Half a croissant, on a plate, with a sign in front of it saying '50c'
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Nitinol car

Nitinol powered car
  (+5, -3)
(+5, -3)
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A while back I learned that if you got a nitinol ribbon and wrapped it around 2 pulleys, then you heated one side and cooled the other, the pulleys would spin. So I thought if you had a battery and an alternator connected to it it could have a seperator with a heater in one side, and an A/C system in the other, and it wouldnt really need any "tangible" fuel other than heat.
Charlesr1, Oct 19 2004

All about heat energy http://www.chatham....PDF/Snodgrass99.pdf
Shows that this idea DOES work, its under Thermal To Mechanical Transformation (p.12) [Charlesr1, Oct 19 2004]

Experiment 74. Thermobile http://outreach.web...ics_fair/Exp54.html
Gives a better explination on the forces going on. [Charlesr1, Oct 19 2004]

Nitinol http://www.imagesco...itinol/nitinol.html
SOme basic info on Nitrinol and a source to play with [csea, Oct 20 2004]

Even more Nitinol
how it was discovered, how it works, and some of its current uses [Cubical_View, Oct 21 2004]


       //and it wouldnt really need any fuel// Thermodynamics breakdown alert. You'll use energy on either/both the hot side or the cold side. Heating and cooling requires energy.   

       Welcome to the 'bakery though. Check out the help file (link on left).
Worldgineer, Oct 19 2004

       This does take energy. It relies on a heat differential, which takes energy to create. That heat differential could be harnessed by another type of heat engine, for example a Sterling Engine.   

       However this is an interesting type of heat engine that I'd never heard of before. Could you post a link to more information about this?
scad mientist, Oct 19 2004

       Unfortunately, I havent seen much information on this, but I will keep looking for more.   

       And I said this takes no tangible fuel, like gasoline. I didnt mean to say it didnt need anything to start it.
Charlesr1, Oct 19 2004

       I agree with [scad] that this an interesting heat engine. However, you're missing the fact that it is a heat engine. Heat engines use a differental in heat to create kinetic energy. The engine in your car is a heat engine - it uses the difference in heat between a burning gasoline and outside temperatures and changes this into kinetic energy.   

       The Nitrinol car would need energy not just //to start it//, but to keep it going as well. Let's take a look at a little piece of the wire. It's warmed up when it hits the water, which makes it turn the pulley. At the same time it has cooled the water a little bit. The piece then travels into the air, where it cools off. After one cycle the air is a little warmer and the water is a little cooler. Eventually the water and the air will be at the same temperature, and your engine will stop.
Worldgineer, Oct 19 2004

       Well, I was hoping that if it could drive an A/C pump and an alternator, it would be able to keep the temperature differential, but I am a high school student, not a physics expert, so im not sure if it could work as efficiently as I imagine it. But its just an idea.
Charlesr1, Oct 19 2004

       And a good one at that. The only part I have an issue with was trying to get free energy from it.
Worldgineer, Oct 19 2004

       You could get the energy to run the car any number of ways.   

       I'm not sure how *practical* this idea is. But I'd love to have a nitinol car, even if just as a toy. Croissant.
Almafeta, Oct 20 2004

       // this takes no tangible fuel, like gasoline. //   

       Then how do you create the needed heat?
waugsqueke, Oct 20 2004

       Well for the heat needed to start it, i would just have a normal 12 volt battery powering a heater, and possibly a starter motor if the engine needs it to get going. And when the engine runs, it will use an alternator to recharge the battery and power the heater to keep the temp. differential.
Charlesr1, Oct 20 2004

       If I recall correctly, Scientific American's "The Amateur Scientist" back in the 1950s or '60s detailed how to create a heat engine based on rubber bands - turns out rubber due to its stretchability has a large capacity to do work based on heat differences (and conversely, to create heat/cold when mechanically stretched/contracted.)   

       This is easy to demonstrate - just take a standard rubber band at room temperature and stretch it, then sense the heat rise by touching it to your face or lips (one of the body areas most sensitive heat.) Then let the stretched band cool off to room temperature, let it contract, and note the cooling.   

       Nitinol has the useful property of being electrically conductive, and can therefore be heated by passing current.   

       It's really interesting to consider all the means of energy conversion to and from thermal / mechanical / chemical / electrical / gravitational / kinetic / nuclear / light / etc. forms. (At least if you are not afraid to demonstrate a bit of nerdiness!) Some of the conversions are well known, and others may be ripe for investigation.   

       See [link] for some more info on Nitinol.
csea, Oct 20 2004

       // i would just have a normal 12 volt battery powering a heater, and possibly a starter motor if the engine needs it to get going. And when the engine runs, it will use an alternator to recharge the battery and power the heater to keep the temp. differential. //   

       So it runs on electricity then. That's 'tangible fuel'. Not sure what you're considering it.   

       Using an alternator to recharge a battery to keep the alternator going is revealing your misunderstanding of some basic scientific principles.
waugsqueke, Oct 20 2004

       Use nitinol for the body. that way, after you bash it against an electric post or something, restoration is only a kettlefull of hot water away.
neelandan, Oct 20 2004

       I thought fatigue would be a problem for anything made of nitinol, but from the link it seems the stuff is good for years of use.
Cubical_View, Oct 21 2004

       Good to see you again, neelandan. In the absence of Vernon, our paths haven't crossed since the crash.
david_scothern, Oct 21 2004

       You're talking about a perpetual motion machine. That's usually grounds for a [mfd].   

