Savonius

Interested and fascinated - I'd love to get any details you have available - particularly of how much water you heated and the design of the heating paddles. I put up a post here a while back asking that exact question (whether you could viably heat your hot water using the energy from a paddle run by a Savonius) - got some interesting replies, but I'm pleased to hear it worked!

For this purpose (heating water) is speed of rotation of much importance? I wondered if you could increase torque by using a bigger radius and more half barrels - eg 4 or 6 mounted on a single horizontal plane - all at the circumference. (In fact that's the way I read the OP which you interpreted as two barrels side by side).

Is there much drag on the back of a barrel? I had in mind some kind of hinged flap(s) replacing the metal curve of the back so the wind could blow straight through the barrel in one direction, but catch the wind in the other (noisy though - and perhaps more complex than the benefit justifies).

Looks like my quest to fill our garden with empty oil drums is back on!

(** long suffering partner rolls her eyes and groans).

Ah, yes, read the interesting thread (Friction heating water) on

http://cr4.globalspec.com/thread/2144

where there are some very relevant comments, including several advocating simplicity.

Yes, a heat-pump will give a far greater efficiency, but you'll need a compressor, a heat-source (ground-loop ?), a heat exchanger to the water, circulating pumps... starting to look like a gas-works compared with an old back-axle...

I too seek simple designs for heat-pumping, for I feel it is the future:

http://simeonlapinbleu.googlepages.com/theliquidpiston

http://simeonlapinbleu.googlepages.com/lordkelvin%27s

Why create heat at perhaps 1000° and then dilute it to bathe the kids. Better to take very dilute heat and scrape it together into a pile...

We used four 'paddles' on the drive-shaft, and five inside the drum. This was to ensure that all the water was not 'squeezed' at the same moment during the rotation, and gave a more regular speed. Our vanes and paddles were made from fairly thin sheet metal (more oil-drums) but formed into 10° triangles to give rigidity. The vanes passed about 10mm from each other.

A standard 40 gallon (180 litre) drum gives two very luxurious baths, more if the water approaches 50°C. This would take all day, with a good breeze, but we rarely used all the water in a day...

RobertOz writes:

> Is there much drag on the back of a barrel? I had in mind some kind of hinged flap(s) replacing the metal curve of the back so the wind could blow straight through the barrel in one direction, but catch the wind in the other (noisy though - and perhaps more complex than the benefit justifies).

There is less drag on the back of the barrel-curve, or the rotor would not... rotate. It would be interesting to know the ratio of drag between front and back... The back of the curve is moving 'upwind', and so its rotational speed must be added to the wind-speed.

I have seen a Savonius with a hemi-cylindrical wind-shield, pivoted about the centre-line, which protected the 'upwind' side of the rotor, these barrels moving in still air instead of against the wind.

This shield could be free to follow the wind direction, with a fantail, or blocked in place to reduce power or even stop the rotor.

Any 'hinged valve' assembly to spill the air has been more than troublesome, and very noisy, but perhaps with modern materials (Silicones?) one could do better. Something like a heart valve?

Del the Cat writes:

> ...the half drums should overlap slightly so that air spills from one to the other, this has been shown to give maximum efficiency...

We arranged the two halves of our barrel on sliders, so that they could be positioned with differing overlaps to investigate this phenomenon. This led to a rotor bearing weights which, as they were flung outwards with speed, slid the two barrel-halves together. The rotor could thus also be clamped shut in gale conditions.

But, and probably because of the non-linearity of this 'spilling' effect, the regulation was not very, er, regular. It did prevent overspeeding, though...

Can one reply to oneself? Here goes...

Lapinbleu writes:

> Our mills usually used car rear-axle hubs as bearings.

A rear axle was almost designed to build a Savonius rotor on: a bit taller than an oil-drum, mounted with knobbly bearings, waterproof...

Weld one of the brake-drums to the backplate: The axle now has a solid and rigorously perpendicular mounting surface, with some chunky studs, the nuts for which are in your pocket.

The upper brake-drum provides an identical surface, but which rotates. You can use the hand-brake cable to slow and stop the rotor.

