Half a croissant, on a plate, with a sign in front of it saying '50c'
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Air turbine heat machine

Not a Gas Turbine, but a pneumatic motor, absorbs heat and cold
  [vote for,

I'm assuming that getting the work directly from LTD (low temperature diff) is expensive, and not easy. But, if I feed it into a working machine, and have the diff "ASSIST" a process, I'll get much more work out of a system like this for a fraction of the cost.

If I have low heat water at 80 degrees C, and cold water at 0 degrees C (with anti freeze) currently I'm supposed to use it only either with a Stirling engine which is noisy and it seems large and expensive, or with a gas turbine (which is MUCH more expensive and) which needs to heat up, to much higher temperatures, in order to work.

If I only have 2500 liters of each (hot and cold) fluid flowing per hour (with that temperature diff you have about 180 kWh) - using an aquarium water pump... and want to make that into useful work with a ~30% efficient engine, putting out ~54 kWh with a generator, how about the following:

Have a small air engine running a generator. The air engine gets its pressure from an air compressor.

At one of the following points (need to decide which is the best or perhaps at all points with different temperatures) have radiators heating the air:

a. The entrance to the compressor, (compressed has more energy)
b. The exit from the compressor, (brings up output pressure)
c. The entrance to the air motor (same as b)

And cool the air with a radiator, at one of the following: a. The entrance to the compressor (compressor works less)
b. The exit(s) from the air motor (brings down pressure, assists the motor.

The heating and cooling can be done "offline" in advance, prior to being consumed by the system, and brought into the system with a vacuum valve. The exits can be cooled themselves, or have the air in their vicinity be extracted, using the ice.

...The aquarium pump cost $50 and has a 6 year (or was it 10 year) warranty !

pashute, Jun 01 2010


       just 2 tell that i just had a real world halfbakery experience: funded dev i was working on found to be baked !
pashute, Jun 02 2010

       Finding things are "baked" is not that uncommon in the real world, even putting aside obscure precidents like Victorian, mechanical fax machines.   

       A lot of people out there are trying to solve problems in isolation and it is easy to overlook developments in other cultures, fields and even the company next door!
Aristotle, Jun 02 2010

       I know, I had this several times with inventions we were developing. But never for something already funded, of course after research. (Nothing to do with the idea here, just was going to add annotation, when I found out about it.)
pashute, Jun 02 2010

       OK, after discussing with my competition, it turns out they are only in the research stage, that some our ideas are different and benefitial to each other, and that their solution is only for a slightly different problem. So we'll be cooperating, and I'm continuing the proj.
pashute, Jun 07 2010

       Anbody has anything to say about this idea?   

       I'm building one, and trying it out.
pashute, Jun 07 2010

       To calculate the maximum available work that can be extracted from a system you should use the Carnot equation   

       E = 1-(Tcold/Thot) = 22.6% for your system.   

       Note that temperatures should be in Kelvin and not Centigrade.   

       Now, there's very little chance that you'd get all of that available energy.   

       Anyhow, even if you only get 10% of it, you'd still be getting 2.26% of the available energy. Which would be:   

       0.0226(efficiency) * 2500 (mass) * 80 (temp) * 4200 (heat capacity) / 3600 (seconds in hour) = about 5.2kW   

       Which is a nice amount of power. Especially if all this heat is free.   

       If you used something like ethanol and instead of compressing it (where it wouldn't boil at 80C), expanded it into a vacuum, a reasonable efficiency could be achieved. Google the “museum of retro technology” for examples using ammonia, mercury and petrol.
saedi, Jun 07 2010

       If I understand correctly, you propose to increase the effeciency of a system which is turning electrical energy to rotary motion to air pressure to rotary motion and back to electricity.   

       I'd be surprised if the little energy you could recover outweighed the losses.   

       Stirling engines are far from noisy (I've built small ones and seen larger ones running).   

       The principal you are proposing to use (recovering heat energy by using it to affect expasion of a gas) is no different to the stirling engine.   

