Issue of the effective filtration area of the filter
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According to various filter standards (SH/T3411, JB/T7538, HG/T21637, etc.), the effective filtering area S2 of a filter equals the inlet area (S1) multiplied by a factor (N), multiplied by the opening rate of the support structure (P1), and multiplied by the opening rate of the filter mesh (P2). First scenario: For a standard basket filter with a single cylindrical filter element, the effective filtering area consists of the pore plate and the filter mesh; the effective filtering surface area is calculated using a formula. For filters with a large inlet diameter, the diameter and height of the cylinder are quite large. As for the dimensions of basket filters specified in standards such as HG/T21637, different opening rates of the filter mesh result in varying values. Then why does the standard specify a specific filtering area? Moreover, when considering the drawings provided by various manufacturers as a whole, and calculating based on their specifications, none of them manage to achieve a filtration area that is more than 3 times higher; furthermore, the calculation formulas used do not take into account the opening ratio twice. Aren’t they worried that the filtration efficiency will not be sufficient? Second scenario: For filter elements with multiple layers or composite filter elements, theoretically the value should be the product of the filtration areas of each layer; however, this calculation yields a very small result. Some manufacturers use addition instead, which results in a significant difference compared to the product method. All experts are welcome to share their opinions. In particular, in the first scenario, where the standards do not specify the porosity of the support structure or that of the filter mesh, how is it possible to determine a specific effective filtration area?
Regarding the question you raised, it is first necessary to understand that the effective filtration area specified in the standards is a theoretical value, used for standardized comparison and as a reference for design. For different filter designs and application scenarios, the method for calculating the actual filtration area may vary. In the first case, standards may provide a basic calculation framework or reference values, but in actual product design, manufacturers may adjust the structural design based on specific usage conditions and filtration efficiency requirements, for example by increasing the length or diameter of the filter element or changing the material of the filter screen to achieve the desired filtration effect. Different porosity levels naturally affect the final calculation results, and the standards do not provide detailed specifications for this reason – as this parameter varies significantly across different applications, making it difficult to establish uniform rules. The difference between the dimensions provided by the manufacturer and the standard recommended values may be due to cost, installation space, or other engineering constraints taken into account during actual production. Furthermore, actual operating conditions (such as the viscosity and temperature of the fluid) also affect the final filtration efficiency and the required filtration area. In the second case, with multi-layer filters or composite filter elements, it is theoretically possible to calculate the value based on the product of the filtering area of each layer. However, this calculation method tends to underestimate the actual filtering area, as there may be some overlap between the filter layers or supporting structures that result in an actual open area larger than the value calculated theoretically. Therefore, some manufacturers may use addition or other empirical formulas to predict a filtration area that is closer to the actual value. In summary, calculating the effective filtration area of a filter is a complex engineering problem that involves various factors and assumptions. Manufacturers and designers usually adjust the design based on specific applications and experience to ensure that the filtration efficiency and flow rate requirements of actual use are met. When selecting and evaluating filters, it is recommended to gain a thorough understanding of the product’s specific design, test data, and application context. .
The porosity of different filters leads to differences in the calculation results
First of all, filtration is not the same as sieving; there are many mechanisms of filtration, and it is not possible to simply multiply the porosity of each layer. If one insists on using perforated filters, the typical porosity for five-layer sintered mesh is 38%
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The fact that you’re asking this question shows you don’t understand filtering