反应工程基础(程易)chapter10-model nonideal reactors.ppt
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1、,Nonideal Flow Characterized by Residence Time Distribution (RTD),Pulse input of tracer,F(t),RTD-方差的加和性,一次矩的加和性,二次矩的加和性,s,s2,假设界面处无返混 ( 小)有,对矮胖反应器:端部的返混贡献很大 对细长反应器:端部返混贡献可忽略,卷积(E(t): 传递函数的概念),Chap9 - Summary,1. E(t)dt: fraction of material exiting the reactor that has spent between time t and t+dt i
2、n the reactor.,2. The mean residence time,3. The variance about the mean residence time is,is equal to the space time for constant volumetric flow, = 0,4. The cumulative distribution function F(t) gives the fraction of effluent material that has been in the reactor a time t or less:,5. The RTD funct
3、ions for an ideal reactor are,Plug flow,CSTR,Laminar flow,6. The dimensionless residence time is,7. The internal-age distribution, I(), , gives the fraction of material inside the reactor that has been inside between a time and a time +d,(自学,P633634),*Simple diagnostics and troubleshooting using the
4、 RTD for ideal reactors*,8. Segregation model,For multiple reactions,9. Maximum mixedness:,For multiple reactions,*迟混与早混(见网络学堂补充材料)*,O. Levenspiel, P358,(a),(b),(c, d, e),Chapter 10 Models for Nonideal Reactors,Overview,Use the RTD to evaluate parameters Model of reactor flow patterns Tanks-in-serie
5、s model Dispersion model,10.1 Some guidelines,RTD data + Kinetics + Model = Prediction,Guidelines to develop models for nonideal reactors,1. The model must be mathematically tractable.,2. The model must realistically describe the characteristics of the nonideal reactors. The phenomena occurring in t
6、he nonideal reactor must be reasonably described physically, chemically, and mathematically.,3. The model must not have more than two adjustable parameters.,10.1.1 One-parameter models,Nonideal CSTRs include a reactor dead volume VD, no reaction takes place,Nonideal CSTRs with a fraction of fluid by
7、passing the reactor, exiting unreacted,Tanks-in-series model,Dispersion model,* This parameter is most always evaluated by analyzing the RTD determined from a tracer test.,Examples:,10.1.2 Two-parameter models,C(t),t,Vs,VD,0,b,s,0,10.2 Tanks-in-series (T-I-S) model,1,2,3,Pulse,V1 = V2 = Vi, = 0,1 =
8、2 = i,First reactor:,Second reactor:,ODE:,Solution:,Same to third reactor .,n CSTRs:,(C2 = 0 at t = 0),RTD for equal-size tanks in series:,: Vtotal/,n: calculated from RTD,Levenspiel book (3rd),First order reaction:,E(),n = 10,n = 4,n = 2,n: non-integer, or integer,First order reaction:,1,n =,If n =
9、 2.53, you might calculate the conversions for n = 2 and n = 3 to bound the value.,Graphical method of evaluating the performance of N tanks in series for any kinetics,Levenspiel, p329,-rA,CA,CA0,CA1,CA2,CA3,CA4,Parallel lines for same size tanks,Slope:,For microfluid:,一级等温反应,二级等温反应,Chemical convers
10、ion of Macrofluids,10.3 Dispersion model,Molar flow rate of tracer (FT) by both convection and dispersion,Da: effective dispersion coefficient, m2/s,Pulse tracer balance dispersion,10.4 Flow, reaction, and dispersion,10.4.1 Balance equations,Second-order ODE,Similar to A:,1st-order reaction,Dimensio
11、nless,Damkhler number for first-order reaction,Damkhler number for first-order reaction,Peclet number,l: characteristic length term,Per: reactor Peclet number, it uses reactor length, L,Pef: fluid Peclet number, it uses characteristic length that determines the fluids mechanical behavior,Empty tube:
12、,Packed bed:,: bed porosity,: pipe diameter,10.4.2 Boundary conditions,Boundary conditions for closed vessels and open vessels.,Closed-closed vessels: assume that there is no dispersion or radial variation in concentration either upstream (closed) or downstream (closed) of the reaction section,Open-
13、open vessels: dispersion occurs both upstream (open) and downstream (open) of the reaction section,Da=0,Da0,Da=0,z = 0,z = L,dispersion,Da0,Da0,Da0,z = 0,z = L,dispersion,Closed-closed vessel,Open-open vessel,10.4.2A Closed-closed vessel boundary condition,Entrance boundary condition,z = 0,z = L,Exi
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