Bff3203-Heat Transfer 21314

MatrikNo:

-1 Universit Malaysia FAHANG Engineerin rechiooçy . CreHivy

FACULTY OF MANUFACTURING ENGINEERING

FINAL EXAMINATION

COURSE : HEAT TRANSFER

COURSE CODE : BFF3203

LECTURER : ASSOC. PROF. DR ABDUL AZIZ JAAFAR

DATE : 18 JUNE 2014

DURATION : 3 HOURS

SESSION/SEMESTER : SESSION 2013/2014 SEMESTER II

PROGRAMME CODE : BFF/BFM

INSTRUCTIONS TO CANDIDATE:

(a) Answer ONLY FOUR (4) Questions

(b) Answers these questions in this Examination paper.

EXAMINATION REQUIREMENTS:

NIL

DO NOT TURN THIS PAGE UNTIL YOU ARE TOLD TO DO SO

This examination paper consists of TWENTY (20) printed pages including front page.

CONFIDENTIAL BFF/BFM/131411/BFF3203

QUESTION 1 (25 MARKS)

A transparent film is to be bonded onto the top surface of a solid plate inside a heated chamber.

For the bond to cure properly, a temperature of 70°C is to be maintained at the bond. The

transparent film has a thickness of 1 mm and thermal conductivity 0.05 W/mK, while the solid

plate is 13 mm thick and has thermal conductivity of 1.2 W/mK

Aft. It 70 \V/rn2KFrer.preffl film

-

()j15 \WuiK

II I mm'1Itt plate

70°(

k 1.2 W/m'K

52°C

List all the engineering assumption to solve the following heat transfer problem (5 marks)

Sketch the engineering model for the following engineering problem (which include the

coordinate system, heat transfer system)

(5 marks)

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If the bottom surface of the solid plate is maintained at 52 °C and the convection heat transfer

coefficient on the transparent film is 70 W/m2K, determine the inside temperature of the chamber

and the surface temperatures of the film. (15 marks)

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In a manufacturing process, a heated 6mm-thick Pyroceram plate is being cooled in a room with

air temperature of 25 °C and convection heat transfer of 13.3 W1m2 T. The heated Pyroceram

plate had an initial temperature of 500 °C, and is allowed to cool for 286 s.



coordinate system, heat transfer system). (5 marks)

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The factory management is decided to replace the existing cooling process with an alternative

cooling equipment, estimate the minimum power requirement of this equipment if the mass of

Pyroceram plate is 10kg. (15 marks)

5

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A 6 cm diameter shaft rotates at 3000 revolutions per minute in a 20 cm long bearing with a

uniform clearance of 0.2 mm. At steady operating conditions, both the bearing and the shaft in

the vicinity of the oil gap are at 50 °C, and the viscosity and thermal conductivity of the

lubricating oil are 0.05 N.sIm2 and 0.17 W/m K.



coordinate system, heat transfer system). (5 marks)

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Determine:

a) The maximum temperature of the lubricating oil and the rates of heat transfer to the bearing

and the shaft

(8 marks)

b) The mechanical power wasted by viscous dissipation in the oil (7 marks)

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QUESTION 4(25 MARKS)

An aluminum plate of 25 mm thickness is attached on a copper plate with thickness of 100 mm.

The copper plate is heated electrically to dissipate a uniform heat flux of 5300 W/m 2 . The upper

surface of the aluminum plate is exposed to convection heat transfer in a condition such that the

convection heat transfer coefficient is 67 W/m 2K and the surrounding room temperature is 20 T.

Other surfaces of the attached plates are insulated such that heat only dissipates through the upper

surface of the aluminum plate.




(5 marks)

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BFF/BFMI13I 411/BFF3203

Determine the thermal contact conductance of the aluminum/copper interface if the surface of the

copper plate that is attached to the aluminum plate has a temperature of 100 T. (15 marks)

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A' large cast iron container with 4 cm thick walls is initially at a uniform temperature of 0 °C and

is filled with ice at 0 T. The container is then exposed to hot water at 55 °C and the ice starts

melting when its temperature rises to 0.1 °C.




