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Unformatted text preview: PEPE 321%
Spring 291i} _. ‘ g .I .
Qm Name K5 ‘2? 1. Write the rate equation (Fisk’s law) for mass difquiOﬂ of species A in a binary mixture of A
and B measured reiative to stationary coordinates and deﬁne all terms used in your expression. (10 points)
5" 7‘ 3? __ _ ﬂ — n " I! 3A — pDABVmA +mA§3§A +323 E W“ ‘mv—" W ,
ABSOLUTE contribution duets consibuﬁon due to 7 5'in diffusion that is motion of A with W“ _ motion of A relative to massavemge motion Relative t6 massaverage moiion of mime
themed of mixture
morﬁmate
system 32A"(i€g331/S ' m2) is the diffusive mass ﬂux of species A measureé reiaﬁ‘ve to stationary coordisaies. r23 " {kgm/s ‘ m2) is the diffusive mass ﬂux of sgaecies B measured reiative to staiioiiaay coordinates. p is the totai mass concentration. DAB is the binary diffusioii coefﬁcient or mass diffusivity. _ :f V is the dei operatof. am is tile mass ﬁaction ofspecies A. 2. Species A is evaporating from a ﬂat surface into species B. The concentration of A in the ﬂee
stream is CA3”. Assume that the concentration profile for species A in the concentration boundary layer is of the fonn_CA(y) I B + Fy + Eyz? where B, F, and E are known constants
at any x location and y is measured along a normal from the surface. . Derive an expression for the mass transfer convective coefﬁcient hm in terms of the _ constants, the concentration of A in free stream C A509 and the mass diffusivity D AB.
' (mpoints) an
1/\ M v £91445 a3 730
.M ‘ so 3 F
2.9% :7 F 4' Zéai : 717 9:5 .  ' _' 1%,. 3.“— 5m My“; . “a E7; {m (27+ /z§)c : 77 cc
, f z W I: ' 'P 2 Z g r: 9%“
’"’ 7350 27:8, :3 50/934 t. y ' 2&32X/0‘6mé 4. Saturated water vapor leaves. a steam turbine at a ﬂow rate of 2.0 kg/s and a pressure of
1.0133 bar. The vapor is to be completely condensed to saturated liquid in a shell and tube
heat exchanger with one shell pass and two tube passes. City water is used as the cold ﬂuid.
The water is to enter the thin wall tubes at 175C and is to leave at 57°C. _ Assume the properties of the water and steam are as follows: .
Saturated water: Cp = 4178 J/kg  K, p = 1000 lag/m3 and a = 3.43 x 104 N  3/1112.
Saturated steam at 1.0133 bar: Tsat 1 373.15 K, hfg = 2257 KJ/kg and k = 0.0248 W/ m ' K.
Assuming that an overall heat transfer coefﬁcient of 8000 W/m2 ' K, determine:
(A) The required heat transfer surface area and (17 points) (B) The water ﬂow rate to completely condense the vapor. (18 points) Heat Exchanger Effectiveness Relations are listed in Table 11.3, which is attached.
57974, 12/74:; STéMM
g _ P :: /, o lg; 8 M
{3‘ z 2’ (3 K0115 ' ‘7“ 2/71;
5 15;! a” . jg 1' 13M.) CPW (EVEN, ‘7‘ ICIW Cplu 137; :3 EH Tm 1V1 of 61+ /(c.,w}(bm:=« ﬁts/4 kf/S)/[aﬂp7?a;£¢qi may
W l; 40?; L f? j gr: 2:; :7 if (man/7106 523 riff N i} é 3“ 5%) {WW1 :? Ne’o v“ aged/Lg): 307(5) sow) k; ...
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 Spring '11
 Dr.Carr

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