|
Some of these posts are very old and might contain outdated information. You may wish to search for newer posts instead.
|
shroombasauce
Stranger



Registered: 07/13/12
Posts: 72
Last seen: 3 years, 3 months
|
Creating a big laminar flow hood! Help is much appreciated
#17050235 - 10/17/12 06:34 PM (11 years, 6 months ago) |
|
|
I'm trying to build a 2' x 4' laminar flow hood using the methods derived from: http://www.shroomery.org/forums/showflat.php/Number/13327748/fpart/1
I plan on getting a HVAC blower for the low low with that alibi stated by total.
I was thinking about using AstroCell II AAF InternationalCleanroom Air Filter. Specs: Efficiency: 99.9997% Resistance: 0.64" W.G. Flow: 668 cfm Size: 22 3/4" x 46 3/4" x 2 3/4" www.ebay.com/itm/AstroCel-II-Cleanroom-HEPA-Air-Filter-AAF-International-23-x-47-x-3-/221051010920?pt=LH_DefaultDomain_0&hash=item3377aabf68
I also saw this one for 75$, but it has a female ducted end to the back of it  I doubt it, but would it still work http://www.ebay.com/itm/Camfil-Farr-Slimline-Hepa-Air-Filter-/251169028706?pt=LH_DefaultDomain_0&hash=item3a7ad73a62
I found the same one without the ducted end for 25$ more. http://www.ebay.com/itm/NEW-Camfil-Farr-22x46x3-100FPM-634CFM-Cleanroom-HEPA-Air-Filter-Megalam-Panel-/200834016460?pt=LH_DefaultDomain_0&hash=item2ec2a3e4cc
If anyone is interested this guy has 4 of these going for 75$ each. http://www.ebay.com/itm/ATMOS-TECH-INDUSTRIES-ATMOS-AIRE-GEL-SEAL-HEPA-FILTER-27-1-8-X-55-X-3-1-2-/200728371903?pt=LH_DefaultDomain_0&hash=item2ebc57e2bf
Which filter would guys recommend? Personally, the Astrocell II appears more aesthetically attractive, but we all know that doesn't matter when it comes to efficiency. I'm planning on negotiating the price down to about $200.
Here's the math that i've done so far.
22 3/4" x 46 3/4" = 1063.6 sqin
Divided by 144 (12^2)
Ends up equaling 7.4 sqft
multiply by the desired 100 ft/ minute
equals 740 CFM minimum
adding an additional 10%-20%
I get 814 to 880 CFM
The resistance is what confuses me a little. The filter is only ~3" thick with Resistance: 0.64" W.G. Flow: 668 cfm.
I'm assuming I should make a 21" plenum and use a 1000 cfm @ 1-1.2 W.G.
is this correct?
Thank you for your time
--------------------
|
shroombasauce
Stranger



Registered: 07/13/12
Posts: 72
Last seen: 3 years, 3 months
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: shroombasauce]
#17063461 - 10/19/12 07:06 PM (11 years, 6 months ago) |
|
|
After further reading, I believe it might possibly work. In addition, the price magically dropped 
The main question that I have is how do I fix the flow to 100 cmf @ 1.2 static pressure (.2 for the prefilter)?
It flows at 668 cfm @ .64" static pressure
I apologize for bumping.
--------------------
|
Terry M
Stranger in a Strange Land



Registered: 06/18/10
Posts: 1,502
Loc: Rhode Island
Last seen: 9 years, 3 months
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: shroombasauce]
#17065876 - 10/20/12 07:29 AM (11 years, 6 months ago) |
|
|
For a flow hood of the type we commonly use here, the filter must be designed for laminar flow. This filter doesn't appear to be. When filtering air to be simply pushed into a clean room, you don't need laminar flow.
When you work in an open space in front of a flow hood which is not sitting in its own HEPA-purified clean room, laminar flow is required. This forces the air exiting the filter to move smoothly, rather than turbulently. The reason this is necessary is that turbulence will very quickly mix the unfiltered room air with the filtered flow hood air, defeating the purpose of the flow hood.
There is another type of flow hood that doesn't require a laminar flow HEPA. That's one which is a nearly closed box with a transparent and angled front wall, and a few inches of opening below this front wall for the insertion of hands and and move things in and out. Sparkle introduced me and others here to this type. It's commonly used in the tropics where contamination is high, so it really really works. The advantage to this type of hood is:
1. The HEPA filter is cheaper because it doesn't need to provide laminar flow, just the same level of particle filtering.
2. The HEPA filter is cheaper because it can be small. All it does is force cleansed air into the nearly closed flow hood chamber. It's typically at the top, so you don't work directly in front of it. It's kind of a self-contained mini positive pressure clean room.
Regards, Terry
-------------------- Liberté, égalité, humidité.
|
shroombasauce
Stranger



