# Is there something like the Poynting vector for hydraulic circuits?

The Poynting vector is a representation of the energy flux in electromagnetics, showing the amount and direction of power flow at different points in space. In electric circuits, the energy is not carried inside the wires (meaning the vector is just 0 inside them?), but by the electric and magnetic fields surrounding the wires. The DC circuit is the simplest case:

Is there an equivalent concept of energy flux for an equivalent hydraulic circuit?

Does the energy flow inside the pipes in this case? I'm guessing the energy flux has some kind of parabolic profile inside the pipes proportional to the flow rate?

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This analogy was used formerly in physics textbooks for starters frequently, but the other way: electric batteries/currents/voltage were explained by pumps/streaming-fluid/height etc. Problem with this analogy: ohms law does not hold for hydraulics when the laminar conditions are exceeded, and even for laminar flow the current/cross section relation is complicated (Hagen-Poiseuille). –  Georg Nov 17 '11 at 17:04
@Georg: The non-linearity is important, but the current cross section isn't relevant is it? The flow of electric current is not uniform with cross section, either. –  endolith Nov 17 '11 at 18:40
Right, as a boy I did not realize that this model had problems. But nevertheless, it is used no longer. –  Georg Nov 17 '11 at 19:12
@Georg: I think it should be used more often. :D –  endolith Nov 17 '11 at 19:27
@Georg: I don't see any problem related to that question. Please be more specific. –  endolith Nov 21 '11 at 13:21