1、誠信應考,考試作弊將帶來嚴重后果!華南理工大學期末考試傳質與分離工程（雙語）試卷A注意事項：1.考前請將密封線內各項信息填寫清楚；2.所有答案請直接答在試卷上；線3考試形式：閉卷；4.本試卷共六大題，滿分 100分， 考試時間120分鐘o題號123456總分得分評卷人1. Fill in the bla nks or choose the correct an swer (30 poin ts)(1) Whe n total pressure in creases, bubble point willin crease, and relative volatilitywill decrease

2、, separatio n of the mixture will be more difficult.(2) Whe n azeotropes are encoun tered, vapor and liquid compositi ons areequal to each other）題 答 不 內 線 封 密and temperatures of liquid and vapor phases areequalas well.(3) For a binary mixture, when the mol fraction of liquid phase is x=0.6, the bubb

3、le point is t1, the mol fraction of the corresponding equilibrium vapor phase is y=0.7, dew point is t2. The relati on betwee n t1 and t2 is the n ( A ).A. t1 = t2;B. t1 < t2;C. t1 > t2;D. un certainAH(4) The reason for 3 5 (s) is to ensure the separation of 一the vapor entrainedLs傳質與分離工程（雙語）試卷

4、A第8頁共7頁一by froth from liquid overflow ing into dow n-comer.(5)During the operation of a plate column, if temperature of reboiler and column pressure decreases, the possible reason is (liquid) weeping密(6)In the total reflux operation of a distillation column, the slope of the operating line in x-y di

5、agram is ( C ).A0;B 0.5;C 1;Da. (7)For the undersaturated moist air with certain humidity, when temperature decreases, its relative humidity willincrease, and its drying capacity willdecrease.(8) ln order to in crease the rate of drying of wet solids mai nly containing bound water, must the airveloc

6、ity be in creased ?( B )A. Yes； B. No.(9) l n the air with25° C, and relative humidity 60%, the equilibrium water content of the wood is*X1 . If the air relative humidity is changed into 40% under the same temperature, the equilibrium water content of the wood becomes x2 The relati on ship of t

7、he equilibrium water content is (B ).A. X； X； B. X； X； C. X； X； D. uncertain.(10) Ge nerally speak ing, the diffusivities of gases in liquid water aremuch smaller tha n ingas phases.2. Questi ons ( 7 points )What is the critical water content (X c) in drying process? Describe the factors that in flu

8、e nee X c. An swer:The critical water content (X c) in drying process is the water content corresponding to the point at which the con sta nt-rate period ends in drying rate curves.XC is in flue need by the property and thick ness of material, and the drying rate.1) XC,hygroscopicXC nonhygroscopic2)

9、 Thickness of material3) Drying rate U(falling rate period comes early).3. (15 points) A continuous distillation column with reflux is used for the separation of a mixture of hepta ne and octa ne (Hepta ne is the more volatile comp onen t). It is required that the distillate product is to contain 0.

10、95 (mole fracti on of hepta ne) and the bottoms product not more tha n 0.02 (mole fraction of heptane). The feed is liquid at its boiling point and contains 0.45 mole fraction of heptane. The vapor and liquid equilibrium data are given in the attached table. Determine:(1) The minimum nu mber of idea

11、l plates un der total reflux.(2) The operat ing line equatio n for rectify ing sect ion.(3) The nu mber of ideal plates if the reflux ratio is 2.5.1yAttached table Vapor-liquid equilibrium data for hepta ne-octa nexyxy1.01.00.3110.4910.6560.810.1570.2800.4870.6730.0000.000Solutio n.(1) Draw the equi

12、librium line and the operat ing line (diag on al li ne), the n draw stepsbetween these two lines. As shown in the following figure, Nmin=8.3 ideal plates plus a reboiler(2( 2)yn 1RdRd iXnXDRd 1If RD=2.5,2.5 0.95yn 1Xn0.714Xn 0.2712.5 12.5 1(3) RD=2.5,yn 12.5 Xn0.950.714Xn 0.2712.5 12.5 1N=15.3 ideal

13、 plates plus a reboiler4. (15 poin ts) A porous solid is dried in a batch dryer un der con sta nt drying con diti ons. Seve n hours are required to reduce the moisture content from 35 to 10 perce nt. The critical moisture content was found to be 20 percent and the equilibrium moisture 4 percent. All

14、 moisture contents are on the dry basis. Assu ming that the rate of drying duri ng the falli ng-rate period is proportional to the free-moisture content, how long should it take to dry a sample of the same solid from 35 to 5 perce nt un der the same drying con diti ons?Soluti on.Accord ing to the as

15、sumpti on of the problem,U kx(X X*)If,qm,GcUcS22.8X1 °.35,X2 0.05,1qm,Gc /2(X1Xc)UcSqm,Gc(XcUcSX*)lnXCX2X*X *Where,12 7h,X10.35,X20.1,Xc0.2, X* 0.04Substituti ng the data give n into above equati on gives''qm, Gc'qm,Gc (Xcx*) , XcX*1 2 (X1Xc)In cUcSUcSX2X *1213.5h5. (15 poin ts) Exp

16、erime ntal data have bee n obta ined for air containing 1.6% by volume SO 2 being2scrubbed with pure water in a packed column of 1.5 m in cross-sectional area and 3.5 m in packed height. Entering gas and liquid flow rates are 0.062 and 2.2 kmol/h, respectively. If the outlet mole fraction of SO 2 in

17、 the gas is 0.004 and column temperature is near ambient with m=35.48 (that is, the equilibrium relation is y*=35.48 x), calculate from the data:(a) The overall number of transfer units based on gas phase Noy for absorption of SO 2(b) The overall height of a transfer unit based on gas phase Hoy in m

18、eters(c) The volumetric overall mass transfer coefficient, K ya for SO 2 in kmol / (ms).Soluti on.(a)Assume a straight operati ng line because the system is dilute in SO2. The data give n areBy a material bala nee.xa 0 yb 0.016ya 0.004V 0.062kmol / hL 2.2kmol/hL(Xb Xa) V(yb ya)X. 0.000338ya mXaya 0y

19、b mXbNoy(b) From(e)mVL35.48 0.0622.21,yL(yb yb) (ya ya)0.004YbYaylZT H oy NoyZtoyNoyHoyZtNoy3.531.167mHoyV/SKyaKyaV/SHoy0.062/36001.5 1.1679.84 10 6kmol/m3 syb 35.48 0.0003380.011996. (18 points) Some kind of wet solids is dried in a continuous dryer under atmospheric pressure.The operati on con dit

20、i ons are give n as follows:States of air:At the inlet of the pre-heater, Air temperature and humidity are: t020°C , andH 00.01kg water vapor /kg dry air , respectively.At the inlet of the dryer,ti 120° C.At the outlet of the dryer, t27 00 C,H20.05kg water vapor/kg dry air.States of wet solids: At the inlet of the dryer, 130°C,w120% (wet basis).At the outlet of the dryer, 2 500C,w25% (wet basi