windmill composter

[StoneHeartFarm]

Re: windmill composter / Minto\'s Wonder Wheel

RPM,

Do you think the longer tanks would take longer to fill? (Condense/evaporate cycle). The weight of the fluid being transferred and the leverage of that fluid on the axle is the force that is turning the wheel. Am I correct? The larger bottles would certainly have the weight and would contain more fluid. But, I'm wondering how easy it would be to heat that fluid for transfer? The smaller the container, the faster it will heat and cool and the faster the contents will heat and cool. So, I wonder if we're looking at a gain in hp but a loss in rpm by going to the larger tanks?

Another advantage to the multi wheel arrangement would be the ability to offset the cylinders from wheel to wheel, so the #6 cylinder on the #2 wheel would be between cylinders #5 and #6 on the #1 Wheel. Would that be an advantage?

SHF

 

[RPM]

Re: windmill composter / Minto\'s Wonder Wheel

Time to get out the slide rule ... I whipped together the attached drawing at lunch-time (sorry, had to do it in PowerPoint as I no longer am in the Mech Eng business /w3tcompact/icons/blush.gif).

I wanted to do this to show what I think are the underlying mechanics of Minto's wheel.

Diagram shows four tanks (simple) on a wheel. Hot water bath is at bottom of diagram. As water heats the tank that is in the water bath, the fluid evaporates and flows up to the opposite tank.

The change in weight due to the fluid moving between the tanks creates the turning moment (torque) that rotates the wheel.

Turning moment would be = ((m1+f1)g-(m2+f2)g).R.cos(theta))

Since m1 and m2 are the same (identical tanks) then they scratch each other leaving ...

Turning moment = (f1-f2)g.R.cos(theta)

So, the logical deductions are:

1. You WANT the wheel to turn slowly. The tanks will take a finite time to heat - transferring the fluid to the top. It's only once this fluid is transferred that the torque will be produced.

2. There is a linear relationship between radius / tank-size and torque.

Note that the torque is not applied evenly as there will be a change with time of the fluid mass as it transfers between tanks. I avoided doing the integration work as there are enough symbols on the diagram already. The controlling variable would be the flow rate of the fluid between tanks (could be controlled by a valve).

Hope this stimulates some further discussion!!

 

[StoneHeartFarm]

Re: windmill composter / Minto\'s Wonder Wheel

RPM

Whoa! the water just got real deep, real fast. /w3tcompact/icons/laugh.gif

I have come to about the same conclusion but in my usual fuzzy math way.

1. If the wheel is balanced, then without outside input, there would be no movement.

2. The ONLY thing that is changing is the gas/fluid which is being heated and moving from one cylinder to another.

3. Therefore the weight of the gas/fluid which is transferred is the driving force. That is what is making the wheel move. Therefore, leverage of this fluid against the axle is the producer of the hp. The more fluid that can be transferred, the more weight against the lever and, hence the greater the hp.

4. Faster speed means less heating time, which means less fluid transfer, which means less weight against the lever, which means less hp.

Assume the wheel has a diameter of 30', with tanks 3' long laid around it with their axis perpendicular (?) to the axle, (In your diagram, turn the cylinders so the tubing goes in the side), to allow the longest heating time.

30'x3.1416=94.25' The outer rim is rotating at a speed of 94 feet per minute. 94/60=1.57 Assuming a heat source 1' square, each 1' section of tank would be exposed to heat for a period of 1.6 seconds. With a water bath, the maxium exposure to heat for a 3' tank in a 3' trough would be approximately 8-9 seconds at 1 RPM.

A smaller wheel, say with a 6' radius and cylinders 1.2' long would follow the same rules, only due to the shorter nature of the tanks and the smaller diameter of the wheel, the speed would be .3' per second. Therefore, a 1.2' cylinder would be exposed to a water bath for a period of .36 second. I would expect a smaller wheel therefore to move slower than 1 RPM.

Assuming a minimum time of 8 seconds to effect the fluid transfer, this would reduce rotational speed on a 6' wheel to approximately 1/2 RPM.

1.2'x12"=14.4"/8sec=1.8 ipsx60sec=108ipm/12"=9' per minute
18.8' cir/9'=2.08 minutes or 1/2 RPM. (Remember, nobody ever accused me of making things too simple.)

With this loss of rotational speed, I would expect a loss of hp. (Much like throttling down an engine). The only solution I can see for increasing the speed and power of the small wheel is to A: use larger diameter tubing to connect the cylinders. B:increase the weight of the wheel to provide similar mass (hp requirement?) C:Use a different tank shape, with heating/cooling fins to provide more surface area for heat transfer. Maybe an oval shaped cylinder?

Hmmm, as simple as this wheel looks, there are an awful lot of factors involved in getting work out of it.

SHF

PS Check my fuzzy math to make sure I'm getting this right. Sometimes I think there's more fuzzy here than just the math. /w3tcompact/icons/laugh.gif /w3tcompact/icons/laugh.gif

 

[StoneHeartFarm]

Re: windmill composter / Minto\'s Wonder Wheel

Wait a minute, you did that on your lunch hour? /w3tcompact/icons/crazy.gif You must have a real good system, I couldn't do that in a week! /w3tcompact/icons/laugh.gif

SHF

 

[RPM]

Re: windmill composter / Minto\'s Wonder Wheel

SHF,

Sorry for the delay getting back on this one - had to print it out to think about it ...

So, really what we are talking about is small wheel vs large wheel and how could we get a small wheel to work and produce useful torque. (I prefer torque to hp - sort of the old diesel vs gas engine thing).

Large Wheel
------------

Key benefit - the large wheel has long levers (arms) - so that a relatively small transfer of fluid from the tank on one side to the other will produce a larger torque (turning moment).

