One of the main methods to test the gas permeability is using partial pressure difference.

用压差法测试塑料薄膜的透气性，是一个长期使用的主流测试方法。

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Permeance (P): The ratio of the gas transmission rate to the difference in partial pressure of the gas on the two sides of the film.

译文：气体透过系数（P）：单位时间内单位压力差下稳定透过单位面积上单位厚度的试样的气体体积。

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After inflexion, the permeation flux is directly proportional to the difference of the square root of the vapour partial pressure on both sides of the membrane.

冷侧真空度拐点后膜的通量与膜两侧水蒸汽分压平方根的差成直线关系，这种关系说明了水蒸汽在膜孔内的传质过程是以扩散为主；

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