CONFIDENTIAL
T]I\IVERSITI TT]N HUSSEIN ONN MALAYSIA
FINAL EXAMINATION
SEMESTERI
SESSION 2OI2I2AI3
SUBJECT
HEAT TRANSFER
CODE
BDA 3063 / BDA 30603
PROGRAMME
3 BDD
EXAMINATION DATE
DECEMBER 2012 /JANUARY 2OL3
DURATION
3 HOURS
INSTRUCTIONS:
r.
ANswER oNLy FrvE ($ QuEsrIoNS FROM sEvEN
o)
QUESTIONS
2.
UNLESS
SYMBOLS I{AVE COMMON DEFINITION
STATED OTHERWISE
3.
STATE RELEVANT ASSUMPTIONS WHERE
NECESSARY
THISQI']ESTIONPAPERCONSISTSoFSEVEN(7)PAGES
CONFIDENTIAL
BDA 3063/30603
Q1
Sketch the temperature profile for the stainless steel spoon that partially immersed in
(a)
boiling water at 95"C in a kitchen at 25"C(4 marks)
(b)
Consider a stainless steel spoon
(k:
15.1
Wm"C) partially immersed in boiling water
Ql (b). The handle
at 95'C in a kitchen at ZS"C As shown in FIGURE
has a cross section of 0.2 cm
surface of the water.
of the spoon
1.3 cm, and extends 18 cm in the air from the free
If the heat transfer coefficient
at the exposed surfaces of the
spoon handle is 17 Wm2'C. Determine ;
(i)
the tip temperature of the spoon handle; and
(ii)
spoon handle'
the temperature difference across the exposed surface of the
(16 marks)
Q2
(a)
Explain combination criteria for a fin Biot number.
(4 marks)
(b)
into a thin-walled glass whose
To warm up some milk for a baby, a mother pours milk
glass is 7 cm- She then places the glass
diameter is 6 cm. The height of the milk in the
is stirred constantlY, so that its
into a large pan filled with hot water at 60"c. The milk
transfer coeffrcient between the water
temperature is uniform at all times. If the heat
long it will take for the milk to warm up
and the glass is 120 wm2 ."c, determine how
be the same as those of water'
from 3oc to 3g"c. Take the properties of the milk to
(i) what is the characteristic length and Biot no for the glass of milk?
(ii)
(iii)
can the milk in this case be treated as a lumped system?
WhY?
(16 marks)
BDA 3063/30603
e3
(a) (i)
Explain how does the convection heat transfer coefficienL ft differ from the
thermal conductivity, fr of a fluid.
(ii)
For the parallel flow over the flat plate, sketch the temperature profile for the
surface temperature larger than fluid temperature.
(5
(b)
Air at Z7"C
marks)
and velocity of 5 m/s passes over the small region A" Q0 mm x 20 mm) on
a large surface which is maintained at
surface temperature
of I27"C. In order to
fin of diameter 5 mm and length 20
of fin is
mm is affrxed to A,as shown in FIGURE Q3 (b). The surface temperature
increase the heat transfer rate, a stainless steel pin
assumed to remain at 127"C. Determine;
(D
(ii)
the maximum possible heat transfer rate through the fin; and
installation
the percentage increase in the heat transfer rate from r4" due to
of
the fin.
(15 marks)
e4
(a)
convection with an
Define natural convection and explain the situation of natural
aPProPriate il lustration'
(6 marks)
(b)
affay of equally spaced
An electronic device is to be cooled in air at}}"cby an
(b). The frns average temperature
vertical rectangular fins as shown in FTGURE Q4
is 100"C. Estimate;
(i)
(ii)
(iiD
(iv)
the optimum spacing between the fins;
the number of fins;
the rate of heat transfer from one fin; and
the total rate of heat dissipation'
(14 marks)
BDA 3063/30603
Qs
(a)
To simpliff the analysis of heat exchanger, several approximations are usually made.
Discuss three (3) of them.
(6 marks)
(b)
A shell-and-tube heat exchanger with l-shell
pass and 2O-tube passes is used to heat
oC) in the shell, with hot water in the tubes. The tubes are
glycerin (Cp:2490 J/kg .
thin-walled and have a diameter of 1.5 cm and length of 2 m per pass- The water
enters
enters the tubes at 100"C at a rate of 5 kg/s and leaves at 55"C. The glycerin
at l5"C and leaves at 55oC. Determine the mass flow rate ofthe glycerin and
the shell
the overall heat transfer coefficient of the heat exchanger.
(14 marks)
Q6
(a)
to double the
consider a heat exchanger that has an NTU of 4. Someone proposes
order to increase the
size of the heat exchanger and thus double the NTU to 8 in
whether you
effectiveness of the heat exchanger and thus save enerry. Discuss
will
support or reject this ProPosal.
(5 marks)
J/kg ..C) leading to a shower enters a thin-walled double-pipe
to 45"C by
heat exchanger at l5oC at arateof 0.25 kg/s and is heated
(b) Cold water (Cp:41g0
counter-flow
hot wate r
(cp: 4lg0 J/kg . oc) that enters at 100"c
heat transfer coeffrcient is 950
w#.
at arate of 3 kg/s. If the overall
oc, determine the rate of heat transfer and the
the e - NTU method'
heat transfer surface area of the heat exchanger using
(15 marks)
BDA 3063/30603
e7
(a)
Explain what view factor is and state when will the view factor from a surface to itself
is not zero.
(3 marks)
(b) Calculate the view factor Frz between the rectangular surfaces as in Figure Q7 (b).
(12 marks)
(c)
:
Two very large parallel plates are maintained at uniform temperatures of 71 600 K
:
:
Determine
and TZ= 400 K and have emissivities er 0.5 and ez 0.9, respectively.
of the
the net rate of radiation heat fiansfer between the two surfaces per unit area
plates.
(5 marks)
BDA 3063/30603
FINAL EXAMINATION
BDD
SEMESTER / SESSION
: SEMESTERrl20l2l20l3
PROGRAMME
COURSE
: HEAT TRANSFER
COURSE CODE
BDA3063130ffi3
Spoon
t:
Tro= ?5sC
't
18 cm
Boiling
rvater
95
sc
FIGURB 91
ft)
--i{
45,
FTGIIRE 03 &)
D t+-
BDA 3063/30603
FINALEffi
I
l20rl-2012
SEMESTER / SESSION
: SEMESTER
COURSE
: HEAT TRAT{SFER
FTGURE 04
F-2
:3BDD
COURSE CODE
: BDA 3063/30603
ft)
FIG.IIRE 07
- END
PROGRAMME
--{
ft)
Or QrrEsTroN -