       In order to run any system with losses, an energy source is required. In this system, you have no input. You create a heat differential, the engine turns. OK so far. You use the torque created to power an alternator. OK so far. The alternator charges a battery. Still ok. The battery powers a heat pump. Still ok. That heat pump provides the heat differential to keep the engine running. That's where it all breaks down.   

       Since there are losses in each step of the process, you'll never be able to break even. The heat pump must do work to move the heat, and this requires energy. If everything were perfectly efficient, you'd break even and the system would just keep running. If you tried to extract energy to do any work outside of the system, the heat pump would have less energy to do its job, and the thermal differential would become smaller. Eventually, there would be no differential, and your engine would stop.   

       In the real world, since there are losses in any system, you're already going to be extracting energy, simply by radiating heat.   

       As an engine, this idea is going nowhere, literally. As a potential waste heat recovery device, it has potential.
Freefall, Oct 21 2004

       You could use a conventional fuel to heat the nitinol ribbon. Wonder how efficient the stuff is?
Bal, Oct 21 2004

       I understand where you are coming from, but if the heat side is well insulated, it might last a lot longer. But I would never expect it to be even close to perpetual. I was thinking of a cheap, clean vehicle that you can go short distances in, If anything this is just an idea to spark better ideas with.
Charlesr1, Oct 21 2004

       [mfd] removed, since you're removing the perpetual motion part. Though I think you'll find that warm water won't get you very far very fast.
Worldgineer, Oct 21 2004

       this is already a well documented concept, using a different "working fluid" than most heat engines. problem arises in implementation, and that's why we still see these mainly in toys and hobby stores.   

       however, MEMS and nanotech have made the technology of interest once again, as new design paradigms and limitations have opened the doors.   

       i got ya with the tangible fuel part...i'm not gonna knock you like everyone else and assume you meant that this is a perpetual machine...although it is interesting to note that b/c nitinol engines require an energy sources that is spatially configurable, it would be possible to drive it in an imaginable world through any temperature gradient (sustainable by solar energy of course).
jc_01, May 25 2005

       I'd be interested to see how much power can be derived per degree of heat differential. I fear the number to be too small for realistic power generation, unless you have a very large differential. I like the imaginary world where differentials run amuck and little vehicles zip around on them all day long.   

       What if you put one end in the sea, and another in, oh, let's see... space?   

       Could the process be scaled down for nanomotors?
daseva, May 25 2005

       I only picked up on this a short while ago and felt that the core idea it shouldn't be dismissed that quickly. The thermobile is a very interesting device. The thread, as it reads, appears to assume that the work is performed along thermodynamic lines, ie the temperature gradient. You make the hot end hotter and the cold end colder and you get more work from it. In the case of nitinol, one of a group of SMA's (shape memory alloys), this is not so. The work is performed by molecular forces. For the thermomobile there are two crystal states that are of interest. Martensite where the crystal will deform easily and the Austenite phase where the crystal returns to its "memory shape". The temperature gradient is required to overcome the hysteresis, which for nitinol is about 10 degrees. The transition from Martensite to Austenite occurs at about 70 degrees C and the transtion forn Austenite to Martensite occurs at about 60 degrees C. It follows then that the amount of heat required to perform this change is the specific heat of the nitinol ribbon per degree multiplied by the length multiplied by 10 degrees. Increasing the temeperature gradient doesn't get more work from the system. In fact if it is too great it can be counter productive. Any heat used in heating above the higher transition temperature or cooling below the lower transition temperature is heat wasted. In that respect it is not a conventional heat engine.   

       The really important question here is "where does the effort come from?". The short answer is from the crystal lattice of the nitinol as it resumes its "memory shape" in the Austenite phase. The force exerted during this transition is considerable. Wearing the "you can't get something for nothing" thermodynamics hat again, logic says that the heat has to play some part. It is possible that the heat required to overcome the hysteresis, plus the force required to deform the crystal in the Martensite phase is equivilent to the amount of work you can get from the system. Some heat will also be released during the deformation which will need to be replaced to achieve the Austenite phase again. However, having played with nitinol for a few years now my gut feeling is that, this is not the full answer. It needs a better mathematician than me to prove it though. For example the hysteresis varies between different SMA's as does the force available from the transition but the specific heat remains more or less constant. If the heat used and force required for deformation are not equivalent to the power produced in the Austenite phase, and the plus is in favour of the Austenite phase you may be on to something. My heart would like this to be so but my head tells me it can't be. I have never seen it adequately explained where the "extra" force appears from.   

       My interest in the thermomobile though is for a different type of vehicle. The standard setup is two wheels, a brass wheel acting as a heat reservoir, and a larger wheel. The brass wheel is heated to above the transition temperature of the nitinol, with the models you immerse the brass wheel in hot water, and with a little push start the wheels will spin. The device is one of high torque and low rpm. Suppose however that you replace the brass wheel with a sintered platinum wheel and you direct a gentle flow of methanol vapour onto this wheel. The platinum will catalyse the methanol and produce heat. You control the methanol vapour flow thermostatically so that just enough heat is produced to raise the temperature of the platinum wheel above the transition temperature. Residual heat could be used to assist the vapourisation of the methanol. It wouldn't win any prizes for speed but it should go one heck of a long way on a litre of fuel.   

       Sorry about the length of this posting
myxamycota, Aug 23 2005

       As for a source of heat, why not use the cooling system of a liquid-cooled combustion engine? Since heat is a waste product of gasoline combustion, why not put some of that heat to use to assist in propulsion? Of course, this idea is entirely impractical -- the last thing we need to add to our cars is a bunch more belts, gears and bearings to break.
junglefish, Aug 23 2005


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