Enhanced experimental study on the head loss and filtration performance of annular flow disc filter

As a three-dimensional flow channel, the laminated filter has a complex structure, and it is easy to appear phenomena such as too short blocking time and increasing head loss caused by sand interception in the operation process. According to the relationship between head loss and cross-sectional area, an annular flow channel laminated filter was proposed. The circumferential flow channel was added on the lamination surface, which increased the flow direction of the flow channel and played the role of dividing the radial flow channel, achieving the purpose of hierarchical multi-layer filtration in the lamination and improving the number of available flow channels. In order to explore the advantages and disadvantages of the linear flow channel and annular flow channel laminated filter for irrigation water filtration capacity. Through indoor comparative experiments, 120 mesh laminated filter, namely the filter particle size of 125 μm was used to test the head loss and filtration performance of the two filters under four kinds of sand grading median particle size (106, 121, 126 and 165 μm), three kinds of sediment content (0.10, 0.15 and 0.2 g/L) and five kinds of inlet flow (1.5, 2.0, 2.5, 3.0 and 3.5 m³/h), a total of 60 groups of tests. The dependent variables were the head loss, the sediment retention capacity and the median particle size of the interception, and the independent variables were the inlet flow, the sediment concentration and the median particle size of the inlet. The evaluation indexes were the head loss, the plugging uniformity, the sediment retention capacity and the particle size distribution of the interception sediment. The multiple regression equation was established to verify the correlation between the head loss and the filtration capacity. The entropy weight method was used to determine the optimal lamination of the head loss and the filtration capacity. The results show that: under the condition of clear water, the maximum flow head loss of the annular flow laminated filter is 9.1% lower than that of the trapezoidal linear filter. Under the condition of sandy water, the time for the head loss to reach 8m is 1.5-10 times longer than that of the trapezoidal linear filter, and the maximum head loss is reduced by 52.5%. The total sediment retention capacity is increased by 0.5%-6.3%, and the average sand removal rate is increased by 0.22% for the sand with the median particle size greater than 110 μm. The siltation channels of the trapezoidal linear filter account for 25%-86% of the total number of channels of the trapezoidal lamination, while no siltation phenomenon is observed in the operation cycle of the annular lamination. The head loss of the two kinds of laminated filters was positively correlated with the sediment concentration, inlet flow and inlet median particle size, the sediment retention was positively correlated with the sediment concentration, inlet flow and inlet median particle size, and the interception median particle size was positively correlated with the sediment concentration and inlet median particle size. The annular flow channel laminated filter was more suitable for irrigation water with high sediment concentration and high median particle size distribution than the trapezoidal linear laminated filter. Therefore, the optimal laminated filter can be designed by considering the change of the geometric distribution of the flow channel of the laminated filter, which can reduce the filter head loss and extend its backwashing cycle without reducing the filtration capacity.