h a l f b a k e r yExpensive, difficult, slightly dangerous, not particularly effective... I'm on a roll.
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Solar ovens are Baked (no pun intended) and are fine in sunny parts of the world; but what about when it's cloudy - or dark ?
However, in the Winter, it can be quite windy; hence the idea.
Many UK properties have a (now redundant) chimney stack arising from the kitchen. The idea would be to
place a large windmill at the top of the chimney.
The energy collected by the windmill is transmitted down the flue by a sectional tubular shaft. At the base of the chimney, the shaft is coupled to the oven, which has a sealed chamber containing a convetional brake drum or disc, and a set of friction pads. A centrifugal governor controls the amount of pressure applied to the pads.
When the wind blows the disc spins; friction makes it hot. When the wind is strong, the disc becomes VERY hot. The windmill has a varaible-pitch device to stop too much energy being collected and burning the food.
The system would be very efficient as it converts mechanical energy directy into heat; there is no intermediate electrical generator/heating coil stage.
A 2m diameter windmill can collect several killowatts of power - enough to heat a typical domestic oven. The idea would be to use the system in the manner of a slow cooker, for foods that require steady average heat over along period, like stews and casseroles.
The sealed chamber prevents fragments from the friction process from contaminating the food. Geared fans stir the air on both sides of the dividing membrane making it a fan oven and ensuring efficient heat transfer.
Rotation Outlet
http://www.halfbake...a/Rotation_20Outlet
your appliance fits well with this [FarmerJohn, Aug 15 2002, last modified Oct 05 2004]
Not windy enough!
http://cleantechnic...wer-doesnt-pay-off/
If only it were a little windier in the UK! [mylodon, Sep 04 2008]
[link]
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Easier, I think, to power an electrical generator and use a conventional electric oven. |
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Also, the placement bothers me: a large windmill would be more than enough to topple most chimney stacks, which are do not usually have much lateral strength (growing up, I saw the aftermath of several collapses, including one into a friend's bedroom) (fortunately no one was injured). |
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DrCurry: Electrical generators waste a lot of energy in the generation process, through iron and copper losses, and through friction. The direct mechanical transfer of energy is very efficient. |
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Chimney stacks could be strenghtened with reinforcing straps and bars. It's not that difficult. Using an electrical generator would add to the weight at the top of the support gantry; for the pure mechanical version, the only weight is just the windmill rotor and a couple of bevel gears. The self-feathering mechanism keeps the lateral force on the gantry to an acceptable level. |
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Maybe if you fill the chimney shaft with concrete around the drive shaft. You could use this to make a heat sink too. See link on wind power rotation 'grid'. |
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Concrete works well for compressive situations, but isn't that great in bending. And the roof might need an upgrade as well. |
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My question is this: what materials do you use for the brakes? You wouldn't want to have a bunch of brake shoe dust in your food, and the smell of hot brake metal isn't particularly pleasant, either. Food protection from a greasy mechanical monstrosity is going to be a tough challenge. |
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The other problem is timing. To be effective, the thing is going to need some sort of energy storage system, whether it be electrical, flywheel, or what. You don't always want to cook when the wind blows, nor does the wind usually blow that hard 'round suppertime. |
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"Looks like its pizza delivery again tonight, kids. The wind just refuses to blow." |
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Chimney flues are rarely straight. Also, a conventional alternator would, as DrC suggests, be far more efficient. |
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Angel: No, that's my point. It wouldn't be more efficent. By definition, it can't be. Energy is dissipated in the generator though electrical resistance, and magnetic effects (Back EMF, iron losses). Then there would be resistive losses down the cable - look up the total power transfer theorem, and impedance matching (I will provide a link).
In this design, 100% of the mechanical energy arriving at the oven is converted into heat. That just leaves the mechanical losses in the transmission system. Bevel gears on the windmill will probably have less loss than the step-up gearbox needed for a generator, as they are a 1:1 ratio; and the drive shaft - if built with decent bearings - should be nearly lossless; maybe 3 - 5 % at the most. The generator alone will waste 25 - 30% of the inpout energy as heat.
Thermodynamically, direct mechanical transmission is more efficient than converting to electrical energy, then to heat. Give me a few days and I'll post the equations and the figures. |
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//Chimney flues are rarely straight//
I knew it. I just knew it.
Due to housing ordinances, a modification of such extremes - whether portable, semi-/permanent would likely have regulations on several levels, whether municipal, county, state, federal.
