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Molflow-Residence Time

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Molflow-Residence Time

I am wondering if there would be a way of calculating the residence time of particles inside a chamber.


Yes, you set a pump at the chamber exit and measure MPP (mean pumping path) with formulas, or create a flight time histogram.


I've made one sample file with a time-dependent simulation.

A simple cylindrical chamber, 5 cm radius and 25 cm length, pumped at one extremity via a 6.3 cm hole and a pumping speed of 80 l/s. Molecular mass 28 a.m.u. (CO or N2) and T=20 C (293.15 K).

I've simulated a very short burst of 1E-8 s duration, and followed the simulation for 1 s at 10E-3 s intervals... see screen-shot and zip files in the two dropbox links.

I have then fitted the exponential decrease of the pressure vs time, and fitted it to an exponential function, giving the characteristic time of 0.027942 s.

A quick estimate using the MPP (mean pumping path, an internal variable in Molflow+... MPP (it's in cm!) divided by the most probable molecular speed (sqrt(2*R*T), in m!)... gives 0.0281879 s... i.e. less than 1% difference with respect to the exponential fit value.

Hope it helps, cheers.

Molflow+ file: 

ppt with graphs and explanations: 

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