ias mains mechanical engineering 1988

8/21/2019 IAS Mains Mechanical Engineering 1988

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2/7

4

5.

6.

7

(a)

(b)

In

figw-e

I a wedge and block is shown. Calculate the force P that will cause

the

wedge and

block to slide. Take the coefficient of friction as 0.2 for all sw-faces.

A refrigerator uru t we1ghing 30 kgf IS

to

be supported by three spnngs of n k g m

each If the umt operates at 5

80

r p m , what should be

the

value

of

spnng con t

on

y

10% of the shaking force of he uru t

1s

to be transmitted

to

the supportmg

SECnON

~

Answer bnefly and prec1sely and three of the foll owmg (Each answer s h o u l e e d

20

0 words)

(a) ~ ~ s h a p e of a cutting tool in orthogonal rake system is e ~ 0 , 6, 7, 5, 60, 0

(b)

(c)

(d)

(a)

(b)

Show with the he p of a sketch the angle of the cutti tool h respect to the tool reference

system.

W[:h] [ e c ;

:::;c]h[:.t]

circle diagram c e s , show that

P stnj3 cosj3

PIO ~

What should be the properties of ide tting tool material? What are the ingredients of a

carbide cutting tool? What o g are provided

on

coated carbide tools?

Flow

ECM

differs t h D respect to the mechanics of material removal and energy

sources.

List o ffactors w

e

tool life

of

a cutting tool.

Show the effec m ining time on the flank wear of the cutting tool at different cutting

s p e e ~

(c) In a l the followtng observation have been made

........ speed m/mm Tool hfe nunutes

~

30 126

........ 25 310

~

Calculate the Taylorian exponent and the constant.

(d)

In bar drawing through frictionless die, derive an expression for the drawing stress. Strain

hardening and strain rate effects maybe neglected.

(a)

(b)

Also determine the maximum possible reduction in area of cross-section of the bar.

Explain the effectiveness of he Stock-Time diagram of controlling of stock.

Draw the operating characteristic curve for a single sampling plan. Show on it the consumer

risk and producer risk.

(c) A company consumer 75000 pes of electrodes yearly. Following costs are involved.


3/7

8.

a)

b)

c)

d)

Costp r electrode= Rs. 5 5 0

Procurement cost

p rlot

= Rs 120


4/7

lr

..

~ : ~ - - ; : ~ ; : ~ : : : : : ; ~ ; ~ ~ : . .............

1

-

._i.,i

II

.. II

'iit 1:?rt;;1:? r i . n ~ r i . n ~ r i . n ~ r i . n ~ ~ j ~ ~ ~ ~ j ~ ~ ~ ~ ~ ~ ~ ~ i ~ r , ~ ~ ~ ~ ~ ~ ~ i ~ i ~ : i i f < ~ r ~ ~ r i i ~ ~ i i ~ ~ i i ~ ; , 1 : ? r t ; ; 1 : ? r t ; ~ ~ II

Wli APE:R l

Time Allowed: Hours Maximum marks:

3

I

2.

3.

SECnON

200 words)

(a) Show that wtth the concept of reverstble engtnes, a temperature sc (20)

A missile is travelling with a Mach number

of7

The

atmospheric air is 45C.

Find the stagnation temperature of the nose of th

~

formula used. (

2

O

Explain the concept

of

critic

A

insulation ~ is its practical importance?

Derive

an

expression for critical radius r ~

(20)

What is Reynolds Analogy? De e tile mple Reynolds

an


5/7

b)

4 a)

b)

coefficient between the steams and well is 50 kcal/m

2

hr C.

The length

of

the well is 5 em

and well wall thickness is 3 mm.

K (for well wall metal =

40

kcal/m

hr

C

Prove the formula used.

(30)

Two Iarge parallel planes are situated 3 mm apart in air one has an emissivity of

0.0

6 and is at

a temperature

of

30

OK,

and the other has an emissivity

of

0.15 and is at a temperature

of

40

0

K Calculate the percentage change m the total heat transfer rate by

co

ond

surface so

as

to reduce tts emtssnn ty to 0 0 3 Assume thermal conductivity o 0 2

cal/sm

K

0

(30)

Show

by

dimenstonal analysts that

tn

forced convection J

Nu = 1/J Re,

Pr'

u

)

pT

when

fri

ct1 onal heating

tn

the flutd cannot be neglected 4

( .1

(20)

In an

otl cooler, ethylene glycol flows through a-thin'i?-pn

1\

tube of dtameter 25mm at the

rate of 220 kglhr, 650kglhr of coohng water annular space formed by this

tube and another tube The otl enters at d l e q u t r e d to leave at 50C, while the

water enters at 20C Calculate the length he equtred when

1)

the otl and water move n o

oSt

dtrectton,

(ii) the oil and water e same direction.

