Pipe size adjustment with pulp consistency 1

[fjr26]

The number below are velocities in pipes depending on stock consistencies, from what i know these are the recommended velocities you should aim for in your pipes. But i am trying to understand how companies that design pipes come up with these numbers, and if it has anything to do with the Duffy method for pulp friction loss calculation. They usually have a fixed flow and try to change pipe diameter thus changing the velocity in order to get optimal results for their pipe system.

Pipe size(diameter)/velocity is adjusted with c%
Water: discharge pipe: 3-4m/s
Stock 0.1% to 1%,discharge pipe: 2.5-3m/s
Stock 1.1 to 2.5%, discharge pipe: 2-2.5m/s%
Stock 2.6 to 3.5%, discharge pipe: 1.5-2m/s
Stock>3.5%, discharge pipe: 1.5m/s
Gravity line or lines on inlet to pump, velocity is 1m/s
Thank you,
Fadi

 

[Artisi]

Who is setting the velocity numbers, the pipe suppliers?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[fjr26]

The pipe system designers, the company which designs the piping system: pipe material, pipe size (diameter)and a lot of other stuff (like KADANT). I'm not sure if pipe suppliers do that too.

 

[Artisi]

The velocities you have listed are nonsense.
If you want correct velocities use Duffy's data,available on the net, check Gould pump website.
I did a lot of work with Geoff Duffy and his data is valid.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

This post was hidden away in the process forum and this was my reply there.

I don't know a lot about pulp mixtures and what their viscosities are, but from the data above my suspicion is that the viscosity increases a lot over that percent and hence what they are trying to do in a fairly course manner is keep the pressure drop similar for each percent increase and hence as viscosity increases you decrease velocity to hit the same band of pressure drop.

If you have available the viscosities for those percentages this might shed a bit more light, but that's my best guess at the moment.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

LI. Suggest you look at Goulds / Geoff Duffy pumping paper stock data. Interesting subject, for example, once velocity reaches a certain point friction loss drops to below that of water.
For over 10 years before Duffy rewrote the rules, I used standard water friction data for upto 6% stock which is the approaching the upper limit for std. paper stock pumps. For interest at 6% you can walk on the stock with snow shoes (so Duffy said although I never tried it).

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[fjr26]

Why are those values nonsense ? These values were given to me by the head of engineering at the tissue mill i am interning at, saying that they were standard values used by pipe system design companies. Can you please explain in which way do you consider them nonsense?
Can you please also explain how duffy's method is used ? I know it is used to calculate pulp friction losses, but then what? assuming i am designing a piping system. I read the TAPPI technical sheet and the explanation about the pulp flow at low, medium and high velocities.
also in duffy's method,bulk velocity is known whereas when designing a piping system and trying to find the optimal diameter, it would be a result of that diameter and thus wouldn't be known. (is it assumed and then changed by trial and error until the pulp friction loss value is minimal ?)

Thank you for your quick response btw

 

[LittleInch]

Try looking at this and following the links

http://www.eng-tips.com/viewthread.cfm?qid=119063

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[fjr26]

Thanks LI. i'll check it out.

 

[Artisi]

LI. Good research, I had forgotten all about that thread.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

It's amazing what data there is here when you look for it.

It's pretty clear to me that this stuff is a bit weird in it's properties, but equally has been studied a fair bit and there is a lot of history and background to it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ione]

Not my field of expertise, anyway the attached file could give you some guidance

 

[fjr26]

Yes i read this TAPPI TIS, very interesting. I'm here to try to understand it better

Could someone answer these questions that i previously asked pls

"Why are those values nonsense ? These values were given to me by the head of engineering at the tissue mill i am interning at, saying that they were standard values used by pipe system design companies. Can you please explain in which way do you consider them nonsense?
Can you please also explain how duffy's method is used ? I know it is used to calculate pulp friction losses, but then what? assuming i am designing a piping system. I read the TAPPI technical sheet and the explanation about the pulp flow at low, medium and high velocities.
also in duffy's method,bulk velocity is known whereas when designing a piping system and trying to find the optimal diameter, it would be a result of that diameter and thus wouldn't be known. (is it assumed and then changed by trial and error until the pulp friction loss value is minimal ?)"

 

[Artisi]

I would ask your head of engineering on what data / why he has set these velocities, he may well have a valid answer that would be interesting to hear.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[fjr26]

Alright, thank you all very much for your help!

 

[LittleInch]

Piping system designers work to a variety of competing drivers, namely cost of the pipe and equipment, cost of the design and analysis work, pressure drop, flow velocities, process requirements (temperature, pressure etc), working within a pressure class of equipment (e.g. ASME class 150) and tie-ins to other pieces of equipment.

They tend over time to develop certain guidelines to get them an initial sizing and layout without having to spend hours analyzing each small section of pipe. These guidelines have generally proven themselves over time to provide the optimal solution or fairly close to it. They are though guidelines and this issue of velocity in pipes appears on a regular basis with engineers wanting hard numbers and code references. They don't exist.

As the percent pulp increases, from what I've seen, the viscosity does increase, but might start at low percentages to be lower than water, but ends up higher. Thus as your percent goes up the pressure drop goes up if you try to maintain the same velocity and gets to a point where it is more economic to increase the pipe size to reduce the velocity and pressure drop to a more reasonable number.

You might have other issues when you work with non Newtonian fluids like pulp - I saw somewhere you don't want to go too slow otherwise the stuff starts to stick and jump along the pipe (!!) and at reducers it can lock up. Then you need to find someone who's done this before and understand the weird behavior of the fluid.

good luck!

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[fjr26]

Yes I've been told that those velocities were developed over time and were "guidelines"as you said. That's why i wanted to understand from artisi why he considered them nonsense.

That's what i thought at first, and i think there is some truth to it. But according to G.G.Duffy's model of the pulp friction loss curve, for a constant consistency (percent pulp), friction loss increases linearly, decreases until a velocity point called the onset of turbulence where it is minimal, and increases again to become lower than water once velocity reaches the onset of drag reduction.

Behaviour of pulp flow at different velocities is explained a bit in the TAPPI TIS along with Duffy's method and i have read a bit about pulp rheology.

I am trying to understand the procedure of finding optimal velocities and pipe diameters using (or not) Duffy's method for pulp friction loss calculation. Preferably using duffy.

 

[LittleInch]

Like I said - weird stuff.

If you have the time and inclination to read up on it you will pretty soon find yourself knowing more than many people who have been working with it for years... Just be sure to not rely on a single source of information, but try and make sure more than one source is there. If you're working in an operating plant, you have an ideal chance to take actual measurements and see of your calculations get close.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[fjr26]

Yes I will do just that, thanks a lot for your help and your time.