Registered: 07/13/12
Posts: 72
Last seen: 3 years, 3 months
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: Terry M]
#17147156 - 11/02/12 09:11 AM (11 years, 6 months ago) |
|
|
I ended up emailing the seller about the atrocell II and he replied:
"You ask great questions that require a bit of engineering. Laminar flow is often determined through use of Bernoulli's Equation. As for the filters, we have used these to build hoods to filter out particulate matter (mainly fibers, but also biologics). They are typically used for clean rooms (ie - semi-conductor fabrication). If they are rated at 668 cfm, that will be laminar flow. From the size of the filter you should be able to calculate the rated linear flow rate. We also have other HEPA filters in our store (http://stores.ebay.com/Supply-Wrangler)."
I also emailed this other guy about this filter and he replied:
This filter is exactly what we use in our laminar flow hoods. We get 90-100fpm (feet per minute) at approximately 0.5 to 0.6wg across the filter. For more laminar flow, say within 10-20% deviation, we add a perforated diffuser at the blower outlet and a perforated screen at about 3-6 inches after the filter. A filter this size would require a 1/2hp motor in a 10-10A blower, capable of 1250cfm at 1.0wg. These numbers will vary according to the actual design."
Im pretty sure option 2 seems like the best bet.
What do you think?
--------------------
|
Kanji

Registered: 01/04/09
Posts: 86
Loc: Near the edge
Last seen: 6 years, 1 month
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: shroombasauce]
#17154095 - 11/03/12 03:29 PM (11 years, 6 months ago) |
|
|
Quote:
shroombasauce said: "You ask great questions that require a bit of engineering. Laminar flow is often determined through use of Bernoulli's Equation. As for the filters, we have used these to build hoods to filter out particulate matter (mainly fibers, but also biologics). They are typically used for clean rooms (ie - semi-conductor fabrication). If they are rated at 668 cfm, that will be laminar flow. From the size of the filter you should be able to calculate the rated linear flow rate..."
This is correct. But a sufficient Reynolds Number is required for true laminar flow.
Quote:
shroombasauce said:
This filter is exactly what we use in our laminar flow hoods. We get 90-100fpm (feet per minute) at approximately 0.5 to 0.6wg across the filter. For more laminar flow, say within 10-20% deviation, we add a perforated diffuser at the blower outlet and a perforated screen at about 3-6 inches after the filter. A filter this size would require a 1/2hp motor in a 10-10A blower, capable of 1250cfm at 1.0wg. These numbers will vary according to the actual design."
This is correct. I don't understand how the pre-filter diffuser will work but in theory the perforated screen will work if it is reducing the reynolds to an amount that is laminar flow.
|
shroombasauce
Stranger



Registered: 07/13/12
Posts: 72
Last seen: 3 years, 3 months
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: Terry M]
#17283196 - 11/26/12 06:11 AM (11 years, 5 months ago) |
|
|
I came to the conclusion that im going to build mine with an ulpa filter instead of a hepa b/c it has higher resistance & filters down to the .1 micron. The seller claims it has .3 wg @ 90 fpm, but i feel like its probably higher than that. I'll add a perforated protective screen to increase the resistance. The only question, is how big and spaced out should the screen be?
BTW, the filter is 3.5" thick. 26 3/4" X 47" = 1257.25 sqin
Divided by 144 (12^2)
Ends up equaling 8.73 sqft
multiply by the desired 100 ft/ minute
equals 873 CFM minimum @ ~1/3 hp
adding an additional 10%-20% due to an imperfect world
I get 960 to 1047 CFM @ unknown W.G. + .2 prefilter + unknown resistance from perforated screen
Do you guys see any problem with my blue prints?




