practice final spr 04 solution

# practice final spr 04 solution - SO LUT[040 ME CHE 109...

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Unformatted text preview: SO LUT [040 ME/ CHE 109 Final Fall 2002 Name Problem I. A cylindrical enclosure of radius (r=2m) and height (h=0.75m) has emissivities as Lshoxn in the figure. The 3 surfaces are maintained at uniform temperatures as shown. A :J ' / £1 = 0.6, T1 = 800K 19 “2 = 0.5, T2 = 500K block, T3 = 600K wad? (be, 3 t1 “afﬁrm. a 3:9, L); “5’5 PG 01, ﬁhsim,‘ LOAD“ ‘ (x: / Cs 2” hi‘ \ 10 pts. Ia. Draw the radiation resistance network; La 0% Gm 3% r5 §, \\2. J}; 4‘. i , x l a, +1; rm 6‘1“ 44¢. (“hall ‘ 1"»' - I "\iL“‘ it“ 00’“), FL“; a” {/lj'm‘i.) (L ' bu") / L ‘ 10 pts. lb. Calculate the View factors F12 and F13 . idem - LA/g’.n‘§ Fl‘j-ci"4i?> L: Nizi’z; ZI’V'I v, I - . _. r L t K _ . '- /F - _....__—‘- ’ . . &»JL:1 9.)! 1“ 2. km Qapts. IIIc. Write the equations to solve for the radiosities, J1 and J 2. Do not solve the equations. The only unknowns in the equations should be J1 and J 2. PM’ Your C42“ “" { {jun @"WJi f Jabylb ._._L___.___..____. W1 *Bl‘lLlJ A"? 52), *Ol'OSJy/g '1 “435135 lax/“W? mam-\$92)“ P214451} W ’ {25133; 63, wwwmx- b7h Z EllD7‘JZ *J3 J2 LO _ , .5 \. a); + Lip-Wm JL l t 10 pts. IV.d. Calculate the total radiation heat transfer from surface 1. t ' a _ -8 §¢lv‘€ "Leif \Jl: Lr-l-SjriES/(ifo ‘________’___,____,,L ,;,;792<zc"4 3 56:67; 4 4— 6214} J, Problem II. An aluminum ball (25 cm diameter) is to be cooled from 0°C to 150°C by blowing air at 300K and 3.5 m/s. Assume the thermal conductivity 0 the aluminum is 237 W/mOC over the entire temperature range. 10 pts. II.a. Calculate the forced convection heat transfer coefficient for the ball TM; -— 200K ‘Ts; 3‘801511192 mans K . ~ 0 1" M . ., . ., t :.olo( W/,,V,»C v: I-élwc 5 . T" k \— [IQSXIO‘S pr: g-gfrl-Ciixfﬁ:EVI‘UL?’«(NUS Re a 350.9 ; (3.9 m/s ( ,29 m) v [512‘10‘9 MZS 15 pts. IIb. Calculate the time required to cool the ball. U the transient analvsis from chapter4in the text. CE ‘2 51451 ’7; 1 {jiﬂlétf‘éci‘gfgs {6:97.33 BiZl’ll/é.’ L°:_l.cD K 3 s (14 w x ,c‘tlml/231 L[~4ch i.‘.»-—-uc:>';e\ u a c. LS A‘ _ X . _, if) 5 we! ) KL C (QC? V #3" ‘ 14399 7 ,._ r v "V (J ’ W CW», .1 I Lattixloél"), vh , TC, - 7 #364910 w _ *‘0 b a t) A” ; I U ﬂ» ’3" \ 04c; :2 t; T.. __ Tr}, “ 3U” ‘ .. Problem III. An electronic box that consumes 180W of power is cooled by a fan blowing air into the box enclosure. The dimensions of the box are 15 cm x 60 cm x 60 cm and all the surfaces of the box are exposed to the Too=20° vent for part c AII‘ Figure for Problem III ambient except the base surface. Temperature measurements indicate that the box is at an average temperature of 34°C when the ambient temperature and the temperature of the surrounding walls are at 20°C. If the emissivity of the outer surface of the box is 0.65, determine 10 pts. a.) The fraction of the heat loss from the outer surfaces of the electronic box due to radiation. 3 ‘7 B A r '5 5 ’ (2(ZC ; Q (T I5 ”” 1gpts. b.) The fraction of the heat loss from the outer surfaces of the electronic box due to natural convection. ﬁts-13 q E. . , A“ . AW 2 ,1, V1- {Vic-H5 ...
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practice final spr 04 solution - SO LUT[040 ME CHE 109...

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