Because the lower half-shaft is blocked any rotation of the upper must result in torque on what was the input side of the differential. That, too, has a nifty universal joint attached.

Because the differential normally reduces the speed of the prop-shaft by 2 or 4 : 1, you get a corresponding increase in speed on the output shaft, which is also horizontal. Handy, that, for power take-off...

Differentials are not made to work like this, but you'd be a long time wearing one out. What was it now? Sawdust?

"Can one reply to oneself?"

Ya, it's called bi-polar personality . I'm doing this when nobody listens to me...or when Hot disagrees with tech. Overall' I'm Hottech.

BTH, very good posts, Blue Rabbit. Andy also made a very valid point.

Hottech writes:

> "Can one reply to oneself?"

> Ya, it's called bi-polar personality

Hoo! Gemini, that makes two; Gemini rising, that's four already...

A bit schizo and there's eight of us in here... Getting a bit crowded...

²(;o'# Beard, beret and roll-up...............................

Thanks Lapinbleu that makes sense now you've pointed it out to me. I'm fasinated by your hot water system and will probably try and pick your brains in the future.

Alan

I am also interested, please write further about your experiences asap. Thanks.

Thanks Andy I'm just going out to the workshop to modify my design. Thanks for the input.

Alan

You wrote:-

We have built simple centrifugal regulating devices for Savonius rotors, which slid the two halves of the drum towards the centre with increasing speed.

I am interested, please post. Thanks in advance.

I used to work for an automotive testing company back in the late 70's and the engine test beds used to run 24/7.

The load put on the engine was by way of water filled drums, such as you describe...

With a V8 running at full throttle the amount of hot water produced is phenomenal!!! Plus we had 12 engine test beds, so the hot water was piped around the company and sold to neighbouring companies...

A very effective Combined Heating and Testing system...

The occasional fire when a oil line burst onto a red hot exhaust manifold, or when an engine was tested to destruction and blew up, made a refreshing change to the humdrum life!!

John.

Electroman writes:

> ...by way of water filled drums, such as you describe... With a V8 running at full throttle the amount of hot water produced is phenomenal!!!

I can well imagine. All the shaft horsepower must end up in that water.

And the thermal efficiency of a 70's V8 would have still been dreaming of 20%, so at least four times as much heat is lost in cooling the block. Did you use this as well ?

No, the test engineers had to simulate actual road conditions with load and throttle settings etc... So the heat produced by the engine was wasted by using hurricane force huge fans blowing air through the cooling radiator fins and over the engine.

Those fans were something else!! they would easily blow you off your feet... Walking through the test beds late at night it often made me wonder at how the place managed to stay up, when you have 10 of the 12 engine test beds running, some with screaming engines at various stages of power settings and of life testing... It was quite unnerving to only find a few technicians wandering about amidst all the heat and the noise of raw power!!

It was incredibly well insulated for noise, as the building was in the middle of a residential area and as soon as you walked outside the sounds were minimal...

This was ERA (formally known as English Racing Automobiles) and we would always get the latest sports cars in on the rolling roads and the engines on the test beds...

John.

Hi Electroman.

What you described is called; "A water brake Dynamometer". I built a small one to test my Stirling engines back in the 1980s, the heat produced can be so hot that there has to be an inbuilt expansion chamber! I also built a small disc brake lever arm dynamometer for testing my model plane engines.

The Swedes have used Savonius rotors for the past 45 years to produce electricity, and you can often see them in use in remote log cabin locations!

Spencer.

The others have given some good answers already..but another point is the half drums should overlap slightly so that air spills from one to the other, this has been shown to give maximum efficiency.... obviously you can't do this if you extend it latterally.

Del

A big part of the effectiveness of the savonius rotor comes from the 's` shape.

You'd do better, per unit area, to extend it vertically.

How come #13 gets a 'good answer' for what I said at #5 !? .

Just 'cos he nicks a pic' of Wiki ! What a swizz I shall write to my MP's Son about it (English topical political joke)

Del

Hi Kris.

I just love it, this is a very elegant design and I would love one.

By the way, I could not find the village/town where you live on any of my OS maps, where do you live, what county?

Spencer.