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Author: Subject: fume hood design
thorazine
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I was wondering if was a good ideia use parquet on the floor of the fumewood! It's chemical resistant and cheap..
entropy51
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 Quote: Originally posted by thorazine I was wondering if was a good ideia use parquet on the floor of the fumewood! It's chemical resistant and cheap..
I use ceramic floor tiles. After over 10 years use they are just like new, but as S.C. Wack suggests, I don't pour chemicals on them. I try to always pour chemicals over a metal or plastic tray that will contain a spill.
bob800
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Also, what type of ducting should I use? Is ordinary galvanized steel ducting OK? Also, how necessary is it to place the motor at the end of the duct if it's separated from the air flow?

[Edited on 31-7-2010 by bob800]
watson.fawkes
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 Quote: Originally posted by bob800 Also, how necessary is it to place the motor at the end of the duct if it's separated from the air flow?
Ducting is rarely perfectly airtight without using the proper duct mastic. Before the fan, duct generally has negative &Delta;P with respect to ambient; after it, positive. Be careful about that leakage flow after the fan.
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What about glass over hardwood for the "floor"? What is generally used in commercial fume hoods? In the fume hoods at my school they seem to be some sort of very dense painted (black) wood. What is this material? The sinks are made of the same material, by the way.

"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think, free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
bob800
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The fan I'm considering supplies this chart:

CFM @ 0.000-In. SP 463
CFM @ 0.100-In. SP 425
CFM @ 0.200-In. SP 388
CFM @ 0.300-In. SP 338
CFM @ 0.400-In. SP 250
CFM @ 0.500-In. SP 161
CFM @ 0.600-In. SP 50

Is this drop acceptable for a fume hood blower? How much resistance does an average duct have? I measured my hypothetical duct to be roughly 45" inches total, which includes 1 turn. The blower is a Dayton 1TDR9, here the Grainger link: <a href="http://www.grainger.com/Grainger/wwg/search.shtml?searchQuery=dayton+blower+1TDR9&op=search&Ntt=dayton+blower+1TDR9&N=0&sst=subs et">http://www.grainger.com/Grainger/wwg/search.shtml?searchQuery=dayton+blower+1TDR9&op=search&Ntt=dayton+blower+1TDR9&N=0&sst=sub set </a>

[Edited on 2-8-2010 by bob800]
peach
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You could line the duct with plastic to improve it's chemical resistance and sealing.

For the surface, I'd cover it with a sheet of toughened glass. Alternatively, buy an old, shallow, wide Belfast sink. I don't know if they're called that in the US. The big, heavy, white ceramic ones you'll often see farms being retired to water or feed troughs. You might call them Shaker sinks in the US, I'm not sure.

They're glazed ceramic, needless to say, and very heavy duty. They also come with a premoulded 'trough' shape and a plug hole which is excellent, because it means any spills will slosh up the sides and back down, then down the plug, which can be connected to a bin of some sorts. Also, if a fire breaks out, it's not going to spill out of the sharp corners or melt through seams at those corners.

Additionally, the glaze is a continuous surface, there are zero joins. Which means there's nowhere for things to seep or rot through. It's also mirror smooth, making it hard for spills to stick.

All you'd have to do then is build up the walls. 1" thick play would be very stable. You could then add a lining of plasterboard, which has a 30 minute fire rating for a half inch sheet. Then tile over that and you'll have a nearly 100% ceramic lined hood. Silicon up the seams with high temperature silicon.

To save effort and time, get the timber yard to chop the 1" ply to size on their wall saw, for a few dollars; measure three times, carefully first. The plasterboard can be glued to the ply. You can cut it to size by scoring it along a a straight edge (bit of timber) and then snapping it, works perfectly and is 'the plaster's preferred method'. The sizes here don't need to be mm perfect, you can have 1/4"+ gaps around the edges and be okay. Buy some cheapo tile adhesive and some dirty cheap white, flat bathroom tiles, stick them on. Grout. Bingo...

Commercial hoods tend to use high density plastics or stainless. But the ceramic will fare better still; for example, the corrosive gases and acids will rot the finish of stainless. Normal stainless also has a 'grain' to the surface, allowing things to get trapped in those. The chemical resistance, safety properties and complexity, depend how handy you are with your handies, as always.

