Air bearings

As far as I am aware air bearings are exactly like ordinary hydrodynamic bearings, ie ones which just use oil. The difference is that they use air as the working fluid. ISTR that the reason is significatly lower drag, as air is *MUCH* less viscous than even very thin oil. unfortunatly this means it runs out of the bearing much quicker as well...(imagine a *REALLY* leaky Myford spindle) I suspect you can run an air bearing without a dedicated external supply of air, if there is a turbine wheel packing air into the bearing, but it would need to run at a very high speed, much more than a wind generator would ever run at.

Of course air bearings are not very good at taking end thrusts... so that would probably mean a seperate thrust bearing anyway?

how about real bearings, like you get for car wheels for instance. not so 'flash', but more likely to work...

Hmm, vertical would remove the end thrust, but of course then you have gravity to contend with, so you still need a thrust face of some sort.

If hes in a urban enviroment its unlikely that the generator will ever produce enough power to justify its existance, much less recover the amount used to make it...

just charge him commercial rates for the work, that should put him off...

Dave

On or around 23 Oct 2006 10:39:54 -0700, "mark" enlightened us thusly:

I know a man who does...

Frankly, I doubt it. I suppose it's possible that you could have a big funnel that faces into the wind and collects wind to make the bearings go, but I can't see that being reliable. My (limited) knowledge of air bearings is that they require high-precision engineering and an air supply.

more conventional bearings... thrust race at the bottom and plain ball race further up, or rollers further up.

If I were doing it, I'd used proprietary sealed ballraces of some suitable sort.

Inclined to agree. The chap I know who does know about air bearings works for a precision engineering lot - he was talking about drilling 0.4mm holes, ISTR, or somesuch. The bearing has to fit very closely to the shaft without touching, too, and still needs an air supply. If they're made well enough, the air supply isn't very much, but it's still going to compromise your ability to generate power, either that or the thing needs an external air supply, and thus external power, to operate. I reckon it's unlikely to be worth it for the small gain in efficiency.

I thought air bearings were for high speed applications

Turns out Im slightly off the mark, the wikipedia has a couple of good pages on this:

The foil bearing operates without an external pressurised air supply, but is only viable for turbomachinery, as it relys on high rotational speed to pull in the required air for lubrication.

Dave

Viscous drag (losses) from the oil film is a function of shear velocity and viscosity.

Since the rpm of these machines is so low I doubt that the difference in parasitic losses among sleeve bearing with thin oil, ball bearing with thin oil, or air bearing with small compressor, would be worth worrying about.

I'd choose shielded ball bearings and oil them once-in-a-blue-moon with synthetic spindle oil. If the rotational speed is really low a light grease may also suffice if the temperature swings are not too great.

Wolfgang

mark wrote:

Thanks guys ...think I've managed to put him off .. by telling him hundreds of people are all trying to develop the same things ...many with university backing etc and the fact that, what ever you come up with ...Is going to have to be competitive in a market filled with B&Q type Chinese items. There is no chance ...in such conditions.

So told him, to get His thinking cap on, and to come up with something unique, that does not have anything to do with wind generators.

Then....... I will think about it.

All the best.....mark