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Hot superconductor

PostPosted:Thu May 27, 2004 4:31 pm
by shakir
Consider a normal generator with copper wires as its coils etc... as the armature is rotated, an emf is induced in it and we have a current flowing through it. As u know, since the coils will have a finite resistance, power is going to be dissipated in the form of heat in the coils. Copper, having a positive coefficient of thermal resistance (its resistance increases as its temperature increases, linearly) so, in a conventional dynamo, as u rotate the coils faster, a larger emf is induced, hence a larger current & hence greater power dissipation. In effect, as the coil is getting hotter, its efficiency is going down.

Now, coming to my idea... (for which u will need to have a little knowledge about thermistors, rather semiconductors). A little theory first: semiconductors have a negative coeff of thermal resistance. This means that the resistance of a semiconductor actually DECREASES as its temperature INCREASES (this happens in an exponental manner). If the coils are made of semiconductor material (problems involving their fabrication shall not be dealt with right now of course) are replaced by their copper counterparts, this is what i expect will happen: the coils will no doubt have an initial resistance. As the coils rotate in the dynamo, an emf is induced which gives raise to a current in the coils, which will no doubt cause power dessipation (P=i^2R) which literally means heat... which, in this case means lowering of resistance of the coils, which will mean a larger current flows thru them, which in turn means greater power dissipation, which again means lower resistance... & so on and on... it would never stop. Please let me know of any loophole that i may have overlooked.

Reward: well, seeing this actually work would be a reward in itself for me. Perhaps if this thing is named after me, it would be a suitable reward for me!

PostPosted:Mon May 31, 2004 3:56 pm
by Rishi
1. Thre are positive temperature coefficient (PTC) thermistors and negative temperature coefficient (NTC) thermistors. So, one has to start with the right kind.

2.Semiconductors have resistivities that are many orders of magnitude higher than that of copper. Negligible current will result from such a dynamo.

3. Even if a high conductivity NTC material (Not semiconductors) is used heat loss from the device has to be accounted for. This loss will make the final temperature of the device some finite value at which the windings will have some resistance.

4. For argument's sake even granting that the resistance reaches zero (Super conductivity achieved) the external load to which the emf is connected will have some resistance which will limit the power.

Rishi

PostPosted:Tue Jun 01, 2004 5:24 pm
by shakir
well, rish, (piont 4 first).what good is a dynamo if you dont intend to connect a load to it? i want to wliminate the power loss at the point of generetion.(if uve touched a bycycle dynamo after even 15 mins of uasage, u'll kno just how warm or should i say hot it can become)this dynamo should be better than a conventional one. anyway,
1.obviously u will have to use a 'NTC'. a 'PTC' will behave allmost like a copper wire, so theres no piont in using that, is there?
2. u r right, semiconductors(SC's) do have a larger resistance than copper wires.so, my dynamo would probably suit a nuclear power generator. the superheated water which is ejected after the steam impinges on the turbines can b made to pass along the dynamo so that it gets heated,to sufficiently reduce the resistance of the SC coils.
3.i am not trying to say that this thing will really superconduct.it will only tend to(theoretically, at least, its impossible for the SC to superconduct(see a graph of resistance vs temp for a SC & u'll kno why)

cmon now u admin guys... this idea surely doesnt belong in the docks!! i want outa here!!!

PostPosted:Thu Jun 03, 2004 12:58 pm
by Steve
shakir wrote:cmon now u admin guys... this idea surely doesnt belong in the docks!! i want outa here!!!

That's the fate of all ideas that violate the second law of thermodynamics. ;-)

PostPosted:Thu Jun 03, 2004 1:00 pm
by Steve
Steve wrote:
shakir wrote:cmon now u admin guys... this idea surely doesnt belong in the docks!! i want outa here!!!

That's the fate of all ideas that violate the second law of thermodynamics. ;-)

At second thought... it's the SciFi-Pond. Here ya go... :-]