[EDIT] CAN WE PLEASE MERGE AND STICKY THE FUME HOOD QUESTIONS? YOU GUYS WILL NAIL REPEAT QUESTIONS IN THE ASS, LET ALONE THOSE COMING FROM NEW THREADS, AND YET THIS ONE IS HERE ALL THE TIME. IT'S DILUTING THE INFORMATION AND CLOGGING THE FORUM. STICKY IT. I'D ALSO RECOMMEND A STICKY FOR VACUUM AND HOTPLATE QUESTIONS. [/all caps]

[Edited on 2-8-2010 by peach]

watson.fawkes
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 Quote: Originally posted by bob800 How much resistance does an average duct have? I measured my hypothetical duct to be roughly 45" inches total, with 1 turn.
Search for "duct loss" to find many resources, such as this nomogram. Such a short run of duct, though, has minimal loss. Much more important is going to be how your intake air is supplied. If your hood is in a relatively-sealed room with closed door, you'll have difficulty sucking in air, and total system resistance will be high. If you provide an explicit inlet to the room for makeup air, you'll have little problem. Often makeup air is supplied as an air curtain in front of the hood. There's no need for a small system to have the makeup air supply be powered.
bob800
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Thanks for all the help. I found a bunch more fume hood threads which answered my remaining questions (I didn't see the 'subject only' button in search. Duh! 5 billion more threads).

However, I still have a remaining question: How much space does a 24/40 ground glass distillation setup take? I don't have one (I currently use a retort for corrosives) but may buy one eventually.

 Quote: Originally posted by peach [EDIT] CAN WE PLEASE MERGE AND STICKY THE FUME HOOD QUESTIONS?

Here, I made a url for every single fume hood thread (don't know how to make a sticky thread, so someone else can copy/paste this into it):

[EDIT] Make sure you have each link on only 1 line. A few links don't fit and won't work unless you delete the spaces in the middle

 Code:  [url=http://www.sciencemadness.org/talk/viewthread.php?tid=14233&goto=search&pid=183724]fume hood design[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=14158&goto=search&pid=182505]fume hood Vs. Range hood[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=13308&goto=search&pid=170307]Questions about fume hoods and Filtering Exhaust[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=13246&goto=search&pid=169350]Some fumehood trivia[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=13238&goto=search&pid=169251]Using a chimney as an exhaust route for fumehood[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=13052&goto=search&pid=166104]DIY fume hood - how many air exchanges per minute?[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=12400&goto=search&pid=155515]idea for slight improvement of fume hood[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=11841&goto=search&pid=147485]How to Make a fume hood[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=11755&goto=search&pid=145803]fan selection for homemade fumehood - help[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=11754&goto=search&pid=145799]what can i coat the inside of my homemade fumehood with?[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=11145&goto=search&pid=135726]homebuilt fume hood[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=10425&goto=search&pid=124994]motor for fumehood[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=9058&goto=search&pid=104431]Installation of fume hood[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=8949&goto=search&pid=102993]DIY fume hood air flow design optimization[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=7253&goto=search&pid=82753]fume hood Construction[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=5260&goto=search&pid=59587]Hows this for a fume hood?[/url] [url=http://www.sciencemadness.org/talk/viewthread.php?tid=3903&goto=search&pid=43862]fume hood safety[/url] 

Hope this helps.

[Edited on 3-8-2010 by bob800]
peach
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 Quote: Originally posted by bob800 However, I still have a remaining question: How much space does a 24/40 ground glass distillation setup take? I don't have one (I currently use a retort for corrosives) but may buy one eventually.

I worked it roughly out in my head but thought the numbers were off, so I quickly set my B24/29 to check. And was much pleased to discover I was within a few cm of the rough value. It's about 70cm tall if you're using a hotplate, 1l RBF, three way head, thermometer adapter and thermometer.

I'm using the shortest length coil condenser Quickfit do, which is something like 26cm in length from memory. The longer version is only slightly longer and the short one condenses all the solvents I've put through it within the first turn or two of the coil.

In total, its about 70cm wide again.

Of special note is that it will actually get wider if you use smaller flasks, who's addition funnels usually stick out the side at an angle as opposed to going in straight up (as they do for 1l and up flasks).

