Charge Transport Equation
The default node attributed to The Transport of Charge Carriers Interface models charge transport through diffusion and convection and solves the charge conservation equation for one or more charge carriers i:
(3-17)
Equation 3-17 in its form above includes drift in electric and magnetic fields, convection in flow fields, and diffusion due to charge carrier density gradients. See more details in Transport Mechanisms.
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ni is the number density of the charge carrier (SI unit: 1/m3)
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Γi is the total flux (SI unit: 1/(m2·s))
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Γci is the convective flux (SI unit: 1/(m2·s))
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Γdi is the diffusive flux (SI unit: 1/(m2·s))
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wi is the drift velocity in electromagnetic fields (SI unit: m/s)
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zi denotes the carrier charge (SI unit: 1)
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μi denotes the carrier mobility (SI unit: m2/(V·s))
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Di denotes the carrier diffusion coefficient (SI unit: m2/s)
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E is the electric field (SI unit: V/m)
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B is the magnetic field (SI unit: T)
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 u is the flow field velocity vector (SI unit: m/s)
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Ri is a reaction rate expression for the species (SI unit: mol/(m3·s))
The electric field E, magnetic field B, and the velocity field u can be expressed analytically or obtained from coupling the physics interface to one that solves for the field, such as Electrostatics, Magnetic Fields, and Laminar Flow, respectively.
On the right-hand side of the mass balance equation (Equation 3-17), Ri represents a source or sink term, typically due to chemical reactions. To specify Ri, another node must be added to The Transport of Charge Carriers Interface — the Reaction node for example, which includes an input field for specifying a reaction expression using the variable names of all participating species.