Blower design

[ThomasVaught]

I will wait for the drawing or a pic.

The reply I made was for a proper entry adaptor INTO the Boosting
device. (Like a Turbocharger or supercharger). Tony's answer makes
me think you guys are talking more about the actual wheel/blade
geometry inside the case. Now I am confused.

Tom V.

[Tony]

Tom, it probably does not matter how much of the blower intake is rotating, and how much is stationary.

The required shape and flow pattern to transfer the air from a round incoming duct, into the wheel, could be designed in a variety of ways.

[ThomasVaught]

Thanks Tony

Tom V.

[Tony]

Here is an excellent picture taken by Brooks, shamelessly stolen by me from another thread.
It shows a particularly well proportioned rotor design.

Notice how the air path between the rotor blades maintain a fairly constant flow cross sectional area. The air exit at the periphery is roughly (at least by eye) one third the height, and three times the width of the entry dimension at the central intake.
The other point to notice, is the approximate four to one ratio between the air inlet diameter, and the height of the blades at the entry point.

While these particular blades extend full distance from the entry diameter to the periphery, in many rotors this is not always done. In one commercial rotor I have in my flow bench at the moment, the blades are very short, only three inches long arranged around the outside edge of the rotor. The hub area is still flared outwards, but it is completely open with no blades in the flared mid section.

A home built rotor could have parallel walls in the outer section where the blades are, and then have a gradual outward taper towards the inner hub area. That should greatly simplify construction without straying to far from the theoretical ideal. A short bladed rotor seems to work just as well as a long bladed rotor with no obvious disadvantage.

[bruce]

Well finally had some more time to work on the blower today, here is a pic of the inlet still have a couple of holes to drill but wanted to get an idea of how it would look/work before I drilled to many mounting holes.

The blower wheel is positioned in the housing but not permanent it is in there for mock-up only. The inlet has a lip that sticks out and the blower wheel can sit over top of this lip, I'll get a pic showing that later.

[bruce]

another view

[SWR]

Looking good,Bruce. Looks like I'm getting one of those...as I was just quoted $6460 (!) for a blower capable of 700 cfm @ 60",which wasn't very tempting to my wallet.. Could really get a few Ameteks for that amount,too...

[bruce]

If it works as designed I'll sell you one for half that and split my half with Tony!



Edited By bruce on 1187804916

[SWR]

[bruce]

The whole idea behind this blower project (besides building it for myself because I'm cheap and can't afford +$6000) was to design something that would work for the average flowbench builder. Additionally, do away with those screaming little blowers and cut down on the power requirement (amps).

Although, it was discussed if it could also be built by the diy'er. I personally don't think this project will be in the scope of the home diy'er. Some parts are going to have to be made with a lathe and a milling machine. The blower will be running around 4000rpms, things rotating at that rpm tend to make a mess when they come apart, so it's not something to be "hacked together" in my opinion and that has been on my mind during this build.

But for the time being we need to get it working first . . .

[SWR]

Bruce,maybe some mild-steel plating on the outside of the housing as a "blast shield" would be an idea..? Or coating the housing in Kevlar matting...

[bruce]

I guess the concept is design for no failures. I should need to extra shielding with this design. But wanted to point that out in my previous post to anyone else who might try and "build your own".

Larry C. can attest this blower is built to last, he was in my shop on Saturday and saw it in person.

[Tony]

The price of commercial high pressure blowers is an absolute joke, especially when you see how they are actually put together inside. A lathe certainly makes things a lot simpler, but I still believe it could be fabricated entirely with very simple tools, or at least with the basic power tools that most home handymen have these days.

The drive hub of the rotor could be made from a commercial steel chain sprocket that already comes with an appropriate taper lock center and keyway to fit onto the motor shaft.

The boss of the sprocket could be bolted through a piece of flat sheet steel plate and secured with some bolts. Anyone could do this with hole saw and some patient filing to get a nice snug fit. Once the uncut steel sheet with it's hub is fitted to a dummy shaft, it can be rotated to accurately scribe out the final rotor diameter. Cutting out the rotor diameter entirely by hand is a lot of work, but far from impossible. From there, the aluminium blades, and very light weight shroud cover would be attached with pop rivets.

Because the motor shaft passes right through the main rotor backing plate, it cannot escape. If something lets go, the whole thing will probably go out of balance and get the shakes, but it cannot really explode and launch itself through the ceiling.

An outer blower casing can be made several different ways, The requirement is very simple. The air coming off the rotor just needs to be collected and have a very easy means of escape down the discharge pipe with minimum pressure drop. As long as the flow area is made very large, the actual geometry of the outer housing does not seem to be at all critical. This is all far easier than you might expect.

It only needs to be made a sexy smooth snail shape if you are aiming for absolute minimum packaging and weight. Something made considerably oversize will flow the air coming off the rotor just fine.

The beauty of building you own blower, is that once you have finally decided to make the break away from vacuum motors, there is no real size constraint on how big you build it. The only problem will be, do you have sufficient shaft horsepower available to turn it ?

A wild off the wall guess might be 5Hp for 500 CFM at 30"
10HP might get you 500 CFM at 60" or 1,000 CFM at 30"

[SWR]

Tony,the commercial blower that did 700 cfm @ 60" ( and 1200 at 30" ) required 12.5 Kw at 240V / 50Hz to pull that depression. On the other hand,the easy thing is to just hook everything you got into the circuit you're intending to run the motor from,and keep adding stuff until you blow the fuses. Then you can calculate what amount of Kw you actually pulled. Nope,just doing the calcs doesn't always cut it. I have 240V x 16 amps in one curcuit in my basement. Thats 3840W. I've hooked up 3 1400W motors,one 2000W panel heater and a 500W halogen light (combined 6700W ) to that circuit...and for some reason it didn't blow. But,adding another 1000W heater... darkness was imminent. :p

[Tony]

Let's see. By my rough figures 700 CFM at 60" might need about 14Hp shaft drive power at a fairly typical sort of blower efficiency. and you say the commercial blower ratings are 12.5 Kw of electrical input energy to do that.

12.5Kw x 1.341 = 16.76 Hp if the motor were 100% efficient.
16.76Hp (electrical) ingoing, and 14.0 Hp (mechanical) coming out would be 84% efficient, which is exactly about what I would expect for a typical induction motor. So I wold say that commercial blower is spot on with the numbers, hardly surprising.

If you have a 16A circuit, you should be able to draw 16 amps forever. Anything substantially more should blow a fuse or trip a protective breaker. If not, something is not working, and you stand a pretty good chance of overheating the wiring. Or worse.

If you are going to draw some serious power, I suggest you have the wiring and the protective devices checked by an electrician to see what the ratings really are, or you may be sorry.