Solutions+to+Final+Exam+Fall+2008

Solutions+to+Final+Exam+Fall+2008 - fl/w wax 5 Final Exam...

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Unformatted text preview: fl/w wax 5 Final Exam ME 3345 Heat Transfer Fall 2008 Hesketh FINAL EXAM TLME ALLOWED 150 Matures Name: Grade: Question. 1 (20 pts): multiple choice (circle the correct answer): 1.1 Total Hemispherical Emissivity is equal to Total Hemispherical Absorptivity: A — Always B For diffuse gray surfaces C — for diffuse surfaces 1.2 Parallel flow and counter flow heat exchangers have the following characteristics: A -« T he same heat transfer coefficient. 3 ., l’arallel flow are more compact that counter flow. ' Counter flow are more compact that parallel flow. l3 rl‘he angle factor or View factor can only he applied to problems with: Diffuse surfaces malform irradiation Steady-state 1.4 In pipe flow the thermal flow development length is largest for: 1.5 The thermal equivalent circuit can M be applied to problems with: ”A _ radiation .3“ heat generation C — transient analysis, Page 1 Final Exam ME 3345 Heat Transfer Fall 2008 Hesketh Question 2 (Meats): Tsun = 5800K Solar Irradiation , . Solar lrra diatlon 0.9 0.2 D=10m Consider the sollar radiation furnace shown above. The cylinder of diameter 10cm, iength fire. has a spectral ahsorptivity shown and is a diffuse surface. Determine the nett heat flow to the surface given that the surface temperature is 500K and the soiar radiation heat flux is 15th W/mzx and the ambient air is at a temperature of 300K. Assume the hemispherical reflector has zero absorptivity and that aii of the incident radiation is reflected onto the cylinder. Also assume that the convection coefficient can he represented by a flat plate with the same projected area° Assume uniform irradiation and neglect convection from the ends of the cylinderg = 9.8m2/s Properties air: it = one W/rnzK, v = 45 x 10" mzls , a = 66 x to" mzls , ri- m ass AT:?,¢S’J’IV‘0: 7—7?0C7 , $_A; 0‘7? 4— «Q‘ka/ ' Joli: % k: g: F5*>‘ 7i gag/“F579 ”(I 5—“ 0»th 0-?)714 0.274002 5 0*ny [fig/6 flflfl/flflm/ Rep/7 .foflzéfl/Vfl/A/és g Fog/C T: Ida/C )\/¢4x= 2.23:? M éam £170 Alfiyxfaos— /f00. F—0_A=€7'0[fg> g =5 6‘7K0'0/gé) F74 0‘2’{/HO-0/35’>:O‘2/ Page 2 ’7 2,“, x firm : PLAN? 4;. _, “’00fo [00 ff— 44 xfi’xO-/></ daNVéL’f/DN 7;: YWOK 3 :4“: I Ra]: it YETL F ’7; "77%;“; ('1— I? :— I r W 2;; 400x [égxéaé fl {x(0§7a[0? Tyflflt/cé/vx FLOW 6L 5 ___/,__/’—~ 0333 {17; = 5/1651. 3 [I7 1»: Wk 5 4L MW/M 5mm W WWW“; gag/1 ___, gal/L4 %f me ,e p Una/MAJ Final Exam ME 3345 Heat Transfer Fall 2008 Hesketh Question 3 (20 pts) SIDE VIEW L genie line "71am \ % Combustion chamber 0.1m i1 eometty shown heiiow are attached to a combustion 0 WHITE. Thetmai conductivity of At is convection coefficient is 1100 ‘W/nt2 K. state conditions9 neglect Annniai‘ heat sink tins with g chamber which produces a heat than of 100,00 200 W/mK and steel is St] W/mK. The externai Caicnllate the internai temperature of the wail under steady- radiation, assume no contact resistance. {Hintz sketch the equivalent circuit and caicniate the tin resistance hased upon the fin efficiency is given by Figure in the equation sheet} [‘3 3L Z Web/f / tab 0 Page 3 LL: r5 7. szr—‘ézrda m I; {0: 4P: L J ' £35.. 5/: 7’1 ’ 5 (3 [Vt/0) Zpayél ‘ xe z) 4 fi’ 504‘? OW "Fr-sf}: ,g‘IOI I? 0.3/ A ‘C’ F :: (—(é—éA/L“ LCJM F ”C VAL/{IVE #1450 [name 7} may 0” f [670 50253 [C £}j““{"—Ffl / affxf-Efgc/Qa /W A 7% 7.9? / 5 KM f RA 5 ‘1’“ : n7c7x2r€g>¢ify / A4é ‘ / /)”/jykws> my K6951 5 flf+£4+ E4 (5 Z: M / {La—~25. -—._ --.- 226 e gé—Aoé W57? 015 flé—ZK/fl7 f MM % : fire/£54 filf %¢H f :ZTfiaL/xz‘? “/0 Wk: TM: @pggf 0.9767 1423’ 7—”: /00 9c Final Exam ME 3345 Heat Transfer Fa112008 Hesketh Question 4 (20 pts) 7 20mm TS 150mm $9 A vertical array of square printed circuit boards of 150mm height is air cooled such that the maximum temperature on the boards does not exceed 60 C with an ambient temperature of 25 C. Determine the aiiowabie snrt‘ace heat flux from the electrical components under the following conditions: (a) Free convection oniy (h) Downward air flow at velocity of 0.6nn/s (c) Upward air flow at velocity of 0.3nm’s and free convection. Properties air; it = one iii/mac, v = is x to" nizls 9 a = 25 x to6 inzls , Pr = mo g=9.8rnfs2 (Assume steady state conditions and. negiect radiation) Final Exam ME 3345 Heat Transfer Fall 2008 Hesketh Question 5 (20 pts) A sheflntube heat exchanger with one shetl pass and 20 tube passes used hot water on the tube side heat oil on the shell side. The singte copper tube has inner and outer diameter of 20 and 24mm and. a length per pass of 31m. The water enters at 87 C and 0.2Kg.s and leaves at 27 C. Inlet and outtet temperatures of the oili are '7 and 37 C. What is the average convection coefficient for the tube outer surface. Properties water: k = 0.65 W/mzK, u = s x 10'4 mzls 9 Cp = moo J/kg K, Pr = 3 Thermal conductivity of copper = 400 W/mK. Page 5 00/4 hcflt Zn‘fléL 4340 fig FLOW ~44 IV“: 9023/84%/9r :/20 r amt/away: :(qaov/WK (7-02 #0 :3 #flvL :Wxa.02.¢x?x20 : (FIZQL/Mafll k A f, I fi— # ,1... _, MAJ] - 9 4/“ 294 M44 AL/4L 2,71%” #4:.5’24C/ 2.3700 ?Q€Ox§‘77 nyggv w?,¢w_, A» .7, 7 427 (M/WEK ...
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