IAS Mains Mechanical Engineering 2006

8/10/2019 IAS Mains Mechanical Engineering 2006

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2

3.

4

d) What are the various types

of

plain carbon steel? List important mechanical properties and

their common industrial applications.

20

a)

b)

a)

b)

a)

15

30

SECnON

5. Answer any three of the following:

a) During orthogonal machining with an HSS Tool, the r ke angle w s 50, the unreformed chip

thickness was 0.2 5 mm and width of cut w s 4 mm. Assuming shear strength of work

material to be 350 N/mm

2

and coefficient of friction to

be

0.5, estimate cutting force and

thrust force.


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20

b) List various types of chips that are formed

in

cutting and the conditions

in

which they occur.

20

(c) Following is information regarding a manufacturing enterprise:

d)

6.

a)

b)

Total fixed costs= Rs. 4,500

Total variable costs= Rs. 7,500

Total

sales=

Rs. 15,000

Uru

ts sold= 5,00 0

Ftnd out

t)

Break-even

pomt

m umts

(u)

(tv) Volume of sales to earn a profi t of Rs 6,00 0

111) Profit

A

work

measurement study was conducted

t

a manufactunng com any for 8 hours and

following observations were made: . .

Idletime: 15

CJ '

Performance rating: 120

Allowance tune: 12 of standard t ime flj

Number ofunits produced: 320

Calculate the standard

time

for the task.

20

Prove that

in

ing esistance-cap acitance relaxation circuit with a constant DC source,

for maximum p ' fe ' v , the discharge voltage should be

72 of

supply voltage.

How is th

MR

R ted by variation

in

resistance, mean current, capacitance and spark

gap?

M1 M1 M

M4 MS

Ob

Jt

30

7 4

28

4

J

4

24

Z7

21 Stl

J3

4

S2

33 3 35

J4

25 58 to

36

36

S

9

62 41 34 99


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I

P A P i : ~

mil

SEC11 NA

Answer any three of the following -

(a) With the help

of

Maxwell's relation

of

thermodynamics, prove

b)

c)

coefficient,

IJ J of

a gas is given by the foll

w i n ~

expression:

~ J = ~ ) k = ~ : [ ; ; ) J ~

A 0 8

kg

metal

bar

kept initially at

50

0C is removed sudden y fro an o en and quenched

by immersing

it in

a closed tank containing 12 kg

of

water keptin iti

li

00C.

The

metal

and water can be modeled

as

incompressible and the

s p e i f i ~ t e r

and metal are 4.18

kJ/kg-K and

05

kJ kg-K respectively. The heat transfer

o

tank may

be

neglected.

Work out the following

J

20

(i) Draw the system and system boundary ~ ~

u m p t o n s

made

(ii) The final temperature

of

metal bar T

(iii)

The

entropy produced

Draw the characteristic curves b etw the o ng parameters for an SI engine

(i)

Air

standard efficiency v mp sion ratio

(u) Relative effictency

~

ratio

111)

Brake thermal ef, ten vs oad

(tv) Volumetnc

~

~

ngme speed

(v)

P e a k e

ature vs Equtvalence ratto

Dtscuss

st

m f i n each case m the

hght

of destgn parameters

4 5

(d) A

rect

co

tp

er plate I0 em

x 50

em, having a mass of I kg and at a temperature of

I

0

C, st

ded vertically in still air at 20 C so that 50 em side is vertical. Neglecting

feet, find heat transfer coefficient due to natural convection and initial rate of

of

th

e plate

in

C/minute

for copper=

38

3 Jlkg-K

\. -n?e

properties

of

air at mean temperature 0C are

p

=

106

kg/m

3

,

v = 18.97

x

1

6

m

2

/s

Pr = 0.696, Cp = 1.005 kJ kg-K

k = 28.96

x

1

3

W/m-K

IJ = 20.1 x 1

6

N-s/m

2

.

You may

use

the following correlation:

Nu 0.1 (Cr

Pr)

113

Will the result change

if I

0 em side

is

vertical? Why?

