A Theoretical Question

[DaninVan]

This is only a concept at this point; just need some basic feedback, please.
i picked up a couple of very small duct style fans...
https://www.aliexpress.com/item/1005007 ... f19c1VIBkS
They arrived today and I'm pretty happy with them. they seem to move a fair amount of air and are pretty quiet.
OK, here's the question: one alone is rated at 38cu m/Hr (of air movement. If I gang them up in series, how will that effect efficiency?
By series and efficiency, mean butted up output of one to the input of the second one, in a tight straight line...no leakage.

[sunnybob]

By forcing more air into the second one than the motor is rated for, it will over run the motor. By not allowing free air to pass from the first one you will strain that motor. The turbulence between the two will be horrendous. You might possibly get more than 0ne rated air flow, but I dont see how you can match the two separate ratings, let alone increase the total.
P.S. I am not a scientist.

[DaninVan]

By forcing more air into the second one than the motor is rated for, it will over run the motor. By not allowing free air to pass from the first one you will strain that motor. The turbulence between the two will be horrendous. You might possibly get more than 0ne rated air flow, but I dont see how you can match the two separate ratings, let alone increase the total.
P.S. I am not a scientist.

Thanks, Bob; that's the sort of feedback I'm looking for. I sort of imagined the first one would act as a supercharger, ramming air into the second stage, but I see your point. They're small motors and I definitely don't want to damage them.
Another option might be to operate them in parallel(?).

[sunnybob]

Youre asking questions from the wrong end.
What are you trying to do with the fams?
When it come to circular tubes and air flow, the numbers get very weird very quickly.
I barely remember an apprentice examination question from 60 years ago where you needed a 4" pipe to convey the anount of volume you needed, but you could only fit 1" pipes through a wall So how many 1" pipes would you need to convey a 4" pipes worth?
the answer is NOT 4. I believe it was sixteen (allowing for frictional drag of the pipe walls as well).
tell us what you want to achieve, and we just might have the answer

[Cherryville Chuck]

I agree with Bob that you will not get 76 cu m3 by running the fans in series and you will probably overwork the lead fan due to back pressure. You could run two separate ducts which is the most efficient or into a plenum and one larger duct out of the plenum but you'll likely lose a little efficiency because of turbulence in the plenum unless it is very well designed with no corners or lips. Distance also factors in. On a long run you need to go to a larger duct to reduce resistance. I got a bit of an introduction into this in my power engineering courses.

Bob you are correct about pipe size too. Flow is proportional to the area of the pipe cross section. Since all the factors cancel out except for the differences in diameter/radius you can just compare the squares. A 2" pipe squared is 4 and a 4" is 16 so you'd need four 2" pipes to equal a 4".

[DaninVan]

At this point it's merely conceptual. For illustration purposes only, consider a 1cu. ft square box with an exhaust port (tight fit) around the outflow end of the fan. For arguments sake it's in the middle of any one side, near the bottom.
Now, lay a pleated type air filter over the top. That's it. Will it extract air reasonably efficiently? Say very fine dust generated almost on top of the filter (inches away).

[sunnybob]

Short answer = No.
Slightly longer answer = it will work a little, but nowhere near as well as want it to.
Mate, whatever kind of dust extraction you want, I can be sure someone will sell it to you all proven and ready to use. It might cost more than your two cardboard toilet rolls and a piece of sticky backed plastic though
Example;- My wife has a pyrography set. The burning wood smells and some woods can give off harmful fumes right under her nose and mouth. I was looking at making some kind of smoke hood and she spent 5 minutes online and found a custom made portable 6" square mains powered fan that not only sucks the fumes away, it has a carbon impregnated sponge to absorb them as well. Job done, move along the bus please.
Re inventing the wheel is never a rewarding job.

