Universiti
Malaysia
PAHANG
Engineering Technology Crealinily
FACULTY OF MANUFACTURING ENGINEERING
FINAL EXAMINATION
HEAT TRANSFER
COURSE
COURSE CODE
:
BFF3242
LECTURER
:
DR. ZUBAIR KHALIL
DATE
:
7 JUNE 2017
DURATION
:
3 HOURS
SESSION/SEMESTER
:
SESSION 2016/2017 SEMESTER II
PROGRAMME CODE :
BFF/BFM
INSTRUCTIONS TO CANDIDATE:
1. This question paper consists of FIVE (5) questions.
2. Answer ALL questions.
3. All answers to a new question should start on a new page.
4. All calculations and assumptions must be clearly stated.
5. Candidates are not allowed to bring any material other than those allowed by the
invigilator into the examination room.
6. The questions should be answered in English.
EXAMINATION REQUIREMENTS:
HEAT AND MASS TRANSFER: FUNDAMENTAL & APPLICATIONS: TEXTBOOK
DO NOT TURN THIS PAGE UNTIL YOU ARE TOLD TO DO SO
This examination paper consists of FIVE (5) printed pages including the front page.
BFFIBFM/1 61711/BFF3242
CONFIDENTIAL
QUESTION 1 [10 MARKS]
In your own words, sketches and expression, explain the terms below. Also mention
similarities, and differences where applicable;
a) Gröber charts.
(1 Mark)
b) Preservation method for different type of foods.
(3 Marks)
c) The U-factor and R-value.
(2 Marks)
d) Newtonian fluids.
(1 Mark)
e) Nusselt number, Prandtl number, Reynolds number.
(3 Marks)
QUESTION 2 [15 MARKS]
A person is found dead at 10 AM in a room whose temperature is 23 C C. Reason of death
was reported to be brain damage caused by very high fever. The temperature of the
body is measured to be 27 C C when found, and the heat transfer coefficient is estimated
to be 35 W/m2 K because of the ceiling fan left switched on. Modelling the body as a 30
cm diameter, 160 cm long in dimension, estimate the time of death of that person.
(15 Marks)
2
CONFIDENTIAL
BFF/BFM/161711/BFF3242
QUESTION 3 [20 MARKS]
A 0.4 cm thick, 10 cm high, and 15 cm long circuit board houses 150 closely spaced
logic chips on one side, each dissipating 0.5 W. The board impregnated with copper
fillings and has an effective thermal conductivity of halves the pure copper (thermal
conductivity of pure copper, 401 W/m2 K). All the heat generated in the chips is
conducted across the circuit board and is dissipated from the back side of the board to a
medium at 20C, with a heat transfer coefficient of 100 W/m2K.
a) Sketch the system
(2 Marks)
b) Determine the temperatures on the two sides of the circuit board.
(6 Marks)
c) Now a 0.2 cm thick, 12 cm high and 15 cm long aluminium plate (thermal
conductivity, 237 W/m 2 K) with 1000, 2 cm long aluminium pin fins of diameter
0.1 cm is attached to the back side of the board with a 0.05 cm thick epoxy
adhesive (thermal conductivity, 1.8 W/mK). Sketch the system.
(2 Marks)
d) Determine the new temperatures on the two sides of the circuit board.
(10 Marks)
CONFIDENTIAL
BFF/BFM/161711/BFF3242
QUESTION 4 [30 MARKS]
In a fire incident, dried oak trees (thermal conductivity, 0.17 W/mK, thermal diffusivity,
1.28 x iO m2/s) that are initially at a uniform temperature of 20 C. Due to the
location of the incident and windy condition weather, fire and rescue team have
difficulty trying to extinguish the fire, so the trees are exposed to hot gases at 450 °C for
a period of 7 hours, with a heat transfer coefficient of 205 W/m2K on the surface. The
ignition temperature of the tree is 410 °C. Assume the trees have an average diameter of
35 cm.
a) Solve the above problem using one-term approximation method.
(15 Marks)
b) Solve the above problem using Heisler charts.
(10 Marks)
c) Compare both result, and determined whether these trees will ignite as the fire
sweeps through them.
(4 Marks)
d) Discuss the possibilities of other alternate method such as lumped system
analysis or else are possible to obtain more accurate results.
(1 Mark)
4
CONFIDENTIAL
BFF/BFM/1617111BFF3242
QUESTION 5 [25 MARKS]
A 5-cm diameter shaft rotates at 4500 rpm in a 15 cm long, 8 cm outer diameter cast
iron bearing (thermal conductivity = 70 W/m K) with a uniform clearance of 0.6 mm
filled with lubricating oil at 80 °C. The bearing is cooled externally by a liquid, and its
outer surface is maintained at 40 °C. Disregarding heat conduction through the shaft and
assuming one-dimensional heat transfer;
(a) Sketch the model of the shaft system
(5 Marks)
(b) Determine the rate of heat transfer to the coolant
(10 Marks)
(c) Determine the surface temperature of the shaft
(5 Marks)
(d) Determine the mechanical power wasted by the viscous dissipation in oil
(5 Marks)
END OF QUESTION PAPER
5