(5 marks)

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Determine:

a) How long it will be before the ice inside the container starts melting if the heat transfer

coefficient on the outer surfaces of the container walls is very large. (8 marks)

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b) The rate of heat transfer to the ice through 1.2 in wide and 2 m high section of the container

wall when steady operating conditions are reached if it is assumed that the heat transfer

coefficient on the inner surface is 250 W/m2 °C

(7 marks)

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An electronic device dissipating 18 W has a mass of 20 g, a specific heat of 850 J/kgK, and a

surface area of 4 cm2 . The device is lightly used, and it is ON for 5 min and then OFF for several

hours, during which it cools to the ambient temperature of 25 °C

List all the engineering assumptions to solve the following heat transfer problem (5 marks)



(5 marks)

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Determine:

a) The temperature of the device at the end of the 5 min operating period, if the heat transfer

coefficient is taken to be 12 W/m 2 K. (8 marks)

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BFF/BFM/1 31 411!BFF3203

b) The temperature of the device at the end of the 5 min operating period, if the device was

attached to an aluminum heat sink having a mass of 200 g and a surface area of 80 cm and

the heat transfer coefficient is taken to be 12 W/m 2 K. (7 marks)

END OF EXAMINATION PAPER

15

CONFIDENTIAL


APPENDIX

Table 1 : Thermal oronerties of air Specific

Thermal Densityheat at Dynamic

Air temperatureconductivity constant viscosity

(W/m2K)(kg/rn3)

pressure(x iO Pa.$)

(J/kgK)

40°C 0.02735 1.092 1007 3.261

Table 2: Thermal properties of solid substances at 300K

Specific heat at constant Thermal

Substances conductivityDensit1' pressure

(W/m2K)(kg/rn) (J/kgK)

stainless steel14.9 7900 477

AISI 304

silver 429 10500 235

aluminum 235 2770 875

copper 401 8933 385

Cast iron 80.2 7870 447

Pyroceram 3.98 2600 808

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Transient temperature distribution in a semi infinite wall due to a prescribed boundary conditions

Specified Sufiice 1inp.eraru re, J = constant:

iIx.t)—T,. x CIIL J anti q(r) =

Tx Ti

Spcc!ted Sui:fnee Heat Flux. € = constant:

:j4at ( x2\ T( 1) — J=—-f-----L,c1i -------1 - terf(1

k:v iT ' 4aj/

Cünvectinn on th q.t) --- T(O, 1)1:

Y(x.z)—T1 ( x \ (kx h2ar erki...

\2 \/t1 \ k k

(2 x

X erfcV-.

at k

Sufaee, e = co,1an t:

T(x, t) -kVji

Where all symbols take the same physical descriptions taught in the course

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Table 3 : Complementary Error Function Table

Complementary Error FuntIon Tablecife(Yi

I

_Th_ erk() Yj erfr(V) YJ erfr(1) YJ erfc() YJ erTh(I) J! erfr(ti) 0 1000300 0.5 0.1795OC I 015729) 1,5 0.338

_2 0.00467 B 23 0.000407 3 0.000022thI

Q.c?t 0.9B717 O.!iI 0.1707556 1.0 2 1 0.15310 1 . 51 0.032723 201 0.004175 251 0003B6 3.01 0.00002.074

002 0.077435 032 0..1E2101 1.02 0101E2 Q357 :000421 2.152 OM0365 3.02 0-0000117

- o. i.o 1.53 0A30484 2.03 :UC0404 .253 0.00346 3.03 0.00001827

o.c'i 0.054880 0.1 0.445001. 1.04 0.11 130 1.54 0.020414 .2.04 0O03914 254 0000328 3.434 0.00001714

0.05 O.MW528 0.55 0A3,6677 1.05 0.1.7G.1 155 0.028377 2.0 0.00374,2 01100211 30S 10.00001&38

0.06 0.0237.8 0.5 0.28,381 1.00 0.1338LC 1.S 0.027372 2.06 000377 2.56 QQ4 306 M0001 9,18

0.07 . 0.921142 0.57 0.420184 1.07 0.1 :30227 157 0.020307 2.07 0.003418 2.67 0.000278 3.07 0.00001 .114.

