In article ,
says...
In article , Ned Simmons
says...

I've heard the term "lumped", but don't have even a vague
notion of what it means. I assume it's a simple concept?

Yes, the idea is 'lumped' vs 'distributed' circuit
elements. For example, you could imagine a circuit
that has a battery, a wire that leads to a resistor,
and then another wire that connects back to the battery.

In most cases, almost all the power shows up in one
spot - dissipated in the resistor.

Now change the setup a bit to have the resistor hooked
up to the battery with nichrome wire. Now some power
shows up in the resistor, and some shows up in the
wires themselves. It makes sense to look at that second
type as more of a distributed element load.

You can also see the same effect with a tuned cicuit
that consists of a single capacitor and coil, hooked
up with traces on a circuit board. If the tuning
frequency is low enough, the circuit board traces
are simply 'wires' and don't have to be considered.
This is a lumped element circuit.

Then make the tuning frequency very high, and the
circuit board traces become part of the tuning
circuit - with their capacitance and inductance
contributing to the overall tuning. At some point,
the traces themselves become the tuned circuit
elements. So at high frequencies it's a distributed
circuit.

My point was, looking at only one location of the
regulator/tanks setup will lead to confusing
conclusions. The overall system will obey conservation
of energy laws if all the energy can be accounted for.
This includes things like the internal thermal energy
of the gas, any mechanical work that is done, the
kinetic energy of the flowing gas, and whatever potential
energy is still stored in the compressed gas in various
locations.

OK, I see what you're saying. I think it's a matter of
perspective and the level of understanding you're shooting
for.

For the example I was using - the isothermal
reservoir/regulator/piston system - saying, "the loss
occurs in the regulator" doesn't really have any bearing on
the solution of the problem. However, if you're trying to
understand why the regulator gets colder, saying "the loss
occurs in the regulator" obscures the explanation. In one
case you're looking at the process as a whole, in the other
you're trying to break that process down into smaller
chunks. Is that your point?

Similarly, in the electical analogy, wouldn't you
eventually want to abandon the concept of power loss in a
resistor when looking for a very fundamental understanding
of the loss?


A hydraulic regulator is functionally the same as a
pneumatic regulator, but it does get hot in operation.
Would you say that energy was lost in the regulator in that
case? (Again with the sloppy language.)

Hydraulic fluid of course is incompressible. But as
long as the regulator isn't getting hot simply because
the fluid flowing through it is hot, then I would
tend to say that yes, that would be a sign that
there is a sort of lumped element loss at that point
in the hydraulic circuit.


The oil gets hot when it loses pressure in the regulator,
so even though the oil entering the regulator may be at
ambient, the oil heats the regulator. Of course, unlike
electric current flowing thru a resistor, the oil also
carries heat away. Another chink in the electrical analogy.

Ned Simmons