Mechanical engineer here. Sorry if i'm late, but i think this is very interesting.The forward facing blades are often used in industrial practice, just slightly different: short blades to reduce friction and in higher number. The low efficiency figure you got was absolutely due to the massive friction the air was producing on the blades. Side note: straight blades are used for dirty air flow (less change of blockage) and backward curved blades are used when higher pressure is needed more than high flow. You actually got the very same results that i got when I did the very same work but with a CDF simulation program, i'm so happy about this.
Those biscuit joints was extremely clever. I have spent long hours in a woodshop starting early in age. I built and sold a lot of stuff. Wish i new what i know now after watching your videos! You are an awesome person. I need to get my butt back in my own woodshop
Thanks for paying attention in physics, trigonometry, English, etc. Your videos are both informative and interesting. You have that uncanny knack of being able to take a potentially arcane subject and make it enjoyable for scholars and laymen alike. I also enjoy your Canadian accent and cadence. Keep it up young man!
The way you drew your radius for your housing is ingenious and really all your compass work has taught me how versatile of a tool it can be, also i have never seen a motor reversed like that. I really like your accesible approach and breakdown of your projects and very clear and thorough explanation of what you are doing. I dont know how you learned to do all these things the way you do but it is knowledge i am grateful that you are sharing with us (me).
I really enjoyed your video! 0:11 I love how you made your own large adjustable compass out of wood. 0:27 And you guide the sawing of the curved vanes freehand so quickly and accurately. 3:25 And what a great idea for joining the pieces by cutting slots and gluing in little bits of wood. Lots of good ideas and techniques in this video.
Hi, I'm a FireTruck technican. Fire pumps use backward curved impellers to gain higher pressures. I'm also a polymath, love studying stuff. I just wanted to let you know that forward curved blades require a different housing design. hard to explain in words quickly here so I suggest Google images and it makes sense right away. but basically the outlet must be offset and angled tangent to the tip of the blade angle.
I've built a couple of the impellers based on your original design with the backward curved blades turned by a 1.5 horse motor. I've been using them in the shop to drive a dust collector with 4" PVC piping to good effect. I've learned a few interesting things as a result. First is that wood vanes in a spherical pattern collect a lot dust on the inside curve of the blade because of the creation of a static vortex (I think) at the midpoint. This is exacerbated because of the relatively rough texture of the wood vane. The collection is also uneven, causing the impeller to lose balance as it runs. Tapping the impeller to loosen the dust helps, but it isn't entirely effective. As a result I've moved away from wood vanes to fiberglass. It allows me to easily create hybrid vane shapes and have a very smooth, static resistant surface. Also, I find them infinitely easier to manufacture consistently compared to cutting vanes from a blank on the bandsaw. I'm currently running with a parabolic (near) shape that starts with a sharp curve and ends nearly flat. This prevents the dust buildup and produces a 20% higher air volume with only a 10% increase in motor amperage. I don't have measurements for air speed or static pressure lacking the instrumentation (and the inclination to build any) to measure them. Anyway, I thought you might find this interesting.
Are non-circular curves any harder to make from wood? Sure, they are harder to plot because compasses will give you a circular arc, but if you print a template out you could just cut them on a bandsaw roughly the way Matthias does here. (Providing the curve isn't so great you run into problems from the non-uniform thickness if you stack the blades together - but if the shape is that critical you'd cut them out individually with waste on either side)
You run into non-uniform thickness all the time. I had a lot of variance between the blades even though they were cut from templates. You adjust for it when you balance the impeller, but I just found that I got something much more consistent in density and shape with the fiberglass. Plus, they were significantly stronger at roughly the same weight.
That is effectively what I have done. The shape is that of an air foil with a slightly flatter return (back) side. It made manufacturing a little easier to do that. I would change my mould again to use a full airfoil the next time.
One of the best experimental tutorial available on youtube. Thanks for describing in such easy manner. Now whenever i found Blower like this i watch its pattern and movement.
Great video! I recently made a video upgrading my Harbor Freight dust collector with a larger backwards curved impeller and lots of people have indicated that "the blades are facing the wrong way". I'll definitely have to point them over to your video so they can see your experiments. The the larger backwards curved impeller made a huge difference for my dust collector.
I don't know if you might find this suggestion useful, but I thought I might give it a try. I have thought of drilling small holes large enough for a regular-sized toothpick to fit in where the vanes are glued to the hub plates. They don't have to be very deep, 1/4" should be fine. The idea behind this by placing 4 or 6 toothpicks on each vane's side where they are glued to the rotor plates is to give additional structural support to resist the centrifugal forces, and to avoid the glue shearing off while the rotor is spinning for a prolonged period ( e.g. several hours a day ). This might avoid the vanes flying off being catapulted uncontrollably across the workshop and getting someone seriously harmed, if (s)he's in the straight line of fire.
A great experiment,.. especially while using this blower for a rc hovercraft to optimise power consumption and air flow... ! Thanks a lot and a big thump up for your efforts! Holger from Subwaterfilm
Most backward inclined fans have a fan performance curve that is quite a bit steeper regarding static pressure. They are generally used with exhaust fans. Forward curved fans have traditionally been used in systems, like a furnace, because they have a fairly consistent CFM. But extra static pressure degrades their performance, they are a low pressure device. Commercial exhaust fans, like we would use for dust collection would generally use straight blade backward inclined or airfoil backward inclined wheels. Dust collection is a high static requirement and your backward inclined wheels should give a very stable performance over a widely varying load. As soon as you add a load to those fans, all your performance will change drastically. Backward inclined performs better with higher static on the suction side. Just my opinion.
