Dear Erica,

The pressure drop as a result of a bend in a pneumatic conveying line is in most calculations accounted for by assuming an extra section of pipe of an equivalent length.

A more sophisticated way is to calculate the velocity loss in the bend and calculate the re-acceleration pressure drop after the bend.

It is advised to consult well known and experienced manufacturers instead of designing a pneumatic conveying installation yourself. Especially, when you are undertaking this effort for the first time.

Success

Teus ■

Dear Erica,

For Tee's, conveying system pressure drop will increase much more than that for commonly used long radius bends. There is no theoretical method for calculating this pressure drop, at least as yet. But a lot of experimental work has been done on it by many researchers. This work compares the pressure drop due to various types of bends and Tees. As expected, pressure drop due to Tees is much higher than that for long radius bends. This information is available in the published literature.

Sincerely,

Amrit Agarwal

Consulting Engineer

Pneumatic Conveying Consulting

Charleston, WV, USA

Email: polypcc@aol.com ■

Dear Erica,

The pressure drop, because of a bend depends on the product velocity loss in the bend and the involved air velocity.

In a Tee bend, a higher percentage of velocity loss can be expected than in an intermediate radius bend. An equivalent length, replacing a Tee is then a bit longer.

How long, I do not know, because I always calculate directly the material velocities and the subsequent acceleration pressure drop.

I understand that you split a powder material flow into two flows towards 2 different destinations.

That means that initially, the flow splits in two, whereby the air velocity in the two pipes is decreased to half the original value.

Probably the shorter branch will carry the full flow and the longer branch gets plugged.

have a nice day

Teus ■

This bend pressure loss comparison with R/d is a very old academic debate. Over the past 3-4 decades there have been a number of papers published on this topic. Most of these papers are contradictory. Some claim that blind tee produces lower pressure drops and others have opposite claims.

The interesting point which I found was that the researchers using poly pellets as test material which unfortunately has been the “Pet Academic” test material in the past have always claimed that the blind tee reduces the bend pressure losses. Test with fine powders come out with opposite results.

In my opinion this is probably due to the elastic nature of the pellets and during head on impact in the tee the pellets rebound back ( 3rd law of Newton comes in mind) with equal momentum and re-accelerate faster which fine powder do not do, as most of the powder particle will break in impact and absorb the particle momentum energy . On long radius bends the pellets smear on the outer bend wall and constantly loose velocity. The velocity reduction in log radius bends higher hence the higher pressure drop. So I think one needs to take into account material properties also for a good comparison.

In industry people often use blind tee's as it is well know fact the they produce lower produces less angel hairs which also supports my above mentioned opinion. But then as a often say it is an academic debate and people can disagree with my opinion. Below are some of the academic papers which specifically study the effect of bend radius on pressure drop.

Bonnin, JC. Bouard, R 1990 “Bends in air-cement flow”, Pneumatech 4, 4th Conference on pneumatic conveying technology, Glasgow, UK.

Mills, D, Mason, JS, 1985 “The influence of bend geometry on pressure drop in pneumatic conveying system pipelines”, 10th Bulk solids conference, Illinois, USA

Marcus, RD, Hilbert, JD, Kilinzing, GE, 1984, “The flow through bends in pneumatic conveying systems”, J. Pipelines No. 4, pp. 103-112

Park, Y, Zenz F, 1980 “Pressure loss in horizontal to vertical upflow elbow”, Pneumotranport 5, 5th International conference on the pneumatic transport of Solids in Pipes, London, UK, paper D3

Yang, WC, Anestis, RE, Gizzie, RE, Haldipur, GB, 1987, “Pneumatic transport in a 10-cm pipe horizontal loop”, Powder Technology, No. 49, pp 207-216. ■

Dear Erica,

What you have is a "Flow Splitter", not a Tee. I can give you some guidleines on a Flow Splitter. These are:

1. The incoming leg should be vertical.

2. Solids coming in should be evenly dispersed in the air stream across the entire cross sectional area of the incoming leg .

3. The outgoing legs should be horizontal.

4. Assume that the air flow will be split 50/50 at the split.

5. Select pipe diameters to maintain the required air velocity after the split. For example, if the incoming pipe diameter is 6 inch, outgoing pipe diameter should be 4 inch.

6.Provide enough horizontal length after the splitter to re-accelerate any solids whose velocity has reduced.

7. Use flow control valves after the split to make adjustments to air flow, if needed

8. For pressure drop, use the published data.

These guidelines are based on my experience.

Hope these will help you.

Sincerely,

Amrit Agarwal

Consulting Engineer

Pneumatic Conveying Consulting

Charleston, WV, USA

Email: polypcc@aol.com

Ph 304 346 5125 ■

Dea rAmrit,

I wonder how that works reliably. Regulating the air flow in an air/material mixture.

Have a nice day

Teus ■

Teus,

This valve is a Pinch Valve, installed horizontally in flow direction. Its sleeve must be of a material that can withstand abrasion.

Amrit Agarwal ■

Teus,

This is a pinch type valve with an abrasion sleeve installed horizontally. Sleeve may need replacement due to abrasive wear otherwise the valve will work.

Regards,

Amrit ■

Dear Amrit,

I understand that there is a controllable “artificial” resistance built in each leg.

Closing one leg directs more air into the other leg.

The question now is; on basis of what reference signal or variable are the two control valves operated?

Assume that both control valves are open, how and when do you decide to partially close one of the two valves and which one and how far?

There can only be “one pressure” in the T-junction.

Intriguing case.

Have a nice day

Teus ■

Teus,

Your question is quite simple. I will let some one else answer it.

Regarsd,

Amrit Agarwal ■

I always thought pinch valves were open or close. So in my opinion pinch valves cannot be used to control flow control !! I have never seen a positioner for pinch valve it will be good to know if there is one available.

