Calculation of interception rate of mesh filter and analysis of its influencing factors

This study analyzed effects of inlet pressure, filter screen aperture and median particle size of sand on interception rates of filters in order to maintain the good permeability of filter screens and improve the interception rate of the filter screen in the engineering application of the screen filter. A full test and a three-factors-and-three-level orthogonal test were conducted. Five different inlet pressures were designed including 0.02, 0.04, 0.06, 0.08, 0.10 MPa. Seven kinds of filter screen apertures were 125, 150, 180, 210, 250, 300 and 350 μm. The median particle size was from 60 to 300 μm. The results showed that the cake produced in the filtration process was the main reason of the interception phenomenon. The larger the inlet pressure of the filter tended to lead to more significant interception phenomenon and the higher interception rate. The inlet pressure had a very significant impact on the interception rate of the filter. The interception rate increased with the increase of the filter screen aperture when the ratio of the filter screen aperture to the median size of sand was less than a critical range from 1.80 to 1.88. However, the interception rate decreased with the increase of the filter screen aperture when the ratio was higher than the critical range. A model of intercept rate estimation was fitted with the determination of coefficient of 0.94, indicating that the model has a high accuracy. The larger inlet pressure of the filter could result in the more concentrated distribution of intercepted sand particles at the outlet. It indicated that filter performance could be improved by reducing the skeleton density of the filter element at the outlet and designing the filter outlet segment into a circular arc shape with a large front and a small rear to increase the water passing area at the outlet. When the inlet pressure increased from 0.02 MPa to 0.10 MPa, the interception rate of 250 μm filter increased by 38.49%, while that of 125 μm filter increased by 88.94%. At the 15 min of the experiment, the composition of the sand particle size in the outlet water from the 250 μm filter under the inlet pressure of 0.01 MPa was similar to that in the initial outlet from 180 μm filter under the inlet pressure of 0.02 MPa. The filtration accuracy of the filter after a period of operation was more than expected. Therefore, the inlet pressure rather than adjusting the whole equipment could be an option to obtain good performance of filtration during short-term irrigation processes. This study provides valuable information for improving the interception rates and filtration effects of filters in irrigation projects.