[WaterFarmFan]

Originally Posted by WHIPEDMEAT

check out the patents you can find something useful

https://patents.google.com/?q=fume+hood&oq=fume+hood

Nice. Lots of red meat to chew on.

[WaterFarmFan]

Originally Posted by Gray Wolf

A schematic of how I built our's is attached. The front door was plexiglass framed in 3/4 plywood.

The air is exhausted through a rear plenum, with a slot at the bottom and top, and some intermediate ones.

Exhaust slot velocity is 1000 surface feet.

Makeup comes in the side and is distributed via a bottom air knife. That sweeps the heavier than air vapors into the lower slot and the upper ones pick up any lighter than air or mixed air.

Most helpful. Do you have a photo of the completed box and air knife portion? Is it basically a large lip in front?

Originally Posted by Gray Wolf

Carbon filters are for smell and won't last long in an active exhaust hood. Better a tall stack with a injector cap to mix the exhaust thoroughly.

Check out Industrial Ventilation, A Manual of Recommended Practice, for design criteria, cfm and velocities.

Will check that out. I have to be as stealthy as possible, so a tall stack is probably out. I was thinking about creating a ducting system with two paths right off the hood using wye branches. I would only use carbon for the most hazardous solvents and sensitive times of the day, with the damper open for the rest. Something like this maybe:



This seemed to have some good info about filters - https://www.labconco.com/articles/co...-ductless-hood

[WaterFarmFan]

Originally Posted by G.O. Joe

It would make sense to simply put a table in a 4x4 tent with the fan intake along a top rail and vented out, and fresh air coming in from the opposite bottom. Or you could put the carbon filter on your face.

I am picking up some used restaurant stainless prep tables and trying make a more proper lab environment. What are your thoughts on solvent retention by active carbon with say ether or pentane? Do these solvents revert to liquid within carbon pores? Will the solvent naturally try to escape from the carbon?

While the micro-pores are crucial to solvent retention and hence, compliance with the prescribed VOC emission limits, the access pores in the macro- and meso-pore range facilitate desorption of the solvents from the activated carbon.

The activated carbon is charged in fixed-bed adsorbers and should offer as low a flow resistance as possible. This is the reason why 4mm extruded carbon pellets are the adsorbents of choice for this application. Depending on the type of solvent to be removed, activated carbon grades of different raw material origins or low-ash carbon grades are employed to give the best treatment result.

https://www.donau-carbon-us.com/Prod...lruckgewinnung

It is not that I want to prevent all vapors from escaping, but more that I want to limit large releases. It would be great if the solvents naturally purged themselves over time from the carbon.

[WaterFarmFan]

Originally Posted by Gray Wolf

Industrial Ventilation recommends 100 to 200 surface feet capture velocity, and 1000 cfm slot velocity.

I see how to calculate the face velocity, but how is the slot velocity calculated? My friend can have metal laser cut in any pattern via CAD, and I planned to just copy the slotting pattern found in some of the $$,$$$ models.

[WaterFarmFan]

Originally Posted by SkyHighLer

The fan doesn't need to be explosion proof to be effective, the rating only means in case of an external explosion the fan motor is protected from the flames reaching the windings, and hopefully it will continue to function.

Attic gable mount exhaust fans are an inexpensive high CFM choice.

Do you think the Hyperfan that I listed would be an acceptable option for this application with the solvents that I listed above?

[Gray Wolf]

Originally Posted by SkyHighLer

The fan doesn't need to be explosion proof to be effective, the rating only means in case of an external explosion the fan motor is protected from the flames reaching the windings, and hopefully it will continue to function.Attic gable mount exhaust fans are an inexpensive high CFM choice.

Ummmm, you are at times pulling fumes within the LEL of the solvent. If the motor is in the air stream, it needs to be enclosed or sparkless.

It's isn't about the flames reaching the windings, it is about the slip ring sparks igniting the fumes.

[Gray Wolf]

Originally Posted by WaterFarmFan

I see how to calculate the face velocity, but how is the slot velocity calculated? My friend can have metal laser cut in any pattern via CAD, and I planned to just copy the slotting pattern found in some of the $$,$$$ models.

If you wish to design exhaust systems, I highly recommend picking up a used copy of Industrial Ventilation, a manual of recommended practices, by the American Conference of Governmental Hygienists. I still use a 17th edition, which still works.

It is the standard for the industry and the bible that we used in aerospace to design ventilation and exhaust systems precisely by the numbers.

If you have to move 900 cfm from a 3' wide exhaust plenum, and you want the velocity at 1000 surface feet,

Since the air stream is moving at 1000 surface feet and you have to move 900 cfm, you need .9 square feet of slot.

900cfm/1000sf = .9 square feet of slot opening.

.9cu/ft/3' slot length = .3 feet slot width

.3' X 12 = 3.6" wide

3.6"/ number of slots = individual slot width

[Gray Wolf]

Originally Posted by WaterFarmFan

Do you think the Hyperfan that I listed would be an acceptable option for this application with the solvents that I listed above?

What are the specifications for the Hyperfan? You want your fan to have adequate cfm, at the static pressure that you are operating with. For our application it will take a centrifugal fan.

Here is a link with some of the design criteria and formulas:

https://www.captiveaire.com/manuals/...airsystems.htm

[Gray Wolf]

Originally Posted by WaterFarmFan

Most helpful. Do you have a photo of the completed box and air knife portion? Is it basically a large lip in front?

You can't get a good view of the air knife, but here is a view of the open cabinet showing the back of the knife and the plenum face with one slot at the bottom and one near the top. Air inlet is out the side of the building.

[Gray Wolf]

Originally Posted by WaterFarmFan

Will check that out. I have to be as stealthy as possible, so a tall stack is probably out. I was thinking about creating a ducting system with two paths right off the hood using wye branches. I would only use carbon for the most hazardous solvents and sensitive times of the day, with the damper open for the rest. Something like this maybe:

In addition to a tall stack with an evase discharge to mix the air, you can also add odor. A ghetto scrubber for grows, used to be a box full of toilet bowl crystals for the air to blow through.