@@claytrocious7000 no difference in behaviour...aero propellers cavitate in air too...exactly the same as a prop in water...foils stall in water exactly the same as they do in air, just visibly easier to see any cavitation bubble...still the same in air
Excellent demonstration! It's obvious that "forward" impeller perform two different and opposite actions - centrifugically pushes air from center to outside and simultaneously pull it back to the center by raking scoops. There is another kind of blower called "cross-flow" with half-opened casing. It is widely used in the wall-mounted air conditioners, and it has a "forward" petals because of somehow different physics inside.
Nice experiment and video. Good designer and maker skills. Measuring instruments at hand. Results and conclusions recorded on paper. A science man indeed.
I was going to post the following but saw your comment... And thx Matthias for answering: "Can you test with straight fins NOT perpendicular to the tangent? Rotor I have has straight fins, but they are at an angle relative to the radius. I believe that may be the most efficient AND easiest to manufacture..."
Very cool test... I know that there are probably millions of different possible setups so it's difficult to test! I'd like to see impellers with different blade numbers, curves, angles, cambers, toes, etc! Thanks for the good info though!
Tank for the video...and also all the work that you've done to make it. My main interrogation was the same that you seem to have before testing it and i got my answers...and seeing you working make me learned even more than what i was looking for at first. Tank again.
Great experiment! I have been involved in many discussions about this very fact. You should calculate the Velocity Triangles (easy to do) for your rig since you have flow numbers. That would be the icing on the cake and would further explain the results you obtained. One other measurement you could make is the difference between the inlet an Discharge Temperature. Hopefully, at your low speeds, you would see the forward leaning blades producing the highest temperature. Comment on VT's: What you want on the exit is for a flow particle, flowing along the surface of the blade to exit the OD without any shearing. Shearing is wasted energy and further heats the discharge.
i actually had to do this exact same study for a blower before. One thing we did to make it fast for the test was to make the outside curved wall with cardboard instead of wood. We had the outside wall made in about 5 minutes. Foam core, cardboard and a hot glue gun is like magic with these studies.
Overall there's not a huge difference in performance between a true spiral, a stepped spiral, and an eccentric circular housing unless you're trying to meet the absolute max performance and efficiency. Overall the best spiral will actually depend upon the purpose, air movement and how much back pressure is created by the system often measured in inches of water. Usually due to the mass of the air you can get the best performance if the first part of the spiral (the part coming out from the edge of the impeller wheel) has the greatest slope compared to the rest of the spiral. Don't know if that makes sense but it's to allow more air flow due to the mass of the rotating air requiring more room around the entire diameter. Hope that makes sense.
I still think you and Jorg Sprave should do a collab, I love both of your channels, and I believe a lot of his fans would like your channel too! and vice versa!
Great video Matthias! the difference in tangential exit velocity you talked about with your marble analogy is why the blade angle causes the fan to require more or less power. For a given flow rate into the impeller, forward fins require the motor to add more angular momentum, straight fins are middling, and backward facing fins allow the air to exit at a slower tangential velocity than the rotor itself. all about rotational momentum! :) very neat set of tests.
Interesting point. So, with deeper blades near the middle, going shallower towards the outside (and housing to match) would work as follows: near the middle, a larger volume of air would be drawn in & accelerated towards the outside, where the speed & pressure would be increased. I've tried making a blower like this, seemed to work well, & got steel up to melting/sparking point with charcoal as a fuel.
working as a mechanic in the cement industry in the past I had a lot of work repairing big blowers, mostly for dust collection. All of their impellers were mounted in backwards curved configuration.
Matthias, thank you for this awesome video. I have been planing for about a week now to build a hand crank blower, based on another of your videos, for my mini forge. This video is a great help.
Nice vid, thanks matt. Now, not sure if I can explain clearly enough: at the centre of the impeller, the air is moving slower (smaller diameter), so to maximise airflow, the blades need to be deeper; then tapered towards the outside to maximise exit speed. Any housing needs to be accurately made for tight fit to prevent air bypassing the blades, a sort of Archimedes curve. The exit port needs to be sharp & as close to the blades as poss, for max efficiency. The inlet port neds to be large ( max volume, slow speed) and the outlet smaller (for max speed). Each of these variables need to be experimented with. I have used the back half of a bicycle with the chain-driven gears (by hand) to make a forge blower, a hobby sideline, which can get steel to welding (sparking) temperature for welding. Interesting.
The "backwards" Config is always used in every professional ventilation/air conditioning/heating/cooling systems. I worked on an built several systems on many industrial customers, with machines you could live in if the housings were empty, with a fuckton of ft³/h and in the basics its all similar to what you have built and concluded there. so: big thumbs up! :D
Matthias - Such a great experiment and video. I learn so much from your videos and they always send me to the workshop to experiment on my own. Thanks!
The results are somewhat inconclusive since you would need to optimise the outlet housing of each configuration to really determine the overall efficiency of each. In this example the housing that was built to a size it suited the straight blades best.
I googled around a lot a few years ago for answers to this. Not much to be found, but I did find an anecdote about forward making more volume at the same RPM
I'm right in the middle of designing a big whole shop DC system. Something in the 10HP to 15HP range (Although I found a 30HP motor for $100. Hmmmm.) And I found on Bill Pentz site he recommend this book "How to design and build centrifugle fans" by David J. Gingery gingerybookstore.com/product36.html It's been a good read for sure. Bill Pentz has a ton of good info, but his design is about building a good system that fits under a 8' ceiling where I have 20' ceilings in my shop so no need for this constraint.
I got inspired by Matthias videos on this topic a while back and found this when I was trying to find something to read on the topic. www.saylor.org/site/wp-content/uploads/2011/09/Chapter-3.5-Fans-Blowers.pdf Seems like backwards facing is usually most efficient and provides most bang for the buck. Not so strange given the geometry and the flows. Forward facing means that the air has to accelerate a lot when going out and this cause friction loss. This may be minimized by using a backwardsfacing blades which allows the air to move more in a straight line along the radial direction of the fan.
