Energy exchanges; sign conventions
Introduction
In order to carry out an energy balance, it is necessary to establish the sign conventions for the energy exchanges between the studied system and the exterior.
Thermo-dynamic convention
The convention utilized in thermodynamics for energy exchanges (mechanical work, heat, electrical energy, mechanical energy, etc.)* between a system and the exterior is given in the table below.
| Energies received by the system are considered > 0 | Energies released by the system are considered < 0 |
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- The power consumed by the system is considered positive if it corresponds to an entry of energy into the system over the considered period.
- The power delivered by the system is considered negative if this corresponds to an output of energy from the system over the considered period.
Electric convention (dipoles)
For an electric system with two terminals (dipoles), there are two sign conventions: the receiver convention and the generator convention. These two conventions are detailed in the table below.
| Receiver convention: | Generator convention: |
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If the system is limited to one electric component, we note that the “receiver convention” is compatible with the thermodynamic convention, therefore; it is the one which is adopted. This convention is adopted in Flux for all the components including passive components such as: resistors, inductors or capacitors; power or voltage sources and components associated with regions of the finite element domain (of stranded conductor type or solid conductor type).