20

.:;


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2 (a)

(b)

3. (a)

(b)

A counterflow heat exchanger acting as a recup erator,

of

gas turbine receives compressed air

operating

at

steady state at 65 0 K, 12 bars and exits at 850 K, 11.6 bars. Hot combustion from

the exhaust of gas turbine enters as a separate stream at I 000 K, 1 1 bars and comes out at I

bar. The mass flow rate of each stream is 200 kg/s. The heat transfer from the outer surface of

the heat exchanger

to

surroundings may be neglected. The changes in kinetic and potential

energy are negligible. Take To = 228 K and

Po

= I bar. Assume ideal gas model for

combustion gas. Work out the following:

30

(i) Draw the system and show the temperature distribution for each stream

(ii) The exit temperature

of

combustion gas

(iii) The net change in the flow energy rate from inlet to outlet for each stre

(iv) The energy distribution rate

0

(v) Comment on the results

During summer to cool water for drinking purpose, 2 kg of iceGt

-3

t

an insulated

container which is subjected to atrno spheric pressure of I bar.

Assume sp ectfic heat of tee ts 2 09 3 kJ kg-K and Iatent hea0 ~ 5 kJ kg Work out the

followmg

.

30

(u) The temperature of the mtxture

(1)

Draw the system and showtheprocessrB

Q ~

t c e and water

111) The change of entropy for mstant, usp c

Derive an expression for air-fuel

r a t i o

y

a simple carburetor, neglecting the effect

of

compressibility Discuss the

t m p l e carburetor. What are the modifications

incorporated for its use in

e s ?

1

O+ IO+I

0

A four-stroke petrol engin 30

kW at 2600 r.p.m. The compression ratio of the

engine is 8 and its fuel o is 84 kglh with calorific value

of 44

MJ kg. The air

consumption

of

the

a.

easured by means

of

a sharp edge orifice

is

2m

3

per

mm.

If

the ptston d i s p l

v

ume ts 2 hters, calculate

(1) etnc ctency

el ra

lio

....

e a n

effective pressure

B - e thermal efficiency

~ " ' : : l l . Relative efficiency

6 X 5

e

ambient temperature of air can be taken as 27C, R for air as 287 J/kg-K

andy=

14. The

barometer reads 755 mm ofmercury.

4.

A counterfoil, concentric tubes heat exchanger is designed to heat water from

20 C

to 80c

using hot oil flowing through the annulus. The oil temperature gets reduced from

160 C

to

140 C.

The nominal diameter

of

the inner tube

is 20 mm

and the corresponding overall heat

transfer coefficient is 500 W/m

2

-

K. The heat transfer rate from the oil is 30 00 watts.

Determine the length

of

the exchanger. Because

of

fouling after some days

the

outlet

temperature of water reduced to 65 C for the same flow rates and same inlet conditions.

Determine the outlet temperature

of

oil, the fouling factor and the new heat transfer rate.

Sketch the heat exchanger arrangement and the temperature pro files.

30


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6. (a)

(b)

and flows at a velocity of I 0 m/s. If the steam mass flow rate is 90 kg/s, find the number and

length of coils.

For steam at

60

bars, take the following values-dry saturated steam h = 2784.3 kJ/ kg, at

500e superheated steam temperature=

3422.2

kJ/ kg and specific volume

Vrop

=

0.05665

m

3

1kg. The steam enters the superheater as ry and saturated.

20

A v refrigerating machine using R-12 refrigerant pro duces I 0 tonnes

of

refrigeration at I 0

oe

when the ambient is at

35e.

A

temperature difference

of

minimum

5e

is required at the

evaporator and condenser for spontaneous heat transfer The refrigerant 1s ry s t u r

the

outlet and to the 1nlet

of

compressor The ad1abattc effic1ency

of

the

c o m p r e s s o ...

enthalpy at the end of1sentrop1c compression 1s estimated to be 370 kJ/

kg

:)eternu::p p

20

ii)

-J

Explain

cooling load estimation for comfort air-conditioning in the

~ b i ~

concept

of

different Sensible Heat Factors SHFs) and Importance m

atr-condittonmg system

30

7

. l

P n the concept

of

types

of

s1m1lanttes between model and prototype What do you mean

6y"d1storted model? What are 1 s advantages? It 1s proposed to

des1gn

a ship The proposed

ship prototype)

1s

havmg a length

of

50

m and a wetted surface area

of

2

00

0

m

2

wtth a

speed of 40 kmlh

A

model of

I

2 0 1s to be tested m the

Iab

oratory at a velo a ty

correspondmg to the w Ne resistance The total drag of the model 1s

50

N Deternune the

following:

15 25

i) Wave resistance drag of the model

ii) Wave resistance drag

of

the prototype

iii) Friction drag of he prototype

Give,


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8.

(b)

(a)

(b)

. . d I

2

Fncllon rag,

R

1

= C JPAV

2

where

A= Wetted surface area

CD =Average friction drag coefficient

0

074

for Re

Documents

IAS Mains Mechanical Engineering 2006