Re: Velocty Range For Ducts Without Dust
Typical velocity range in ducts is between 20-35 m/s.
There is no text book upper limit, pressure drop will increase with the increase in air velocity. It will be limited by
If the velocities are very high you will be wasting kw’s. ■
Re: Velocty Range For Ducts Without Dust
Dear Mantoo,
Thak you for your reply.
As I calculated for a duct with dia. of 2000mm, the pressure loss for velocity of 20m/sec is 0.014 mbar per meter of duct and for velocity of 35m/sec is 0.04 mbar per meter of duct.
So these values are very low and by increasing the velocity more the pressure loss will increase very slowly and we don't have anxiety for wasting alot of power.
Do you have any suggestion?
Regards, ■
Re: Velocty Range For Ducts Without Dust
A common reference for dust systems is:
Industrial Ventilation
A manual of reccomended practice
American Conference of Governmental Industrial Hygienists
There may be some guidence on ducts without dust (unsure).
For a given system with a variable velocity (and hence flowrate) the system resistance is proportional to the square of the velocity, considering: H=flv^2/2dg (friction factor x length x square of velocity / the number two x diameter x gravitational constant). For the purists the "f" is proportional to velocity (through Re number) however I am neglecting that for now). The entry / bend / exit losses are also proportional to the square of the velocity: H=kV^2/2g (k coefficient and the others as stated earlier).
Regards,
Lyle ■
Re: Velocty Range For Ducts Without Dust
I calculated the resistance by that formula, but as I mentioned the resistance in ducts by large diameters is very low that by increasing the velocity it has a little increase.
We in our system have some permanent ducts and we want to increase the flow in those ducts as high as possible through our projet.
I want to know is there any other limitation beside the resistance that was calculated by that formula or not? ■
Velocity Range For Ducts Without Dust
abdorrahim
The friction loss calculation for ducts without dust is the same for ducts with dust (except in pneumatic conveying systems).
Friction loss per unit length for large ducts is indeed much lower than for small branch ducts.
Lyle mentions "Industrial Ventilation". This is your best guide for design or alteration of systems.
For many years, I have used the formula which is used to construct the friction loss chart (Figure 5.21 in my edition).
Loss/100ft.=2.74(V/1000)^1.9/D^1.22
Loss = inches water.
V = velocity, fpm.
D = duct dia. inches.
An Excel spreadsheet makes it easy to use and does the conversions to ISO units.
Michael Reid. ■
Re: Velocty Range For Ducts Without Dust
abdorrahim
why u want to increase the velocity inside the duct? do you want to improve the grindability of you mill. ■
Re: Velocty Range For Ducts Without Dust
Dear mall,
In one of cement factories in our country they want to omitt the cooling tower because of deficit of water in their region.So for cooling the air we should add some fresh air to the system.
And this is the reason, that we want to know if the existing ducting system is suitable for the added flow rate or not! ■
Ducts Without Dust
abdorrahim,
Have your thought about whether your gas cleaning device (baghouse, ESP) can handle the increased gas flow?
Michael Reid. ■
Re: Velocty Range For Ducts Without Dust
Micheal,
yes we have considered the changes.In the system they want to omit the ESP and add a baghouse instead for the new flow. ■
Velocty range for ducts without dust
Dear all,
We are working on ducting systems in raw mill department in a cement mill.
I have a question.I know that we have velocity limitation in ducts, but my question is that; Is there any limitations for velocity in ducts without any dust and just air, if the head of fan be enough for the pressure fall in ducts ?
And if there is limitation what is the optimum range for this kind of ducts without any dust?
thanks, ■