化工传递过程原理课件：第六reaction-II_482002516

1、Mass Transfer with Chemical Reaction (II)Reaction time tr Diffusion time tDThe dimensionless ratio:02()DADtk=tD/tr0000()()AAiAAAAiAAkCCkIkCCk Rate enhancement factor0200/ 2()()2()AiAAiAAiArCVAavgVACCCCCtRRdCAsymptotic behavior:Slow reaction regime: 1 Instantaneous reaction regime:II1IIII0jjjABOnly o

2、ne reaction may takes place in one phase00000/1AiAAAAAAxxxCCdCINNDDdx The boundary concentration relations001jABjBjijAiABDCCCCID22AAVAd CDRdx22jB jBjVAd CDRdx2222jjBAjABd Cd CDDdxdx0jjBBdCDdx 000AAAAiAxdCDIkCCaxThe condition where the enhancement effect is negligible:Average curvature Average gradie

3、nt/film thickness 0()/VAavgAiAARCCD202AiArDVAavgCCttRD1I Slow Reaction2rDtt000AAAiAxNkCC 1001jBBjAAiAjD CDICC00202()()AiACAVAAACAAiADRCdCkCCAArDktrDttI0002AiACAVAAACxAdCRCdCdxD Instantaneous ReactionWith film model and Ficks law0jjjAB()/jjBAjKCC0rt II001jABjBjijAiABDCCCCID01AiAICC001jjjjAAijABBv DCC

4、D C0jjjAB iBjBDCCD01AiAICC 111011BBAiACDICD 102 103K11011BBAiACDIC D Physical interpretation of mass transfer with instantaneous irreversible reaction1220201BBAACDICD 1 120011/jjAAjBBjID CCD 0K 11 01AiAICC 001jjjjAAijABBv DCCD CIIThe Slow-Fast Transition The transition region around =1With film theo

5、ry 20()ADAiAMDItCC 00002AiAAACAACCAVAAACdCDkRCdCMD22000AAAiAAAiAAxrDIkCCNCCMDt For a first order irreversible reaction0()0VAAAARCkCC / tanhI 1I film theorysurface renewal theoryThe Fast-Instantaneous Transition( )AAiCCo x2()jjBB iCCo x1222,nAAVAAB iB iB id CDRCCCCdx00()(1)jjjAB iBjAiABDCCCCID0 x AAi

6、CC0AACC 0AdCdx 000AAAAiAxdCIDkCCdx References and Further Readings1. Astarita, G., Savage, D.W. and Bisio, A. Gas Treating with Chemical Solvents, New York, Wiley, 19832. Cussler, E.L. Diffusion Mass Transfer in Fluid Systems, 3rd ed., Cambridge University Press, New York, 2007Imagine the mass trans

7、fer of component 1 across a thin film with the thickness l. The concentration of component 1 at interface is c1i , and the concentration in the bulk fluid is c10=0. A zero-order reaction is taking place within the film. (a) what is the differential equation and boundary conditions for the concentrat

8、ion of component 1in the film? The reaction rate is r1= -k when c10 r1 = 0 when c1=0(b) What are the mass transfer coefficient and the rate enhancement factor?Problem IProblem IIIn a gas liquid mass transfer apparatus, A is removed from the gas (containing A and B) through the gas-liquid interface,

9、which is impermeable to B. When A enters the liquid, it reacts with species C to form D (A + C D) at a constant (zero order) reaction rate, RAV. Assume that the mole fraction in the liquid is very low and that the equilibrium conditions at the interface are CAG* = m CAL*The diffusivities of A in the gas phase and the liquid phase are DAG and DAL respectively. If the system is modeled in terms of the two film theory as show in the