Perm (unit)

A perm is a unit of permeance or "water vapor transmission" given a certain differential in partial pressures on either side of a material or membrane.

Definitions

U.S. perm: The U.S. perm is defined as 1 grain of water vapor per hour, per square foot, per inch of mercury.

1 U.S. perm	= 0.659045 metric perms
	≈ 57.2135 ng·s⁻¹·m⁻²·Pa⁻¹

Metric perm: The metric perm (not an SI unit) is defined as 1 gram of water vapor per day, per square meter, per millimeter of mercury.

1 metric perm	= 1.51735 US perms
	≈ 86.8127 ng·s⁻¹·m⁻²·Pa⁻¹

Equivalent SI unit: The equivalent SI measure is the nanogram per second per square meter per pascal.

1 ng·s⁻¹·m⁻²·Pa⁻¹	≈ 0.0174784 US perms
	≈ 0.0115191 metric perms

The base normal SI unit for permeance is the kilogram per second per square meter per pascal.

1 kg·s⁻¹·m⁻²·Pa⁻¹	≈ 1.74784x10¹⁰ US perms
	≈ 1.15191x10¹⁰ metric perms

German Institute for Standardization unit

A variant of the metric perm is used in DIN Standard 53122, where permeance is also expressed in grams per square meter per day, but at a fixed, "standard" vapor-pressure difference of 17.918 mmHg. This unit is thus 17.918 times smaller than a metric perm, corresponding to about 0.084683 of a U.S. perm.

gollark: Yes.

gollark: Well, plus or minus an hour, yes.

gollark: I can see that by looking at the corner of my screen anyway.

gollark: At least with the command line you have autocomplete, autocorrect, and more importantly *an actual list of available commands*.

gollark: They aren't intuitive, really. Voice makes you EXPECT you can talk to it in a normal human-ish way, except voice assistants are really limited and will trip over on anything complex.

References

Michon, Gérard P. (April 29, 2003) "Permeability and permeance". Final Answers: Physics of Gases and Fluids. - accessed August 13, 2007

This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.