Dear Tanase, Indeed, it is a…
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
Teus
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Teus
clogging regime
Dear Mr. Teus,
Thank you very much for your valuable comments and clarifications.
I very much agree with your statement: "local gas velocity > local suspension velocity"
It is clear that if this is not the case, the clogging will start with dune formation (horizontal) and back flows (vertical) and soon will lead to clogging (for dilute phase and lower pressure).
As for the dilute phase, i do not find any other connection of Re but only to the definition of Lambda with Blassius for turbulent regime.
For Froude, there some research papers that are relating Fr to the mixing ratio.
However, thank you very much and wish you health and keep up with professional advice and guiding for us.
Sincerely yours,
Tanase TANASE
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In reply to Dear Tanase, Indeed, it is a… by Teus Tuinenburg
I have never herd of…
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.
Regards
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Dear Mr Mantoo, The mixture…
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.
Regards
Teus
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Teus
In reply to I have never herd of… by Dr. Mantoo
Dear Dr. Mantoo, Thank you…
Dear Dr. Mantoo,
Thank you very much for your attention to our problems.
Since i already answered to Mr. Teus, please both uf you excuse my late anwer. I was incredible busy.
Regarding the "clogging regime mixing ratio", what i mean it is a different point of view for the same statement of Mr. Teus and yours that "the air speed should be higher than the saltation/floating speed of the product".
To be more specific, if we define the capacity of the line, for some given conditions of pipe diameter, material, available pressure, etc. as a function of mixing ratio, than the domain of variable (mixing ratio) is closed on the left (as for zero product is zero capacity) and open to the right. The function can come closer and closer to a maximum mixing ratio but will never reach the limit on the right.
I still do not know if Froude is relevant for pneumatic conveying, but if this valid for larger pipes i think that should work also for smaller pipes (for same conditions)
I very much agree with you about the contribution and the work made by Mr. Teus on this web site.
Many thanks to both of you and wish you good health.
Sincerely yours,
Tanase TANASE
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In reply to I have never herd of… by Dr. Mantoo
clogging regime mixing ratio and pressure gradient in vacuum dilute phase pneumatic conveying
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,
Tanase TANASE
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