It is necessary to have a comprehensive understanding of the flow mechanisms within drip irrigation emitters to design emitters that have a high anti-clogging performance. The use of computational fluid dynamics (CFD) to research the flow characteristics is appropriate because the labyrinth flow path is narrow and its boundary is complex. In this paper, a CFD for numeric model was developed for numerical simulation of the velocity distribution and turbulence intensity distributions within labyrinth emitters. A two-dimensional digital particle-tracking velocimetry (2D-DPIV) visual display system of the full flow fields was also constructed using plain laser inducement fluorescence velocity measurement technology, custom-made fluorescent particles and a plane model of the emitters. The object lens of a microscope was fitted to a conventional charge coupled device (CCD) camera to overcome the contradiction problems between the image viewing area and resolution power within the flow path. The measured turbulence and velocity distribution characteristics within the labyrinth flow path were in good agreement with the calculated CFD results. This enabled the optimal emitter design patterns to be determined based on the hydraulic characteristics and clogging resistance in the labyrinth flow path.

CFD and digital particle tracking to assess flow characteristics in the labyrinth flow path of a drip irrigation emitter

The energy dissipation mechanism and anti-clogging properties of drip irrigation emitters are closely related to flow characteristics of the fluid in its flow paths, and flow field tests using modern flow visual technologies were carried out by a large number of designers. The Digital Particle ImageVelocimetry (DPIV) system was built for un-disturbed flow tests in the labyrinth path. In this article, the flow field was measured in the flow path section, the structural unit and the local region near sawtooth. Under the pressure level of 10 Kpa, 50 Kpa, 100 Kpa and 150 Kpa, the flows in the two labyrinth paths were in the turbulence state, with flow stagnation regions and whirlpool regions in the structure of the labyrinth path sections. The flow stagnation regions should be eliminated as much as possible. But the vortex should be fully developed, which could increase the self-cleaning capacity and the anti-clogging capacity of the emitter. With respect to the anti-clogging performance and the energy loss efficiency of the emitter, the M-type flow path is better than the K-type flow path.

Flow Characteristics in Energy Dissipation Units of Labyrinth Path in the Drip Irrigation Emitters with DPIV Technology

A kinetic model for biofilm growth inside non-PC emitters under reclaimed water drip irrigation.

In this paper, 13 fractal flow paths were designed and the effects of flow path geometric parameters on the internal flow characteristics and hydraulic performance explored. The results showed as the flow path width increased from 0.9 to 1.3 mm, the flow velocity followed from 1.83 to 2.43 m s−1. There was significant difference in the turbulence intensity. The flow velocity (about 2.14 m s−1) and turbulence intensity distribution (5.6–48.1%) in flow paths with different depths were approximately the same. Different flow path lengths would obviously affect the values of the flow characteristics, while the distributions were similar. The length increased from 128 to 256 mm, the flow velocity decreased from 2.52 to 1.84 m s−1 and the maximum turbulence intensity dropped from 55.6 to 40.1%. As for hydraulic performance, the flow regime indexes were all about 0.49. The flow coefficient was obviously positively related to flow path width and depth, but very negatively correlated with flow path length and a prediction model of flow coefficient was constructed (R2 = 0.94). After comprehensive consideration, the optimized flow path width was about 1.0 mm, the length should be less than 224 mm, and a series of emitters with different flow rates could be developed by changing the depth. Copyright © 2016 John Wiley & Sons, Ltd.

Effects of Flow Path Geometrical Parameters on Flow Characteristics and Hydraulic Performance of Drip Irrigation Emitters

Drip irrigation has become an application trend of water-saving irrigation technology due to its excellent water-use efficiency. However, the energy dissipation form of the commonly used labyrinth channel is relatively simple, and the corresponding energy dissipation mechanism research is inadequate. This article proposes a new kind of channel structure of drip irrigation emitters based on the structure of scalariform perforation plates in plant xylem vessels. We establish a total of 16 sets of orthogonal structure schemes. Using numerical simulation and physical experiments, the hydraulic performance and energy dissipation mechanism of the perforated drip irrigation emitters (PDIE) are studied. The results show that the flow index of PDIE is 0.4665–0.5266. The hydraulic performance of PDIE in the high-pressure zone is the best, and the flow index is 0.4665–0.5046. As the pressure increases, the velocity of the flow of the upper perforation increases rapidly, the flow ratio decreases, the flow index decreases, and the hydraulic performance improves. To further verify the energy dissipation mechanism, a lower flow ratio and a better hydraulic performance were obtained through appropriately expanding the upper part of the upper perforation inlet to the channel boundary. The research sheds new insights for optimizing the hydraulic performance of PDIE. Results reported here provide a theoretical basis for the structural design of drip irrigation emitters and the energy dissipation mechanism research.

https://www.mdpi.com/2073-4441/13/2/171/pdf

Yunkai Li

Papers

Effects of fractal flow path designing and its parameters on emitter hydraulic performance