How Coalescing Filters Work

What is the working mechanism of the coalescing filter with glass fiber material as the core of the filter element?

Answer: Air flows in from the middle of the filter element, and oil droplets are collected through four mechanisms: gravity, inertial collision, direct interception and penetration.

Effect of gravity: When the airflow velocity in the filter is low, most of the oil droplets with a diameter of 20-50μm will be collected by gravity free fall before reaching the filter layer, and the airflow will continue to fall and be collected when the airflow passes through the filter. . The greater the velocity of the airflow, the less efficient it is.

· Inertial collision: Suspended particles with a diameter larger than 1 μm usually have a large impulse. Not always consistent with the airflow path. As a result, it will inertially hit the fiber layer. The greater the air velocity, the greater the collision rate.

·Direct interception: particles with a diameter of 0.3-1μm move with the airflow, and most of them will be intercepted and separated by the fiber layer at 1/2 of the filter element. The smaller the particle, the lower the interception rate.

· Penetration: diameter less than O. 3 μm particles. Because its mass is too small, it no longer has the usual characteristics of liquid. They move in an irregular Brownian motion. It is inconsistent with the airflow path. It is because of this movement that it can be captured by a finer filter layer. The particles are smaller. The more intense the Brownian motion, the greater the chance of capture.

What are the main features of HEPA filters?

Answer: The diameter is O. Particles of 3 μm are neither mechanically nor efficiently trapped. Evaluating whether a filter is efficient is to see whether it has the ability to capture particles of this size to the maximum extent.

What is the simple working process of an efficient coalescing filter?

Answer: After the compressed air enters the middle of the filter element, it is collected by the filter layer through gravity, collision, interception and penetration. After the oil droplets have been removed by the filter layer, they are first collected. Small oil droplets first aggregate into large oil droplets, and when the mass of the aggregated large oil droplets is large enough, they will settle to the bottom of the filter layer. Then it flows into the filter bag and is removed from the system by manual or automatic oil discharge device.

What are the design requirements for an efficient coalescing filter?

A: Fiberglass is water repellent but not oil repellent. The oil forms a thin film on the fiber surface, which interferes with collection and increases the functional diameter of the screen element. For this, finer fibers must be chosen in the design.

The design of the filter layer mainly considers the control of the airflow velocity and the physical environment of the filter layer. It is only necessary to ensure that the material has a large enough surface area to keep the air velocity as low as possible, so that the interception, collision and diffusion effects are more effective. On the other hand, the designed filter bed should also be thick enough to allow the particles to have sufficient residence time. Finally, there should not be too many fiber layers in the filter element, which will hinder drainage, increase pressure loss, and reduce filter efficiency.

The collection of oil droplets is a physical process, and the physical characteristics of pressure, flow rate, humidity and impurities themselves will affect the aggregation results. Therefore, the configuration, arrangement, size and type selection of the filter layer are also critical.

Does the filter element of the coalescing filter have a service life?

Answer: Yes. In theory, the filter layer can remove liquid indefinitely and maintain its high efficiency. In fact, the increased pressure drop caused by the continuous collection of liquid by the filter screen during use will lead to a certain effective service life of the filter layer.

Why does the filter element of the coalescing filter use a porous foam layer (or cover)?

Answer: In the filter element design of general coalescing filters, porous foam layers or covers are set inside and outside the filter layer.

When the oily air flows through the filter center layer, it flows radially into the flexible inner porous foam jacket. On the one hand, it acts as a diffuser, pre-filter and space stabilizer for the airflow; on the other hand, it changes the airflow (expansion or contraction) through its own adjustment, so that the airflow can generate gentle pressure on the filter layer to ensure its integrity and effectiveness when working .

Oil droplets are intercepted and collected as the air flows through the filter layer. After the oil accumulates, it flows through a hard metal tube to the outer porous foam cover (covered outside the metal tube). The outer porous foam cover has a large non-absorbent surface, which allows oil to quickly cover its surface under the action of gravity. Flow to the bottom, thereby preventing the oil from re-entering the air flow. When the oil accumulates at the bottom of the cover (no air dead zone), the foam holes are blocked and the oil falls into the collection tank.

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