Chuck, my comment on the pipe sizes; It was low pressure gas in the pipes, so flow resistance had to be factored in. Every single fitting and per foot of pipe run had its own resistance / friction chart hence the much higher number of pipes in my example (although it might not have actually been 16

[Cherryville Chuck]

Chuck, my comment on the pipe sizes; It was low pressure gas in the pipes, so flow resistance had to be factored in. Every single fitting and per foot of pipe run had its own resistance / friction chart hence the much higher number of pipes in my example (although it might not have actually been 16

Resistance calculations can get quite complicated, with type of pipes, the way pipes join, flow/pressure sensors, pipe reductions, distance, etc factoring in. I gave the generalized basic answer which would be fairly accurate at the fan, pump, etc outflow point.

[Cherryville Chuck]

At this point it's merely conceptual. For illustration purposes only, consider a 1cu. ft square box with an exhaust port (tight fit) around the outflow end of the fan. For arguments sake it's in the middle of any one side, near the bottom.
Now, lay a pleated type air filter over the top. That's it. Will it extract air reasonably efficiently? Say very fine dust generated almost on top of the filter (inches away).

It has to do at least somewhat on the filtration capability of the filter medium plus the square area. As an example if the filter area was only equal to the size of the fan outflow and it had high filtration factor you would starve the fan for air, making it work harder. If the filter has a much larger surface area there is no issue. The fan will work a bit to move air.

I bought a cheap clamp meter (amp tester) from Princess Auto a few years ago on sale for $10. It's worth having and works well enough to answer questions like this one. You have to separate the power wire from the neutral to get a reading. Check its draw with no ducting so you have a base line value. For checking plug in tools I wired up an outlet box with two separate wires to a plug.

[sunnybob]

I have tried to find a very relevant video, but my online presence is very limited, so maybe you can. Its by Stumpy nubs woodworking and he actually put two extractors in sequence then parallel and was using a test meter to show the problems. But I saw this a couple of years ago now and his output is so large that I cant find it.

[DaninVan]

Thanks, guys; I've been over in Victoria for the past week...just got back today.
All good info, to be ruminated upon whilst trying to get to sleep tonight.
I think you answered my original question about connecting in series ((don't!)

[DaninVan]

It's no longer theory!

I went ahead and built the portable sanding table thingy; I still have some finish work to do and some refinements, but I plugged it in and tried it...no actual dust involved, but man, does it ever suck air through it. Once i do all the final bits I'll test the outflow with my digital anemometer and see what kind of airflow i actually get. Here's a few pics...

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[Biagio]

Nice idea Dan, and ‘workshop heirloom” construction.

You have given me an idea, I was going to build a sanding table connected to a shop vac. I bought some purpose-made punched metal plates for the top some time back, but have not had time to do anything with them.Your idea frees up the shop vac for connection to the sander itself.

I expect if you don’t get enough suction, you could add a second fan (I think you bought more than one) either on the same end but opposite, or at the other end, without worrying about series or parallel effects.
We don’t have furnaces in this part of the world, so furnace filters are rare and expensive. I will probably vent mine into a can of some sort. I cannot imagine that sanding dust (as opposed to wood chips) will damage the fan’s impeller.

[sunnybob]

Bear in mind the concentration of dust being sucked in and that filter will clog pretty darn quick. I would suggest a large bag filter attached to the outlet of the fan, or you will be cleaning that after each use. Sanding dust will stick to the blades over time. they will need scraping off every so often.

[Biagio]

Good points, Bob. I might rework the idea to have the fan outboard, sucking through my Oneida cyclone separator, and blowing out through a HEPA filter. Much smaller rig than another shopvac.

[Cherryville Chuck]

I seem to recall Herb making one of those a while back Dan and he improved dust capture by adding sides or at least partial sides and a back.

One type flow design is induced draft. This is done where you don't want the fan in the dirty/hot/corrosive/etc airstream. You use the fan to blow a stream of air past a port and that creates a vacuum at the port opening. It's obviously less efficient than a direct draft design. An example would be to take a Y fitting and blow air into one of the Ys and out the main stem. Air would be sucked into the other Y.

[DaninVan]

Bear in mind the concentration of dust being sucked in and that filter will clog pretty darn quick. I would suggest a large bag filter attached to the outlet of the fan, or you will be cleaning that after each use. Sanding dust will stick to the blades over time. they will need scraping off every so often.

