quiz+4+Key+2010

quiz+4+Key+2010 - PEPE 321% Spring 291i} _. ‘ g .I .- Qm...

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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 mass-avemge motion Relative t6 mass-average moi-ion 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‘6-mé 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 Cpl-u 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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quiz+4+Key+2010 - PEPE 321% Spring 291i} _. ‘ g .I .- Qm...

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