The removal of particulate matter from the gas stream is easier than the removal of particulate matter from the liquid due to the greater contact mechanism between the particles and the pore surface. When particles are trapped in pores that are smaller than the particles themselves, the screen retention mechanism may hold the particles. This adsorption capture by direct interception involves both gravitational settlement and electric attraction.
Inertial impact and diffusion interception cause the second mechanism, which is the trapping of adsorptive particles. Even if the airflow bends, the large particles entrained in it have more inertia and follow a more straight path. This is especially visible in larger particles, as they are more likely to attach to the solid filter's surface.
Particles that are too small to withstand the impact of inertia, on the other hand, may be suspended in the airflow. They may, however, be small enough to contact the filter surface due to diffusion movement. The low viscosity of the airflow, like inertial impact, allows for diffusion capture of suspended particles.
Because there are so many different types of filter media, knowing what factors influence the efficiency of air and gas filters can help you make the best decision for your application. Alfa Chemistry can assist you in selecting the optimum materials for your development plan by drawing on our significant experience in making healthcare media. Our air and gas filtration membranes include, but are not limited to, the following:
- ACP (Acrylic Copolymer) - Hydrophobic
- PTFE (Polytetrafluoroethylene) Supported - Hydrophobic
- Glass Fiber Supported - Hydrophobic
- Melt-blown PP (Polypropylene)
Water Intrusion Pressure
Instead of the bubble point test, which is used with hydrophilic membranes, water incursion pressure is used to confirm the pore size of hydrophobic membranes. Water is normally placed on one side of the membrane filter, and the pressure is gradually increased until the water is forced through the filter structure and seen to flow out the other side of the membrane. When choosing a hydrophobic membrane for your application, be sure that the pressure the membrane is exposed to during use is not greater than the rated incursion pressure. By preserving the droplets in the filtrate, this will ensure that the membrane functions properly.
The differential pressure (∆P) is the difference in pressure between the system pressure before the fluid enters the filter (upstream pressure) and the system pressure after the fluid has passed through the filter (downstream pressure). This element must be examined in the design stage when selecting filter media to guarantee that any flow rate requirements of the final equipment are met.
Air Flow Rate
Factors including pressure difference, porosity, pore size, and effective filtering area (EFA) influence the air flow rate of the hydrophobic membrane, and eventually, the design of the equipment should be led to maximize the filter's capacity.
The medium is frequently exposed to atomized particles of standard size in order to test the retention effectiveness of the hydrophobic membrane. This retention efficiency is measured using the bacterial filtration efficiency test method, which is a standardized test. This is a measure of filter efficiency based on a 0.3 m Staphylococcus aureus aerosol challenge that penetrates the filter at a predetermined flow rate.
The capacity of filter media to preserve integrity and functionality at high temperatures is known as thermal stability. Thermal stability is critical when it comes to filter sterilization. Certain filters cannot be autoclaved due to a lack of heat stability. Chemical compatibility and thermal stability are linked: several types of filter media may be chemically compatible at room temperature, but not at high temperatures. The maximum operating temperature under defined conditions can be used to determine thermal stability.
The ability of a medium to withstand chemical compounds is defined as chemical compatibility. Compatibility is limited to a single chemical or chemical combination at a certain temperature. You must confirm the compatibility of the filter with the fluid before selecting it. Compatibility is influenced by temperature, concentration, applied pressure, and exposure time.
Filtration materials are carefully chosen since they are resistant to a wide range of chemical solutions. Nonetheless, it's critical to know how the filter element and the fluid to be filtered interact in real-world situations.