Visualizing particles movement characteristics in drip irrigation emitters with digital particle image velocimetry

Abstract: Understanding the movement characteristics of particles is very important for solving the clogging problem in drip irrigation emitters. The key to solve this problem is to make sure that the emitter itself has a high resistance to clogging. Particles are the main component of clogging substance in emitter, accounting for 99% or more. Through selecting the appropriate emitter flow path structure parameters and optimizing the flow boundary, a good flow condition in the path could be ensured, in addition, the transport capacity of particles in the flow path gets improved. Furthermore, the intention of controlling near-wall attachment of particles can be achieved. However, it is very difficult to test the flow in the critical scale flow path due to its complicated structure, narrow flow path, and non-transparent appearance. There were a few reports on the whole field measuring about water-sand two-phase flow in emitters. Therefore, this paper researched flow characteristics in a simplified model of emitter, which only reserved the flow path for energy dissipation. We tested the flow characteristics in the terminal unit structure. At the same time, a processing method for transparent model was proposed in this paper, and we improved the Digital Particle Image Velocimetry (DPIV), by changing the lens of the CCD camera into the close-up lens of Nikon D50. We visualized the movement characteristics of particles in emitters with improved DPIV test system. The results showed that it was feasible to test the motion characteristic of particles in simplified transparent model with the improved DPIV test system. It was turbulent in emitter. And the flow state, vortex distribution, the intensity of flow lines, as well as following performance of particles did not change as the increasing working pressure in emitters. There was a linear relationship between size of flow path and working pressure. The small change of pressure did not significantly change the following characteristic of particles in the central region and the near-wall region. Under the same working pressure, the particles maximum velocity decreased with the increasing particle size, but the distribution trends of the flow lines and the vorticity of particles with different sizes were consistent. The particles following characteristics decreased with the increasing size, in both the central region and the near-wall region. The research could provide the theoretical basis for the analysis on the solid-liquid two-phase flow and the anti-clogging design in emitters.