clogging regime mixing ratio and pressure gradient in vacuum dilute phase pneumatic conveying

Posted in: , on 20. Apr. 2024 - 19:11

Dear Sirs,

I'm sorry to see that the dynamic of discussions here has came to an almost silent state.

I have something unclear and i would kindly ask for your opinion on it. And i'm referring to pneumatic conveying, in vacuum, of course dilute phase.

There is a parameter called Clogging constant. And this parameter is related to the clogging regime mixing ratio, to the Froude criteria and also to the cross section area of the pipe. For the definition of this Clogging regime mixing ratio there are some formulas that does not take into account the nature of product but only the dynamic of the regime and they are actually deducted by regression .

I suppose that the clogging regime mixing ratio is also directly related to the pressure gradient.

And i suppose there is direct multiplication with the value of the absolute pressure gradient with the clogging constant, cross section area and Fr^2.

Do you have any information or experience about it ?

Thank you very much for your valuable help and your time.

Sincerely yours,




Dear Tanase, Indeed, it is a…

Erstellt am 15. May. 2024 - 10:31

Dear Tanase,

Indeed, it is a pity that the pneumatic conveying forum has died out.

In my opinion, choking will start when the local gas flow is not able to carry the particles in suspension.

Therefore,, the local suspension velocity is important.

Condition: local gas velocity > local suspension velocity

The lowest local gas velocity occurs along the pipe wall, where the first sediment occurs, leading to choking in the end.

The material property suspension velocity and friction loss factor as well as the Re-number are very important here.

The use of the Fr-number in pneumatic conveying is a misconception with the gas velocity head.

Have nice day




I have never herd of…

Erstellt am 15. May. 2024 - 11:22

I have never herd of clogging regime mixture ratio. At least not in any pneumatic conveying text book. As Mr Teus has correctly stated if the material falls out of suspension the line will block also if the Solids loading ratio is very high then clogging will also occur. As at high solid loading ratios the pressure drop will be higher and can lower the velocities so the material falls out of suspension. Other scenario is accumulation of material after bends and fittings. 

Froude number relevance is debatable. In my openion it has more  relevance in bigger bore pipes in lean phase for calculating pick up velocities. 

I think Mr Teus has been doing a very good job here  in educating people over the past few decades so  no one needs any advice on this forum anymore. 



Dear Mr Mantoo, The mixture…

Erstellt am 15. May. 2024 - 01:30

Dear Mr Mantoo,

The mixture ratio is also referred to as Solid Loading Ratio.

The SLR causes material friction between the pipe wall and inter particle collisions.

 As a result this causes particle velocity reduction.

After that, the gas low accelerates the material.

When, locally, the deceleration of the particle is more than the gas flow acceleration, then the particle velocity reduces and the mixture density (SLR) increases.

With the, locally, increasing mixture density the, locally, Solid Loss Factor increases exponentially and the velocity loss also. Reducing the particle velocity even more.

Thereby, the local mixture density increases and the system is approaching choking.

(Locally too much material in the pipeline).

This theory can also be applied on the accumulation of material after bends and fittings.

Choking, which is a local phenomena in the pipeline, can be caused by:

  • Too high solid feeding loading ratio at a conveying pressure lower than the maximum compressor pressure.
  • Too low gas flow, causing material to fall out, causing a too high local solid loading ratio.

Mr Mantoo, thank you for your nice comment in your reply.

Thanks to the many questions over the past decades, I was triggered to think about pneumatic conveying theories and that resulted in the forum discussions.






Antwort auf von Dr. Mantoo