Download AKTU (Dr. A.P.J. Abdul Kalam Technical University (AKTU), formerly Uttar Pradesh Technical University (UPTU) B-Tech 5th Semester (Fifth Semester) 2015-2016 Heat Mass Transfer Nme 504 Question Paper
(Following Paper ID and Roll No. to be filled in your
Answer Book)
Roll No.
B.Tech.
(SEM. V) THEORY EXAM. 2015-16
HEAT & MASS TRANSFER (EME-504)
[Time:3 hours] [MaximumMarksleO]
SECTION?A
1. Attempt all parts. All parts carry equal marks. Write
answer of each part in short. (2x10=20)
(a) What do you mean by thermal conductivity? Why
good electrical conductor materials are also good
heat conductors?
(b) What do you mean by thermal cotact resistance?
(0) State Wein?s displacement law.
((1) What do you mean by critical thickness of
insulation?
(e) De?ne the term ?Irradiation? and Radiosity?.
18000 (1) ' P.T.O.
(f) State the assumptions made in lumped heat capacity
method for analysis transient heat conduction
problem.
(g) De?ne response time of a thermocouple. What
does it signify?
(h) Explain black body, white body, gray body and
opaque body.
(i) What do you mean by fouling factor in analysis of
heat exchanger?
(j) A black body emits radiation of maximum intansity
at wavelength of 0.5 m. calculate its surface
temperature and emissive power.
SECTION?B
N ote: Attempt any five questions from this section.
(10x5=50)
Derive the general heat conduction equation in
cylindraical coordinates.
Derive the Von-Karman integral enegry equation for the
?ow past a ?at plate.
What are the applications of ?ns? Establish an expression
for temperature distribution in a straight ?n of
rectangular pro?le, when ?n tip is unsulated.
l 8000 (2) NME-504
During heat treatment, cylindraical pieces of 25 mm
diameter, 30 mm height and at 30 ?C are placed in
furnace at 750 "C with convective heat transfer
coef?cient 80 W/mz-deg,Calculate the time reqired to
heat the pieces to 600 "C. What will be shortfall in
temperature if pieces are taken out from the furnace after
280 seconds? Assume the following properties:
k=40 W/m ?C. c=480 J/kg K. and p = 7850 kng.
The insulation board for air conditioning purposes
comprises three layers. A 12 cm. thick layer of grass
(k=0.22 W/mK) is sandwiched between 3 cm thick layer
of plywood (k = 0. 15 W/mK) on each side. The bonding
is achieved with glue which does not offer any resistance
ot heat ?ow. If the side surfaces of board are maintained
at 40 "C and 20 ?C temperature, determine the heat ?ux.
How would the heat ?ux be affected if instead of glue
the three pieces are fastened by steel bolts (k=40 WmK)
of 1.2 cm diameter at corners. ?
Consider radiative heat transfer between two large
parallel planes of surface emissivity 0. 8. How many thin
radiation shields of emissivity 0.05 be placed between
the surfaces to reduce the radiation heat transfer by factor
75?
18000 ? (3) P.T.O.
A Counter ?ow heat exchanger is used to cool lubricating
oil of a large industrial gas turbine engine. The oil ?ows
through the tube at 0.9 kg/s (C: 2.18 kJ/kgK) and the
coolant water ?ows in the annulus in the opposite
direction at the rate of 0.1 5 kg/s (op: 4.18 kJ/kgK). The
oil enters at 425 K and leaves 345 K while the coolant
enters at 285 K. how long must the tube be made to
pcrfrom this duty if the heat transfer coef?cient from
oil to tube surface is 2250 W/mzK and ?om tube to water
is 5650 W/mzK? The tube has a mean diameter 0f-12. 5
mm and its wall presents negligible resistance to heat
transfer.
The nose section ot?a?missile is formed ofa 6mm thick
stainless plate and is held initially at uniform temperature
of 88 ?C. The missile enters the denser layers of the
atmosphere at very high velocity. The effective
temperature of air surrounding the nose region attains
the value 2200 ?C and the surface convective coef?cient
is estimated at 3405 W/mzK. Make Calculations for the
maximum permissible time in these surroundings if the
maximum metal temperature is not to exceed 1095 ?C.
Also workout the inside surface temperature under these
conditions. The properties for steel are: p =7800kg/m3,
k = 54 W/m "C, Cp= 465 J/kgK.
18000 (4) NME-504
SECI'ION-C
Note: Attempt any five questions from this secrtion.
10.
ll.
(10x5=50)
(0) Explain the analogy between momentum and heat
transfer in turbulent flow over a ?at surface.
(b) A ?at plate is 2 m long, 0.8 m wide and 3 mm thick
Its density and speci?c heat is 3000 kg/m3 and
700J/kgK respectively. The plate is having initial
temperature is 80 ?C. A stream ofair at 20 ?C of
biown over both surfaces of the plate along its
widht; at a velocity 2 m/s. calculate rate of heat
dissipation from the plate and initial rate ofcooling
of the plate. The proprties ofair are:
,0 =1.09 kg/m-?g k =023 W/m "C, C= 1007 J/kgK,
,u =2.03 x 10?5kg/ms, Pr 2 0. 698
Nua =0.664 (Ref5 (Pr)"'33 For Laminar F low
Nuu=0.0336( Rex)??8?83 6(Pr)?*33 for Turbulent Flow
(a) What do you mean by shape factor? Write its salient
features.
(b) De?ne internsity of radiation. Prove that the
internsity of radiation is 1/7: times of the total
emissive power.
1 8000 ? (5) P.T.O.
12. (a)
(b)
l 8000
Di??erentiate between Drop wise Condensation and
?lm wise condensation.
Engine Oil (cp =2100 J)kg ?C is to be heated from
20 ?C to 60 ?C at a rate of 0.3 kg/s in a 2 cm diameter
thin walled copper tube by condensing steam
outside at a temprature of 130 ?C (Hfg=2174
kJ/kg) for an overall heat transfer coef?cient of
650 W/m2 ?C, Determine the rate of heat transfer
and the length of the tube required to achieve it.
__x?
(6) NME-504
This post was last modified on 29 January 2020