0.05 0.902922 0.58 0.412077 I.M . 0.120674 1.66 0.025463 2.08 0.003202 2.66 0.000264 3.03 '0.00001320

0.00 0.859719 056 0404001 1.02 0.123107 1.60 0.024035 2.09 0.003120 2159 0.000249 3.09 0.00001213

0.1 0.887537 0.6 0.396141 1.1 0.1 19795 11 0.022052 2.1 0.002479 2.6 0.000236 3.1 0.00001165

011 0.876377 0.61 0.358319 1.11 0.116467 1.61 0.02270 2.11 :00045 .2.61 0.000223 3.11 0,00001092

0.12 0.885242 0.62 0.380589 1.12 0.113212 1.62 0.021062 2.12 0,002716 2.62 0.000211 3.12 0.00001023

0.13 0.854133 0.63 0.372054 1.13 0.110020 1.63 0.021157 2.13 0.002653 2.63 0.000200 313 000003958

0.14 0.843053 0.64 0.365411 1.14 0.106918 1.64 0.020376 214 0,002175 2.134 0.000180 3.14 0.00000607 0.15 0.833004 0.55 0,357071; 1.15 0.103876 1.85 0.019624 2.15 0.002361 .2.65 0.00017.8 3.15 000000340

0.16 0.820088 0.56 0.350623 1.16 0.100901 1.813 0.018805 116 0.002253 2.136 0.000169 116 0.00000786 0.17 0.810308 0.67 03.13372 1.1:7 0.098000 1.67 0.018153 2.17 0.0021i9 2.67 0.000159 3.17 0.00000736 0.16 0.799064 0.68 0.338218 1.1.8 0.045163 1.66 0.017507 2.18 0.002019 2.138 0.0001.51 118 '0.000001390

0.19 0.758160 0.60 0.320160 1.19 0.022392 1.60 0.010847 2.19 0.001454 .2150 0.000i12 3.19 0.00000614 0.2 0.777207 0.7 0.322199 1.2 0.080026 1.7 0.016210 .2.2 0.001863 2.7 0.000134 3.2 0000006433

0.21. 03564.78 0.71 0.315335 1.21 0.097045 1.71 0.01559.3 2.21 0.001776 231 0.000127 3.2,1 0.00000504 0.22 0.755704 0.72 0.308567 1.22 0.084468 1.72 0:014097 2.22 0.001692 2,72 0.000120 3.22 0.00000527 0.23 0.741077' 0.73 0.301896 1.2.3 0.081050 1.73 0.014422 2.23 0.001612 2.73 0.000113 3.23 0.00000102 0.24 0.734300 0.71 0.295322 1.24 0.0704951.74 0.013865 2.24 '0.001536 2.74 0.000107 3.24 0.00060460 0.25 0.723674 07-5 0.258845 1.2.5 0.077100 1.75 0.013328 2.25 0.001463 2.75 0.000101 3.25 0.00000430

0.25 0.713100 0.76 0.252463 126 0,074751 1143 0.01.2810 2.26 0.001303 2.78 0.000096 3.26 0.00000402 0.27 0.702582 0.77 0.276179 1.27 0.072426 '117 0.012302 2.27 0.001326 2.77 0.000000 3.27 0.00000376 0.25 02692120 0.78 0.269900 1.28 0.070256 138 0.011826 2.2.8 0-00 12.622 2.78 0.000384 3.28 0.00000351 0.20 0661717 0.70' 0.203807 110 0.0138101 '1.70 0.011350 .2.20 0.001201 .239 0.000090 3.29 0.00000328 0.3 0:671373 0.8 0.267804 1.3 0.065944 149 0.010002 2.3 '0.001113 2.8 0.000075 3.3 0:00000306

