h

10

n a body is plane

If 1 o a e stress for the material in

siun or compi·ession is 100 N I mn12

c · v the valu~s of factor of safety with

each of the following criteria for failure • (i) Max Stress Criteria

(ii) Max Shear .Stress Criteria

(iii) Max Strain Criteria

(iv) Max Distortion energy criteria I 0

A-GUG-K-NFB 12 (Comd.)

·~

•

5. (a)

. · Section. 'C' . '

(ii)

• (iii) ·Explain why -th~ strengt

of die-cast- parts 'ght ratio

cr ases with

. (iv)

decreasing ~all c n . Explain the term stack mold :tg.

typ1 configuration · of 9.!re .ess grinding mentioning

~--11'.1-v- £ag e ai1d. use. Draw tool life - cast alloy, High speed stee-l

5x4=20

~ plain the difference. between infiJtra+ tion and impregnation in powder n1etallu~gy; Give at ieast two ex~mpJes of each.

. . Why are the following ch~racteristics of metal important in sheet metal forming

{' .

l. Grain size and

2. Yield po~nt elongation

Why i:lre pure metals more easily cold worked than alloys ?


'·

(iii) In the desigr~ of the gatilig system what technique~ are used for 1ninimizing

·turbulence ? Show with. a fiQure the .....

effect of alloyi.ng elen1ents like Mn, Ni ~md :n on the eut:ectoid tetnpcraturc.

(iv) Exp1ai·n with figures plnnetary milljn0

J.ndicate shnilarities between a vef tc·a boling 1nill and a jig-bor!ng mac · n ~......._

x =20

• . 6. (a) (i) Discuss short circuiti1 rr m ta transfer in

G!\.1AW nlentiQn · ~ (r · • s"""'Suitubilit.y. Also

define the ten 'figure.

(i i)

(iv) What are a manipulator, \~rist imcl end effector for a robot ? \Vhy has the wire EDM process become. so wide1y accepted

. i1l industry ? 5x4=20.

A-GUG-K-NFB 14 (~ontd.)

...

' . .

(b) (i) Explain ·why metal powders are blended. ... Describe what happens during sintcring.

2 .(i i)

(iii)

cuts .

.7. (a) Transportation

p L A NT

A B c D

1 10 8 -10 8

2 10 7 9 10

3 . .11 9 8 7

4 12 14 13 10

15


,

(b) \Vhat are moving average and exponential smoolhing models for forecasting?

A de~lership for Honda City c"rs sells · a . parti~ular tnode1 of the car in various n1onths of the year. Using the Jl)oving average method, find the exponential smoot.hing forecast for tl~ month of October 2010. Take expone tJa smoothing constant as 0·2 :

Jan. 2010

Feb. 20.10

March 2010

April 2010

·May 2010 80 cars

June 100 cars

July 85 cars

60 cars

75 cars 15

Exp'...tnd the following : • •

(i) ASCII

(ii) BCD

(lii) MDI

(iv) RAM

(v) ROM lO.

A-GUG~K-NFB 16

..

Education

Ies conventional-mechanical-engineering-2010