Re: The Lowest Pick Up Speed For Dilute Phase Conveying
On small bore pipe you can take it down to 11 m/s. check this thresd for pipe dia relationship.
https://forum.bulk-online.com/showth...ghlight=froude ■
What Is Froude Number?
Thank you!
I try to understand that Froude No. will not change for the same pellet or powder.
Thus if for 4" pipe bore the saltation velocity is 11m/s the saltation velocity for 8" pipe will change to 2^(1/2)*11= 15.55m/s.
For 16" pipe bore the saltation speed will change to 22m/s.
Am I right? ■
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Another Question To Mantoo
And for pp pellet 3mmX3mm what do you think is the lowest wind speed for 8" ,10" and 12" pipes? ■
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Re: The Lowest Pick Up Speed For Dilute Phase Conveying
Unfortunately most of the research carried out in this area is on 2-4 inch pipe and it suggest that the results you have come up with should hold. I personally have not tested Froude No to pipe dia. relationship for 10, 12 or 16 inch nor have come across any published data but as a general rule I add would 2 m/s extra to this figure to be on the safe side and probably 4 m for 16”. This safety margin also helps in coping with the pressure fluctuations / RV air leakage. This increase in velocity is due to decreased pipe wall affect (smaller high turbulent region) due to increase in cross sectional area of pipe.
Also remember particle size is not the only factor affecting this, particle shape density etc also have influence on it. ■
My Opinion
Originally posted by shenjie2004
And for pp pellet 3mmX3mm what do you think is the lowest wind speed for 8" ,10" and 12" pipes?
The lowest wind speed for pp i calculated is approx.12.3/s, i don't think the bore of pipe is a main element that affects the lowest speed.From the suspended velocity calculation formula,we can see there is no relationship between suspended velocity and Pipe bore.
BR ■
Mantoo And Jim
"probably 4 m for 16"
do you mean add 4m/s for 16" pipe?
Yes I agree suspension related on not only size but also shape and true density.
And is there any relationship between saltation speed and suspension speed?
Normally I use 2 times suspension speed as pick up speed and never failure. ■
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Re: The Lowest Pick Up Speed For Dilute Phase Conveying
4 m/s added to the calculated pick up velocity.
I normally check the pick up velocity experimentally and it also never fails.
Their are a few equations avaliable to calculate pick up velocity you will have look into research papers for that. ■
Shall We Do In This Way?
(for rotary valve positive dilute phase)
reduce blower slightly and monitor the pressure by control system. then if the pressure raises sharply stop rotary valve until pressure recover.
record wind speed and raise 1m/s of wind speed then we get the lowest speed. ■
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Re: The Lowest Pick Up Speed For Dilute Phase Conveying
Dear shenjie2004
1) Calculate or measure the suspension velocity at the considered gas conditions. (pressure and temperature)
2) calculate the gas velocity along the pipe wall from:
v(wall) = ( -0.165 + 0.0369 * ln(Re) ) * v(mean)
3) as the gas velocity must be higher than the suspension velocity (otherwise there will be no pneumatic conveying), take the gas velocity along the pipe wall as 2.0 to 2.5 times the suspension velocity at the considered gas conditions.
The real pick up velocity at the intake will be higher, as the product has still a low velocity at the intake region, causing less area for the gasflow.
BR
teus ■
Teus
Re: The Lowest Pick Up Speed For Dilute Phase Conveying
Originally posted by Teus Tuinenburg
Dear shenjie2004
1) Calculate or measure the suspension velocity at the considered gas conditions. (pressure and temperature)
2) calculate the gas velocity along the pipe wall from:
v(wall) = ( -0.165 + 0.0369 * ln(Re) ) * v(mean)
3) as the gas velocity must be higher than the suspension velocity (otherwise there will be no pneumatic conveying), take the gas velocity along the pipe wall as 2.0 to 2.5 times the suspension velocity at the considered gas conditions.
The real pick up velocity at the intake will be higher, as the product has still a low velocity at the intake region, causing less area for the gasflow.
BR
teus
Dear Teus,
with function in item 2 wall velocity is somthing like 1/3 time of mean velocity. is it important for conveying?
or should the wall speed higher than suspension speed?
if so lowest wind speed should be about 3 times of suspension speed.
Has the lowest wind velocity something to with pipe diameter? ■
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Re: The Lowest Pick Up Speed For Dilute Phase Conveying
Dear shenjie2004
1)wall speed (v-wall) is lower than the mean gas velocity in the pipe cross section (velocity profile), due to wall friction.
2)The gas velocity along the pipe wall must be higher than the particle suspension velocity. (otherwise the particle will not be conveyed).
3)As the Reynoldsnumber is a function of the pipe diameter, the influence of the pipe diameter is accounted for.
take care
teus ■
Teus
Re: The Lowest Pick Up Speed For Dilute Phase Conveying
Originally posted by Teus Tuinenburg
Dear shenjie2004
1)wall speed (v-wall) is lower than the mean gas velocity in the pipe cross section (velocity profile), due to wall friction.
2)The gas velocity along the pipe wall must be higher than the particle suspension velocity. (otherwise the particle will not be conveyed).
3)As the Reynoldsnumber is a function of the pipe diameter, the influence of the pipe diameter is accounted for.
take care
teus
As I calculated with below data:
Viscosity of air: 0.0000202(60 DEGC)
Pipe diameter: 0.25m
Renoldsnumber: 463787
v(wall) /v(mean)= ( -0.165 + 0.0369 * ln(Re) )
= 0.316
V(mean)/V(wall)=3.16
That means v(mean) should be higher than 3 times of suspension speed. instead of 2~2.5 times
anything wrong? ■
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Re: The Lowest Pick Up Speed For Dilute Phase Conveying
with formular Re=desity*Velocity*diameter/viscosity
the smaller the pipe is, the smaller the Renorldsnumber is. So that v(wall) is smaller for smaller pipe.
that means pick up speed for smaller pipes should be higher than bigger pipes.
