What is the difference between internal pressure and external pressure Hollow Fiber Ultrafiltration Membrane?

As a supplier of Hollow Fiber Ultrafiltration Membranes, I’ve encountered numerous inquiries regarding the disparities between internal pressure and external pressure hollow fiber ultrafiltration membranes. In this blog, I aim to delve into these differences comprehensively, providing valuable insights for those in the water treatment industry and related fields. Hollow Fiber Ultrafiltration Membrane

1. Structural Design

The most fundamental difference between internal pressure and external pressure hollow fiber ultrafiltration membranes lies in their structural design.

Internal pressure hollow fiber ultrafiltration membranes have a design where the feed water is introduced into the inner cavity of the hollow fibers. The fibers are typically arranged in a bundle, and the pressure forces the water to pass through the membrane wall from the inside out. This design allows for a relatively simple and straightforward flow path, making it easier to clean the membrane surface. The inner diameter of the hollow fibers in internal pressure membranes is usually around 0.8 – 1.2 mm, which provides sufficient space for the water to flow through without significant pressure drop.

On the other hand, external pressure hollow fiber ultrafiltration membranes operate by introducing the feed water to the outside of the hollow fibers. The water then permeates through the membrane wall into the inner cavity of the fibers, and the filtered water is collected from the inside. The outer diameter of the hollow fibers in external pressure membranes is generally larger, around 1.5 – 2.5 mm. This larger outer diameter provides more surface area for filtration, allowing for higher filtration fluxes.

2. Filtration Mechanism

The filtration mechanism also varies between internal pressure and external pressure hollow fiber ultrafiltration membranes.

In internal pressure membranes, the feed water is pushed through the membrane wall by the pressure applied inside the hollow fibers. The membrane acts as a physical barrier, allowing only water and small molecules to pass through while retaining larger particles, such as suspended solids, colloids, and bacteria. Since the feed water flows from the inside out, any particles that are retained on the membrane surface can be easily removed by backwashing. Backwashing involves reversing the flow of water through the membrane, which dislodges the accumulated particles and flushes them out of the system.

External pressure membranes, however, rely on a different filtration mechanism. The feed water surrounds the outside of the hollow fibers, and the pressure forces the water to permeate through the membrane wall into the inner cavity. The larger outer surface area of the fibers allows for a more efficient filtration process, as the particles are distributed over a larger area. In addition, the external pressure design provides a self – cleaning effect to some extent. The cross – flow of the feed water along the outside of the fibers can help to prevent the accumulation of particles on the membrane surface. However, backwashing is still required periodically to maintain the membrane performance.

3. Resistance to Fouling

Fouling is a significant issue in ultrafiltration processes, and the resistance to fouling differs between internal pressure and external pressure membranes.

Internal pressure membranes are generally more prone to fouling compared to external pressure membranes. Since the feed water flows from the inside out, the particles in the water tend to accumulate on the inner surface of the hollow fibers. This can lead to the formation of a cake layer, which increases the resistance to water flow and reduces the filtration efficiency. However, the relatively small inner diameter of the fibers can make it easier to clean the membrane surface during backwashing. By applying a high – pressure backwash, the accumulated particles can be effectively removed from the inner surface.

External pressure membranes, on the other hand, have better resistance to fouling. The larger outer surface area of the fibers allows for a more even distribution of particles, reducing the likelihood of cake layer formation. In addition, the cross – flow of the feed water along the outside of the fibers helps to prevent the particles from settling on the membrane surface. However, if the feed water contains a high concentration of large particles, there is still a risk of fouling, especially at the entrance of the fiber bundle.

4. Operating Pressure and Flux

The operating pressure and flux are important parameters in ultrafiltration processes, and they also differ between internal pressure and external pressure membranes.

Internal pressure membranes typically require a higher operating pressure to achieve a given filtration flux. This is because the water has to flow through the relatively small inner diameter of the hollow fibers, which creates a higher resistance to flow. The operating pressure for internal pressure membranes usually ranges from 0.1 – 0.3 MPa. However, the flux of internal pressure membranes can be relatively stable over time, especially if proper backwashing and chemical cleaning procedures are implemented.

External pressure membranes, on the contrary, can operate at a lower pressure to achieve a similar filtration flux. The larger outer surface area of the fibers allows for a more efficient filtration process, reducing the resistance to water flow. The operating pressure for external pressure membranes typically ranges from 0.05 – 0.15 MPa. However, the flux of external pressure membranes may be more affected by the feed water quality and the degree of fouling.

5. Application Scenarios

The differences in structural design, filtration mechanism, resistance to fouling, and operating pressure make internal pressure and external pressure hollow fiber ultrafiltration membranes suitable for different application scenarios.

Internal pressure membranes are commonly used in applications where the feed water has a relatively low concentration of suspended solids and colloids. For example, they are often used in the pretreatment of reverse osmosis systems, the purification of drinking water, and the treatment of industrial wastewater with low turbidity. The relatively simple design and easy – to – clean feature of internal pressure membranes make them a popular choice in these applications.

External pressure membranes, on the other hand, are more suitable for applications where the feed water has a high concentration of suspended solids and colloids. They are widely used in the treatment of surface water, seawater desalination pretreatment, and the treatment of industrial wastewater with high turbidity. The better resistance to fouling and the ability to operate at a lower pressure make external pressure membranes a more efficient and cost – effective solution for these applications.

Conclusion and Call to Action

In conclusion, understanding the differences between internal pressure and external pressure hollow fiber ultrafiltration membranes is crucial for selecting the most suitable membrane for a specific application. Whether you are dealing with low – turbidity water or high – turbidity water, there is a membrane option that can meet your needs.

As a trusted supplier of Hollow Fiber Ultrafiltration Membranes, we have a wide range of products to offer, including both internal pressure and external pressure membranes. Our membranes are made of high – quality materials and are designed to provide excellent filtration performance and long – term reliability.

Water Treatment If you are interested in learning more about our products or would like to discuss your specific water treatment requirements, please feel free to contact us. We are committed to providing you with the best solutions and the highest level of customer service. Let’s work together to achieve your water treatment goals.

References

Cheryan, M. Ultrafiltration Handbook. Technomic Publishing Co., Inc., 1998.
Baker, R. W. Membrane Technology and Applications. Wiley, 2004.
Strathmann, H. Synthetic Membranes: Science, Engineering and Applications. Springer, 1994.

Yuanxian High-tech Material Trading (Tianjin) Co., Ltd.

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