F2007_Exam1Solt - NAME SECTION YOU ATTEND 1 pm 2 pm...

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Unformatted text preview: NAME SECTION YOU ATTEND 1 pm 2 pm Separations Processes CHE 363 September 19, 2007 W Open book, one 8.5 x 11 inch cheat sheet, caiculator, your brain, 50 minutes. 1. Short answer (please justify your answer; space indicates the expected levei of detail): (3 pts each) a. Consider a small moiecule like lactic acid found in milk. Rank the diffusion coefficients for tactic acid in milk (DLAWk), in the plastic miik container (DLAMSg-C) and in the surrounding air (Amy). ‘ ' __I ' a” i i I DEA 41:1?“ ‘20 DLA mil: >> Ding pmSmQ «- M?— # 1L. CM; 2:) [ egg“; xv 5 L W {C3 % Eli/1‘.” ' 34L 96L m b. Why do mass transfer coefficients vary with partition coefficients but heat transfer coefficients do not? Heat?) £955 agate/Q “Powwgstu/‘A tut Iii/“lartststf fiMiibi/LM 1g {yard}!!- "lf'bkéwéfgr‘fi gnaw—{mcl—{W 2‘; LL Stew efiut’filfgrfltfle Waffl'tiigflhgw (gift, if“; "') c. Efthe flow rate v doubles, how much will the diffusion coefficient D change? How much will a mass transfer k coefficient change? a but.“ Wart guriafa‘tmflcn'ltwg Ctr/Lamaltrrlflast 0% / t a (From Gofmfazl‘apwj‘ of “Jams (o‘v' Simflap) “#2 0% M fl 6. What are the units of flux? (N1 or m orjt or c1v°...) we 2. in microelectronics, silicon wafers are spunucoated with a polymerized organic film (“photoresist”), which is ~ 5400 A thick, and has a density of 0.96 g/ cme’. After etching, the photoresist is removed by soaking the wafers in a large volume of strong organic solvent. The maximum solubility of photoresist in the solvent is 2.23 x 10'3 g/ cme’. Ef all the photoresist dissolves in 10 minutes, what is k? (15 pts) {Home «3:5 fiwlm +5 $W/eiluf L5 a@. fill”? __ E; ‘ QM} am N/ (jguk W MAM WWE 2 + :1. éw‘w 15?: Sea/aean k? is lofi ‘, Sa/mfli H : QW?§MJ’I+ Xflrrflfi’ glam WW éafdfiflc am 563fo .‘ Accumul'cueb/i :: V)pwg=¢wsasi’ é? _, +EM +4 da‘gfiaflvflaall 4 Q “Kerwin. k<CSa+ I'D/it) ': 6'flliw}cvfiaca,' 3% I; {Oflé’ 54QQ%)( M g “:{n MM A M}e\' #1 - SAXQO ‘ a.“ . My; lfl : 3/0“ mm {M} I A10”3 ‘Bv/ Cm?” ® :3 {Vi/l l infill” +9 magma F;th PWb€£ML I ,_.--—- cflffl‘sflj i—s filmirl’ Pwialvam} €33“ lose glam lawblgaLL ‘E/Xw 3. In an effort to slow global warming, you are replacing the water in your CO; absorption column with a reactive soivent; thus. when 002 diffuses from the gas into the iiquid it reacts with piperazine in the liquid. Thus XL (the concentration of CO: in the buik liquid) is kept very close to zero. (10 pts) a. On the gas—liquid interface below, diagram the concentration profile: i) at the gas—liquid interface without reaction. , {my/ON ii) add (and label) a second line showing the concentration profile in *l/ the liquid when reaction is present. iii) Which will have a greater overall fiux? L iv) draw the concentration profile of the piperazine in the liquid E52. 0 WM i053?” 03/ mm. if iii/i, 6%” em“ ' , D m keg (cans mantaan We; 00") i ‘3 —~ AC. 105 U i 3 1 w/ mum ‘ concentration= zero b. If the totai volumes of gas and iiquid are large, would you expect the profile near the interface to be at steady state or unsteady state? @ S BL is gene-«ii @[a-ttvwe +0 fiat/(Mich Uuium-QS) 3 So mPMLLa estabiisioes q Stalin: I MW Pleat/Q iflfii c. To develop a flux equation incorporating the effects of reaction, first write a balance on the liquid side of the interface, starting with A = I—O... The desired answer will be a differential equation —— do not solve it. What are your boundary conditions? Q ': {~(9 -i- @ O : mllfis m, )fifli - Y‘PGA Wth': KCCQC Jaye/fight O 3 Jim T 'i! winged, d. Based on your result above, wouid it be more appropriate to use a mass transfer coefficient k or a diffusion coefficient D when you have a reaction in the bulk? ED D We man émwws in wrong vol”,th 4. A ventilation pipe has been instailed on top of a storage tank containing a hazardous voiatiie chemical; unfortunately your current emission rate (moles/time) is double the EPA iimit. Your boss telis you that it you to cap the current pipe, cut a hole and add a second pipe with the same tength but half the cross—sectional area, you will meet EPA criteria for emissions. (15 pts) a. Write equations describing the rate of mass toss (20) over the ventitation pipes in “g 5’ both cases. b. Recognizing that in the new design, the rate of toss must be the same in the "’ [3 larger pipe and the smelter, find an expression for the concentration x, at sz. c. Compare rgator the old and new designs. By how much wiii emissions be t 5 reduced? HINTS : you may consider this to be a dilute solution; you have sufficient information to get a number; it is somewhat similar to the ethanol evaporating in a tube. “--L.A2= 0.5m Otct dcmgn New demgn " M 1:. a o m w it cl 1 9,1; «a Equations and information which may be useful N1 = kLAcL = kGAcG = kxAx = kyAy = kpApi N1: cm :1} + 61v” 3 -D(dc1/ dz) + 01v” dM/ dt = AN1 R {gas constant) = 8.31 J/ (moi-K) : 82.05 atm—cmal (moi—K) = 1.98 call moi—K Safest correiations for k: M‘ "Physical Situation Basic Equation Ww‘m {L45 {LS dvo [ v 25 b «— v 0 [3.6-1 2 1.2(1m gym [ _ v Liquid in a packed tower Gas in a packed tower Faiiing fiizmS Membrane Laminar flow through circular tube ...
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F2007_Exam1Solt - NAME SECTION YOU ATTEND 1 pm 2 pm...

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