6. (a) Explain the Concept of Wien's displacementlaw. (6)

(b) Three thin walled infinitely long hollow

cylin~ers of radii 5 em 10 em and 15 em are arrangedconcentrically in which Tl = 1000 K and T3 =300 K.Assuming &1=&2=&3= 0.05 and vacuum in the spaces

between cylinders, calculate the steady statetemperature of cylinder surface 2 and heat flow per m2area of cylinder 1. (8)

7. (a) Detennine the overall heatcoefficient of a double pipe heat exchanger.

transfer(6)

(b) Water at the rate of 0.5 kg/s is forced

through a smooth 25 mm ID tube of 15 m length. Theinlet water temperature is 10°C arid the tube wall is ata constant temperature of 40 DC.What is the exit watertemperature? Average properties of water arcCp= 4180 J/kgDC ; J.l=a.8x10:-3Pa-s and k = 0.57W/moC. (8)

8. (a) Derive the general mass diffusion equationin stationery media. (7)

(b) Discuss Various regimes of boiling. (7) .

[B 2499/I/08]

[03 - 4102]4

[03 - 4102]

IV/IV RE. DEGREE EXAMINATION

First Semester

Mechanical Engineering

HEAT AND MASS TRANSFER

(Common for Mechanical, M.P. & I.E., Metallurgicaland Marine Engineering)

(Effective from the admitted batch of 1999-2000 andafter batches)

Time: Three hours Maximum: 70 marks

Answer question No.1 and answer any FOUR questionsfrom remaining.

Assume suitable missing data wherever necessary.

~=~swers to question No.1 must be at one place.r,. A N I '

1/ r - -" /\ \ All questions carry equal marks.

~... I r~ \" \

I

~: {1/~;~~~I: fl

.

,;eat transfer data book is ,permitted.""l' ;

\, I "

~?~';F n ~'.

-" "<'.a};" Derive the expression For log ~ean area of ~,,~ sphere. (2)

(b) What is meant by time response of athermocouple? (2)

ANDHRA UNIVERSITY

Department of Mechanical Engineering ANITS

~/"" A ',f'. "I / .'. -- ~

-" ",'*. /,' A

I( . <.~ '.j

J

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jl 'f,1J,..~' Ii

. (C). Discuss th.

e te~pe.

rat~ distribution in\\.ai~~~~ '

.

.

.

:..

1/ (b) Athennocouple junction of spherical form i.

CIrcular pipe when the flow IS lanunar under const~46' .' Jibe used to measure the te111perature of a gas stremn.wall temperature condition. (2) ~,.,- The junction is initially at 20°C and is placed jn gas

(d) What is Colburn J- factor. (2) stream v.;hich is at 200 °G. Determine (i) Junctiondiameter needed for the thermocouple to have thermal

I(e) Define Planck's law of radiation. (2) time constant of one second and (ii) Time required for

(f) Why the effectiveness of a counter flow heat the thermocouple to reach 197°c Assume the thermo-exchanger more than parallel flow heat exchanger. (2) physical properties ask (thermocouple junction) = 20

( ) E 1...~... th°

gnifi f S hmid . b W/mK ; h =350 W/m2K ; c = 0.4 kJ/kgK and p= 8000g xp c:u..u e SI . cance 0 . c t num er

in convective mass transfer. . (2) kg/m3. (6)

2. (a) Discuss the electrical analogy for solvingconduction heat transfer problems. (7)

(b) A standard.cast iron pipe (di~ 5 cm and do-5.5 em) is insUlated with 85% magnesium insulation(k = 0.02 W/mOC).Temperature at the interface betweenthe pipe and the insulation is 300°C. The allowable heat

loss through the pipe is 600 W/m length of pipe and forthe safety, the temperature of the outside surface ofinsulation must' not exceed 100°C. Determine

(i) Minimum thickness of insulation required and(ii). The temperature of inside surface of the pipeassuming its thermal conductivity 20 W/moC. (7)

4. (a) Write short notes on hydrodynamic andthermal boundary layers on a flat plate. (6)

(b) Air at 20°C and a atmospheric pressure isflowing past a flat plate at 3 m/s velocity. The plate isheated over its entire length to a uniform temperature

of 60°C. Calculate the heat transfer from the first, 30 cm Ilength of the plate, Also calculate the drag force exerted )'

on the first 30 cm length of plate. Use the analogybetween fluid friction and heat transfer. . (8)

3. (a) Derive the equation for heat transfer through\

rec;tangular fin. ' (8)

5. (a) Derive the equations for mean velocity andmean temperature for a laminar flow inside tube. (8)II

(b) Discuss the physical sigIrificance of Stanton:number and number and Grashoff number (6)I

, II

2 [03 - 4102] 3,

[03 - 4102] III

ANDHRA UNIVERSITY

Department of Mechanical Engineering ANITS