Bob; it's only for a bit of light hand sanding. I plan on shop-vaccing the filter between uses. SWMBO Jr. won't invite me back if I mess up her dinnette area...

[DaninVan]

Nice idea Dan, and ‘workshop heirloom” construction.

You have given me an idea, I was going to build a sanding table connected to a shop vac. I bought some purpose-made punched metal plates for the top some time back, but have not had time to do anything with them.Your idea frees up the shop vac for connection to the sander itself.

I expect if you don’t get enough suction, you could add a second fan (I think you bought more than one) either on the same end but opposite, or at the other end, without worrying about series or parallel effects.
We don’t have furnaces in this part of the world, so furnace filters are rare and expensive. I will probably vent mine into a can of some sort. I cannot imagine that sanding dust (as opposed to wood chips) will damage the fan’s impeller.

Thanks! (I'm afraid to ask what "workshop heirloom" implies... you calling me a fossil?! )
On the second fan item, yes, I'd already considered that. You wouldn't believe how quiet this dust collector is; waaay quieter than something like a hair dryer. Maybe close to the heater in your car, at 1/2 power.
I'll report back in a week, after we've actually used it, over in Victoria

[DaninVan]

That whole thing, not including the top and bottom, from a doorskin, was made from a rough sawn 1"x6"x6' Western Red Cedar fenceboard that had been lying around in the woodshed for probably 10 yrs. After I ran it through the planer ( my new one with helical carbide cutter head... ) it looked like furniture quality material!

[Biagio]

“ Thanks! (I'm afraid to ask what "workshop heirloom" implies... you calling me a fossil?! )”

Nah Dan, I was referring to the cabinetmaker quality of an otherwise utilitarian workshop aide.

I bought three similar fans, but about 6” diameter, when I was thinking of a laminar-flow ventilation solution for my consulting room during the pandemic. They give a good blast of air from about two meters away, slightly louder than your model, but still fairly quiet (I detest noise).

We used to have conscription here many years ago. During my time as a military medical officer, I was posted to a sick bay for a large training camp, during colds and flu season. I found that by some peculiarity of building design, if I opened two windows on opposite walls, there was a howling blast of air across the room. I positioned myself upwind and the patients downwind, never even caught a sniffle in spite of coming into contact with dozens of sick kids daily. Those viruses were blown right to perdition.

[Stick486]

Nah Dan, I was referring to the cabinetmaker quality of an otherwise utilitarian workshop aide.

Nice bail...
But we know better...

[Cherryville Chuck]

“ Thanks! (I'm afraid to ask what "workshop heirloom" implies... you calling me a fossil?! )

We used to have conscription here many years ago. During my time as a military medical officer, I was posted to a sick bay for a large training camp, during colds and flu season. I found that by some peculiarity of building design, if I opened two windows on opposite walls, there was a howling blast of air across the room. I positioned myself upwind and the patients downwind, never even caught a sniffle in spite of coming into contact with dozens of sick kids daily. Those viruses were blown right to perdition.

Makes sense. I saw a chart about two years ago for how long particles can stay airborne. Viral particles of 0.2 microns could stay aloft for up to 19 days. I attribute that to the fact that at that size they are nearly massless. So even a slight movement of air should carry them along.

[Biagio]

Makes sense. I saw a chart about two years ago for how long particles can stay airborne. Viral particles of 0.2 microns could stay aloft for up to 19 days. I attribute that to the fact that at that size they are nearly massless. So even a slight movement of air should carry them along.

True, even those that settle on the ground or flat surfaces can be stirred up into the air again by very mild air currents. I did a course on airborne infection control some years ago. The same applies to Tuberculosis bacilli, even though they are substantially larger and heavier than viruses. The trick is to avoid swirls and vortices in the airflow, otherwise you are just distributing them around more efficiently.
Hence laminar flow AC. In specialised operating theatres, especially for orthopaedic procedures (infections inside bones are hell to deal with), a curtain of air is directed down from the ceiling through special louvres to shape the flow, then extracted around the floor-wall junction. Even possible to achieve in a tent-based operating theatre in the field - most military field theatres would have laminar flow nowadays.
But laminar flow is expensive. An alternative is to use UV lights of a specific wavelength and intensity to inactivate the bastards, but that has its own challenges. Peculiarly, if TB bugs are inactivated by UV, then blown out into the outdoors, exposure to sunlight re-activates them, in spite of the UV component in sunlight.