In both the cases assume

t of the oil

0.

654 kcallkgC, film coefficient of heat

5. Answer any three of the ng four parts (answer to each part should be in about 200 words):

a)

u s s

an

the statement that factors tendmg to mcrease detonation m SI engmes

tend

to

knock m CI engmes

-

\

(20)

b) 1Mth graphs, the effect

of

followmg parameters

on

the performance

of

hqw d flat

o l a r collectors

\ 7jf Number ofglass cover plates

(u)

F1wd tnlet temperature, and

111) Selective surfaces

(20)

c) What are the essential differences between Pressurized Water Reactor (PWR) and Boiling

Water Reactor (BWR) used in nuclear power plants? Discuss their relative merits and

demerits.

(20)

d) Explain 'thermal comfort' and 'effective' temperature'. How comfort chart is constructed and

used?


6/7

6.

7

8.

a)

b)

a)

b)

(a)

(20)

Explain what is meant by the term 'polytropic efficiency' of an axial flow compressor. What

is the use of expressing efficiency in this form ?

Derive an expression for polytropic efficiency

in

terms of y (ration of sp eci fie heats)

and index

n.

(15)

A reaction turbine used 10,000

kg of

steam

per

hour. A one point in turbine the blades are 25

mm

high (at exit) and the discharge angle of both fixed and moving blades is 20 . eam

leaves the fixed blades at a pressure of 3 kgflcm

2

with a dryness fraction of 5

velocity of

120

rrJs Assuming that the ratio of axial velocity of flow to blade v city 0.70

at entry to and

0.

76 at exit from the moving blades, find the speed of theG ne revl

mm

and the horse power developed in this particular blade ring. Neglect ct f blade

thickness but assume a tip leakage of 6 of the total steam.

~ (45)

Show that for a simple ideal gas turbine (Joule) cycle the condi x i m u m specific

outputis ~

T2=T,

-'

where

T2

=temperature of air after isentropic compre ion i

n

compressor:

and T, =temperature of exhaust gases after s i o n in turbine

(15)

In a Pelton wheel installation the head Ia to the nozzle is 300 m and the coefficient of

velocity for the nozzle is

0. 98.

The wheel diameter is I

8

m an he

n

le diameter

125

nun. The buckets deflect the jet

through 16

5.

Assuming

'elo city of the jet over the buckets is reduced

by

16 ,

cal

cui

ate the theoretical sp d

mm

for maximum hydraulic efficiency. What is the

hydraulic efficiency whe run n t this speed, and what is the power developed in kW?

(45)

Differentiate

e

p l

fl

sh chamber and accumulator

in

vapour compression refrigeration

systems. When u s e d

t h a t ~ fa flash chamber has

no

effect on the thermo dynamics of the operating

cycle.

(15)

b) mer air conditioning system is

to

be designed for a hall using the following data:

de design condit ions= 35 C DBT and 27.2C WBT

Inside design conditions = 25 C

DB

T and 50 RH

Solar heat gain through walls,

roof

and floor= 600 0 kcallhr.

Solar heat gain through glass = 550 0 kcallhr

Number of occupants = 3 8

Latent heat gain per person=

9 0 kcallhr.

Sensible heat gain per person = 75 kcallhr.

Internal lighting load= 20 I amps of I 00 W each and 15 fluorescent tubes of 8 0 W each

Sensible heat gain from other sources= 15,000 kcallhr


7/7

Infiltrali on air = 2 I m

3

/min

40 fresh air and

60

recirculated air are mixed and passed through the conditioner coil

which has a due point temperature of7C.

Sketch the block diagram of the system and show the processes on skeleton psychrometric

chart, giving enthalpy values at each salient point and calculate-

i) the amount

of

total air in kgihr;

ii)

D

T

and

RH

of

supply air

in

the hail;

iii)

iv)

the capacity of conditioner

in

tons of refrigerali on;

bypass factor

of

the coil.

ias mains mechanical engineering 1988

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