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Relationship between thickness of microporous membrane and porosity and flow rate

Issuing time:2024-05-22 10:37

There is a close relationship between the thickness of the microporous membrane, porosity and flow rate. Changes in each element here will affect the overall filtration speed and effect of the membrane. Here is a simple analysis:

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First, let’s talk about the thickness of the microporous membrane. For composite membranes, the thickness of the membrane refers to the overall distance above and below its two surfaces or between layers. Thicker membranes usually provide more space for fluids to flow through the porous structure. , but this excessively thick membrane will lead to an increase in liquid flow resistance due to a longer path or a higher pressure drop across the membrane, which will directly lead to an increase in pressure drop during the transition process, because 1. Thicker The membrane provides a longer path for fluid filtration, which means that the fluid must travel a longer distance to pass through the membrane. While the fluid flows through the longer path, it encounters more resistance and friction along the way. An increase in this distance and an increase in contact area with the membrane material will result in a higher pressure drop; 2. Thicker membrane materials will produce more pore shrinkage, because thicker membranes generally contain more pores within their thickness. With multiple layers or structures, since these layers have smaller pores or narrower fluid flow paths, it is inevitable that the fluid will experience higher flow resistance when passing through these shrinking pores, which will also lead to filtration pressure drop. increase; 3. Another thing that everyone easily overlooks is the viscous resistance. The thickness of the film will affect the flow profile of the fluid, because in a thicker film, the fluid velocity near the center is higher, and the interaction with the film material will produce a greater The friction force, which is the viscous drag force, also results in a higher pressure drop across the membrane. Theoretically, the relationship between membrane thickness and pressure drop is not linear and depends on many other factors, such as membrane porosity, pore size distribution, and fluid properties.

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Let’s talk about the porosity of the membrane. Porosity refers to the volume distribution number of voids or pores in the microporous membrane. Intuitively speaking, it is the amount of open space for fluid flow. A higher porosity means a greater number of interactions. Connected pores can promote the transport of fluid through the membrane. When the porosity of the transition membrane is higher, there are more available pathways, or interconnected gaps, on the membrane body, so that the fluid can also flow through a greater number of openings. Channels or pores reduce flow resistance to a certain extent and promote higher flow rates; on the other hand, high porosity also reduces the resistance to fluid flow. With more open space, the fluid encounters The fewer obstacles there are, the less friction it will have, ultimately resulting in a smoother, faster flow.

Similar to the thickness index above, porosity can only be said to be one of the factors that affects flow rate. Other factors include membrane pore size distribution and fluid properties (such as viscosity). In actual applications, larger porosity is not always better. The best porosity range must be selected based on the actual filtration situation. If it exceeds this range, too high porosity will also lead to a decrease in mechanical stability or damage to membrane separation. efficiency and other anomalies, so the smartest choice is to find the right balance between porosity, mechanical strength and required flow characteristics is critical to optimizing the performance of the transition membrane.

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Finally, let’s talk about the flow rate. As we have said before, the flow rate through the microporous membrane is affected by many factors, including membrane thickness and porosity. Generally speaking, if you want to simply increase the filtration speed, choose a higher membrane porosity. And thinner membranes are the direction of choice because thinner membranes can provide a shorter diffusion path for the fluid, reducing flow resistance, while higher porosity can provide more usable channels for the fluid, promoting greater flow. Of course, to ensure the filtration effect, other parameters such as pore size distribution, membrane material characteristics, pressure applied during filtration and fluid viscosity must also be comprehensively considered.


The above is a simple analysis of the relationship between microporous membrane thickness, porosity and flow rate. As a microporous filtration membrane made of polymer material, the selection needs to be based on the needs, flow requirements of the filtered liquid, filtration effect, influencing factors, etc. Only through judgment and analysis, combined with various membrane indicators from material suppliers, can the most suitable membrane material be selected.


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