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Copyright of Journal of Irrigation & Drainage is the property of Journal of Irrigation & Drainage Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study aims to evaluate the filtration performance of sand filters using fractal dimensions. Three kinds of sand filters were also selected with particle size in the range of 1.0-1.18, >1.18-1.4, and >1.4-1.7 mm. The Yellow River sediment in the people's Victory Canal was collected as impurity particles in the raw water. The distribution of particle size in the Yellow River sediment was measured using a laser diffraction particle size analyzer (Mastersizer 3000, Dandong Baite Instrument Co., Ltd). It was found that the calculated mean values of skewness and kurtosis were 0.12 and -0.01, respectively, for the samples from the Yellow River sediment, indicating an outstanding normal distribution. Additionally, the samples were also collected from the Yellow River sediment in Lankao County, thereby verifying the distribution of particle size. It was found that the skewness and kurtosis values of the sediment sample in Lankao County were -0.11 and -0.23, respectively, where the frequency distribution of particle size also conformed to the normal distribution. An industrial CT scanner (C16M3201, Luoyang Tengda Testing Service Co., Ltd) was used to map the filter layer. The image processing and pixel coverage were utilized to calculate the porosity of cross section, the box-counting fractal dimension, and the ratio of the minimum to the maximum aperture (aperture ratio) in the three kinds of sand filter layers. The results showed that the porosities were 0.421, 0.431, and 0.439, respectively, while the box-counting fractal dimensions were 1.695, 1.709 and 1.726, respectively, and the aperture ratio was 1/17, 1/18, and 1/21, respectively, for the three types of layers. Then, the applicability of fractal theory was also evaluated for the quartz sand filters. Subsequently, a fractal model of filtration probability was established for the sand filters. The ranges of pore diameter in the three kinds of sand filters were 59.5-1 002, 66.9-1 220, and 72.9-1 503 μm, respectively. In the sediment of the Yellow River from the people's Victory Canal, the probabilities of impurity particles above 100 um passing through the sand filter were 0.67%, 0.81%, and 0.93%, respectively. In the Yellow River Sediment from Lankao County, the probabilities of impurity particles above 100 μm passing through the sand filter were 0.62%, 0.80%, and 0.91%, respectively. It inferred that the presence of surface filtration was proved theoretically. A systematic investigation was also made on the influence of surface filtration on Backwash frequency. Consequently, an optimal filter layer was achieved to reduce the surface filtration, particularly with the particle size in the range of >1.4-1.7 mm suitable for sand filters. The finding can provide strong support to explore the internal structure of sand filters and the selection of filter material. [ABSTRACT FROM AUTHOR]

Sand filter is considered to be one of the best choice to prevent clogging in micro-irrigation system. Head losses in media filter are produced by the friction loss due to the internal auxiliary elements of the filter container and the resistance offered by the media layer. The underdrain element is a core component in sand filter. To deeply understand the hydraulic behavior of underdrain, the experimental and numerical investigations were conducted to explore the flow resistance characteristics and flow field distribution in the underdrain. Laboratory experiments of filtering and backwashing were conducted in Farmland Irrigation Research Institute, Chinese Academy of Agricultural Sciences, Xinxiang, China. A trapezoidal underdrain element applied commonly in domestic market was selected in the experiment. It was installed in a scaled sand filter based on a commercial filter with 600 mm internal diameter. The sand filter model were tested at eight filtering velocities ranging from 0.010 to 0.040 m/s, and eight backwashing velocities ranging from 0.005 to 0.040 m/s, which were consist with the actual commercial filter operation. The experimental variables were monitored in real time by a data acquisition system consisted of a flowmeter and pressure transmitter. The internal flow behavior through the filter was simulated using the Computational Fluid Dynamics (CFD) method. A CFD model of the underdrain was developed by ANSYS Fluent 15.0. The geometry of the underdrain and its unstructured mesh were designed by ICEM software. Due to the turbulent flow regime in the underdrain and layer, the realizable k-ε turbulence model and the porous medium model were selected for solution. The computing area and the boundary condition of inlet and outlet were proposed. To ensure the reliability of the numerical simulation, the experimental values were compared with the simulated results. The results showed that the simulated values of head loss were in good agreement with the experimental values with the relative errors between 3.54% and 6.53%. The tested results showed that as the filtering velocity increased (>0.024 m/s), the pressure drop produced by the underdrain improved more significantly than the media layer. When the velocity increased to 0.040 m/s, the 72.3% of the pressure drop were produced by the underdrain. At the same filtration velocity, the pressure drop of backwashing mode was higher than filtering mode. The results confirmed that it was important to select appropriate filter model and avoid overload operation for the irrigation system. The simulated