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

According to the literature, several units have been defined for Water Vapor Permeability. Which one is the most widely used? WVP is the mass of water vapor transmitted through a unit...

Effectively a moisture vapour transmission rate (MVTR) is a measure of the passage of vapour through a material (such as a vapour barrier, film or fabric) of a given unit area per unit time under pre-specified temperature and humidity conditions. WVTR is …

2023年7月1日 · An often overlooked technical performance characteristic of mechanical pipe and equipment insulation is water vapor permeability (WVP). ASTM International defines WVP as “the time rate of water vapor transmission through unit area of flat material of unit thickness induced by unit vapor pressure difference between two specific surfaces, under ...

2024年7月23日 · 02 水蒸气渗透性（WVP） 样品必须满足两侧的条件。它们适用于指定的温度和湿度。条件指定在给定时间内通过样品单位面积的水蒸气质量。这发生在一定的水蒸气压力差下。该质量的测量单位为克/平方米帕斯卡小时 (g/(m²-Pa-h))。 03透水系数

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. The US perm is defined as 1 grain of water vapor per hour, per square foot, per inch of mercury. 1 US perm = 0.659045 metric perms ≈ 57.2135 ng·s⁻¹·m⁻²·Pa⁻¹.

2019年6月28日 · Water vapor permeability is an important basic one. WVT is the water vapor quality passing through the unit area of the sample vertically within the specified time at the speed of g/m²·h or g/m²·24h under the condition that the sample is keeping the specified temperature and humidity on both sides.

2020年8月20日 · Water vapor permeability (WVP) is a measure of the passage of water vapor through a membrane. It is the rate of water vapor transmission per unit area per unit of vapor pressure differential under test conditions. The higher the value of the permeability of the material, the more rapidly vapour can pass through it.

Specific test methods for measuring water vapor permeability are given in ASTM Standard E96. For many engineering materials, vapor permeability is a strong function of mean relative humidity. Wet and dry cups cannot adequately characterize this dependence on relative humidity.

2024年7月23日 · 02 Water Vapour Permeability (WVP) The specimen must meet the conditions on both sides. They are for the specified temperature and humidity. The conditions specify the mass of water vapor that passes through a unit area of the specimen in a given time. This happens under a certain difference in water vapor pressure.