I don't think you will find scientific papers about this, because that is established fluid mechanics. If you want some theory read for example "Fluid Mechanics" by Joseph Spurk. That is the english version of the book we used at uni. But that may well be a bit over the top for just designing a blower for your shop vac.
Hello Matthias, George in MI here. After 40 years of work for Black & Decker / Dewalt and always being fascinated by blower design as well I've always noticed one thing when comparing the uses of forward curved vs backward curved air movers. All of our vacuums, blowers etc used the backward curved wheels and spun at relatively high speeds. When ever I've worked on things that used forward curved blades, furnace blowers vent fans etc, their blades where much shorter (rim to center) and they typically rotated at slower speeds typically moving lots of air without much noise. What I'm getting at is that I don't know if just reversing the same wheel is a very valid comparison. I think you'd have to redesign the whole wheel (same diameter and width) to really see their differences.
this would be an inexpensive initial experiment. well done...well thought out. the final experiment may be more balanced if using aluminum or other type metal... depending on weld or fasteners. love it. Thanks
It's a bit like wood working meets mythbusters - love your videos Matthias. It's a bit hard to see, what was the noise difference between the straight and forward facing impeller? Also I wonder if there is some useful information to be found in the pc building community, since there is always a discussion about air pressure, air flow, rpm, and noise of different fans over there.
I designed and printed a turbine with complex curves and an airfoil cross section. Would have been very difficult to fabricate otherwise. www.thingiverse.com/thing:772107/#made It spun pretty fast in the wind from my shop vac. I put it outside and it got destroyed in a windstorm. :)
Bill Morrow did you do any type of tempering? Like acetone or heat treatment before or straight off the bed? I've seen a few places discussing how much stronger prints are with those
I think I remember reading similar results in the Bill Pentz information on air cleaners. Always nice to review and reintroduce great basic information like this! I think his also talked of some of the stresses on the fan, but that just could be my remembering being inconsistent at times.
i'd say it's because the shape of the curved impeller makes it harder for the air to escape from the constraints of the blades, similar to how it's harder to scoop with a spoon instead of glide over top. first will give you more stuff for more effort, second will give you less stuff for less effort, if you know what i mean
A higher number of fins increases efficiency, as well as the inlet and outlet angles of the fins < 30º. For high pressure pumps longer fins (and smaller angles) are used.
when marking your 1/2 way radius why did you not scribe an arc from the start point and again from the finish point ? the intersection will be the centre that joins the two. easier and accurate.
Thank you very much for sharing this. I have been thinking quite a long time about the blade shapes and how efficient they are. you put it down in experience nicely.
It's a bit late and I think there is a good chance that you already know this, but what you described as "backwards fins" is actually a design used for cooling PC components. Overwhelming majority of parts using this design are graphic cards, but I did see at least one motherboard and one CPU cooler with this solution.
Interesting video, but it comes as no surprise to anyone who deals with blowers for pipe-organs. They all have the impeller fins pointing, as you would term it, 'backwards.'
+offshoreorganbuilder - The best of them all that provided wind for the largest and highest pressure organs ever built anywhere were by Spencer Turbine Company - The famous "Orgoblo" two stage straight fin blower. However, the fins at the intake end (Center of the fan) were curled to scoop the incoming air into and along the fins. The center static dividers do have curved guide fins feeding wind into the second stage. In installations where there was an abundance of high pressure reeds there was a third stage behind the second stage. This boosted wind pressure as high as 20" static. This system eliminated the use of a second independent blower to do the same job. Yes these blowers were noisy (Understatement) but they did the job far better than these newer blowers.
you did a fantastic experiments and made it simple and clear to understand the basic difference between the curve design and its pros and cons... thank you for making such video😊
I know you are a real engineer, but either you did this experiment for the rest of us, or you have misplaced your ASHRAE manual. Forward curved fans produce tons of air at low back pressure, and backward curved fans produce much more air flow against back pressure. So for your dust collector system, a backward curved fan is the clear winner.
i sure do miss the old Lindsay Catalogs with the stuff like dave gingery in it. where has my youth gone. anyway, your channel helps me relive the glory days :)
This is very cool. Dude diy’d a whole engineering test bench made for pennies. This is pathway to custom building fans for specialist applications. Every University should have a test bench like this. Even tafe and high schools.
Your backward curved impeller is correct, but your "forward curved" is not an actual forward curved impeller - it is a backward curved impeller running in reverse, which is very inefficient (and a tested way to burn out fan motors). To create a true forward curved impeller you need to remove your blades and rotate each of them by 180 degrees then reattach them. Feel free to ask me, I am an HVAC professional.
Pump Hydraulic Engineer here. If you underfile your backwards curved blades, you can increase the static pressure the impeller puts out. That is you make a straight cut tangent to the suction side (the concave side) from the trailing edge inwards, thinning the trailing edge. This will also however reduce the flow rate
Very impressed with your workmanship and testing! I see your measuring rpms. I think you'll get more data by plugging your motor into a simple $20 'Kill-a-watt' meter. This will give you a look at motor input power, and it's a very simple addition to your teet setup.
That was quite a demonstration. I always learn something from your videos, even though I just turned 74 years of age. I think I inhaled too many fumes from model airplane paint when I was a kid.. 😎
I really like this man he his a good illustrator he will teach you things like a primary school teacher ..teaching A,BC..😁😁😁 well done sir.....much love from nigeria...
"So that tells me if you're limited by RPM but not by power, you can get more airflow like this." - That was your first deduction? Not "The speed output is limited by the housing size and exit port." which is the only observation you could accurately make from those figures?
Interesting observation. If it was given a bigger outlet to achieve maximum speed you may have also seen a decrease in amps drawn. But I think the take away from this is forward facing gives you greater flow less pressure, straight gives you a middle ground, and backwards gives you less flow but more pressure. He might have even reduced the size of the outlet for the limited flow reversed to limit the speed and increase the pressure.