I was thinking a screen with lots of small holes close together would be the best choice, such as:
Hole diameter (D): 3/64 inch (.045) Thickness: 20 gauge Staggered Center(C): .081 inch Maximum open area: 28%
or
Sheet Size: 36 X 113 inches Hole diameter (D): 1/32 inch (.033) Thickness: 24 gauge Staggered Center(C): .077 inch Maximum open area: 20%
I would really appreciate any thoughts or constructive criticism.
Thank you in advanced.
--------------------
Edited by shroombasauce (11/26/12 06:30 AM)
|
Terry M
Stranger in a Strange Land



Registered: 06/18/10
Posts: 1,502
Loc: Rhode Island
Last seen: 9 years, 3 months
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: Kanji]
#17283462 - 11/26/12 07:53 AM (11 years, 5 months ago) |
|
|
Quote:
Kanji said:
Quote:
shroombasauce said:
This filter is exactly what we use in our laminar flow hoods. We get 90-100fpm (feet per minute) at approximately 0.5 to 0.6wg across the filter. For more laminar flow, say within 10-20% deviation, we add a perforated diffuser at the blower outlet and a perforated screen at about 3-6 inches after the filter.
The only thing that concerns me is the "more laminar flow" phrase. Flow should be well into the laminar flow range (low Reynolds number), and away from the transition region between laminar and turbulent flow. If the filter can't achieve this by itself, you should find out from the manufacturer the exact specs for the diffuser and screen to lower the Reynolds number and achieve clean laminar flow.
- Terry
-------------------- Liberté, égalité, humidité.
|
shroombasauce
Stranger



Registered: 07/13/12
Posts: 72
Last seen: 3 years, 3 months
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: Terry M]
#17285180 - 11/26/12 03:14 PM (11 years, 5 months ago) |
|
|
The dude replied with:
"We only check for turbulence with a smoke stick WITH the hepa perf grill installed, downstream of the filter. We acheive laminar flow from the perf grill all the way to the front opening of the hood. Air speed is recorded 6" off the face of the hepa grill (industry standard) with a Shortridge Velgrid which averages 16 points per reading. No air is permitted to be pulled in from outside the hood into the sterile work area. We do not check for laminarity without the perforated hepa grill installed."
Seems relatively legit, what do you guys think?
--------------------
|
donrjuan
On the Grind


Registered: 10/20/10
Posts: 534
Loc: State of Boredom
Last seen: 3 months, 10 days
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: shroombasauce]
#17301636 - 11/29/12 07:09 AM (11 years, 5 months ago) |
|
|
I am building one myself. All of the data I have poured over is saying that there is no one vent or layer that suddenly produces the Laminar flow. Instead it has to do with the static pressure of the filter. I ended up going with a filter from Filtera-B2B 24" x 24" x 5 7/8" @ 1" WG. Even when speaking to them they recommend a higher static pressure for for Laminar flow. Also a sufficient plenum to allow for pressure to build evenly on the filters back is critical. I collected all of my data here on the forum but if any of this seems wrong, someone chime in since I am building this thing in a week.
|
Terry M
Stranger in a Strange Land



Registered: 06/18/10
Posts: 1,502
Loc: Rhode Island
Last seen: 9 years, 3 months
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: donrjuan] 1
#17302120 - 11/29/12 09:28 AM (11 years, 5 months ago) |
|
|
Quote:
donrjuan said: I am building one myself. All of the data I have poured over is saying that there is no one vent or layer that suddenly produces the Laminar flow. Instead it has to do with the static pressure of the filter. I ended up going with a filter from Filtera-B2B 24" x 24" x 5 7/8" @ 1" WG. Even when speaking to them they recommend a higher static pressure for for Laminar flow. Also a sufficient plenum to allow for pressure to build evenly on the filters back is critical. I collected all of my data here on the forum but if any of this seems wrong, someone chime in since I am building this thing in a week.
Sorry donrjaun, but static pressure doesn't directly determine laminar flow. Laminar flow physics belongs to a very well understood branch of fluid mechanics known as fluid dynamics. Laminar vs. turbulent flow is determined by Reynolds number R, which can be defined as (don't worry, this is simpler than it looks):
R = VD/ν
where: V is the velocity of the fluid through the hole or holes D is called the hydraulic diameter, which depends on hole shape, but for a circular hole is identical to the diameter of the hole ν is called the kinematic viscosity, which is fixed for a given fluid and temperature, e.g. air at 20°C.
A low Reynolds number (less than about 2300) means laminar flow. A high Reynolds number (over about 4000) means turbulent flow. Numbers in between these mean a transition region, which isn't laminar but isn't quite turbulent either. To be safe, it's best to use a Reynolds number which is well under the limit of 2300. Reynolds number is dimensionless, meaning it doesn't matter what units we use to calculate it (inches, meters, cubits), just as long as they are consistent with each other.
Now to the above equation, which I'll repeat here:
R = VD/ν
ν we can ignore, as it is a constant that can't be controlled. But D is hole diameter, which we can control. Likewise, V is velocity of the fluid, which we can also control.
Here's where it becomes really simple. Since both V and D are in the numerator of the equation, Reynolds number decreases as either or both decrease. In other words, for the required low Reynolds number, we need both small hole diameter and low flow rate.
So a bunch of small holes are required. There also need to be many of them, so that flow isn't restricted so much as to try and jam the air so it flows faster through each hole.
This ain't rocket science. Osborne Reynolds discovered it more than a century ago, and it has worked great ever since!
Regards, Terry
-------------------- Liberté, égalité, humidité.
Edited by Terry M (11/29/12 10:05 AM)
|
donrjuan
On the Grind