Chocking the flow after the splitter is not a good idea. Almost all the installation I have seen people are after equal splits. If an uneven split is required just increase the length or number of bends in one leg and the rate in that section will decrease. ■

Dear Mantoo,

I assume that you are referring to pinch valves, which are closed by compressed air around a rubber or elastomeric sleeve.

However, there are also mechanical closed pinch valves, whereby the sleeve is squeezed between two plates or bars. The controlled position of the 2 bars convert the pinch valve into a control valve.

see:

http://www.redvalve.com/rv/index.php/content/view/40/77

I fully agree with you that

If you state that you can cause an uneven split by just increase the length or number of bends in one leg, (which is the same as throttling with a pinch valve) suggests that it should also be possible to cause an even split.

I still do not see how that can be arranged and have a stable conveying system and I puzzled from time to time all weekend, trying to figure that out.

The cryptic answer of Mr Agarwal did not help either.

Have a nice day

Teus ■

I can understand the cryptic replies you are getting on the splitting flows. Unfortunately it is one area where the academic research is lagging. I have never seen an academic paper on splitting the pneumatic conveying flow. So the people who have some experience guard there knowledge & to a certain extent it is understandable. There is huge financial gains associated with it, as this technology is used in injection systems feeding into furnaces & kilns. Very few companies offer these systems and big blast furnaces can have 24 – 60 splitted branches feeding into a single furnace.

Thanks for the pinch valve reference I have never seen it in powder handling; waste water / acid industry maybe. By the way blind tee never works as a good even splitter. ■

Dear Mantoo,

Splitting a gas flow (SLR=0) or a liquid flow is done by making the branches of equal resistance as much as possible. (F.i. a tree structure)

Splitting a pneumatic conveying flow this way could only work when the air/material mixture behaves like a gas or liquid flow.

Low SLR and high velocities in combination with the right geometry of the junctions then might bring success.

The high velocities and low SLR generate a homogeneous, gas like, pneumatic flow and the junction geometry splits the material flow by dividing the material flow on the basis of inertia.

(Maybe, this is what Mr Awargal was hiding in is cryptic reply?)

Pinch valves are used in cement conveying installations quite often.

Open, mechanical pinch valves have the risk that when a sleeve bursts, all the cement in the pressure tank is blown out at full rate and that there is no way to stop it, other than to release the pressure from the tank as fast as possible.

A burst, closed pinch valve contaminates the pneumatic control system through the solenoid valves.

Have a nice day

Teus ■

Originally Posted by Mantoo

This bend pressure loss comparison with R/d is a very old academic debate. Over the past 3-4 decades there have been a number of papers published on this topic. Most of these papers are contradictory. Some claim that blind tee produces lower pressure drops and others have opposite claims.

The interesting point which I found was that the researchers using poly pellets as test material which unfortunately has been the “Pet Academic” test material in the past have always claimed that the blind tee reduces the bend pressure losses. Test with fine powders come out with opposite results.

In my opinion this is probably due to the elastic nature of the pellets and during head on impact in the tee the pellets rebound back ( 3rd law of Newton comes in mind) with equal momentum and re-accelerate faster which fine powder do not do, as most of the powder particle will break in impact and absorb the particle momentum energy . On long radius bends the pellets smear on the outer bend wall and constantly loose velocity. The velocity reduction in log radius bends higher hence the higher pressure drop. So I think one needs to take into account material properties also for a good comparison.

In industry people often use blind tee's as it is well know fact the they produce lower produces less angel hairs which also supports my above mentioned opinion. But then as a often say it is an academic debate and people can disagree with my opinion. Below are some of the academic papers which specifically study the effect of bend radius on pressure drop.

Bonnin, JC. Bouard, R 1990 “Bends in air-cement flow”, Pneumatech 4, 4th Conference on pneumatic conveying technology, Glasgow, UK.

Mills, D, Mason, JS, 1985 “The influence of bend geometry on pressure drop in pneumatic conveying system pipelines”, 10th Bulk solids conference, Illinois, USA

Marcus, RD, Hilbert, JD, Kilinzing, GE, 1984, “The flow through bends in pneumatic conveying systems”, J. Pipelines No. 4, pp. 103-112

Park, Y, Zenz F, 1980 “Pressure loss in horizontal to vertical upflow elbow”, Pneumotranport 5, 5th International conference on the pneumatic transport of Solids in Pipes, London, UK, paper D3

Yang, WC, Anestis, RE, Gizzie, RE, Haldipur, GB, 1987, “Pneumatic transport in a 10-cm pipe horizontal loop”, Powder Technology, No. 49, pp 207-216.

Dear Mantoo

Can you forward the article as mentioned above for pressure drop at bend

Apparantly i tried to find it, but google doesnot gives teh specific data every time

my email ID

chaubey.07@gmail.com ■

Dear Erica,

I found a very old article (in German unfortunately) about T-junctions in pneumatic conveying lines:

"Lempp, M.: „Die Strömungsverhältnisse von Gas-Feststoff-Gemischen in Verzweigungen pneumatischer Förderanlagen“ Aufbereitungstechnik No.7, 1966, pp 81 -91"



I have added a short summary and 2 pictures of this article as an attachment.

If you are interested in reliable working splitters and manifolders for pneumatic conveying lines (2 - 8 lines), please visit our Website. Altogether we are in the "splitter business" since more then 30 years and have of course a lot of experience.

Just now we have finishd a new article in English were we compare a lot of splitter designs.

If you are interested, I will send you a copy.

Best regards

Klaus Schneider

KS-Engineering,

href="https://forum.bulk-online.com/attachment.php?attachmentid=45075&d=1453219399" title="Name: Lempp.pdfViews: 97Size: 433.8 KB">Lempp.pdf ■