The height will go up by around 36cm if you add a standard length Vigreux column.

You'll need an extra 10cm to clear tapers as you put it together, exchange things, take it apart...

And a decent amount of room on either side of the glass for adding hoses. In particular, vacuum hose is extremely thick and has quite a large bend radius, so you'd want to make sure the vacuum enters the hood on the same side as you like having your receiver. I always have it set up left to right. Not sure, but I expect 'the lefties' may do it the other way round (unless forced not to in school due to the layout of the services on the fume hood).

Good work on the link collecting. Now we need A MODERATOR to merge them and sticky.

[Edited on 3-8-2010 by peach]

bob800
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Thanks for measuring your setup. OK, I've figured out almost everything, however I need some feedback:

1. Dimensions: You said your setup is 70 x 70 cm, so I'll make my hood 2.5 x 2.5 feet (76 cm). If I'm correct, 2.5 feet * 2.5 feet * 60 = 375 cfm, which is in range of my blower. I don't understand why the depth of the hood isn't taken into the calculations? Should it be? PLEASE CORRECT ME IF I'M WRONG

2. Blower. I think I'm getting the Dayton 1TDT2. It's $164 straight from grainger, but I found a few$99 new on eBay. It's 549 cfm at 0.00 In. SP. Here's the full chart:

CFM @ 0.000-In. SP 549
CFM @ 0.100-In. SP 538
CFM @ 0.200-In. SP 510
CFM @ 0.300-In. SP 500
CFM @ 0.400-In. SP 480
CFM @ 0.500-In. SP 450
CFM @ 0.600-In. SP 435
CFM @ 0.700-In. SP 390
CFM @ 0.800-In. SP 360
.

Is this OK if I only have 45" inches of ducting including 1 turn as long as I make sure air can get into the sash?

3. Lining-Material- Does epoxy paint\spray paint stick to wood? If so, that's what I'm going to use, maybe ceramic tiles if it's not resistant enough.

4. Sash- I know it's not perfect, but I don't know what else to use other than regular glass with a sheet of polycarbonate glued to it. I'm not going to be mixing up nitroglycerin or anytingin my hood, so I'm not too worried about explosions. I'll use the bolt idea stolen from some other members of science madness to provide a few fixed settings.

5. Baffles- I don't think I'll install baffles unless my hood doesn't work properly. Do you think they're necessary?

6. Ducting- PVC seems too hard to work with, and I can't find anything wrong with plain galvanized steel ducts as long as I don't boil HCl for hours on end.

entropy51
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 Quote: Originally posted by bob800 Thanks for measuring your setup. OK, I've figured out almost everything, however I need some feedback: 1. Dimensions: You said your setup is 70 x 70 cm, so I'll make my hood 2.5 x 2.5 feet (76 cm). If I'm correct, 2.5 feet * 2.5 feet * 60 = 375 cfm, which is in range of my blower. I don't understand why the depth of the hood isn't taken into the calculations? Should it be? PLEASE CORRECT ME IF I'M WRONG
You're wrong.

The equation is Face Velocity x flow area = CFM . 60 is the conversion for minutes to seconds. If you wanted 75 ft/min face velocity then the required CFM = 75 x 2.5 x 2.5 = 469 cubic ft per minute. If you mostly operate with the sash half closed, then the flow area and the CFM is also cut in half for the same face velocity and so you need about 235 CFM.

But you will need to use the charts that are discussed above to find the static pressure drop in your duct to find the actual CFM the blower will pull when attached to your setup.
bob800
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If I read correctly the nomogram for 5" and 600 cfm shows 8 INCHES FRICTION!!!. That's way too much... Could I adapt the pipe to say 8" and read the chart from there? Or would the adapter still add a lot of friction? Or is the motor wheel just not physically big enough?

[Edited on 3-8-2010 by bob800]

[Edited on 3-8-2010 by bob800]
peach
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Entropy is correct, it's the area you need to consider when working out the flow velocity.