Thank you for benchmark and test! My little recomendation, please make blades more thinner, and make edges sharp, for better aerodynamical results. It decrease noise, too.
There should be a restrictor on the output of that squirrel cage look at your heating and air conditioning blower motor there's a restrictor it helps that efficiency I guess in the pressure and the volume
There should be a restrictor in there for the output are the blower motor the squirrel cage check your heating and air conditioner at Saint there it's in there what kind of engineer
With adjustable angle curved blades you could have any possible configuration or a fixed number of preset configurations, like the gearbox in a car, this also makes sense because you'd want a preset for the first 1/2 second, another for higher air pressure, lower air pressure, air moisture, debree particles, etc.
I enjoyed every bit of this until you mangled "jai alai." It's pronounced HIE-a-lie. My son noticed what I've noticed: a lot of woodworkers seem to spend a lot of time building tools so they can build tools that make it easier to build more tools. This is especially true with the more engineery builders like Matthias and Marius.
You really need to test for a flow versus static pressure versus power for each impeller. Each design, at a given speed will have a different sweet spot in this three dimensional space. Very interesting experiment. If you can find a little variable frequency drive, you can add the fourth dimension of speed to that characterization.
Matthias, I love your videos but I must say that turbomachinery is a very well-established discipline and the maths involved is very accessible. Blade angles can be calculated and optimised in advance based on an operation point (pressure and flow rate) of your choosing. Much less costly than finding out by building lots of prototypes!
Hello, you are doing a great job. I've been doing experiments like you, but you're doing it better. You have amazing order in the workshop and I really like your movies. Take care. Regards Robert from Poland
Mechanical engineer here. Sorry if i'm late, but i think this is very interesting.The forward facing blades are often used in industrial practice, just slightly different: short blades to reduce friction and in higher number. The low efficiency figure you got was absolutely due to the massive friction the air was producing on the blades. Side note: straight blades are used for dirty air flow (less change of blockage) and backward curved blades are used when higher pressure is needed more than high flow. You actually got the very same results that i got when I did the very same work but with a CDF simulation program, i'm so happy about this.
Those biscuit joints was extremely clever. I have spent long hours in a woodshop starting early in age. I built and sold a lot of stuff. Wish i new what i know now after watching your videos! You are an awesome person. I need to get my butt back in my own woodshop
As an engineer who was looking for a concise intro to impeller basics and design, this was invaluable. Great video, will definitely watch your others!
You put a lot of time and effort to produce a 10.5 minute video. My hat's off to you. Thanks for the video.
Thanks for paying attention in physics, trigonometry, English, etc. Your videos are both informative and interesting. You have that uncanny knack of being able to take a potentially arcane subject and make it enjoyable for scholars and laymen alike. I also enjoy your Canadian accent and cadence. Keep it up young man!
The way you drew your radius for your housing is ingenious and really all your compass work has taught me how versatile of a tool it can be, also i have never seen a motor reversed like that. I really like your accesible approach and breakdown of your projects and very clear and thorough explanation of what you are doing. I dont know how you learned to do all these things the way you do but it is knowledge i am grateful that you are sharing with us (me).
I really enjoyed your video! 0:11 I love how you made your own large adjustable compass out of wood. 0:27 And you guide the sawing of the curved vanes freehand so quickly and accurately. 3:25 And what a great idea for joining the pieces by cutting slots and gluing in little bits of wood. Lots of good ideas and techniques in this video.
Hi, I'm a FireTruck technican. Fire pumps use backward curved impellers to gain higher pressures. I'm also a polymath, love studying stuff. I just wanted to let you know that forward curved blades require a different housing design. hard to explain in words quickly here so I suggest Google images and it makes sense right away. but basically the outlet must be offset and angled tangent to the tip of the blade angle.
I've built a couple of the impellers based on your original design with the backward curved blades turned by a 1.5 horse motor. I've been using them in the shop to drive a dust collector with 4" PVC piping to good effect. I've learned a few interesting things as a result. First is that wood vanes in a spherical pattern collect a lot dust on the inside curve of the blade because of the creation of a static vortex (I think) at the midpoint. This is exacerbated because of the relatively rough texture of the wood vane. The collection is also uneven, causing the impeller to lose balance as it runs. Tapping the impeller to loosen the dust helps, but it isn't entirely effective. As a result I've moved away from wood vanes to fiberglass. It allows me to easily create hybrid vane shapes and have a very smooth, static resistant surface. Also, I find them infinitely easier to manufacture consistently compared to cutting vanes from a blank on the bandsaw. I'm currently running with a parabolic (near) shape that starts with a sharp curve and ends nearly flat. This prevents the dust buildup and produces a 20% higher air volume with only a 10% increase in motor amperage. I don't have measurements for air speed or static pressure lacking the instrumentation (and the inclination to build any) to measure them. Anyway, I thought you might find this interesting.
I always have the blower after the filter. Haven't had issues with dust buildup myself.
Are non-circular curves any harder to make from wood? Sure, they are harder to plot because compasses will give you a circular arc, but if you print a template out you could just cut them on a bandsaw roughly the way Matthias does here. (Providing the curve isn't so great you run into problems from the non-uniform thickness if you stack the blades together - but if the shape is that critical you'd cut them out individually with waste on either side)
Your comment makes me want to mess with airfoil (wing) shaped blower blades.
You run into non-uniform thickness all the time. I had a lot of variance between the blades even though they were cut from templates. You adjust for it when you balance the impeller, but I just found that I got something much more consistent in density and shape with the fiberglass. Plus, they were significantly stronger at roughly the same weight.
That is effectively what I have done. The shape is that of an air foil with a slightly flatter return (back) side. It made manufacturing a little easier to do that. I would change my mould again to use a full airfoil the next time.
