What are the criteria for evaluating the performance of fillers?

The geometric property data of fillers mainly include specific surface area, porosity, filler factor, etc., which are the basic parameters for evaluating the performance of fillers. (1) Specific surface area: The surface area of the filler per unit volume is referred to as the specific surface area, denoted by a, and its unit is m2/m3. The greater the specific surface area of the filler, the larger the gas-liquid mass transfer area it provides. Therefore, specific surface area is an important indicator for evaluating the performance of fillers. (2) Porosity: The volume of voids per unit volume of the filler is known as porosity, denoted by e. Its unit is m3/m3, or it can also be expressed as a percentage. The greater the porosity of the filler, the greater the ability for gas to pass through and the lower the pressure drop. Therefore, the porosity is another important indicator for evaluating the performance of fillers. (3) Packing factor: The ratio of the specific surface area of the packing to the cube of the porosity, that is, a/e³, is called the packing factor and is denoted by f; its unit is 1/m. The packing factor is divided into the dry packing factor and the wet packing factor. The value of a/e3 when the packing is not wetted by the liquid is known as the dry packing factor, which reflects the geometric properties of the packing ； After the filler is wetted by the liquid, a liquid film forms on its surface, and both a and e undergo corresponding changes. The value of a/e at this point is known as the wet filler factor; it indicates the fluid dynamic properties of the filler. The lower the f value, the less the flow resistance.