pressure and velocity contours showed that the structure without slots at the top of underdrain increased the non-uniformity of the flow streamlines and affected the backwash efficiency. Due to the narrowing of the flow section gradually from the layer to the underdrain outlet, the flow velocity increased drastically. When filtration velocity was 0.030 m/s, the velocities at the narrow slots and the entrance of the collector reached 2.57 and 4.01 m/s, respectively, resulting in significant pressure drop in the two region subsequently. The pressure contours of the collector at different cross sections showed non-uniformity due to the violent disturbance of the flow. In view of these results, a spherical flat underdrain with smaller aspect ratio and more uniform slots distribution was designed. Compared to the trapezoidal underdrain, the distance of the flow through the underdrain decreased by 14% and the passing area increased by 27%. In addition, the diameter of the tube outlet increased to 30 mm. The modification favored vertical flow through the porous medium and the underdrain chamber with a more direct exit, thereby reducing pressure drop. The CFD simulations of the modified underdrain showed the smoother streamline around the underdrain for filtering mode and a smaller vortex scale for backwashing mode, indicating excellent passing capacity and backwash efficiency. The study could guide the design of filter for irrigation equipment manufacturer, irrigation project designer and field operator. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Drainage & Irrigation Machinery Engineering / Paiguan Jixie Gongcheng Xuebao is the property of Editorial Department of Drainage & Irrigation Machinery Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Drainage & Irrigation Machinery Engineering / Paiguan Jixie Gongcheng Xuebao is the property of Editorial Department of Drainage & Irrigation Machinery Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Backwashing of quartz sand filter in micro-irrigation is an effective way to realize the regeneration of quartz sand filter media. Analysis of flow field in the backwashing process of quartz sand filter and determination of reasonable backwashing velocity play an important role in the design and operation of the quartz sand filter. The method of numerical simulation has obvious advantage in the analysis and investigation of the flow field in the filter layer. In order to realize the numerical simulation of the backwashing process of quartz sand filter, the geometric model of quartz sand filter was established through Gambit software, and the mesh division of the geometric model was carried out. Because the backwashing process of quartz sand filter layer is a solid-liquid multiphase flow system interacted by both water and quartz sand, in which quartz sand particles are distributed only in a part of the region during the process of backwashing, not being carried away to outside of the filter by the stream, and in which quartz sand accounted for a larger proportion of the whole volume, the Eulerian model was adopted as a model for numerical simulation of backwashing. At the same time, because the backwashing process of quartz sand filter layer is a dynamically stable process, the transient simulation solver was adopted. The simulation objects were three kinds of quartz sand filter layer with the same thickness of 400 mm, but the equivalent particle size were 1.06, 1.2 and 1.5 mm respectively. In order to verify the reliability of simulation results, backwashing experiments were conducted in Farmland Irrigation Research Institute, Chinese Academy of Agricultural Sciences, in 2014. The parameters such as backwashing velocity, pressure drop and expansion height of filter layer were measured. The simulation results were compared with the experimental results. Comparison showed that the maximum simulation error of the whole pressure drop of filter layer was 7.03%, and the maximum simulation error of filter layer density was 1.93%. It was proved that the numerical simulation results were reliable. On this basis, the fluctuation trend of pressure drop with time and the variation trend of the mean value and the standard deviation of the pressure drop with backwashing velocity in backwashing process of quartz sand filter layer were analyzed. If the standard deviation of pressure drop is large, it shows that the fluctuation of pressure drop is unstable, and the unstable fluctuation of pressure drop will affect the effect of backwashing. This result can determine the reasonable range of the backwashing velocity. Then, the distribution rule of the filter layer density with time, the variation trend of the mean value and the standard deviation of the density with the change of the backwashing velocity were analyzed. When the density is close to the static density of the mixture composed of water and quartz sand, the effect of backwashing is poor. When the standard deviation of density is too large, partial concentration phenomenon will appear in the filter layer, which will cause negative influence on the effect of backwashing. Thus, the reasonable range of the backwashing velocity was determined. After combined the rules of pressure drop fluctuation and density distribution, the reasonable ranges of the backwashing velocity of three kinds of filter layer are obtained as 0.0149-0.0212, 0.0146-0.0218 and 0.0191-0.0261 m/s respectively. The research results provided a theoretical basis for the mechanism of quartz sand filter in the process of backwashing. It also provided a technical support for the operation of the sand filter. [ABSTRACT FROM AUTHOR]