Laser Exhaust Filtering Unit

[Christian Vallejo]

Hello everyone. I am a newbie, and I need some feedback on my idea for an exhaust/filtering unit. Commercial units are too expensive, and I believe I can make it Work by myself. I am also a designer, so I decided to give it a try.

The reason why I went with a round shape (tube) instead of a box is turbulence. (Maybe in this case turbulence is a good thing since it will create small vortexes allowing the fumes to stay longer in the chambers) I only have a 650CFM blower, so I need to make up for it in efficiency, so it has to be round. (I have no idea about airflow dynamics, all this is based upon observation).

Also I wanted acrylic in order to "see" if the unit was filtering properly or in a case of a fire.

In the design it is not shown, but I start with a simple filtering cloth (furnace filter - 3 layers) to catch big particles, then I carry on to three sets of active carbon filters in a row. I am using the plastic housing of an activated carbon filter used for household furnaces, but I am adding an extra 2 inches of activated carbon to them in a "sandwich". so I will have at the end of it all a 2 and a half inches of carbon per stage.

My train of thought is to be as efficient as possible and also remove as many twists and turns coming from the 6" venting hose.

All commercial options have one or even two 90° airflow turns, Maybe it is done to increase the filtration time, but quite frankly it looks inefficient.

Please remember that this unit will connect straight from the blower to the outside. The reason being is that I work in an office building and the smell from acrylic cutting will make me vacate the premises. So in order to have a roof over my head and my laser cutter whilst working, I am using this contraption.

Also I am attaching a picture of a previous idea to capture all the smell which also included a hood over the machine to catch any other fumes coming from the machine itself. I had a professional quote that idea but it was over $6.000. But that was a sure fire. It had a double filtration Carbon-Hepa with Hepa pre filtering, extraction blowers at each filtering station. It was overkill.

Please all comments on the current idea are more than welcomed any help will be highly appreciated.


Kind Regards.
Chris.

[Dan Hintz]

The carbon thickness looks good, and having three is good for surface area... the problem with the design is you're forcing your air to go through three layers of filtering, which will reduce your CFM significantly. You will be better off with a single layer of carbon and a much larger diameter tube (like double the diameter, or more). If you're already limited with extraction power, you're going to quickly kill it with such a design.

Take a look at my blog post for a different design that takes these problems into account.

[Christian Vallejo]

The carbon thickness looks good, and having three is good for surface area... the problem with the design is you're forcing your air to go through three layers of filtering, which will reduce your CFM significantly. You will be better off with a single layer of carbon and a much larger diameter tube (like double the diameter, or more). If you're already limited with extraction power, you're going to quickly kill it with such a design.

Take a look at my blog post for a different design that takes these problems into account.


Dear Dan:

Thank you very much for your reply. I based my design on your >$200 unit. Which I consider to be a simple yet elegant solution to this issue.

My main concern was airflow rate, so that is why I believe that a straight tube should work better than two 90° turns for the airflow. Most likely I am wrong on this, but it makes sense to me.

I agree that in theory the second and third chambers would have little flow, so how about adding another inlet with a 400 cfm blower that I have around.

Like so...


313186


By adding this secondary blower, I would be able to increase the flow rate, but also dilute in a contained area the smoke with fresh air. Without the hassle of having the flow turning and keeping everything as streamlined as possible, a decent flow rate could be achieved for the third chamber. I remember reading how the airflow increases if within the same current you add additional air. It is the same principle how they make the Airbus A380 massive inflatable slides. Compressed air alone wasn't able to inflate the slides fast enough, so they added addition air inlets to let the incoming fresh air work with the compressed air increasing the speed of inflation thus reducing critical inflating times during an emergency.

So my train of thought is that by adding an additional blower even at a lower speed the air flow could accelerate after hitting the wall from the first chamber. thus allowing to have a proper filtration and flow rate on the second and third chambers.

Remember that it is a straight exhaust and there are no other connections or tubes or hoses after this unit. Also the hose that connects the unit to the blower is only about a meter in length, this is required to give the unit a little 20 degree angle upwards. Again I am thinking on flow rate efficiency here.

Any ideas or comments would be highly appreciated. I need this to work, and I presume to be on the right track.

Thanks in advance for your time.

Warm Regards.

Chris.

[Dan Hintz]

I agree that in theory the second and third chambers would have little flow, so how about adding another inlet with a 400 cfm blower that I have around.

Combining multiple blowers never works the way people intend. In your case, the first chamber may have a stagnant flow as one blower competes with the other, and the remaining two chambers will have reduced flow.

[Christian Vallejo]

Dear Dan:

Thanks for your advice. I appreciate it. Have been testing and working with my original set up (without the second blower) and it works surprisingly good. I do see just a little hint of smoke out the filtering unit, but almost no smell. So I guess that for my application it worked perfectly!

I was very afraid about smoke and odors, but using the filter and venting outside works like a charm. I don't believe it works for an indoor use, and although I am cutting 0.3mm acrylic I am very afraid of poisonous gases so I would never use it in an enclosed area like other people.

Once again thanks for the advice. And Take care mate!