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OfflineFrank Zappotecorum
Smooth-Brained Mycophagist
I'm a teapot User Gallery


Registered: 01/01/17
Posts: 138
Loc: Scamdinavia
Last seen: 8 months, 20 days
Filter for a flowhood: Questions regarding higher than optimal CFM
    #26618130 - 04/21/20 03:49 PM (3 years, 9 months ago)

Howdy everyone, hope you're all good with the pandemic and whatnot.
I know this is a tired topic (apologies) but I don't know a lot about fluid dynamics and a lot of the information on here is either contradictory, confusing or doesn't have a lot of super in-depth explaination (for instance, I can find nothing on why the magical 1"WC is necessary for generating laminar flow when pressure doesn't appear to factor into the Reynolds number equation others that I've found for calculating laminar flow)
ANYWAY: I'm looking at a 24X24X6 filter that's 99.99% efficient for 0.3um particles but generated 1"WC static pressure at 580CFM. I'm asking for the filter diagram but no response yet.
Assuming that we can use the reynolds number calculation for a pipe (with 0.3um diameter as that's our "pore size" we'll still have laminar flow if 580CFM through a 24X24 conduit flows at 145 FPM. But I don't know if we have to consider the fact that the conduit is 24X24 in the Reynolds number equation (somehow). How do we include Static Pressure into these calculations? I'm very lost (as you can see)
Assuming my math and understanding of laminar flow is somewhat correct, I see no reason that this filter wouldn't work, but I don't want to create a wind tunnel that would blow plates out of the working area. 145 FPM is 45 FPM faster than the recommended 100 FPM but I don't know how much that is in terms of being able to blow shit around.

Tl;Dr: would a filter that generated 1"WC at 580 CFM accomplish laminar flow? If so, would subsequent flow of 145 FPM create a wind tunnel?


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What are all these leaves doing in my mouth?
I ain't got a lot but peep my Trade list


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InvisibleDigit
Surreal Estate Agent
Registered: 08/10/15
Posts: 69
Loc: tierra incognita
Re: Filter for a flowhood: Questions regarding higher than optimal CFM [Re: Frank Zappotecorum]
    #26618151 - 04/21/20 03:59 PM (3 years, 9 months ago)

I don't know about the numbers but I know I have a massively overpowered fan for my little 12x12 filter, it will put out a lighter from 3 feet away, but it works fine for my purposes anyway. I've never had a plate get blown off the table. The only thing is paper towels get blown onto the floor unless they're wetted with alcohol.
I'm pretty sure having too much wind is a lot better than not having enough.


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Question everything.
Believe nothing.
Think for yours3lf.


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OfflineFrank Zappotecorum
Smooth-Brained Mycophagist
I'm a teapot User Gallery


Registered: 01/01/17
Posts: 138
Loc: Scamdinavia
Last seen: 8 months, 20 days
Re: Filter for a flowhood: Questions regarding higher than optimal CFM [Re: Digit]
    #26618428 - 04/21/20 06:31 PM (3 years, 9 months ago)

Word, do you know how many CFM you're moving?


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What are all these leaves doing in my mouth?
I ain't got a lot but peep my Trade list


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OfflineSkynni
Stranger

Registered: 03/29/20
Posts: 10
Last seen: 3 years, 4 months
Re: Filter for a flowhood: Questions regarding higher than optimal CFM [Re: Digit]
    #26618449 - 04/21/20 06:37 PM (3 years, 9 months ago)

Hi there,

Your fan is too powerful by nearly 1/3rd ? I agree with Digit that even a mismatched fan and filter would probably function well enough,  however, you may be able to reduce the cfm with a fan speed controller if your fan is compatible with one which you can easily make with a lighting dimmer / rheostat or a potentiometer. Some fan motors also have different wiring options for adjusting the speed.


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OfflineFrank Zappotecorum
Smooth-Brained Mycophagist
I'm a teapot User Gallery


Registered: 01/01/17
Posts: 138
Loc: Scamdinavia
Last seen: 8 months, 20 days
Re: Filter for a flowhood: Questions regarding higher than optimal CFM [Re: Skynni]
    #26618667 - 04/21/20 08:26 PM (3 years, 9 months ago)

Yeah for sure Shroomdog69, If I wanted to flow 400 CFM (recommended for 24x24) I'd definitely power it down but depending on the filter's specs it might be too low to maintain static pressure for efficiency, as I understand it


--------------------
What are all these leaves doing in my mouth?
I ain't got a lot but peep my Trade list


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OfflineFrank Zappotecorum
Smooth-Brained Mycophagist
I'm a teapot User Gallery


Registered: 01/01/17
Posts: 138
Loc: Scamdinavia
Last seen: 8 months, 20 days
Re: Filter for a flowhood: Questions regarding higher than optimal CFM [Re: Frank Zappotecorum]
    #26618792 - 04/21/20 09:24 PM (3 years, 9 months ago)

It seems like I can rig it up to work so I'm gonna get it :laugh: Floyd's gonna be in business


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What are all these leaves doing in my mouth?
I ain't got a lot but peep my Trade list


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