[Cherryville Chuck]

Makes sense. I saw a chart about two years ago for how long particles can stay airborne. Viral particles of 0.2 microns could stay aloft for up to 19 days. I attribute that to the fact that at that size they are nearly massless. So even a slight movement of air should carry them along.

True, even those that settle on the ground or flat surfaces can be stirred up into the air again by very mild air currents. I did a course on airborne infection control some years ago. The same applies to Tuberculosis bacilli, even though they are substantially larger and heavier than viruses. The trick is to avoid swirls and vortices in the airflow, otherwise you are just distributing them around more efficiently.
Hence laminar flow AC. In specialised operating theatres, especially for orthopaedic procedures (infections inside bones are hell to deal with), a curtain of air is directed down from the ceiling through special louvres to shape the flow, then extracted around the floor-wall junction. Even possible to achieve in a tent-based operating theatre in the field - most military field theatres would have laminar flow nowadays.
But laminar flow is expensive. An alternative is to use UV lights of a specific wavelength and intensity to inactivate the bastards, but that has its own challenges. Peculiarly, if TB bugs are inactivated by UV, then blown out into the outdoors, exposure to sunlight re-activates them, in spite of the UV component in sunlight.

If you watch flowing water hit a rock you see the water curl around and flow towards the back of the rock like you say. So you'd want enough separation between you and your patient that the airflow would merge again. That was interesting about operating room airflow. Strange how a TB bug can be reactivated in sunlight. Most bugs don't survive well in oxygen and sunlight. During my logging career if I was sick but well enough to go to work I did because I seemed to get well quicker in the fresh air and sunlight than if I stayed home.

[DaninVan]

Makes sense. I saw a chart about two years ago for how long particles can stay airborne. Viral particles of 0.2 microns could stay aloft for up to 19 days. I attribute that to the fact that at that size they are nearly massless. So even a slight movement of air should carry them along.

True, even those that settle on the ground or flat surfaces can be stirred up into the air again by very mild air currents. I did a course on airborne infection control some years ago. The same applies to Tuberculosis bacilli, even though they are substantially larger and heavier than viruses. The trick is to avoid swirls and vortices in the airflow, otherwise you are just distributing them around more efficiently.
Hence laminar flow AC. In specialised operating theatres, especially for orthopaedic procedures (infections inside bones are hell to deal with), a curtain of air is directed down from the ceiling through special louvres to shape the flow, then extracted around the floor-wall junction. Even possible to achieve in a tent-based operating theatre in the field - most military field theatres would have laminar flow nowadays.
But laminar flow is expensive. An alternative is to use UV lights of a specific wavelength and intensity to inactivate the bastards, but that has its own challenges. Peculiarly, if TB bugs are inactivated by UV, then blown out into the outdoors, exposure to sunlight re-activates them, in spite of the UV component in sunlight.

If you watch flowing water hit a rock you see the water curl around and flow towards the back of the rock like you say. So you'd want enough separation between you and your patient that the airflow would merge again. That was interesting about operating room airflow. Strange how a TB bug can be reactivated in sunlight. Most bugs don't survive well in oxygen and sunlight. During my logging career if I was sick but well enough to go to work I did because I seemed to get well quicker in the fresh air and sunlight than if I stayed home.

Also, you got paid...

[DaninVan]

“ Thanks! (I'm afraid to ask what "workshop heirloom" implies... you calling me a fossil?! )”

Nah Dan, I was referring to the cabinetmaker quality of an otherwise utilitarian workshop aide.