What's wrong with using PVC? There's a ton of it at the hardware store, you can cut it with a hacksaw and the fittings simply push together to provide a seal. The seal also can't fall apart, as the washers point inwards, like wipers, which prevents the pipe from sliding back out. In fact, it's physically impossible to pull them apart without releasing the collet. That's a lie, I did manage to pull a connection apart at one point, using the bucket of an excavator that was being driven by ten HP+ of hydraulic pumping; I did so intentionally before anyone jokes about it

110mm foul drain pipe isn't very expensive, it has a large ID, it's very smooth and fairly resistant. If you use 110mm, taper the edges of the cuts with a file and lubricate them up with something slippery; washing up liquid, KY, Molykote, Krytox, vacuum grease, Teflon grease, Vasoline, anal lube....

The lubricant won't make them fall apart, but they will slide together a lot quicker. Awwwww....

If you're concerned about safety, use toughened glass. If you call around the custom glass places, they'll have it. Bathroom suppliers or people involved with things like glazing for schools are good bets. The bathroom places will use it to produce things like panes for showers, or curve it to make walk in showers. You can even buy the toughened panes as components for showers from numerous places. But you'll probably need someone with a diamond saw to cut it, as the scratch and snap method is unlikely to work.

If you use a sheet of polycarbonate, that's fairly expensive to start with. Not as expensive as the toughened glass is likely to be, but on the way. Then add on the complexity of making a dual layer screen and the potentially shit performance it may give; e.g. bubbles between the layers, delamination, build time, etc. And you're on the way to the toughened glass being a time, money & effort saver. Delamination is a good probability if it's being exposed to odd, concentrated solvents, acids, bases and other reactive thingymejiggies.

If you choose the polycarbonate way, you'd probably want the plastic on the outside, as the glass will be more resistant. Whereas the plastic may fog up when exposed to certain things.

If you're doing things involving highly corrosive or toxic gases, the fume hood should be there only to mop up the escapees, not the bulk of it. Using greased tapers, keck clips and wash bottles will take care of 99%+ of the fumes. I can easily generate large quantities of HCl(g) and not even be able to smell it with my nose against the glass.

Fume hoods encourage lazy and dangerous attitudes towards letting things escape and hoping they'll be picked up and absorbed or blown off. Get rid of the risk as it leaves the glass.

It's akin to HazMat suits. The only time you should need one of them is when you're cleaning up someone else's mess or an accident, not for everyday work (unless you work in a nuclear power station, germ warfare or nerve agent factory, and even then, it shouldn't be in the atmosphere in the first place).

[Edited on 3-8-2010 by peach]

entropy51
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The face velocity you need depends on the toxicity of the material you are working with. Unless you plan to work with HCN or phosgene you may need less face velocity during most of the operations you conduct in the hood. The required face velocity also depends on the amount of toxic or stinky stuff you plan to release into the hood. If you plan mostly small scale experiments you can also get by with a lower face velocity.

My hood has a very low face velocity with the doors ("sash") open. But I keep the doors closed during most of a reaction or distillation and the face velocity is much higher during those conditions. It apparently works because I am here to talk about it in spite of having done some risky work in that hood.

I would recommend that you stick close to the design space (CFM, duct dimensions, face area) that Magpie has used in his hood because he is a chemical engineer and he uses his hood quite a bit.

I'll say it once more: keep the vapors and fumes confined in the glassware and scrub the effluent stream leaving the glassware. It's not a good idea to boil HCl or evaporate ether in open vessels in a home-made hood.

If you don't conduct high hazard operations in your hood, I suspect the blower you mentioned last is not an unreasonable choice. If need be you can adapt the scale of your reactions to the performance of the hood.

Magpie may have had similar experiences as I did: when I took organic there was one hood in the entire lab with 30 students. We poured the Br2 into our addition funnel in the hood and then took it back to the bench (with a stopper) and attached it to the flask and conducted the bromination. It was unpleasant, but no one died. Moderately good ventilation is better than none at all!

[Edited on 3-8-2010 by entropy51]
peach
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 Quote: Originally posted by entropy51 It apparently works because I am here to talk about it in spite of having done some risky work in that hood.

Not sure about that, I dread to think what's lurking in my balls to surprise me later in life. I should probably make better use of them now before they go supernova, then shrivel up and need chopping off.

If I were working with anything you mentioned, I'd have gotten rid of it before it ever left the glass. E.g. base washes, solvent scrubbers and so on... back to the wash heads, my best friends in the ethereal glassware domain.