Registered: 10/20/10
Posts: 534
Loc: State of Boredom
Last seen: 3 months, 10 days
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: Terry M]
#17304933 - 11/29/12 06:38 PM (11 years, 5 months ago) |
|
|
Well I knew that there was no way it was as simple as I put it. I am sure the components I have sourced will work out based on the writings of others, even if I do not fully understand all of the science. All great info though Terry. I followed many of your original posts when choosing my parts for the build. I am going to snag your write up and add it to my compiled info for my journal. I am sure others could benefit as well. Thanks
|
vladtepes
Radical


Registered: 06/15/08
Posts: 352
Loc: new england
Last seen: 6 years, 13 days
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: donrjuan]
#17305157 - 11/29/12 07:25 PM (11 years, 5 months ago) |
|
|
I went and built a laminar flow hood... then i found a guy in central mass willing to let me make payments on a real used flowhood... Just met me all he wanted was a handshake... truth is he has so much used lab equipment that he is practically willing to give it away. Hell he said "even if you miss a payment or need time, honestly I would not even care if you fucked me over because we have a hard time moving this stuff and the old man is extremely willing to negotiate and let things go cheap, because we get this stuff dirt cheap"... I would not want to fuck him over so I did not take that offer, plus they are rather large and hard to move. But this guy has EVERYTHING for a biolab, except microscopes because he said they always end up broken before they get them back to the shop. But yeah we was going to give me a unit like this for 400 and could make payments.
www.cleequipment.net Here is their website... He puts things on his website a lot higher than he is willing to take lol. If you are in this area its the way to go, wish I found him before I ordered my shit.
Pretty sure he is getting his stuff from labs that shut down or upgrade and sell their used shit at auction dirt cheap to people who have to move it which is worth more to the seller than the equipment itself which has already paid for itself anyways so they are not losing anything.
-------------------- “If the words 'life, liberty, and the pursuit of happiness' don't include the right to experiment with your own consciousness, then the Declaration of Independence isn't worth the hemp it was written on.” ― Terence McKenna My Trade list
|
teknix
𓂀⟁𓅢𓍝𓅃𓊰𓉡 𓁼𓆗⨻



Registered: 09/16/08
Posts: 11,953
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: vladtepes]
#17306927 - 11/30/12 02:15 AM (11 years, 5 months ago) |
|
|
Flowhoods are over-rated imo. I think with the same equipment you could duct the filtrated air in to a large room to create a positively pressurized lab. Maybe I am underestimating a flowhood, but I never turn the one in the lab on, no one does, still air and proper attire and correct procedure works wonders imo.
Build a large 5 sided plexi-glass box and you will get the same results.
Edited by teknix (11/30/12 02:27 AM)
|
donrjuan
On the Grind


Registered: 10/20/10
Posts: 534
Loc: State of Boredom
Last seen: 3 months, 10 days
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: teknix]
#17313341 - 12/01/12 06:33 AM (11 years, 5 months ago) |
|
|
I am sure they are worth having. I am moving into filter bags now and the fact that I can work in the open after years in a GB means the world to me. You will spend 3X as much on plexi-glass vs. hard wood ply, I looked.
|
teknix
𓂀⟁𓅢𓍝𓅃𓊰𓉡 𓁼𓆗⨻



