Re: Heat to electricity conversion

From: Duane C. Johnson (redrok_at_redrok.com)
Date: 01/29/05 

Date: Sat, 29 Jan 2005 09:49:50 -0600
To: François Guillet <mail.ya.plus@yahoo.com>

François;

François Guillet <mail.ya.plus@yahoo.com> wrote:

> I was investigating about instabilities of an electronic
> oscillator and found I had capacitors very temperature
> sensitive. These capacitors of 10 nF lose 2 to 3 nF when
> heated up to 70° celsius.

> This gave me an idea to convert heat to electricity.
> The energy in a charged capacitor can be expressed as:
> W = 1/2*Q²/C
> If Q is constant (charged capacitor then disconnected
> from the source) and the capacity is decreased then the
> electrical energy in the capacitor is proportionally
> increased. It is a conventional principle: to reduce the
> capacity of a charged capacitor, we have to move away
> the plates from each other, thus to do a work against
> the electrostatic force that exerts on the 2 plates. The
> mechanical work to move the plates away is transformed
> and appears as electrical energy in the final state of
> the capacitor. If the heat do the job then we get a heat
> to electricity converter.

> How the heat acts to decrease the capacity, I don't know.
> May be it's a dielectric expansion or a modification of
> its polarisability?

This concept has been investigated for a while.
In the electronics side of things this would be
called a parametric amplifier.

Yes, amplification of electrical energy can occur in
capacitors pumped by thermal energy.

Just because the effect can be demonstrated
doesn't mean that it is practical.

The problem is this has very low efficiency of
conversion. In this case the energy to change
the temperature of the body of the capacitor
is hundreds of times the electrical energy
contained in the capacitor due to the change
in capacitance.

This same problem is the reason the Minto Wheel
is impractical.

Wasted thermal heating of masses is often the
bane of heat engines.

> This idea could be usefull if we had or built big
> capacitors or supercapacitors with reverse
> capacity/temperature characteristic.

> I googled on the subject but found nothing.
> Is this method known and used ?

> FG

Duane 

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