2009 summer c exam for heat tansfer

7/27/2019 2009 Summer C Exam For Heat Tansfer

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EML 4140 (Heat Transfer) Exam No. 2(100 pts) Summer 2009

Problem NO.1 (40 pts)Problem No.2 (40 pts)Problem NO.3 (40 Pts)

Total100

Instructions:1. Open Book and Open Notes only.2. Please turn off your cell/smart phone during the exam3. You must show all necessary steps and calculations, otherwise no credit will be given4. Please provide all steps in neat and clear manner

5. Sign Pledge : _1 have neither given nor received unauthorized aid on this test nor have I discussed thecontents of this test with anyone during the exam.

Last Name _Student 10 _


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Problem No.1 (40 p ts ) A tube bank uses an aligned arrangement of 30 -mm diametertubes with 5 = 5 =60 mm and a tube length of 1 m. There are 10 Tube rows in the flowdirection (N~ I f f ) and 7 tubes per row (N :::7). Air with upstream conditions of T =2lc and_ .,.. ()c7V = 15 m/s is in cross flow over the tubes, while a tube wall temperature of 100 C ismaintained by steam condensation inside the tubes. Determine the temperature of airleaving the tube bank, the pressure drop across the bank, and the fan power requirement

L>"'-I.~-r\O"'-S. C D SteGtJl-~t"'-H cO'-".Ck\-".D"'-S I (j) .t 'Je~ ' ..'1'~\e.. -ro..d',o..t-"D"'-j d ) A ;r y1'"eSS'\)T"ei ' :> c....?~'D:>'-...\VV\.C\.h\1 DV\... D..-t\iV\1;) " " : : > y \ - e 'n : ) E D UV\..,~-o,v-1 -su


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~It\. r < e :: : s: lo io x t o'1~,""""';( ) v z : 2L )G.V\.d )(:::)

LI? = NL l ' ( p ~ ':1 " I D t (11~lj- ~)( 3D; ! ) J O > I~) ~ q q 3 :::~ = D ooq~ 3 b~,


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Prob lem No.2 (40 pts) - Consider a thi n - wall ed , metallic tube of length L=1m andinside diameter D .= 3 mm. Water enters the tube at m = 0.015 kg/s ando ~ .T=97 C." ,,! i :

A. What isthe outlet temperature of the water i f the tube sur face temperature is< 'maintained at 27 C?

B. If a 0.5 -rnm thick layer o f insulation o f k = 0.05 W/m. K isappl ied to the tube and itseouter surface is maintained at 27 C,what is the outlet temperature of the water?oC. If the outer surface of the insulation is no longer maintained at 27 C but is allowedoto exchange heat by f ree convec tion with ambient air at 27 C, what is the out let

temperature of the water? The free convection heat transfer coeffient is 5 w /rl. K.0I1'-\y~"O"'-'): (l ) ~-\-eQ~y-s\-c..te. c.o\"J,-\-\c ......, (i) 1 = " , - , \ \ y

(5 ) Ne~ \'1 '' o \e -h)~e ~o ,\\ c.o",-J~e.-\'.()r e s,S\o...v...ce be.h.~eeV\ -\-- u\ae v-Jo .. \\ Q ' - " . . d .CbVl..vec..t~"""",- CD~C -t.,c .. \e " '- -i-,

de \le \o ?e J C \ c > ~ -\-~,uvllo"t("tS\stC


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~. =21"'(, .c

. ( lz ~ \< . .- / o. 0(5' ~) . - l Y 05~)

~I::- -A IH - '


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~ 2 1-0C G ,-r :::T - -\ ::7 -0 'i:) .A \'> -' \ l .. '00


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Prob lem NO.3 (40 pts) - Under Steady State operation the surface temperature of asmall 20 - W incandescent light bulb is 1 2 g ' Cwhen the temperature of the room air andc>walls is 25 C . Approximating the bulb as a sphere 40 mm in diameter with a surfaceemissivity of 0.8, what is the rate of heat transfer from the sur face of the bulb to thesurroundings?

VV\.V -+lOv-...~" C D Steo..dy-'S-\-Q..:'~ (Ol-\..J-;-\-\o\/\..') I c D Qu,e..'Sce"'-.-\- r60",-\ C .:," I Su(",cund,vo..asVVI\.H ...i; \o...,~.e.\ . - r L C ' , - " , - \ov\~

( Ts -\-T O o , \ 9' ) \ (. ~"\< .~e\-t'\e';,: T o .. ' c \ e A _L\) V\'" .~;o ~=- 3~ 0 I : = : . ~ + -

i~'e.. l \ " = 11\')L. T or < . 0 . . ' 1 \ e " ~~ \ A .. 0\!V\\o -e '.

3 >lj , j 3 ( t,T) \)( ( ~ \ ) = Y o < .''''C

- ( l : .-\ ( . ~ -,\ 6.0lq~ ~ l - = q .~ ~ ~~ - N 0 D \ \) ) -::. '-- \ '(, 'J ':) ) L 0.040 VV\. .. J ' "",2. Kv 'o c ;, + ,+0 - \"''' '-d Y\ V "",,-e,'\ c...c,,\ Vo..\ves) -\-4 ~Q.\; \o::,~ ~\o\tV\. - \ - 4 ~0\b i' =

~ z: TI ( D . 0 '-\0 ""') f (9 "( , , d'k)(, L , - z ,) I < . + (p.~o)(,," ' I , IO '': ;-,~ " ') l ( . z s In')~- (2n n;~jt = : ( 4, 'to 1-3,9?) v J ~ [ % , t o l W )

2009 summer c exam for heat tansfer

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