Quite different from common sense. ■
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Re: The Lowest Pick Up Speed For Dilute Phase Conveying
Dear shenjie2004,
Your example calculates as follows:
v(wall) /v(mean)= ( -0.165 + 0.0369 * ln(Re) ) = 0.316
when v(wall)= 2 * v(suspension)
then
2 * v(suspension)/v(mean) = 0.316
resulting in:
v(mean) = 2 * v(suspension) / 0.316 = 6.33 * v(suspension)
In this calculation it is assumed that, when the factor v(wall)/v(suspension) drops below
the value of 2, sedimentation in the pipeline starts to build up.
best regards
teus ■
Teus
Re: The Lowest Pick Up Speed For Dilute Phase Conveying
Originally posted by Teus Tuinenburg
Dear shenjie2004,
Your example calculates as follows:
v(wall) /v(mean)= ( -0.165 + 0.0369 * ln(Re) ) = 0.316
when v(wall)= 2 * v(suspension)
then
2 * v(suspension)/v(mean) = 0.316
resulting in:
v(mean) = 2 * v(suspension) / 0.316 = 6.33 * v(suspension)
In this calculation it is assumed that, when the factor v(wall)/v(suspension) drops below
the value of 2, sedimentation in the pipeline starts to build up.
best regards
teus
Dear Teus,
You didn't catch my point.
I mean for a 0.25m(10") diameter pipe, with 19m/s wind speed and temperature 60 degC.
v(wall)=0.316v(mean)
then for a 0.1m(4") pipe, 19m/s wind speed and temperature 60 degC
v(wall)=0.284v(mean)
As you mentioned above, v(wall) should be bigger than v(suspension), and suspension speed is a constant value. then v(mean) for 4" pipe should be higher than v(mean) for 10" pipe.
It looks that the smaller pipe you select the higher velocity you should take.
Regards ■
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Re: The Lowest Pick Up Speed For Dilute Phase Conveying
Dear shenjie2004,
Your conclusion is right.
The theory behind is given in the attachment.
have a nice day
Teus
Attachments
■
Teus
Dear Teus, Thanks For The Artical
Re=(1.293 *273/(273+tambient) * 1/pambient*Volp)/(Pi/4*D*eta(0)*sqrt((
T * ( 1 + C/T(0))/(T(0) * ( 1 + C/T))
what is pambient, VOLP, ETA(0), C, and T(0)?
Thanks ■
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Dear Tues,
Normally our Re No. are between 10^5 and 10^6, So the V(wall)/V(mean) is between 0.39~0.5 form the article.
And the article suggest V(wall)>=2*V(suspension)
So V(mean) becomes 4~5 times V(suspension)
that's terrible! ■
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Re: The Lowest Pick Up Speed For Dilute Phase Conveying
Dear shenjie2004,
pambient = ambient absolute pressure (1 bar)
Volp = pumpvolume in m3/sec
ETA(0) , C , T(0) are explained in the next attachment.
Take care
Teus
Attachments
■
Teus
Re: The Lowest Pick Up Speed For Dilute Phase Conveying
Dear shenjie2004,
It is not that terrible.
In my experience, (grain, derivatives, cement, fly ash etc.) a lot if installations are running at much higher velocities.
Installations running at lower velocities than the 4 -5 times the local suspension velocity tended to form sedimentation in the pipelines.
Take care
Teus ■
Teus
Dear Teus, Thanks For The Artical
sedimentation in the pipe line is not terrible. especially for plastic pellets. For example PP pellets 3X3mm, whose suspension velocity is about 7m/s. We usually use 22m/s as pick up speed. and the acceptable velocity will be not more than 30m/s which is 4 times the suspension speed. the point is reduce product degradation.
My point is although 22m/s is popular I would like to optimise it by lower pick up speed. For sure the lower the speed is the lower degradation is and the lower power consumption is.
Thanks ■
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Re: The Lowest Pick Up Speed For Dilute Phase Conveying
dear shenjie2004,
Particles that are bigger than the thickness of the boundary layer in an airstream can be
conveyed at lower speeds than small particles that will fit in the boundary layer.
Plastic pellets of 3mm can be considered as bigger particles..
Sedimentation will cause a smaller cross section area in the pipe, resulting in a higher gas velocity, thereby restoring the proper velocity.
At the same time conveyed particles are colliding with the sedimentation, causing higher losses than when colliding against a smooth pipe wall.
As Mr Mantoo stated :
“I normally check the pick up velocity experimentally and it also never fails.“
Do not forget that the pick up velocity is pressure dependant.
success
Teus ■
Teus
Merry Xmas!
Do not forget that the pick up velocity is pressure dependant.
pick up velocity denpends on pressure? What is the story behind? ■
Shenjie Tel:+86(0)20 83553890,83550361 Fax: +86(0)20 83542314 [email]sj@chinabulk.com[/email] [url=http://www.chinabulk.com]Sino-Auto Technology[/url]
Re: The Lowest Pick Up Speed For Dilute Phase Conveying
Dear shenjie2004,
Pick up velocity is a function of suspension velocity
suspension velocity is a function of gas density
gas density is a function of gas pressure
ERGO:
pick up velocity is a function of gas pressure
success
Teus ■
Teus
I Get It!
Thanks! Teus ■
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The lowest pick up speed for dilute phase conveying
I found almost all the pick up speed of current PP and PE pellet conveying systems are higher than 22m/s. But I tested successfully with 13m/s.
Is there any relationship between pick up speed and pipe diameter or other factors? ■
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