I bought three similar fans, but about 6” diameter, when I was thinking of a laminar-flow ventilation solution for my consulting room during the pandemic. They give a good blast of air from about two meters away, slightly louder than your model, but still fairly quiet (I detest noise).

We used to have conscription here many years ago. During my time as a military medical officer, I was posted to a sick bay for a large training camp, during colds and flu season. I found that by some peculiarity of building design, if I opened two windows on opposite walls, there was a howling blast of air across the room. I positioned myself upwind and the patients downwind, never even caught a sniffle in spite of coming into contact with dozens of sick kids daily. Those viruses were blown right to perdition.

You're too kind, Sir!

[DaninVan]

Back home today. The 10 yr.old is right into the model making, his 7 yr. old brother, maybe not quite there yet.
I lectured the guys on Xacto knife safety... a bandaid was required anyway...for me!
We haven't finished planking the hulls yet; waiting for glue to dry is a p.i.t.a.

[Cherryville Chuck]

Back home today. The 10 yr.old is right into the model making, his 7 yr. old brother, maybe not quite there yet.
I lectured the guys on Xacto knife safety... a bandaid was required anyway...for me!
We haven't finished planking the hulls yet; waiting for glue to dry is a p.i.t.a.

1 Minute epoxy.

[Stick486]

1 Minute epoxy.

.
Flash the WeldBond...

[DaninVan]

Heh...like my tree hugging daughter & Sil would allow their kids anywhere near solvent based glue!
What's this 'flashing' you speak of? ( We're obviously not talking about dirty old men in raincoats...)

[Stick486]

What's this 'flashing' you speak of?

Apply WB to the mating surfaces..
Pinch together for a few seconds make the application uniform..
Pull apart...
Wait 10~15 seconds..
Put the pieces back together ...
hold in place for 30 seconds or so...
Move on to the next piece..
Clamps usually not required unless you need to bend the piece to shape...
And your time lengths may vary... Experiment..

https://www.weldbond.com/faq

[DaninVan]

Clamps usually not required unless you need to bend the piece to shape...

And that's the problem exactly. The hull planking (each piece, one at a time) has to be pulled into contact with the ribs/bulkheads. It's kind of fussy and time consuming.
Here's how a pro does it...

That solid bow section in the video makes planking the bow waaay easier. The kits we were building required the planks to be glued to the keel, as it rises upwards to the deck.

[DaninVan]

What's this 'flashing' you speak of?

Apply WB to the mating surfaces..
Pinch together for a few seconds make the application uniform..
Pull apart...
Wait 10~15 seconds..
Put the pieces back together ...
hold in place for 30 seconds or so...
Move on to the next piece..
Clamps usually not required unless you need to bend the piece to shape...
And your time lengths may vary... Experiment..

https://www.weldbond.com/faq

I didn't mention that that's how I do a lot of Weld Bond gluing. It's excellent stuff! But as you mentioned, if you need to pull it down to contact, clamping is essential. That initial tack just can't sustain a constant pull-away tension; it'll let go as soon as you turn your back (if it's not clamped)... ;(

[DaninVan]

You guys (South of 49) better stock up on WeldBond; it's made in Canada; could get expensive soon... ;(

[DaninVan]

Whoa!...
!59K views? Seriously?

[DaninVan]

Whoa!...
!59K views? Seriously?

It's gone up another 3K since yesterday; hopefully WoW is getting money from the hits...
Maybe it's time to take a run at OnlyFans?

[Cherryville Chuck]

Whoa!...
!59K views? Seriously?

It's gone up another 3K since yesterday; hopefully WoW is getting money from the hits...
Maybe it's time to take a run at OnlyFans?

I noticed on the last round of posts how high the count was and wondered how that could happen.

[DaninVan]

Whoa!...
!59K views? Seriously?

It's gone up another 3K since yesterday; hopefully WoW is getting money from the hits...
Maybe it's time to take a run at OnlyFans?

I noticed on the last round of posts how high the count was and wondered how that could happen.

Heh...if the guys that make those fans get a small fraction of that count as actual orders they're gonna be wondering WTF just happened!