0.31 0.661002 0.61 0.251907 1.31 0.003937 1.81 0.010475 221 0.001058 .2.81 0.000071 3.31 '0,00000280 0.32 0.650874 0.52 0.246184 '1.32 04361035 1.82 0.010057 2.32 0.001 a-114 2.82 &000067 3.32 0.00000202 0.33 0.610721 0.63 0240476 1.33 0.050985 1.83 0.039053 2.33 :0,000454 2.83 0.006003 3.33 0.00000245 0.34 0:630635 0.84 0.23.4857 1.34 0.058086 '1.84 0.000264 224 0.000435 2.84 0.000059 3.34 '0:00000232 0.35 0.820618 0.85 0.229332 1.35 0.056236 1.85 0.008881) 2:35 0.000889 2.85 0.000056 3.35 0.00000216 0.36 0.610670 0.60 0.223900 1.36 0.054434 1.86 0.008528 2.36 '0.000645 2.86 0.000052 136 0:00000.202 0.37 0.600704 0.87 0.216500 1.37 0.052688 1.87 0.008170 2.37 0.000603 .2.87 0.000019 3.37 0,0.0000188 0.36 0.540901 0.88 0.213313 1.3.8 0.050051 1.66 0.0378441 2.38 0.000763 2.88 0.000040 338 0.00000170 0.30 0.581261 0.89 0.2081.57 1.39 0.040327 1.84 0.007521 2.30 0.000725 2.89 0.000014 3.34 0.00000163

0.4 0.571608 0.9 0203092 11.1 01)47715 1.0 0.007210 .2.4 0.000650 2.0 0.000041 3.4 0.000001.52 0.41 0.562031 0.91 0.146117 1.11 0.016148 1.91 0.036010 2.41 0.000654 .2.01 0.000039 341 0,00000142 0.42 0:552532 0.92 0.143232 1.42 0.014624 1.92 0.006622 2.42 0.000921 .2.92 0.000036 342 0,00000132 0.43 0.54311.3 0.53 0.188437 1.4.3 0.043143 1.43 0.000344 2.43 10.000589 2.93. 0.000034 3143 0.00000123 0.44 0.533778 0.94 0183724. 1.44 0.041703 1-94 &GOGG77 2.44 '0.000559 2.94 0.000032 341 '0.00000110 0.45 0.524518 0.55 0.179100 1.45 0.040306 1.95 0.005821 2.45 '0.000531 2.45 0.000030 3.45 '0.00000107 0.46 0.515345 0.96 0.174076 1.41,3 0.038046 1.46 0.035074 2.10 0.000503 .2.98 0.000028 345 0.00000009 0.47 0.500255 0.97 0170120 1.17 0.037627 1.97 0.030335 .2.47 '0.000477 2.9.7 0.000027 3.47 0.00000092 0.45 0,497250 0.98 0.165704 1.49 0.536116 '1.98 0.005109 2.48 0.000153 2.98 0.000025 3.48 0.00000096 0.491 0.488332 0.96 0.161 402 '1.19 01)35102 1.40 0.004869 2.40 '0.00042.0 .2.49 0.000024 1 3149 '0.00000080

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Table 4: Convection Heat transfer Characteritics for a'Large Plate : Flow and Thermal Properties during Transient Conditions

0.1 Lii 10 100

I r l[ILl 1t I'

I I

() T- T

)

119

08

0.7

0,6

0.5

0.4

03

0.2

0.1.

0 0.01

4. ii

;';1, One term approximation for

I

by A1

given

BI

Temperature Distribution in a plane wall

19

iO 10 1O I.0' 1 10 1U 2 Birh ar/k

Q

Qrhix I 10

0.9

0.8

(1.7

0.6

0.5

0.4

03

(12

0.1

0 101

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Thermal Characteristics in Transient Conduction Heat Transfer Through Plates

T.1

I

0.04 c. (

0.01

0.0(17 0_ 005

Oi)I)3

I., . . zS Iii 14 ] S 72 26 0 50 U 100 110 .lij 300 .OYJ

T (X1/i

Heisler Chart for mid-plane temperature of a plane wall

Grober chart for a plane wall

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Bff3203-Heat Transfer 21314