# Can someone identify what this graph is used for?

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1. Oct 26, 2016

### Dong Aleta

Hi, I was asked by my senior to find out what this graph is and how to use it. No details were given as to where they found it.

I know already that this is used to compare CSTRs and PFRs performance for first order reactions, but I can't deduce what the expressions Dd/(vxL) and kL/vx are for and what the variables represent.

Thanks a lot!

2. Oct 28, 2016

### Staff: Mentor

3. Oct 28, 2016

### Dong Aleta

Hey, thanks for the response!

Yeah, I'm familiar with nomographs. I just can't determine what the variables in the graph represent.

But thanks a lot for this information! I really appreciate it!

4. Oct 28, 2016

### Staff: Mentor

This graph is for a tubular chemical reactor in which there is axial mixing/dispersion. The velocity profile is assumed to be flat. The reaction is assumed to be first order decay. The dimensionless group $D_d/v_xL$ is a measure of the axial dispersion, and is the inverse of the Peclet number. The dimensionless group $kL/v_x$ is the ratio of the residence time in the tube to the characteristic decay time for the reaction.

$D_d$ = axial dispersion coefficient
$v_x$ = axial velocity
L = length of tube
k = first order reaction rate constant