Download AKTU (Dr. A.P.J. Abdul Kalam Technical University (AKTU), formerly Uttar Pradesh Technical University (UPTU) B-Tech 5th Semester (Fifth Semester) 2018-2019 RME 502 Heat And Mass Transfer Question Paper
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B. TECH.
(SEM V) THEORY EXAMINATION 20l8-l9
HEAT AND MASS TRANSFER
Time: 3 Hours Total Marks: 70
Note: Attempt all Sections. If require any missing data, then choose suitably.
SECTION A
l. Attempt all questions in brief. 2X7 = 14
a, De?ne three different modes of heat transfer. Give a practical example where all three modes
are occurring simultaneously.
b What do you mean by the term thermal conductivity? Why good electrical conductor
materials are also good heat conductors?
c? What do you understand by overall heat transfer coef?cient?
d. Write down the significance of critical radius of insulation.
e. State the assumptions made in lumped heat capacity method for analysis of transient heat
conduction problemsl
f. Define Nusselt number and Prandtl number.
g. Explain black body, white body, gray body and opaque body
SECTION B
2. Attempt any three of the following: 7 X 3 = 21
a A gas filled tube has 2mm inner diameter and 250m long, the gas is heated by an electrical
wire of diameter 50 microns located along the axis of the tube, the current and voltage drop
across the heating element are 0.5A and 4V respectively. If the temperature of wire is 175?C
and inside tube wall temperature is l50"C respectively. Find the thermal conductivity of the
gas filling the tube.
b. Derive the expression for temperature distribution and heat dissipation in a straight fin of
rectangular profile when fin is of in?nite length.
c. Explain the physical mechanism of free convection with the help of example and neat
sketch. Discuss the significance of various dimensionless numbers with respect to natural
convection. .
d. De?ne the following terms: Total emissivity, Monochromatic emissive power and
Monochromatic emissivity.
e. Differentiate between dropwise and ?lmwise condensation. Which type has higher heat
transfer ?lm coef?cient and why?
SECTION?C
3. Attempt any one part of the following: 7 X l = 7
a. Derive the 3-D steady state generalized heat conduction equation (without internal heat
generation) in Cartesian coordinate system. Write the assumptions used.
b. An exterior wall of a house may be approximated by a 0.1m layer of common brick (k = 0.7
W/m"C) followed by a 0.04m layer of gypsum plaster (k = 0.48 W/m"C). What thickness of
loosely packed rock wool insulation (k = 0.065 W/m?C) should be added to reduce the heat
loss (or gain) through the wall by 80 percent?
4. Attempt any one part of the following: 7 x 1 = 7
a A ?eel md [ k '? 32 Ws'nf?Cl, 12mm in klleCtCI and (iOmrn long, with an insulated end. is to
be used as spine. It is exposed to surroundings with a temperature of 60?C and a heat transfer
cne??icient (11?55 Wr'mz?t~ The temperature at lhc base of ?n is 95?C Determine:
L The fin efficiency
ii. The tempeiatui'e at the edge of the spine
iii. The heat disslpalmn
b A steel ball (If I Inrn diamcicr IS annealed by heating to 800%": and then slouiy cooled to
127?C in an at 50?C The heal tiansfei coef?cient h ? 20 W III -?C Calculale [In time
required tor air cooling process The properties of steel are l. 45 WI?m?C, p 2 7830
kg/m? and c 600 .lxkg-K?
Attempt any one part of the following: 7 x I = 7
a. Air at atmospheric pressure and 200"C ?ows over a ?at plate with a velocny 0f5 mfs.
The plalc is 15mm wide and is IIIaiIItained at a icmpemture of 120C. Calculate the
thickness of liydrodynainic and thermal boundary layers and the local heat transfer
coc??icuL-nl at a distance of0.5nI from the leading edge. Assume that ?ow is on one side
of the plate.
1) Define the followmg temis Wllll expression
I. Boundaiy layer thickness
ii. Displacement thickness
III. Mementum thickness
iv. Fincrgy thickness
Attempt any one part of the following: 7 X l = 7
a, The large parallel plates with emissivities 0 3 and 0. 8 Eiiehange heat Find the percentage
reduction when a polished aluminium shield of emissivity 0.04 15 placed between them
Use the method of electrical analogy.
b. Derive the following relation for the radiantheet exchange between two gray surfaces:
?0 ) _ AI am? -7?)
n m "?11.. +1 7,. 7?_II:V.*?:; A
_ _ Eu 173.2 E: A:
the following: 7 x 1 = 7
Attempt any one party:
3. Steam at atmosphe pressure enters the shell of a surface condenser in which the water
?ows through a biinille of tubes of diameter 25mm at the rate of 0.05 kg/s. The inlet and
outlet temperatures of water are 15"C and 70?C, respectively. The condensation of steam
takes place on the outside surface of the tube. If the overall heat transfer coef?cient is 230
W/mz"C, calculate the following, using NTU methodi
i The effectiveness of the heat exchanger
ii. The length of the tube ?
iii. The rate of steam condensation
Take latent heat of vapourisation at 100?C = 2257 kJ/kg
b. State Fick?s law of diffusion. What are its limitations?
This post was last modified on 29 January 2020