Re: fluid analogs of battery, resistor, capacitor, inductor

[William Beaty <billb@ESKIMO.COM>]

On Sun, 13 Dec 1998, David Bowman wrote:

> In order for the flow analogy between the fluid and electric currents to
> be in a closer correspondence we should not assume that the pipe is
> unobstructed.  Rather we should think of the pipe as being loosely filled
> with a fixed permeable wadding or stuffing that creates friction with the
> moving fluid throughout the pipe's interior.  This will tend to cause the
> pipe's resistance to be proportional to L/A.  I think D'Arcy's law
> provides a better conduction analog to Ohm's law than Poiseuille's law
> does.  Instead of an open pipe, a fluid flowing through soil or a sponge
> (or maybe petroleum flowing through permeable rock) is a better, albeit a
> higher resistance, analog.


Yes!  Fluidic resistors should be full of packed dirt!


Imagine that water is moving slowly through dirt, and imagine that the
flow velocity is high enough to create significant frictional heat. If a
1mm fluidic resistor is putting out many watts per cm length, then in
order to create an appropriate analogy, we should pack enough dirt into
the tube until the liquid flow velocity is similar to the drift speed of
electrons in an equally heated 1mm wire.

I think the situation is close to petroleum flowing through permeable
rock.  If electron drift speed is a few cm per second, then the current is
immense, and the wires are glowing red.


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