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Unformatted text preview: Page 1 Midterm Exam CEE 218A — Air Quality Engineering
University of California at Berkeley
Fall Semester 2008 NAME: g0 0 VLS an Instructions: answer the questions that follow directly on these pages in the spaces
provided. Use the back of the page if you need more room for your answer. If you believe
there is insufﬁcient information provided to answer a question completely, state
reasonable additional assumptions and proceed from there. The exam is closedbook, but see last page for aid sheet. You may use a calculator. Please write your name in the space provided above! Time: 90 minutes (2: lO—3:40 PM) Question SCORE: OUT OF: 1 10
2 8
3 7 Total 25 Page 2 1. ETHANOL CONIBUSTION (21) Suppose the molar ratio of CO to C02, Q = all) : 0.3 is measured in the exhaust plume
of a passing car that is burning pure ethanol as fuel. Calculate the air—fuel mass ratio
for these conditions. For fuel—rich conditions, the combustion stoichiometry can be
approximated as follows: CH3CHEOH + m E 027+ 3.76 N2] —> a C0 + 1) C02 + 3 H20 + 3.76111 N2 Mew (TaH522. (Raﬁ/13:0,?
 S: 2., £75: a:2~—£=O,L{é ,m t .ECD,%+2H.W+3»I) _'= 2.7?
ma 2 .13 x 26: «ii/mi slim7(a) a (2M; 3W1». .
WE I K Lita 3/W\ law (b) Estimate the percentage increase in fuel consumption for conditions of part (a),
relative to the ideal case of complete combustion. See next page for needed thermodynamic data. EM:( “’4’ ) ,4 Ewe/Mi % ﬂic .._. mmw .i+ a/b age/w [few 3M
E}
.W“(’ mo“ ‘32 CO 1 “132.1 “‘1 3‘?‘t06v Hweo 2 23351 HOE:
aw! (3.
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:: 271k?
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IWW. in M vawwkvm {It ,3; :: "Flour/’ Page 3 (c) The lower heating value for ethanol is 30 kJ g_1. Calculate the adiabatic flame
temperature for ethanol, assuming the following revised stoichiometry: CH3CH20H+3.3[02+3.76N2]*2C02+3H20+0.3 02+12.4N2
WW. cuwraww W G" Taiilqu, — Standard Enthaiy Heat Caaci (J 11101— K‘ ): C}: = a + bT
M00 moi" ) — (:02 (g) —394 000 44.3191 0 00730 co () H110 700 29.6127 0.00301
—242 000 32.4766 0.00862 __ 305041 0 00349 29.2313 0.00307 a ARC :.—. :11; 121% (rs1;)? + [EfCTz—Tfﬂ +
3E6WCTTa) + 336203)] “F 9‘3 [C361, CTJFQ) + CTZP'Eiﬂ + W [an CT «719) + 19:: [TRT30]. ‘ 0:086 (Linda), 4" 313111104" [301* h’i‘ / $307.7 CTFHT") Bicep“? 30111.04r 030161;" [2* q‘aue] “i” Ago T" 0 i
2. acaciaT2" + 597:7"? “1649722 :2 0 9.0Ler ana$b W}
T: 023762K _ EM Page 4 2. PARTICLE COLLECTION IN A DUCT (a) Derive a general expression for the critical particle size DPC at which 50% of particles
ﬂowing through a horizontal section of an air duct will be collected by gravitational
settling, Neglect all other particle collection mechanisms, assume air ﬂows through the
duct at a uniform horizontal velocity U0, that particles are spherical, Stokes law applies,
and neglect slip correction factors. Dimensions of the rectangular duct arc length L, width
W, and height H. The flow is in the L direction, and particle settling occurs in the H direction. “a
7:13 3.: l:
3
BW/“Drvs ’2‘ :59 DP 3} Page 5 (b) Plot a particle collection efﬁciency curve 7] vs. DP/DPC for the duct in part (21).”
Calculate and show values of n for Dp/DPC = 0.5, 1, and 2 on your plot. q as M CD?) .3 DP “’
(my) V93 FDR: 3
D? /DPc 71’ imi— 715;! W . Page 6 3. REFRIGERANTS R—134a is tetraﬂuoroethane (CH2FCF3), and is replacing other reﬁ‘igerants used in
automotive air conditioning systems. (a) Global background concentrations of R—l34a were 35 parts per trillion (ppt; 1 trillion
= 1012) on a mol fraction basis as of mid—2005. Estimate the total mass of R—l34a that had
been emitted to the atmosphere prior to 2005, assuming constant emissions for 10 years
starting in 1995, and an atmospheric halflife of 14 years. A signiﬁcant portion of the R— ;
134a emitted between 1995 and 2005 had already reacted away by 2005. Recall the ﬁrst order reaction rate constant can be written as k : 0.7/1: where ’E is halflife. Poi: may ma: WEIR; ‘ SEX/0,57% ‘frml 9“ 2
“$32 : ligwoowf
emf/mt _ nrm" E x ha: éix/o WI [iv {o m 2: layanxiozi : @254“) pwol (b) Why is R—134a preferred to the previouslyused R—12 (CClgFg)  rwo ma, 5’0 SJ'thﬁfbhﬂﬁ/I‘c 032w. (LLB/6A,
" WM W, vs ﬁve/2 Z) W GWP ...
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