quiz+3+Key+2008

quiz+3+Key+2008 - PTFE 3210 Quiz 3 Spring 2068 Name kg y 1....

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Unformatted text preview: PTFE 3210 Quiz 3 Spring 2068 Name kg y 1. For air—water vapor mixtures in the normal pressure and temperature range of atmospheric air, the wet—bulb temperature measured by the usual type of instrument is very nearly equal to the adiabatic saturation temperature. A. Why is this? (3 points) "Tail/Lb 3557 CW B. Does the equality hold for most gas—vapor mixtures? (2 points) N0 2. What are the meanings of the Biot number and Nusselt number? Give their significance. Are they interehangeabie? 2/10? ’4 L (5 points) BA 3 RcoND 3;: t “E? "7;" Room” A?” a 471. 865' W» ‘7‘" gig? 1‘" “7;? W07 ///7€/W’7"Mé” F 3. When will the thermal boundary layer and the velocity boundary layer have the same thickness? (5 points) a) Lewis number is equal to l 1)) Lewis number is equal to 2 c) Schmidt number is equal to I d) Schmidt number is equal to 2 e) Prandtl number is equal to l f) Prandtl number is equal to 2 4. Air at a free stream temperature of 200°C flows over a surface. The temperature distribution in the boundary layer (from y equals 0 to 0.005 In) is known to be: T = A + By + Cy2 where y m the coordinate perpendicular to the surface (note: y = 0 at the surface) A 2 100°C B = 30,000" °C / m C m — 2 X106OC/I'n2 The thermal conductivity of the air SW, and the thermai conductivity of the surface material is 10 W/m~K. a. Caiculate the heat flux at the surface? (20 points) 17 e17— ) ' (27" "‘" - < b" M 7: 5 +26 Z » ’4” 01a m .2 $1 at 1—..- 5 + (to) =1 15 033 5-20 . 7); W 1/ W '30 000 fin)jo&)—-e- 00 we“; W‘- ,02 J r/ W b. Caiculate the convective heat transfer coefficient. (15 points) «r ) Z 2’”: a W: ow- ED 77am) sew/0) W Z” 2 ?_7:: 0) “335% n W A” [exam-ea»? 4"Z» 041/ a . #606) We“ g. “ 5‘9" f” mos!- W / A f/oo°c~zoo°b "la/00 a 5. Water is being 10st from 3 p001 due to evaporation. You may assume water and ambient air temperatures of 25°C, an ambient relative humidity of 50%, pool surface dimensions of 6 m by 10 m, and a wind speed of 2 m/s in the direction of the long side of the p001. Assume the oon‘eiation for convection mass transfer that is applicable is: Average ShL = (0.037 Reg“5 - 871) Sol/3 Properties for the fluids are listed below. Airuwater Vagor {25°C} DAB 3 0.26 x 10'4 mZ/s Saturated Water Vapor 95°C! Se $9.60 cpm1872 J/kgK. Cp = 1007 J/kg—K 0 = 9.09 x 10'6 N s/m2 a =1.84 x 10‘5 N s/m2 k = 0.0196 W/ (m —°K) k e 0.0263 W/ (m -°K.) p5... = 0.0226 kg/m3 a m 22.5 x106 mZ/s Pr: 0.707 v $15.89 8.10“6 1112/8 Calculate the (25 points) gr: W 2V1: w, W— gee F“ “"7 ’“’ We M 12 c; R arm/es (fa/M) f... [lzé x70 6 2:: W '"F' 1 513‘: X10 ‘MIZ/s v3 4/5 - e a), 603 30 w" 973’] g :73 é 34 52,12, m @‘@3? [Ang W / W 0, 37434" /a3§ ' A L 5%; 3 it“? _. 9'“ .“4 1mg )M etzifix’DM/s $1 .3569. m (W #5? "“' M "" L jO/m 6. Use the attached psychrometric chart to answer the following questions: A. An air—vapor mixture at a pressure of one atmOSphere has a dry bulb temperature of 70°}? The relative humidity of the mixture is 50%. a. What is the humidity ratio (kg of water per kg of dry air) for the air~vapor mixture? I; 0' Wm, 2.1m Aim (5 points) ‘0. What is the dew point of the air—vapor mixture? (5 points) 1: 5 o , g ° F c. What is the wet buib temperature of the air~vapor mixture? (5 points) 5:: 58% °F B. An air~vapor mixture at a pressure'of one atmosphere has a dry bulb temperature of 70°F. The relative humidity of the mixture is 80%. The air-«vapor mixture is cooled under constant pressure of one atmosphere to a final temperature of 50°F. a. Determine the relative humidity for the air—vapor mixture at 50°F. (5 points) 1 oo 2, b. Determine the humidity ratio (kg of water per kg of dry air) for the airwapor mixture at 50°F. 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' M m g 5" 'E'i‘hfiillm' a; 13g '3 I, I ; rm m 1'" "Infill m E Vanin ts.‘ u 5 win 2. IJI% *5 “WW-5g. 5 5" ' fiwfimrgu‘mfie Q... r I ' m mmwfim / ‘mmz‘r .. D . rum. Ming: w W “MWM I *Iémn imam ‘9’ . ' mmmgfiwzm I, .i, ' rn ‘ , c . . " w v I .. * Afiifi / mmwmmmi c ,r/// / , “Hm ,r / ,5” 'gwm a r' 1/ 'z' 1' I". f (‘4 y . ’ 1’ #1353. am" In Adapted by permission from Carrier psychromelric chart, copyright 1946 by Carrier Corporation. Chart A-G Psychromu ric chart. ...
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quiz+3+Key+2008 - PTFE 3210 Quiz 3 Spring 2068 Name kg y 1....

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