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

[jhaible]

> I modelled the resistor as voltage source, the voltage
> beeing proportional to the square of the resistor voltage.
> Then I connected a "heat pipe", of resistors and capacitors
> to model heat transfer. At the end I included a loss
> resistor to the outside. Now i have included an ideal
> diode to prevent backwards heat transfer into the
> resistor when it is switched off. Like this:


Temperature <=> "Voltage"

Energy <=> "Charge"

Energy flow (Power) <=> "Current"


There is no need to model a "diode bahaviour", IMO.

If your source of heat is turned off, but still holds its temperature,
the "voltage" is still there and nothing will flow back.
In other words, the thermal capacitance of your source
stores temperature ("voltage"), and so does the thermal
capacitance of your environment. As long as the environment's
temperature is lower than your source temperature, why
should anything (Energy, "charge") flow back?
It's one capacitor discharging into another one, until
everything has the same temperature in the end.

If, OTOH, you're cooling your source by some other means
after the power is switched off (hard to imagine - but think
of a well-isolated water cooler), then of course the energy
flow would be reverted, i.e. the environment would work
against the cooling. More precisely, as long as the
"internal cooling" results in a source temperature that is still higher
than the environment, the "external cooling" would be slowed
down. And if the "cooled source" has lower temp than the environment,
the environment will try to heat it (or slow down the "internal
cooling".)

No need for a diode - it's all contained in the thermal resistance
and capacitance.

But there is more: Don't underestimate the effects of radiation,
and the effects of air flow.

Radiation might indeed be one-way effect - not entirely, but
here a diode might be considered.

In general, don't expect the thermal resistance to be precisely
linear.

There are  expensive CAE tools with finite element method
especially created for thermal simulation ...

JH.