One of the best experimental tutorial available on youtube.
Thanks for describing in such easy manner.
Now whenever i found Blower like this i watch its pattern and movement.
Matthias,
You never cease to amaze me with your knowledge, ingenuity, talents, & skills.
Thanks for sharing!
Great video! I recently made a video upgrading my Harbor Freight dust collector with a larger backwards curved impeller and lots of people have indicated that "the blades are facing the wrong way". I'll definitely have to point them over to your video so they can see your experiments. The the larger backwards curved impeller made a huge difference for my dust collector.
I don't know if you might find this suggestion useful, but I thought I might give it a try.
I have thought of drilling small holes large enough for a regular-sized toothpick to fit in where the vanes are glued to the hub plates. They don't have to be very deep, 1/4" should be fine. The idea behind this by placing 4 or 6 toothpicks on each vane's side where they are glued to the rotor plates is to give additional structural support to resist the centrifugal forces, and to avoid the glue shearing off while the rotor is spinning for a prolonged period ( e.g. several hours a day ). This might avoid the vanes flying off being catapulted uncontrollably across the workshop and getting someone seriously harmed, if (s)he's in the straight line of fire.
A great experiment,.. especially while using this blower for a rc hovercraft to optimise power consumption and air flow... !
Thanks a lot and a big thump up for your efforts!
Holger from Subwaterfilm
I feel like I just keep getting smarter and smarter everytime i watch your videos!
Video and experiment with great quality. UA-cam needs more people like you.
Most backward inclined fans have a fan performance curve that is quite a bit steeper regarding static pressure. They are generally used with exhaust fans. Forward curved fans have traditionally been used in systems, like a furnace, because they have a fairly consistent CFM. But extra static pressure degrades their performance, they are a low pressure device. Commercial exhaust fans, like we would use for dust collection would generally use straight blade backward inclined or airfoil backward inclined wheels. Dust collection is a high static requirement and your backward inclined wheels should give a very stable performance over a widely varying load. As soon as you add a load to those fans, all your performance will change drastically. Backward inclined performs better with higher static on the suction side. Just my opinion.
I agree.
Try moving water.
I totaly understand everything 🤔🤔🤔🤔🤔🤔🤔🤔🤔
@@christopherhayes9827air...is a fluid just like water...Just 1000x less mass, same principles & physics.
@@Errol.C-nz a big difference is that with water you have to account for cavitation.
@@claytrocious7000 no difference in behaviour...aero propellers cavitate in air too...exactly the same as a prop in water...foils stall in water exactly the same as they do in air, just visibly easier to see any cavitation bubble...still the same in air
Excellent demonstration!
It's obvious that "forward" impeller perform two different and opposite actions - centrifugically pushes air from center to outside and simultaneously pull it back to the center by raking scoops.
There is another kind of blower called "cross-flow" with half-opened casing. It is widely used in the wall-mounted air conditioners, and it has a "forward" petals because of somehow different physics inside.
Matthias' math teacher was right about him needing trigonometry sometime in the future.
Martin H if you do anything that isnt just humanities, something science related, you will indeed need trigonometry sometime
Just a hunch, but i'm guessing Matthias was smarter then his teacher.
Maybe, but that problem with the triangle you could easily do with just a ruler and compass and none of those pesky numbers.
True, I'm a graphic programmer and I do trig every day.
Matthias was right about his teacher needing trigonometry sometime in the future.
I started to manufacture exhaust fans thanks to the videos on this channel. too top, speaking straight from Brazil.
1:30 the craziest thing is that Primitive Technology used a very similar approach when making a volute housing by hand out of clay lol
Nice experiment and video. Good designer and maker skills. Measuring instruments at hand.
Results and conclusions recorded on paper.
A science man indeed.
How about *straight blades at an angle?* I mean having it forward/backward facing, but without the curve.
No doubt less optimal, but I didn't feel like making another one.
I was wondering this too.....I suspect it's numbers will fall out somewhere inbetween the others
How about a forward curved blades impeller a little bit smaller ? Maybe it will turn faster and draw less power but blow the same amount of air.
I was going to post the following but saw your comment... And thx Matthias for answering: "Can you test with straight fins NOT perpendicular to the tangent? Rotor I have has straight fins, but they are at an angle relative to the
radius. I believe that may be the most efficient AND easiest to manufacture..."
How about straight fins that are flexible. They start out straight and then bend a bit as they pick up speed.
Darn envious to see such a sensible, intuitive, educated, versatile mind in action.
I love the way you just pull an electric motor apart as if it was like peeling a banana!
Some people are peeling a banana as if they have to re-engineer an electric motor.
your comment restored my faith in humanity.
sasja de vries. Ummm ok lol
+David Stanton
One key difference... a banana cannot be re-assembled.
Find the right engineer and I am CERTAIN that banana would end up re-assembled. If there is a will...
I always learn more than woodworking whenever I'm here! ".. about woodworking, taking more of an engineering perspective on things.." is apt!! Thanks.
Very cool test... I know that there are probably millions of different possible setups so it's difficult to test! I'd like to see impellers with different blade numbers, curves, angles, cambers, toes, etc! Thanks for the good info though!
this is why cad programs exists, endless configurations and experiments done from home
Tank for the video...and also all the work that you've done to make it. My main interrogation was the same that you seem to have before testing it and i got my answers...and seeing you working make me learned even more than what i was looking for at first. Tank again.
Great experiment! I have been involved in many discussions about this very fact.
You should calculate the Velocity Triangles (easy to do) for your rig since you have flow numbers. That would be the icing on the cake and would further explain the results you obtained.
One other measurement you could make is the difference between the inlet an Discharge Temperature. Hopefully, at your low speeds, you would see the forward leaning blades producing the highest temperature.