Registered: 09/16/08
Posts: 11,953
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: donrjuan]
#17321595 - 12/02/12 03:57 PM (11 years, 5 months ago) |
|
|
A plywood box would be even cheaper, but you would probably want a light in it and silicone the joints to make sure it is air-tight..
Edited by teknix (12/02/12 04:29 PM)
|
RogerRabbit
Bans for Pleasure



Registered: 03/26/03
Posts: 42,214
Loc: Seattle
Last seen: 1 year, 2 months
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: teknix]
#17321612 - 12/02/12 04:00 PM (11 years, 5 months ago) |
|
|
You won't get the same results from a plastic box in the dusty, moldy houses most of us live in. It doesn't take long at all for the prefilter on my flowhood to become dark brown with dust and dirt.
I wouldn't trade my flowhood for anything. I certainly wouldn't do agar work or grains without one. RR
-------------------- Download Let's Grow Mushrooms semper in excretia sumus solim profundum variat "I've never had a failed experiment. I've only discovered 10,000 methods which do not work." Thomas Edison
|
teknix
𓂀⟁𓅢𓍝𓅃𓊰𓉡 𓁼𓆗⨻



Registered: 09/16/08
Posts: 11,953
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: RogerRabbit]
#17321705 - 12/02/12 04:16 PM (11 years, 5 months ago) |
|
|
The fan is pushing air through the filter so it come into contact with most of the particulates in the air, while the box is preventing air-current and particulates from flowing into it. I don't think that the amount of dust your filter collects is any indication of the efficacy of a still air box.
|
Kramer
Laughs for Pleasure




Registered: 07/25/12
Posts: 277
Loc: New York
Last seen: 8 years, 8 months
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: teknix]
#17395627 - 12/15/12 06:15 AM (11 years, 5 months ago) |
|
|
I agree I just finished my flowhood working seated in front of the flowhood is great. Glove boxes, and SAB make me furious when trying to do agar work.
Also I made mine with an Astrocell II and it has perfect laminar flow.
-------------------- Trade List<--Trade List If people do not believe that mathematics is simple, it is only because they do not realize how complicated life is. ~John Louis von Neumann
Edited by Kramer (12/15/12 06:28 AM)
|
TrashMan
Big Dummy



Registered: 11/21/08
Posts: 98
Loc: California
Last seen: 1 year, 1 month
|
Re: Creating a big laminar flow hood! Help is much appreciated [Re: RogerRabbit]
#17405094 - 12/16/12 11:37 PM (11 years, 5 months ago) |
|
|
Quote:
RogerRabbit said: You won't get the same results from a plastic box in the dusty, moldy houses most of us live in. It doesn't take long at all for the prefilter on my flowhood to become dark brown with dust and dirt.
I wouldn't trade my flowhood for anything. I certainly wouldn't do agar work or grains without one. RR
I totally agree. There is no real practical way to do bulk grows without one, and as RR pointed out, agar work, grain work, etc is all at very high risk for contamination with out a flowhood.
I lucked out and picked one up from a college student second hand that is 6' long. It looked almost exactly like the one vladtepes posted above accept it was designed to blow down and into a glass box / work area. I flipped it sideways and it has been my mycological prized possession until recently when my dad found me a 12$ classic Osterizer with a cast aluminum collar at a thrift store.
The ONE feature my flowhood came with, which isn't necessary but is kinda neat if you use your flowhood for THE source of fresh clean air for a small lab as I do, is a rheostat type speed controller for the fan. Again, not sure exactly how much it helps, but you can adjust the speed way down for things like spore work etc.
Anyhow, good luck with your build, and as long as your sterile technique is killer, I think a HEPA will work just fine over an ULPA. My filter is now almost 4 years old in my possession, and this filter was not new when I obtained it. I still RARELY get contamination. And as RR said, within weeks to a couple months depending on the time of year here in Central California, my prefilter get so clogged with crap they are black.
I got so grossed out I duct taped some filters to our homes swamp cooler, much to the displeasure of my wife, and used them through most the summer. When I removed them this fall it was like a sandbox inside.
I use standard A/c filters you can buy at homedepot. I put a washable, then a ultra allergic. Works great.
Good luck! -T
|
|