Originally Posted by francescopozzi

hi

i'm looking for a convenient way to find dense phase pneumatic characteristic after a conveying test in our pilot plant.

is there any way to scale up? i'm not looking for an exact prediction, just an indication for the real conveying.

if you have some books or articles to suggest, it will be really appreciated

thank you

king regards

pozzi

Try this download adress for the "Fluidisisation of bulk solids - broshure and software", published by me in the

Forum: Engineering Software Aspects.



https://skydrive.live.com/redir.aspx...s60rZ0M*8fA%24

regards, Manfred Heyde ■

Originally Posted by ManfredH

Try this download adress for the "Fluidisisation of bulk solids - broshure and software", published by me in the

Forum: Engineering Software Aspects.



https://skydrive.live.com/redir.aspx...s60rZ0M*8fA%24

regards, Manfred Heyde

The Files of the free software, written in VISUAL BASIC and offering a direct way of practicing the main results, are available at the following latest links:

The German version can be downloaded (as zip file) at the following link:

https://skydrive.live.com/redir.aspx...s60rZ0M*8fA%24

An English version of the software can be downloaded (as zip file) at the following link:

https://skydrive.live.com/#cid=0239E...2F136DDE%21936

Another link leads to Google Drive. From there you can download as zip file all programs as well as documents in English and German together.

https://drive.google.com/drive/folde...lRmVXlhR1dabFk ■

https://forum.bulk-online.com/showth...ehaviour/page3

find it at the low end of the discussion ■

Dear Mr. Francesco Pozzi,

Is your question related to a plug conveying system or a continuous pneumatic conveying system?

A plug conveying system is understood as a full pipeline dense phase pneumatic conveying, consisting of two parallel pipes: one pipe is used to convey the material to the destination, the other is used to feed air into the pipeline through the boosters.

A continuous pneumatic conveying system is understood as a system ranging from no or little sedimentation to full dilute phase conveying.

In between the two conveying systems an unstable region is expected.

In my opinion a pneumatic conveying calculation is intended for both purposes.

-A pilot plant test is to measure the material properties, using the calculation method.

-The pneumatic calculation of any installation, using the same calculation method, can then be performed.

An important feature of the calculation is that the measured material properties (material caused pressure drops) are not containing other pressure drops ( suspension, filters, Reynold number, gas pressure drops, etc) ■

Dear Mr. Francesco Pozzi,

A pneumatic plug conveying system is calculated along silo flow formula, whereby the plug resistance is depending on the pipe diameter and the plug length. (Janssen equation 1895)

The plug pressure drop equals the plug resistance.

The sum of all plug resistances equals the pressure drop over the pipeline.

The air pressure between the pipelines decreases from the beginning of the pipeline to the end of the pipeline, increasing the plug velocity.

If the intended software has no plug length input, then that software cannot be used.

If booster injection along the line is used to control the plug, the calculation becomes much more complex, as the air volume increases along the pipe, with a change that the plug conveying changes in dense or dilute conveying.

I have no direct experience with real plug conveying, but what I hear is that plug conveying is very difficult to control and that plugging occurs easily.

(Maybe that is the reason that it is called plug”ging” conveying?) ■

Unlike lean phase there is no credible equation for calculating dense plug flow system.

Janssen equation cannot be used to design the dense phase system.

Best option is to test the material in a test plant and scale up in size. The test should

be carried out at 2 or 3 distances so longer distance can be extrapolated. As long as

the conveying parameters are kept same the bigger pipe can be scaled up based on

certain scaling parameters. Unfortunately dense phase scaling calculations are not

given in text books either. Dense phase specialist companies have there scaling rules

and they seldom come in public domain. I guess this is what differentiate Boys from

Men in the wonderful world of pneumatic conveying. ■

Dear Dr. Mantoo,

The analogy between a column of material moving down in a silo and a plug moving in a pipe is easy understandable.

The pressure difference between the pressure at the back side of the plug and the front side of the plug is then the driving force (corrected for gravity if required).

Causing the driving force and the friction force.

This phenomenon is described in the Janssen equation, but certainly not enough to describe dense plug conveying.

In addition, the porosity and the fluidization behavior of the plug needs to be accounted for in the plug wall forces and stability of the plug.

I did some modelling in this way and managed to get realistic figures, but those were too much depending on a variety of material flow properties.

This modeling algorithm attempt is too tricky to base a dense plug conveying design on.

I immediately agree that I am not an expert in dense plug conveying, but this approach seems to be a logical start for calculations.

I can follow the approach of scale testing and scaling up technics, but I believe that even then some theory must be behind this technology.

Or is dense plug conveying starting with a shot in the dark and trial and error?

Who are the BOYS and who are the MEN in pneumatic conveying?

Isn’t this forum a way to make the BOYS MEN? ■

Dear Mr. Francesco Pozzi,

-For a scaling up a clear understanding of the technology and the physics is required.

-Based on the understanding of the technology and the physics a calculation algorithm must be developed. (gas laws, conservation of energy and Newton laws, etc.)

-This calculation algorithm dictates which data must be measured.

-Running multiple tests under different conditions will reveal the influence of the changed test conditions.

-The obtained measured date must then be used to evaluate the calculation algorithm.

-If the calculation algorithm matches the measured data of the various tests, the same algorithm can be used for scaling up.

This procedure needs to be repeated for each new material.

The problem is now:

-Unlike lean phase there is no credible equation for calculating dense plug flow system.

-Then, it is not possible to measure the required parameters for an unknown calculation algorithm.

-Whether fluidi.exe can be used is impossible to say as long as you do not know how the algorithm works.

Prof PETER Wypych of the University of Wollongong Australia BMEA) has written an article in 1994 about low velocity slug flow pneumatic conveying, where he uses the Janssen theory for calculating the forces, acting on a plug.

Maybe Prof Wypych can help you in project evaluations.

www.bmea.com.au ■

Using Janssen equation to calculate forces acting on single plug is purely academic will not help

help anyone in designing dense phase system. Pressure difference across the plug is not the

only problem to deal with. Since gas is compressible, change in pressure changes a lot of other

parameters and this is happening all the way. There are still a lot of unanswered questions i.e.

As the air expands does the plug length changes ?

if it does how much ?

What happens to porosity of the plug with dilation?

Effect of change in air density on driving forces. List goes on and on......

So in my opinion currently it is not possible to calculate Dense phase plug flow system from an equation accurately.

Also Plug generation and de-generation is a random phenomena in conveying pipe this also makes life difficult.

Only reasonable dense phase scaling information I have come across in public domain is in Dr Mills Book

"Pneumatic conveying design guide" in chapter 14. Similar information is also available in University of Greenwich

Course notes on Pneumatic conveying.

Personally I think there is enough information available in above books to successfully

scale up a reasonable size system if you know what you are doing.

As far as Boys to Men indeed we are trying to make Boys into Men but some Boys will always remain Boys.

My scale of MEN in pneumatic conveying is if you are in the 1 kilometre + club you are eligible.

Regards ■

Dear Dr. Mantoo,

I fully agree, but this simplification is a start to understand the technology.

Again, I fully agree.

To add to your list:

Along the line the air pressure between the plugs increases and the air pocket volume increases also.

The air velocity and the pocket velocity increase likewise.

The number of feed backs is vast.

Again, I fully agree.

I do not agree that it makes life difficult, only interesting. (positive attitude)

Dr Mill defines the driving force over a plug as the pressure difference and longer plugs require relatively (exponentially) longer pressure drops.

That is exactly what the Janssen equation predicts.

Thank you, I was involved in a double tank 4 km pneumatic conveying system with rotary valves to obtain maximum continuity. ■