Chapter 14 MASS TRANSFER

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20040060080010001200Diffusion coefficient, m² / sChapter 14 Mass Transfer14-22E The error involved in assuming the density of air to remain constant during a humidificationprocess is to be determined.Properties The density of moist air before and after the humidification process is determined from thepsychrometric chart to beT1 80º F 1 30% air ,1 0.0727lbm/ft3andAnalysis The error involved as a result of assumingconstant air density is then determined to be air 0. 0727 0.0712 lbm / ft% Error 10030.0727 lbm / ftair,1which is acceptable for most engineering purposes.3T1 80º F 1 90% 100 2.1%air ,2 0.07117lbm/ft3Air80F14.7 psiaRH 1 =30%RH 2 =90%14-23 The diffusion coefficient of hydrogen in steel is given as a function of temperature. The diffusioncoefficients from 200 K to 1200 K in 200 K increments are to be determined and plotted.Properties The diffusion coefficient of hydrogen in steel between 200 K and 1200 K is given as6DAB 165 . 10 exp( 4630/ T) m / s2Analysis Using the relation above, the diffusion coefficients are calculated, and the results are tabulated andplotted below:3.50E-083.00E-08T (K) D AB , m 2 / s200 1.457×10 -16400 1.550×10 -11600 7.348×10 -10800 5.058×10 -91000 1.609×10 -82.50E-082.00E-081.50E-081.00E-085.00E-091200 3.482×10 -8 0.00E+00Temperature, K14-7
Chapter 14 Mass Transfer14-24 "!PROBLEM 14-24""GIVEN""The diffusion coeffcient of hydrogen in steel as a function of temperature is given""ANALYSIS"D_AB=1.65E-6*exp(-4630/T)T [K]D AB [m 2 /s]200 1.457E-16250 1.494E-14300 3.272E-13350 2.967E-12400 1.551E-11450 5.611E-11500 1.570E-10550 3.643E-10600 7.348E-10650 1.330E-09700 2.213E-09750 3.439E-09800 5.058E-09850 7.110E-09900 9.622E-09950 1.261E-081000 1.610E-081050 2.007E-081100 2.452E-081150 2.944E-081200 3.482E-0814-8
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Chapter 14 MASS TRANSFER

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