Dust Extraction

sorry meant to say a 12" pipe... not 45mm. Alot static pressure is 1700kPa shaft diamater 45mm.

In your formula, PSI is the differential pressure across the fan. Efficiency is the fan efficiency, power into the flowing air divided by input power to the blower shaft. 50% would be a typical figure, depending on blower details.

Are you sure about the 1700 kPa? That's 17 bar. 1700 Pa ~ 170 mm water seems more likely.

Cheers........Codey

Welcome to CR4.

It looks like <...HP = (CFMxPSI)/(229xeff)...> is the motor sizing formula.

Flowing fluid will find the path of least resistance. From the three pipes, is one allowing more flow than the other two?

Why would changing the motor improve things?

What is the condition of the fan impeller?

A little out of my area - ok a lot.

However I'll chime in behind PW. If I am understanding; you have 3 hoses of equal size manifolded together to some common line/block/inlet. This arrangement could create a scenario where you are getting more suction from one hose than the others. Pipe/tube sizing and placement as well as respective lengths could be a factor here.

yeah sorry about that not 1700kPa more like up to 6kPa... the design doc had a typo. Blockages have been occuring within the larger pipe so how between each smaller pipe probably isnt the same (flex pipes and in pretty bad condition).

I think i might try and redesign the extraction hood shape for each suction pipe.... its like a rectangle with the front and the bottum gone and the suction is coming from the top. It would work alot better redesigning the shape better i think. Im gonna have a look at some typical industrial extraction systems.

You are correct, sir!

Either the main line is too large or the branches are too small. I'm not clear if the 15m/s (3000fpm) is in the main line or the branches, but if it's in the 12" main then the branches are too small. From the main the first lateral should be 12" x 10" x 7" (the main should reduce to 10"). From there, the next lateral reducer should be 10" x 7" x 7".

The velocity is dropping dramatically from the 4" branches into the 12" main line. Aaron didn't indicate if he's using lateral reducers, but the dust will settle and block the main if there is a significant drop in velocity at any point.

In dust collection pipe sizes, 7 + 7 + 7 = 12 and 4 + 4 + 4 = 7.

TiO2 is the dust being sucked up.... under a micron in diamater. The current hood is approx 35cm away from the dust. Im looking at a book atm to design new hoods as i think for TiO2 15m/s is overkill, i mean this stuff is so fine it gets stuck in the pores of your skin if you touch it. I think that hood design is the key here really... even if i reshape the hood and make it so that the hood is sucking downwards so the particles get pulled into it as they fall. feel sorry for the people working in there lol.

Im looking at a tapered design much simular to the ones used in workshops for metal clippings etc.... you know the ones with the movable flexible pipe.

Hi,

these ultrafine particles hardly need any velocity to keep flowing.

I had 5 µm SiC and similar dust: some centimeter per second is sufficient.

The problem is a vortice-free suction: so you may try a suction head that has very many channels in parallel (as in clean boxes the filter-support).

If you have vortices these will redistribute your particles.

Then I would not use the three hoses in parallel but one motor-one hose!

Where is the air coming from that shall transport the dust?

Very often this is giving problems by turbulence.

I would try much smaller motors (3) and a low velocity of a few m/s.

RHABE

If the flexible ducts are worn and you have to deal with blockages in the main, then you probably need to look at redesigning the entire system. If you want to maintain a fairly constant air velocity, you will need to reduce the size of your main line. Also make sure that you have smooth transitions when a line branches off, and the main should reduce in size when lines branch off. Also, if they aren't already in the system, you may want to include dampers or slide gates for each line to aid in balancing the air flow.

You should have a look at welding fume extraction hoods & tables

Thanks everyone for your replies. The system overalls is quite shocking... the flexible pipes are in poor condition and some i discovered today are held togather with duct tape. As far the project goes, at this stage i think the best thing to do would be to replace the flex pipe and design better hoods (needs to be done anyway) also maybe chuck in some of those "pipe blockers" that one of you suggested. A new system is a bit out of question. But if replaceing the hoods and flex pipe doesnt work then replacing the motor from a 15kW to say a 40kW may be the best option, assuming that the fan is in good nick.

Btw sorry i cant give you guys more information... as i said im a chemical engineering vacation student this isnt exactly my area of expertise lol.

Hi,

don't waste your energy,

4KW will be enough!

RHABE