Comment on VT's: What you want on the exit is for a flow particle, flowing along the surface of the blade to exit the OD without any shearing. Shearing is wasted energy and further heats the discharge.
i actually had to do this exact same study for a blower before. One thing we did to make it fast for the test was to make the outside curved wall with cardboard instead of wood. We had the outside wall made in about 5 minutes. Foam core, cardboard and a hot glue gun is like magic with these studies.
To make a varying pitch spiral, just allow a string to wrap as it draws. Your curves do not gradually change pitch-they change in steps.
Overall there's not a huge difference in performance between a true spiral, a stepped spiral, and an eccentric circular housing unless you're trying to meet the absolute max performance and efficiency.
Overall the best spiral will actually depend upon the purpose, air movement and how much back pressure is created by the system often measured in inches of water. Usually due to the mass of the air you can get the best performance if the first part of the spiral (the part coming out from the edge of the impeller wheel) has the greatest slope compared to the rest of the spiral. Don't know if that makes sense but it's to allow more air flow due to the mass of the rotating air requiring more room around the entire diameter. Hope that makes sense.
@@lazyh-online4839 moron
I watched your video with a rapt attention! I loved how you created this and tested it out! Bravo!
You're my favorite person on UA-cam
GREAT SCIENTIST TYPE
song bob what
Toot Toot 0
Excellent illustration and detailed info. As a mechanical engineer in HVAC/R, this was an interesting video. Keep 'em coming.
I still think you and Jorg Sprave should do a collab, I love both of your channels, and I believe a lot of his fans would like your channel too! and vice versa!
Great video Matthias!
the difference in tangential exit velocity you talked about with your marble analogy is why the blade angle causes the fan to require more or less power. For a given flow rate into the impeller, forward fins require the motor to add more angular momentum, straight fins are middling, and backward facing fins allow the air to exit at a slower tangential velocity than the rotor itself. all about rotational momentum! :) very neat set of tests.
increase the 'diameter' to get more pressure. increase the 'thickness' to get more flow.
Interesting point. So, with deeper blades near the middle, going shallower towards the outside (and housing to match) would work as follows: near the middle, a larger volume of air would be drawn in & accelerated towards the outside, where the speed & pressure would be increased. I've tried making a blower like this, seemed to work well, & got steel up to melting/sparking point with charcoal as a fuel.
working as a mechanic in the cement industry in the past I had a lot of work repairing big blowers, mostly for dust collection. All of their impellers were mounted in backwards curved configuration.
felicitaciones mathias, rus creaciones son fantasticas, muy bonito tu trabajo, saludos.
This video is most useful for every technical person.
Thanks from Bangladesh🇧🇩
I like to think I’m kinda clever. But watching you....makes me realize how much I don’t know. Great Vids!
ChiTownTino likewise
Matthias, thank you for this awesome video. I have been planing for about a week now to build a hand crank blower, based on another of your videos, for my mini forge. This video is a great help.
Awesome experiment! Would it be worthwhile to test a backward-facing rotor with fins that are slightly less curved? Nice job, Matthias!
been thinking the same,
wondered what would happen
Si se lo trduciera Al español seria grandioso
if you have the geometry between the straight and curved you can interpolate the data that you want, though it would just be an educated estimate
Nice vid, thanks matt. Now, not sure if I can explain clearly enough: at the centre of the impeller, the air is moving slower (smaller diameter), so to maximise airflow, the blades need to be deeper; then tapered towards the outside to maximise exit speed. Any housing needs to be accurately made for tight fit to prevent air bypassing the blades, a sort of Archimedes curve. The exit port needs to be sharp & as close to the blades as poss, for max efficiency. The inlet port neds to be large ( max volume, slow speed) and the outlet smaller (for max speed). Each of these variables need to be experimented with. I have used the back half of a bicycle with the chain-driven gears (by hand) to make a forge blower, a hobby sideline, which can get steel to welding (sparking) temperature for welding. Interesting.
When I grow up I want to be just ingenious and precise as you with all the neat tools to go along with it. LOL!
The "backwards" Config is always used in every professional ventilation/air conditioning/heating/cooling systems. I worked on an built several systems on many industrial customers, with machines you could live in if the housings were empty, with a fuckton of ft³/h and in the basics its all similar to what you have built and concluded there. so: big thumbs up! :D
Again, it's 2 am. I should be asleep a long time ago
Me too. My ankle is killing me I dislocated it. Cup of green tea in hand watching clever chaps on UA-cam at 2.15 in the morning
Good design but I think you need less gap between fan and casing. If it was me I,d halve that to give it a little more compression.
Have been*
No regret watching this kind of video bro, any where, any time!
TIme's got nothing to do with it, you are still very much asleep at the wheel.
Matthias - Such a great experiment and video. I learn so much from your videos and they always send me to the workshop to experiment on my own. Thanks!
Would have been nice to test the straight blade fan with the reversed motor just to see if reversing the motor in itself effected the efficiency.
he did I think
The results are somewhat inconclusive since you would need to optimise the outlet housing of each configuration to really determine the overall efficiency of each. In this example the housing that was built to a size it suited the straight blades best.
It would be a waster of time. A straight blower will react the same regardless of what direction it turn.
robert shaw I believe what OP was referring to was to control for a variance in the electrical wiring.
It might if the reversing was done through wiring, but all he did was turn the motor upside down. I don't think that would have any difference.
Nice job - a lot of work involved there to complete this test. Appreciate it being fast forwarded!
I wonder if there's a paper on this lying around somewhere or if everyone who designs a blower calculates it themselves.
Yes good question. I also wonder if you have a certain HP/RPM motor to design around how to calculate for best flow/suction.
