Faculty of EngineeringCredit Hours Engineering Programs

MANF475 : Heat-TransferQuiz-l, Fall20112

Name:

grlin gq{ it^hr^si4lL i*a

f,r-^I-et{a1[Ut EalX

Examination's duration: I hr.Prof. Dr. Gamil W. Younan

ID:

Answer the Following Ouestion:

Question 1 (10 Marks):Hot gases at temperature of 200 oC flows inside a steel tube (k:40 Wm.K) having D;:80 mm & Do:100 mm and the outer surface is exposed to ambient at temperature of 20oC. To reduce the heat loss from gases to the ambient an insulation material havingthermal conductivity t t" is used. The contact resistance between the outer tube surfaceand the insulation layer is 0.02 m2.K/W. If the convective coefficient between hot gasesand tube is 120 Wm2.K, while between the outer surface of the tube, or insulation iayer,and the ambient is 8 Wm2.K, Calculate:i- The maximum value of the thermal conductivity for benefit insulation.ii-The percentage of reducing of heat loss from gases to the ambient when use 50mminsulation thickness with thermal conductivity ki,: 50oZ from maximum value ofbenefit insulation.iii-The outer surface temperature of the insulation.

Question(2):I 5 Marksl :Determine the percentage increase in heat transfer rate associated with attaching aluminium fins(k=180Wm.K) of rectangular profile to plane wall. The fins are 40mm long, 1.0mm thick and areequally -spaced at distance (pitch) of 5mm. The convection coefficient with the bare wall is80Wm2.K, while that with fins is 60Wm2.K. If the wall and ambient temperatures are 180oC and

30oC, respectively, calculate the fin effectiveness t, and the fin tip temperature T1in, consider thefin is insulated end.

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