how select diameter of piping to carry plastic by gravity ? 1

[jmelendezc]

In a Silos of Polyetilene Plant we need calculate severals lines, wich carry Low Density Polyetilene from a Centrifugal Dryer up to a Bin passing across a classifing screen and Magnetic Separator and a Autosampler.

Which is the criteria to calculate the optimal diameter to carry by gravity the pellets of Low Density polyetilene?.

If you know a calculation procedure or bibliografic reference tell me about.

Thanks in advance for this information.


Truly yours
Juan Melendez Cabrera

 

[balu1]

It probably depends on how large flow of polyethylene pellets you need.

Assume, just for the sake of discussion, that those pellets can reach velocity of 0.4 m/s in free fall (very light material, high aerodynamic losses, have you ever seen a chicken's feather falling). In that case volumetric flow through a vertical pipe of A cross section area (theoretical flow area) should approximately (frictional losses not accounted for) be:

Q = k*A*0.4 = (k*(3.14*d^2)/4)*0.4

Where k is coeficient of let's name it real flow area (area reduction). In case of normal fluids (gases and liquids) k is close to 1 but in the case of your pellets it may be as low as 0.5 (I haven't the faintest idea what the real value is). Finaly we come to:

Q = 0.157*d^2

Take care since we assumed speed (or velocity) in m/s we have to be consistent, hence Q must be in (m^3)/s deriving d in m. For example if we need flow of 0.157 cubic meter per second (approximately 5 cu.ft/s)d has to be 1m.

Since we employed a lot of wild assumptions, begining with the flow speed, you should ask somebody who really knows about those pellets. If that thing polyethylene is what I suppose it is (that foamy stuff) than static electricity may be the problem too, reducing flow rate.

 

[jmelendezc]

what is the criteria to velocity in vertical gravity piping for solids falling by gravity?.

Thanks for your help