I googled around a lot a few years ago for answers to this. Not much to be found, but I did find an anecdote about forward making more volume at the same RPM
I'm right in the middle of designing a big whole shop DC system. Something in the 10HP to 15HP range (Although I found a 30HP motor for $100. Hmmmm.) And I found on Bill Pentz site he recommend this book "How to design and build centrifugle fans" by David J. Gingery gingerybookstore.com/product36.html
It's been a good read for sure. Bill Pentz has a ton of good info, but his design is about building a good system that fits under a 8' ceiling where I have 20' ceilings in my shop so no need for this constraint.
I got inspired by Matthias videos on this topic a while back and found this when I was trying to find something to read on the topic.
www.saylor.org/site/wp-content/uploads/2011/09/Chapter-3.5-Fans-Blowers.pdf
Seems like backwards facing is usually most efficient and provides most bang for the buck. Not so strange given the geometry and the flows. Forward facing means that the air has to accelerate a lot when going out and this cause friction loss. This may be minimized by using a backwardsfacing blades which allows the air to move more in a straight line along the radial direction of the fan.
I don't think you will find scientific papers about this, because that is established fluid mechanics. If you want some theory read for example "Fluid Mechanics" by Joseph Spurk. That is the english version of the book we used at uni. But that may well be a bit over the top for just designing a blower for your shop vac.
Hello Matthias, George in MI here. After 40 years of work for Black & Decker / Dewalt and always being fascinated by blower design as well I've always noticed one thing when comparing the uses of forward curved vs backward curved air movers. All of our vacuums, blowers etc used the backward curved wheels and spun at relatively high speeds. When ever I've worked on things that used forward curved blades, furnace blowers vent fans etc, their blades where much shorter (rim to center) and they typically rotated at slower speeds typically moving lots of air without much noise. What I'm getting at is that I don't know if just reversing the same wheel is a very valid comparison. I think you'd have to redesign the whole wheel (same diameter and width) to really see their differences.
Thank you sir, I learned a lot from this video.
The same thing happened to me! 🙂
Me too.
I love UA-cam!
this would be an inexpensive initial experiment. well done...well thought out.
the final experiment may be more balanced if using aluminum or other type metal...
depending on weld or fasteners. love it. Thanks
It's a bit like wood working meets mythbusters - love your videos Matthias. It's a bit hard to see, what was the noise difference between the straight and forward facing impeller? Also I wonder if there is some useful information to be found in the pc building community, since there is always a discussion about air pressure, air flow, rpm, and noise of different fans over there.
I think those were about the same
Sloth in pc this doesn't matter because we don't use radial fans and we don't build our own fans either.... Maybe we should start that
It would be something where 3d printing made sense
I designed and printed a turbine with complex curves and an airfoil cross section. Would have been very difficult to fabricate otherwise. www.thingiverse.com/thing:772107/#made
It spun pretty fast in the wind from my shop vac. I put it outside and it got destroyed in a windstorm. :)
Bill Morrow did you do any type of tempering? Like acetone or heat treatment before or straight off the bed? I've seen a few places discussing how much stronger prints are with those
I think I remember reading similar results in the Bill Pentz information on air cleaners. Always nice to review and reintroduce great basic information like this!
I think his also talked of some of the stresses on the fan, but that just could be my remembering being inconsistent at times.
The straight impeller only had 6 fins where the curved had 8- Could this be increasing the air pressure and straining the motor?
Possibly, but probably not
i'd say it's because the shape of the curved impeller makes it harder for the air to escape from the constraints of the blades, similar to how it's harder to scoop with a spoon instead of glide over top. first will give you more stuff for more effort, second will give you less stuff for less effort, if you know what i mean
A higher number of fins increases efficiency, as well as the inlet and outlet angles of the fins < 30º. For high pressure pumps longer fins (and smaller angles) are used.
You are a real magician. You have golden hands. I do not know English, but with such a nerve-racking watch your videos. (It is transplanted by Google)
when marking your 1/2 way radius why did you not scribe an arc from the start point and again from the finish point ?
the intersection will be the centre that joins the two.
easier and accurate.
a real science channel, one of the very few
I see why it was unbalanced. 0:15 couple of first blades center was on outer circle, then you switched to inner circle.
yes, I noticed that too when I edited the video, fixed the impeller.
Matthias Wandel would it save time if you weighed each blade prior to glue up?
That would help. However the positioning of each vane must be located consistently in relation to the center of rotation.
Thank you very much for sharing this. I have been thinking quite a long time about the blade shapes and how efficient they are. you put it down in experience nicely.
enjoyed!
It's a bit late and I think there is a good chance that you already know this, but what you described as "backwards fins" is actually a design used for cooling PC components. Overwhelming majority of parts using this design are graphic cards, but I did see at least one motherboard and one CPU cooler with this solution.
For future reference, you should weigh the impeller blades before gluing them. ;-)
THIS is a demonstration of the best that UA-cam has to offer. Great video! By the way, who are the geniuses who gave this a thumbs down?
Interesting video, but it comes as no surprise to anyone who deals with blowers for pipe-organs. They all have the impeller fins pointing, as you would term it, 'backwards.'
+offshoreorganbuilder - The best of them all that provided wind for the largest and highest pressure organs ever built anywhere were by Spencer Turbine Company - The famous "Orgoblo" two stage straight fin blower. However, the fins at the intake end (Center of the fan) were curled to scoop the incoming air into and along the fins. The center static dividers do have curved guide fins feeding wind into the second stage. In installations where there was an abundance of high pressure reeds there was a third stage behind the second stage. This boosted wind pressure as high as 20" static. This system eliminated the use of a second independent blower to do the same job.
Yes these blowers were noisy (Understatement) but they did the job far better than these newer blowers.