Key issue - it's too darned big (unless you want to attach seats to the tanks and offer rides /w3tcompact/icons/smile.gif).


Small Wheel
-----------

Key benefit - more practical in terms of construction size etc.

Key issue - much harder to achieve the same torque (as you correctly stated). A greater mass of fluid has to be transferred between opposite tanks to make up for the shorter 'levers' or arms due to the smaller diameter of the wheel.

You really don't want to increase the speed of the wheel too much or the heat transfer from the water becomes an issue - too much splashing. Sooo... looks like three possibilities are:

(a) Larger tanks and greater mass transfer between them (possible as you stated)
(b) Improve the heat transfer efficiency by adding fins to the tanks (or similar - also as you stated) - or increasing the temperature difference between the water and the air.
(c) Use a more volatile liquid in the tanks

We'd probably want to look at (a) and (b) together. (c) starts to raise another concern - this would be turning into a very effective cooling device for the water.

Have to remember the basic law of conservation of energy - the energy generated by the system (wheel hp) cannot exceed the energy supplied by heating of the water.

So ... the maximum hp of the wheel is actually governed by whatever is heating the water - and then factoring that down for losses in heat transfer, friction etc.

Maybe time to spend a bit more effort looking at that heat source ...

 

[RPM]

Re: windmill composter / Minto\'s Wonder Wheel

Just PowerPoint and too many years of experience fooling around with CAD and technical diagramming systems.

The PC is a Pentium III 750 MHz (or thereabouts) laptop with 256MB RAM running Windows 2000. Standard corporate issue these days - a heck of a lot faster than the old Pentium 233 MMX I am typing this on at home.

 

[StoneHeartFarm]

Re: windmill composter / Minto\'s Wonder Wheel

RPM,

I believe you are right. Torque is the operative word here. The websites are all taking about HP, but what this wheel really seems to be producing is torque.

The torque output will be increased or decreased based on the weight of the fluid being transferred, not necessarily the volume, although volume becomes an issue when compared against itself. ie, big wheel propane, small wheel propane. Big wheel freon, small wheel freon, etc.

I think you are seeing the same problem with the big wheel that I am. In most localities, you would need a building permit and would probably be in violation of zoning for something that big. Smaller wheels seem to be the way to go, which is why I am leaning toward multiple small wheels on a common axle, (like "washers on a bolt"). This would allow a greater transfer of fluid due to multiple cylinders, each making up a portion of the whole. We would need enough cylinders to make up the loss in overall cylinder size and the loss in leverage from the shorter arms. (Long throw, light weight=torque. Short throw, heavy weight=same torque. Correct?)

I would expect balancing to be an important issue because one heavy cylinder would tend to hang, slowing the wheel through part of its revolution, and speeding it through the other part. I would expect balance to be less of an issue with wobble, other than a premature wearing on parts. (Darn, the thing might only run for 100 years instead of 500/w3tcompact/icons/laugh.gif.)

Also, how about alcohol as the fluid? I'm thinking something somewhat less explosive than propane. One leak and you've got a fiery wheel in the sky. Make all the neighbors call the cops complaining you're launching UFO's at them. /w3tcompact/icons/laugh.gif

For the heat source, I'm thinking hydronic radiant. They are making small panels now, stand alone jobs. I'll see if I can find the website again and get some info. It would eliminate the water bath and provide a closed system that could be run off a small boiler, easily fabricated. The website is talking about running off a closed loop from buried tubing that is basically capturing ground heat. I only see that working part of the year.

SHF

 

[RPM]

Re: windmill composter / Minto\'s Wonder Wheel

Hmmmm ... the inclusion of external heating sources starts to defeat the purpose. The reason why Minto's wheel is not more widely seen must be due to some of these problems we are running in to!

1. Difficulty getting torque from a small wheel
2. Difficulty handling volatile gases (freon, propane etc.)
3. Difficulty finding a cheap, sustainable source of heat to power the wheel.

By the way, we would either need to keep a gas like freon at a high pressure so it can condense -- or keep a liquid like alcohol at a low pressure so it can easily evaporate. Either way we have to maintain a pressure sealed system. This would require some serious experimentation to find the right pressure to allow this phase change to happen with only a minimal temperature difference (e.g. 3 degrees). The pressure would probably have to be adjusted over the weeks / months of operation to keep this in balance with the ambient temperature.

Although it is an interesting idea, I must confess that I am tilting back towards the windmill idea.

Besides, I was out flying kites with the kids this evening and I had a great time!!

 

[StoneHeartFarm]

Re: windmill composter / Minto\'s Wonder Wheel

RPM

Starting to figure that one out myself. This looks like a really interesting toy, but I'm not sure how much real work could be expected out of it. The main problem appears to be the propane/alcohol. We either have something that is explosive, or something that will be much more difficult to evap/condense. It seems it would be easier to maintain a vacuum than a positive pressure. Just put a one way bleeder valve on the line and let the unit "burp" itself.

Although, under load, any slowing of the wheel would result in a greater movement of the fluid and therefore, more weight on the lever and greater TORQUE. The wheel, once moving, should take a minimal amount of force to keep moving. (A wheel in motion, will stay in motion until stopped by gravity, friction or some other outside source.) So, for a high torque, low output situation, the wheel would be ideal. I just don't know of too many of those.

I may eventually play with a small table top model of this, just to see what can be done, but as a work engine, I think there are probably better solutions.

SHF

 

[StoneHeartFarm]

Re: windmill composter / Minto\'s Wonder Wheel

RPM

Here's a link to the heat exchanger I was thinking of.

http://www.spnwonline.com/Templates/frmTemplateM1.asp?SubFolderID=43&searchYN=N

SHF