This is like I was saying, I think students need teaching that kind of thing first. Letting them get straight to the fume hood encourages the 'I'll just run this lethal stuff in a beaker' mentality. Like the engineers who can CAD model a bridge but have never picked up a hammer.

watson.fawkes
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 Quote: Originally posted by bob800 If I read correctly the nomogram for 5" and 600 cfm shows 8 INCHES FRICTION!!!. That's way too much... Could I adapt the pipe to say 8" and read the chart from there? Or would the adapter still add a lot of friction? Or is the motor wheel just not physically big enough?
That's 8" water loss per 100' of duct. If you have 50' of duct, that's only 4" of loss.
bob800
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 Quote: Originally posted by entropy51 I would recommend that you stick close to the design space (CFM, duct dimensions, face area) that Magpie has used in his hood because he is a chemical engineer and he uses his hood quite a bit.

I agree except that Magpie's hood is much bigger than I need (and the motor is too expensive for me-$400 new). All I need is to be able to barely fit a distil. setup. BTW, do you know of any websites to get surplus blowers? eBay doesn't have a great selection... [Edited on 3-8-2010 by bob800] [Edited on 3-8-2010 by bob800] bob800 Hazard to Others Posts: 240 Registered: 28-7-2010 Member Is Offline Mood: No Mood  Quote: Originally posted by watson.fawkes That's 8" water loss per 100' of duct. If you have 50' of duct, that's only 4" of loss. Oh..... Why didn't I see that? That changes everything... entropy51 Gone, but not forgotten Posts: 1612 Registered: 30-5-2009 Member Is Offline Mood: Fissile  Quote: Originally posted by bob800 I agree except that Magpie's hood is much bigger than I need (and the motor is too expensive for me-$400 new). All I need is to be able to barely fit a distil. setup.
I think that blower may work for you. Just try to keep your ducts as short as possible and avoid bends. There is a certain amount of trial and error involved in any engineering project. And as you've learned, financial considerations involve compromises in performance. Your first trial at a project like this won't be perfect, but the perfect is the enemy of the good enough. I was taught to design to as many significant digits as possible, but that the final delicate adjustment usually involves a ball-peen hammer and a crowbar.
bob800
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So if my duct is around 45 INCHES long, at 5" diameter at 549 cfm, then I'd only have ~ 0.3 inches of S.P.! Then my blower would be PLENTY strong enough! Am I correct?
bob800
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 Quote: Originally posted by peach What's wrong with using PVC? There's a ton of it at the hardware store, you can cut it with a hacksaw and the fittings simply push together to provide a seal

True. But what's wrong with ordinary galvanized steel ducts?
watson.fawkes
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 Quote: Originally posted by bob800 So if my duct is around 45 INCHES long, at 5" diameter at 549 cfm, then I'd only have ~ 0.3 inches of S.P.! Then my blower would be PLENTY strong enough! Am I correct?
It's true if that's 45 inches of straight duct without bends. Bends add to static pressure drop.
entropy51
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You will also have static pressure drops in the adapters you need to connect your hood to the blower and your blower to your exhaust duct. The blower outlet is square and your duct is probably circular. These losses will likely exceed that of the friction loss in the exhaust duct. But I still think you are in the ball park on the blower.

A smooth steel duct will be fine if you don't let a lot of corrosive fumes enter it. If you do let corrosives into it, the blower will also not last long.
bob800
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Quote: Originally posted by watson.fawkes
 Quote: Originally posted by bob800 So if my duct is around 45 INCHES long, at 5" diameter at 549 cfm, then I'd only have ~ 0.3 inches of S.P.! Then my blower would be PLENTY strong enough! Am I correct?
It's true if that's 45 inches of straight duct without bends. Bends add to static pressure drop.

There would be 1 bend which I included in the 45". I found another graph on engineeringtoolbox for duct bends (haven't read it yet): http://www.engineeringtoolbox.com/air-duct-minor-loss-diagra...

[EDIT] @entropy51: Yes, the outlet is square. There's a window directly above my work-area that I'm going to take out and replace with a metal "window" with a hole cut. I think I'm going to mount the blower directly into the metal sheet so I don't need a bunch of custom-made adapters.

[Edited on 4-8-2010 by bob800]

[Edited on 4-8-2010 by bob800]
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