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Soren September 2, 2003 04:32

Concentration to ppm

I am new to working with concentration in CFD. I have simulated the dispersion of gas and got the mass concentraion in the unit kg/m^3.

How can I convert this to a concentration in ppm ?

Thanks in advance.


Bart Prast September 2, 2003 05:40

Re: Concentration to ppm
density_component/density_mixture * molmass_mixture/molmass_component = molecules_component/molecules_mixture

multiply this by 1 million and you will have ppm

(If this is true, where do I send the invoice to?)

Pascale Fonteijn September 4, 2003 16:30

Re: Concentration to ppm

Send it to CFX. They have a very large range of units but no ppm yet. Why not implement this one?

On the other hand, if you can not do these 'back-of-the-envelope-calculations' yourself, you should not be in a position to perform CFD-calculations.


Bart Prast September 5, 2003 03:44

Re: Concentration to ppm
It's not simple. I'm just really good. As this is a really simple formula, people can just put it in ccl or an additional variable. For small ppm ranges I think you run into trouble with respect to accuracy (very small massfractions) in CFX. You might have to do it double precision and I've never been able to do this as it requires a little bit too much memory.

Jan Rusås September 5, 2003 05:54

Re: Concentration to ppm
->Bart, So you give advices that you have not managed to use yourself. You are a true consultant :))

Bart Prast September 5, 2003 06:00

Re: Concentration to ppm
Want any more of these advices? I can direct you to our marketing department. They are in the process of selling my skills.

Jan Rusås September 5, 2003 07:29

Re: Concentration to ppm
I am not surpised that it is the marketing department that takes care of selling CFD consultancy. In many cases,(and in many companies)CFD really is only a marketing stunt.

Bart Prast September 5, 2003 08:08

Re: Concentration to ppm
Hmmm, I cannot say that's the case in our company. It's just that they are a hell of a lot better in selling things than the average CFD engineer (myself not included ;-) )

Bob September 5, 2003 08:57

Re: Concentration to ppm
Now theres a scary thought, a marketing department of an engineering company that knows something about engineering !

Bart Prast September 5, 2003 08:58

Re: Concentration to ppm
Now there's a typical engineering cliche

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