       Why would you expect to do better by adding more layers of energy transfer and consequent losses?
Twizz, Jun 08 2010

       [Twiz] Thanks for the remarks. No, it's mainly heat difference to air pressure, which turns into rotary motion. The reason it turns into rotary motion and not direct motion, is since the working-gas stream is JOINING an existing rotary motion created by electricity - although the original rotary motion is of much less power.   

       About outweighing the losses:
The Stirling engine is supposedly efficient because it is doing cyclic adiabatic then isothermal expansion and compression, using the same working gas. But in the real world, Stirling engines need to be made extremely precise, and even then, I never saw one that gives the efficiency portrayed for in the textbooks. "Far from noisy" - could you put a short vid of a silent Stirling, giving off anything like 5 kW (even 200 W would be good for an example). Or perhaps you could put up a sound wave of a "silent" Stirling engine. The noise comes from the cams no? How do you silence them?

       Your right - the principal I'm proposing, uses the same principal of gas expansion, but I'm not using the gas in a cyclic way (perhaps in the proposed "turbo" I would be using SOME of it.) THEORETICALLY I'm doing something "worse off" - But in the PRACTICAL world: I'm hoping to overcome the need for exact timing and continuous loss of continuous heating during the "cold cycle" - which is about half of the time of the motor!!! You have the flame on the bottom heating the heater, while the Stirling engine has all it's air on the cool side. At that time, what is done with that heat? I'll tell you what I think happens: Most of it, instead of being absorbed, just goes out to the air and is lost. (Think of the flame licker engine, and think that you are "paying" for every second of gas running the flame. Every time the flame is 'outside' your burning gas that's not being used)   

       So in my engine, at least all the heat is consumed .   

       Then you have the energy taken to move the displacer, and the flywheel, and don't tell me that's not energy lost.   

       Last but not least, I have a gut feeling (this is HB here, right?) that the turning of the fans will put the air into "phase" and so the heat will be "directed" losing a bit of chaos, and giving it directed power.   

       The most efficient engine to date for electricity generation is the gas turbine. It works at extremely high speeds. In effect I'm hoping to make exactly that, except using much lower temperatures, and making the difference a bit larger by LOWERING the cold side to ice-cold (using off peak low-cost and more efficiently created electricity).
pashute, Jun 09 2010

       The stirlings I've built are very small and don't have cams. The only noise is from the small amount of play in the plain bearings (larger engines would use rolling bearings) and an almost indetectable fluttering sound, probably from the open end of the power cylinder. There are plenty of videos of stirlings on youtube (although probably not the best way to judge noise levels - adjust the volume 'till it justifes any given argument!). In any stirling, the hot end will have a heat capacity vastly greater than that of the air content. When air is at the cold end, the hot end is buffering heat from the source.   

       However you juggle it, you are still heating air through approx 80 degrees and the effeciency with which you can recover energy from it is limited by that number. Adding more energy to the air before or after adding that 80 degrees will only lead to more losses.   

       I guess one interpretaion of your idea might be 'increase effeciency of heat engine by using heat pump to increase temperature delta'. This description make it more obvious why you won't gain anything.   

       I've not built my flame licker engine yet, but I have a three cylinder design which uses a single flame and thus draws on it 100% of the time.
Twizz, Jun 09 2010

       You'd be better simply creating a steam turbine system using a working fluid that boils at room temperature.
marklar, Jun 19 2010

       Steam (Rankine) engine is expensive, and again needs precise worksmanship.   

       I'm using ice storage for shifting the price of energy to time when it is given practically free, and when it is more efficient to store that energy (since nighttime is cooler). I'm also using low cost near ground geothermal cooling (under vegetation).   

       So that what I'm doing is COST EFFECTIVE. And getting more energy per $ from the sun than PV.   

       I'm getting back MORE than the SPENT energy , even though I'm catching only MUCH LESS than the available energy in my system (which is mostly heat from the sun).
pashute, Jul 22 2010


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