Air Velocity According To Density/Size
The mathematical rlationship you need to use is Stokes' Law, which can be found in most powder text books etc. or a quick web search should do the trick. ■
Mimimum Conveying Velocity
Daniel,
The minimum conveying velocity is based on the saltation velocity. Co-relations that I use for the saltation velocity are those given by Rizk and also by Matsumoto. Basis for using these corelations are:
Use Rizk for coarse particles, 500 microns or larger.
Use Matsumoto for fine particles, less than 500 microns.
Masumoto co-relation has a particle density term in it. From that point of view, it is a better co-relation.
You can find these co-relations in published literature.
Regards,
Amrit T. Agarwal
Consulting Engineer
Pneumatic Conveying Consulting
Email: polypcc@aol.com
Ph and Fax: 304 346 5125 ■
Rough Estimate Of Conveying Air Velocity
dear Daniel,
Determine the floating velocity of the particle at the location in the system, where you want to focus on, with the formal
v(susp) = SQRT (4/3 * d/1.293 * 1/pabs * 273/(273+t) * rhomat/cw)
in which :
d = particle size in m
t = temperature in degrees Celsius
rhomat = material density in kg/m3
pabs = absolute pressure in bar (kgf/cm2)
cw = drag factor of the particle (shape dependent), usually between 0.045 to 0.055
Then the conveying air velocity is approx 4 to 5 times the calculated floating velocity.
Example:
d = 0.000090 m
t = 50 degrees Celsius
rhomat = 3100 kg/m3
pabs = 3.5 bar (kgf/cm2)
cw = drag 0.05
v(susp) = SQRT (4/3 * 0.00009/1.293 * 1/3.5 * 273/(273+50) * 3100/0.05)
v(susp) = 1.2 m/sec
The conveying air velocity at that location = 4@5 * 1.2 = 4.8 @ 6 m/sec
This is a rough approximation to start a design with. Actual field data of the product involved have to be used in the definite design as well as other experiences.
best regards ■
Teus
Re: Relationship, Can´T Find??
Thanks for your help,
I have obtained almost similar results (11m/s minimum) using Rizt correlation (ARMIT) and the formulae proposed by TEUS, since my particle diameter is 0.005m biomass wooden chips.
The transport line has 250m with a deltaP of 4.7bar, my idea is to use a 8bar Pump with air velocities of 20-25m/s transporting a total mass of 3100kg/h of biomass (S:A ratio 4).
Anyway, Thanks again, I have to continue with the study.
Thanks, again Daniel
P.S. TEUS, which name is that correlation given by? ■
Re: Relationship, Can´T Find??
dear Daniel,
You'r welcome,glad to have helped you a bit.
The "correlation" I mentioned is what I found out during my time spent in pneumatic conveying.
As the wall velocity in an air flow is lower than the average air velocity, this wall velocity is a key factor.
The wall velocity has to be a factor above the local suspension velocity in the pipeline.
Knowing the suspension velocity, the required wall velocity of the air can be determined (f.i. 2.5 times) and the mean air velocity can be determined by the ratio (wall velocity)/(mean velocity), which in its turn is dependent of the turbulence of the flow. (Reynolds number).
To get to the definitive design, some iteration calculations are mostlyneccessary.
success ■
Teus
Relationship, can´t find??
First of of all say hello to all members,
I am new in this field of Pneumatic conveying, which I find very interesting. I have read the Handbook of Pneumatic Conveying Engineering as well as the article posted recently to me by A.T. Agarwal, which I have found very useful.
My doubt is, I am trying study how to convey diferent types of biomass (in density and particle size). is there a relationship of particle density and size in order to establish a minimum air transport velocity. I only have found the reference table shown in Perry´s.
Thnaks, Daniel ■