[sdiy] help needed: thermal equations to RC networks analogy

[Magnus Danielson]

From: "Czech Martin" <Martin.Czech at Micronas.com>
Subject: RE: [sdiy] help needed: thermal equations to RC networks analogy
Date: Wed, 12 Feb 2003 10:08:44 +0100

Hi Martin,

> Thanx to all for your input.
> I think I've understood my error:
> I should model the heat source as electrical current source,

Right...

> with parallel heat capacitance (electrical capacitance)

Right...

> and heat resistance to the air volume (electrical resistor).

Right...

> Thus, if the electrical current source is off, it will not
> short anything, so wrong heat backward transfer is not possible.

Exactly.

> The heat output of the heat source should be proportional
> to U^2/R or I^2*R (electrical power).

Right, P simply!

> All the other issues (radiation, nonlinearity) are certainly true.
> Because there is two fans in the tank and isloation arround,
> this could be diminished. Experiment will show.

With enought Rs and Cs around in there you should be able to refine your
model. There's also the possibility to use FEM tools for this. They are
perfect for the task if you need 2D, 2.5D or 3D views.

> Anyway, I have finished this aviary (birdcage) which
> kept me busy for 3.5 weekends now. It has about 1m^3 volume,
> a lot of work...
> Next I can measure static equilibrium and step response
> of the tank.

... which should give you alot of info.

> Not that I *really* need that, but I think it is a nice exercise.

Indeed it is.

> I built the first heat servo system in great haste
> and I have made many compromises just to get something working.
> 
> That is one reason why I never published the circuit or data.
> Because people would think from that that I must be absolutely clueless
> which is only true to some extend ;->

;O)

Cheers,
Magnus