# permeance

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Related to permeance: vapor permeance

## Permeance

The reciprocal of reluctance in a magnetic circuit. It is the analog of conductance (the reciprocal of resistance) in an electric circuit, and is given by

(1)

Eq. (1), where **B**is the magnetic flux density,

**H**is the magnetic field strength, and the integrals are respectively over a cross section of the circuit and around a path within it.

From Eq. (1), it can be shown that Eq. (2) is valid, where *A*

(2)

is the cross-sectional area of the magnetic circuit, *l*its length, and μ the permeability. If the material is ferromagnetic, as is often the case, then μ is not constant but varies with the flux density and the complete magnetization curve of

*B*against

*H*may have to be used to determine the permeance.

*See*Reluctance

## permeance

[′pər·mē·əns] (electromagnetism)

A characteristic of a portion of a magnetic circuit, equal to magnetic flux divided by magnetomotive force; the reciprocal of reluctance. Symbolized

*P*.## permeance

A measure of a material’s resistance to water-vapor transmission, expressed in

**perms**. Equal to the ratio of (a) the rate of water vapor transmission through a material or assembly between its two parallel surfaces to (b) the vapor pressure differential between the surfaces.