@@organbuilder272 Look at the holset turbo design.
you did a fantastic experiments and made it simple and clear to understand the basic difference between the curve design and its pros and cons... thank you for making such video😊
I know you are a real engineer, but either you did this experiment for the rest of us, or you have misplaced your ASHRAE manual. Forward curved fans produce tons of air at low back pressure, and backward curved fans produce much more air flow against back pressure. So for your dust collector system, a backward curved fan is the clear winner.
i sure do miss the old Lindsay Catalogs with the stuff like dave gingery in it. where has my youth gone. anyway, your channel helps me relive the glory days :)
next experiment blower housing shapes :)
Steven Zhang đ
This is very cool. Dude diy’d a whole engineering test bench made for pennies. This is pathway to custom building fans for specialist applications.
Every University should have a test bench like this. Even tafe and high schools.
I sense alot of blowers being remade in matthias' shop.
Valtra Kernow
Well done video without any boring parts and unwanted music. Kudos
Your backward curved impeller is correct, but your "forward curved" is not an actual forward curved impeller - it is a backward curved impeller running in reverse, which is very inefficient (and a tested way to burn out fan motors). To create a true forward curved impeller you need to remove your blades and rotate each of them by 180 degrees then reattach them. Feel free to ask me, I am an HVAC professional.
Can you draw a diagram of what it should look like?
I think it's something like this:
4.bp.blogspot.com/-BC30W46gJ70/UQIeHGrklPI/AAAAAAAAADg/NPj3ukfmvuc/s1600/IMPELLER+DESIGN.bmp
Please be aware - lots of wrong info online on this subject. Ask an industry expert.
Saeed, so you're saying it's the opposite of what the image you posted says?
J DeWitt how so?
Turning the stator around was simple and clever, didnt think of that myself. Thanks for the video!
brachistochrone vanes?
الو
Pump Hydraulic Engineer here. If you underfile your backwards curved blades, you can increase the static pressure the impeller puts out. That is you make a straight cut tangent to the suction side (the concave side) from the trailing edge inwards, thinning the trailing edge. This will also however reduce the flow rate
In Australia, the motors spin the other direction.
Carl Siemens
And they are mounted upside-down
Some motors in the United states are reversible. I've got a 1 hp motor that's reversible.
r/wooosh
Very impressed with your workmanship and testing! I see your measuring rpms. I think you'll get more data by plugging your motor into a simple $20 'Kill-a-watt' meter. This will give you a look at motor input power, and it's a very simple addition to your teet setup.
I highly recommend watching the video that you commented on. It will address your comment.
Very interesting, thanks for shaering
no praeblem!
That was quite a demonstration. I always learn something from your videos, even though I just turned 74 years of age. I think I inhaled too many fumes from model airplane paint when I was a kid.. 😎
It's pronounced "high-lie"
Which word are you talking about?
Jai alai (ˈhaɪ.əlaɪ) - he pronounced it phonetically as ji - a - lie.
Timestamp?
10:15
Ah right. I've never heard of that game, so I'm non-the-wiser.
I really like this man he his a good illustrator he will teach you things like a primary school teacher ..teaching A,BC..😁😁😁 well done sir.....much love from nigeria...
"So that tells me if you're limited by RPM but not by power, you can get more airflow like this." - That was your first deduction? Not "The speed output is limited by the housing size and exit port." which is the only observation you could accurately make from those figures?
Interesting observation. If it was given a bigger outlet to achieve maximum speed you may have also seen a decrease in amps drawn. But I think the take away from this is forward facing gives you greater flow less pressure, straight gives you a middle ground, and backwards gives you less flow but more pressure. He might have even reduced the size of the outlet for the limited flow reversed to limit the speed and increase the pressure.
Thank you for benchmark and test! My little recomendation, please make blades more thinner, and make edges sharp, for better aerodynamical results. It decrease noise, too.
this is cool and all.. but why am i watching this!...
A craftsman and an engineer all rolled into one. Impressive. Thank you.
I like backward blower much faster and very efficient air blow.but i recommend straight Beacause made easily and more power.😁😁😁😁😁😁😁😁😁😁😁😁😁😁😀😀
There should be a restrictor on the output of that squirrel cage look at your heating and air conditioning blower motor there's a restrictor it helps that efficiency I guess in the pressure and the volume
There should be a restrictor in there for the output are the blower motor the squirrel cage check your heating and air conditioner at Saint there it's in there what kind of engineer
With adjustable angle curved blades you could have any possible configuration or a fixed number of preset configurations, like the gearbox in a car, this also makes sense because you'd want a preset for the first 1/2 second, another for higher air pressure, lower air pressure, air moisture, debree particles, etc.
awesome idea.
You do the prototyping, we reap the benefits. Matthias, thank you, thank you, thank you, thank you.
Переведите
Согласен)))
This video is super helpful. The information on the internet regarding how forward vs backward fins work is vague at best.
I enjoyed every bit of this until you mangled "jai alai." It's pronounced HIE-a-lie.
My son noticed what I've noticed: a lot of woodworkers seem to spend a lot of time building tools so they can build tools that make it easier to build more tools. This is especially true with the more engineery builders like Matthias and Marius.
A person can only use so much furniture, but he can never have too many tools.
You say that like it's a bad thing.
Leif Hietala a wise wise man you are 👍
This was the video i was looking for but the title isnt describing it😊 thank you.
Instant like
You really need to test for a flow versus static pressure versus power for each impeller. Each design, at a given speed will have a different sweet spot in this three dimensional space. Very interesting experiment. If you can find a little variable frequency drive, you can add the fourth dimension of speed to that characterization.
Matthias, I love your videos but I must say that turbomachinery is a very well-established discipline and the maths involved is very accessible. Blade angles can be calculated and optimised in advance based on an operation point (pressure and flow rate) of your choosing. Much less costly than finding out by building lots of prototypes!
Hello, you are doing a great job. I've been doing experiments like you, but you're doing it better. You have amazing order in the workshop and I really like your movies. Take care. Regards Robert from Poland