If windmill apparatus is in a fixed location, what is protecting the entirety of the windmill from smoke/creosote/heat? |
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[8th of 7] I have to agree with the others on the use of direct mechanical energy. |
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How big is this windmill that it's going to be able to turn a disc that's being braked? |
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I'm guessing you'll have to use some sort of gearing mechanism to create a great deal of torque and that the gearing will have to change based on the rotational speed of the windmill (regardless of the variable-ness of the pitch of the blades). Mind you, I'm not a mechanical engineer. |
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Mechanical energy is easily converted to heat by stirring a liquid. You don't even need a 'thick' liquid, if you use counter-rotating plates close to each other. Then you can pipe the hot liquid around the oven, or the radiators. |
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pfperry: that was an idea i was also considering but I didn't want to make the idea overly long. A modfied fluid coupling and hydraulic oil would do the trick. Award yourself a notional croissant. |
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phoenix: It's the centrifugal governor that changes the grip of the pads on the disc; the gearing is constant until the windmill reaches maximum safe revs, after which the blades start to self-feather. It's an all-mechanical control sysem with constant gearing. At low revs, the pads come off completely to allow the winmill to spin freely giving low start torque. On consideration, a flywheel somewhere would be a good idea. I thought originally the blades themselfes would be enough, but thinking about it, better to have a lighter windmill and a seperate flywheel in a fixed location. The windmill would be a couple of metres across. |
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I want to use a windmill to heat the house directly, either straight to hot air or by heating water. I know if you just stir water it gets hot (has a special name that I can't for the life of me remember) Has anyone come across any systems to do this? |
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Use AIR friction for heating using a compressor driven by the windmill. I just logged on because I am looking for an efficient design to do this. The problem I see with mechanical is the high wear and replacement hassles |
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Put the windmill over the halfbakery server. The hot air rising from that ought to power all of our ovens. |
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Maybe you could use a system based on inertia welding, sorta': have the windmill rotate a vertically-oriented aluminum rod, an inch in diameter or so, that is gravity fed and whose lower end rests upon a roughened tungsten receiver. Through continuous rotation against the receiver, the lower surface of the aluminum rod would heat to a molten state and continuously slough off into a reservoir, a foundry block (hi-temp ceramic) crucible, beneath the cooking chamber. You'd cook from the heat of the molten aluminum. You'd have to put in new fuel rods from time to time. |
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Oh, and empty the crucible every now and again. |
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I make windmills and the energy one can capture is the swept area of the rotor times the windspeed cubed. So you would need a massive rotor to produce heat needed for baking. A better way to cook with wind would be to have the shaft of the rotor turn a paddle inside a sealed water, or oil box and let the water heat till it boiled. A pressure valve could then let the water or oil out via tubing that passes through a cooking pot. Would also work to heat any space. No need for a chimney. A workable idea. I read about it being done somewhere. |
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I like the idea of a "Friction Oven"
- rubbing your food to heat it up. |
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Although the oven part may not be practical, I love the idea of heating something (perhaps a home in a cold, windy climate) with the friction of a shaft turned by the wind. I do believe your efficiency arguments are correct. The one thing that I am unsure of is the lifetime of the device. The fluid coupleing sounds good. |
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Are there any examples in real life of a mechnical input (shaft turning, etc..) that is used to generate heat? |
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[+] for the idea of using a windmill to heat the house. |
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Windmill on the roof seems like a good idea to help my furnace out. Water boiling and radiators... is there any better way to heat a room with mechanical energy? An no obnoxious grinding noises? |
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As has been pointed out, generating electricity is ineficient, and like most ineficient systems, the waste energy is released as heat. If you had a drive shaft down to the area to be heated, the generator and gearbox inside the conditioned space, and then feed the electricity to a heating element if additional heat is needed in that location, or other uses/locations as needed, it would be just as useful as the friction drive, quieter, and have the possibility to feed electricity back to the grid/other appliances when not needed for cooking. |
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Replacing the water-heater next weekend and futzing around with the chimney so's it doesn't fall off... wish I had [bronco]'s [sep6,2003] addendum. |
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I disagree with the folks who want to get electricity involved. While it is true that the wasted energy in the lower end will go into heat, there is wasted energy at the upper end. An electric system will require a larger windmill than a mechanical one. |
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As for transferring the mechanical energy downward, do not gear the thing for maximum torque. If you do that, you'll need a heavy driveshaft, which is expensive and wasteful. |
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Take the lightest possible driveline, spinning fast (which might allow the use of a flexible shaft for the crooked chimney). Then, at the bottom, use whatever friction device works best at that speed. |
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The friction heater that I am thinking of is a is a soft cloth polishing pad rubbing on the bottom of a copper pot. At high speed it would generate as much heat any other method at any other speed. |
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That system would deliver heat directly to the bottom of the pot, and with a proper pad, keep the pot polished but not wear it out. The pad could be removed, cleaned or replaced easily. The only debris would be cotton (or whatever the pad is made of), and perhaps metal from the bottom of the pot (which is already on the inside). |
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Oh, and the pad could be treated with grease, rosin or all kinds of stuff to manage friction. |
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In sum, a windmill, a fast flex shaft and a cloth pad rubbing the pot. I guess that makes it a stovetop, doesn't it? Well, if you have the cloth polishing a thick sheet on the bottom of an oven, it might work, too. |
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If you want to heat water in a pot, the friction system only needs to go up to 100 C. If you want to bake bread in an oven, you'd need something a lot hotter. |
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//friction device// water seems to be the best: no ablation and no fire-mitigation devices needed. The smaller the shaft diameter, the less the heat-transfer through the shaft... It does seem very counterintuitive though: "I'm gonna stir this water 'til it heats up." <new post added: "Mechanically Powered Hot Water Heating"> |
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// the pad could be treated with grease, rosin or all kinds of stuff to manage friction. // |
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Isn't friction what you want though? |
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Friction is one of those things you have to strike a balance
with, mechanically speaking. Consider a tire on a road: too
little friction and the wheels will spin, too much friction
and your differential explodes. |
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That's why I said "manage friction". I didn't say "eliminate". |
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Rosin would increase friction, grease would decrease it. A mix of the two would give an ideal that could be customized to the system. Too much friction would stop the mill and tear up the pan, too little friction would cause no heat. An adjustable lower end would be handy--pouring liquid on a pad would be fairly simple. |
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Sorry, some days I expect people to follow my feverish thoughts. |
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