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Related to permeance: vapor 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

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

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


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


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.
References in periodicals archive ?
Permeance is lower near the corners of a magnet, making these areas more susceptible to demagnetization.
The non-linear permeances of steel laminations are larger than the other permeances by several orders of magnitude and thus will be disregarded in a first approach.
The inverse transformations (from the T-plane back to the Z-plane) result in a complex permeance function [mathematical expression not reproducible], which is discussed in more detail in [13].
n]) of 22,000 was used as a base polymer due to its satisfactory gas permeance and selectivity purchased from Sigma-Aldrich, St.
The derivative of the permeance with respect to spacing E is then:
The first facing, as bonded to the first major surface of the insulation layer, has a water vapor permeance rating that of about 5 perms or greater so that the first major surface of the faced building insulation assembly formed by the first facing has a water vapor permeance rating of about 5 perms or greater.
Elworthy said he could sympathize with concerns about the permeance of a double-family dwelling and the threat of an absentee landlord, although the same could occur by renting out a single-family home.
There are very few articles discussing permeance correlations with operating conditions that are based on actual experimental data.
20) T 547 om-02 Air permeance of paper and paperboard (Sheffield method) (November 29, 2006) T 403 om-02 Bursting strength of paper (Dec.
E 2178, Standard Test Method for Air Permeance of Building Materials (air-leakage rate of 0.
With a permeance rating of 9, FiberBrace allows vapor transmission outward while its asphalt coating prevents moisture intrusion inward.
The vapor permeance or perm rating of both interior and exterior wall finishes needs to he chosen with due regard for each specific climate.