Contrast experiment on anti-clogging performance of bidirectional flow channel emitters with different structures in drip irrigation

Abstract: The clogging of drip emitters is of great concern to many researchers. A bidirectional flow channel is different from a labyrinth flow channel and it is mainly composed of a structure for dividing water and a structure for blocking water. The main working principle comprises mixing the forward flow and the reverse flow created by the above mentioned structures, and the hydraulic performance is thus enhanced. Although a bidirectional flow channel provides better hydraulic performance, its anti-clogging performance, in particular in cases when muddy water with a high sediment concentration is used, needs to be researched in depth. Hence, periodic intermittent drip irrigation experiments were carried out using muddy water containing sediment particles with different sizes (all less than 0.125 mm), which were screened by a sieving method, and sediment particles were added to give a concentration of 30 g/L muddy water. To provide a contrast, a type of drip irrigation tube with an embedded labyrinth channel was chosen to compare the anti-clogging performance of the channels. Each test comprised 20 irrigation procedures, each for a period of 30 min, which was the same as the test interval. In the 25th minute the emitter flow was recorded in real time, and the measurement was continued for 5 min. After the end of each group of treatments, the test specimens were replaced with new specimens and the system was flushed to ensure that no sediment remained. In these experiments, changes in flow rate were measured under a pressure of 50 kPa. After the end of the trial, the clogged emitters were cut and dried to their natural state, and then the sediment deposited in the bidirectional flow channel was collected; the locations in which sediment was deposited were observed. The structure of the sediment deposits was also observed using an electron microscopy, and the sediment particle size was calculated using Image Pro Plus 6.0 software to analyze the mechanisms that caused clogging by sediment particles with sizes in different ranges. The results showed that the relative flow rates in the bidirectional flow channel were all greater than 75% of the rinsing flow rate; however, the labyrinth channel was completely clogged after 12 irrigation procedures. The significance analysis showed that there were remarkable differences on hydraulic and anti-clogging performance of the 4 types of emitters. The hydraulic performance and anti-clogging performance of the bidirectional flow channel were all better than that of the contrasting labyrinth channel. However, for the emitters with different bidirectional flow channel structures, the better the hydraulic performance of the bidirectional flow channel was, the worse its anti-clogging performance was. The pattern and structural parameters of flow channel significantly influenced the overall performance of emitters in drip irrigation. The concentration of sediment deposits decreased gradually from anterior segments to posterior segments of the bidirectional flow channel. Along the direction of the flow channel, the proportion of sediment particles of which the sizes were greater than 0.03 mm decreased from 7.77% to 2.11%, and the proportion of particles with sizes of less than 0.005 mm decreased from 65.98% to 56.31% and then increased to 69.76%. The variations in particle size along the flow channel directly affected the structure of the sediment deposits. In the anterior and middle segments of the flow channel sediment particles mainly condensed into aggregates, but these underwent flocculation in the posterior segments. The results also confirmed that sediment was easily deposited in the bidirectional flow channel when the sediment particle size was less than 0.03 mm.