N is also, by definition, inversely proportional to the total resistance to gas mass transport, Rtotal. As the membrane module can be described with a resistances-in-series model, Rtotal is related to the sum of the partial resistance in the gas, the membrane and the liquid phase, respectively 𝑅 𝑡𝑜𝑡𝑎𝑙 = 𝑅 𝐺 + 𝑅 𝑀 + 𝑅 𝐵 (8)