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Abstract

By applying Poynting’s reasoning to time-independent laminar flows of incompressible viscous fluids we show that the energy flux for such systems can also be described by a Poynting vector. We discuss two examples of the Poynting model of energy flux: the familiar case of a constant electric current flowing through a wire and a new hydrodynamic case of vertical tube which drains a constant depth reservoir which is filled with a viscous fluid. Finally, we present often ignored physical constraints which these systems have to obey and modify Poynting vector so that it can be used, consistently, in order to obtain the actual energy flux for the two systems.

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