No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Effect of optimization forms of flow path on emitter hydraulic
ResearchGate has not been able to resolve any citations for this publication.
As global concerns surrounding water scarcity and food security escalate, there will be more demand for micro‐irrigation to meet growing food demands. Micro‐irrigation offers many advantages over conventional irrigation methods, including the ability to apply limited amounts of water directly to the crop root zone, incorporation of fertigation, reduced weed and pest infestation, and lower capital and operating costs. In recent decades, there has been considerable growth in the acreage under micro‐irrigation, mainly as a result of lower costs, improvements in filtration and emitter technology, and increased grower confidence in the technology. Research advances and technological improvements have made micro‐irrigation applicable to a more diverse set of applications, cropping systems, and water quality conditions. Cost and availability of water are also major drivers. Research in nano‐ and biofiltration techniques, soil moisture sensors, and precision irrigation shows great promise for the advancement of micro‐irrigation. Nevertheless, several technological challenges remain, especially for non‐row or non‐orchard crops, and in regions where water quality is severely impaired. Innovations in these areas are required, as well as a transfer of the technology to small farmers in water‐scarce regions who traditionally surface irrigate. Copyright © 2013 John Wiley & Sons, Ltd.
Sand filters are commonly used to protect drip irrigation systems especially when large amounts of organic contaminants are present. Moreover sand filters have the advantage of simplicity and large capacities in comparison with other types of filters.The main objectives of this paper are firstly to develop an analytical equation to calculate the total pressure drop in a sand filter taking into account the pressure drop in the underdrain and secondly to validate this equation comparing its results with the obtained experimentally.An experimental study with a scaled commercial porous media filter was conducted with different media bed depths and sand grain sizes. The results obtained with different media bed depths revealed that the Ergun equation underpredicted the pressure drop in the porous media filter.Subtracting the pressure drop caused by experiments with different sand heights shows that Ergun equation works well for predicting the pressure drop in a region of the sand bed sufficiently far from the underdrain, but fails in the region immediately next to this element. To overcome this problem, a new model based on a set of connected channels of the same diameter and progressive reduction of its number as the flow approaches the nozzles has been developed. The results of the model were compared with the ones obtained in the scaled sand filter as well as the ones obtained in commercial sand filters (Mesquita et al., 2012). The new analytical equation improves the results of the Ergun equation to predict the pressure drop produced by the entire sand bed by taking into account the effect of the underdrain (nozzle-type) and can be applied to accurately predict pressure drop in the commercial sand filters commonly used in drip irrigation.
Sand media filters are among the most common filters used in micro-irrigation systems, especially for filtering waters with large amounts of organic contaminants like reclaimed effluents. An experiment was conducted for 1620 h between August 2007 and September 2008 using a reclaimed effluent to evaluate the efficiency of sand filters with sand effective diameters of 0.32, 0.47, 0.63 and 0.64 mm in decreasing turbidity and improving dissolved oxygen concentration. In addition, this study strived to determine the filter ripening period (i.e. the time after backwashing when the filtered effluent has the lowest quality) and the effect of filter backwashing on filtration efficiency. Depending on the sand effective size, the sand filter achieved turbidity reductions of between 59.6 and 85.4% and dissolved oxygen recoveries from 4.5 to 15.7%. During the experiment the filter ripening period was 15 min. Overall, the results support the idea that a daily backwashing is a good maintenance practice since it reduces inefficient backwashings and increases dissolved oxygen, which is interesting when hypoxic water is used for irrigation.
Direct numerical simulations of the velocity and temperature fields for turbulent flow
in a channel are used to examine the influence of Prandtl number Pr on turbulent
transport. The Reynolds number, based on the half-height of the channel and the
friction velocity, is Reτ = 150. Prandtl numbers of 1.0, 0.3, 0.1, 0.05, 0.025 were
studied. The bottom and the top walls were kept at constant temperatures of +Tw
and −Tw. The influence of Pr on Reynolds transport, on the turbulent diffusivity, ατ,
and on the spectral density function of the temperature fluctuations was studied. The
observation that spatial variations of the ratio of the turbulent diffusivity to the value
observed at Pr = 1.0 are not large is used to propose a method for calculating average
temperature fields. The decrease in ατ with decreasing Pr is related to observations
of the increased damping of high-wavenumber temperature fluctuations. Molecular
conductivity, at smaller Pr, is pictured to act as a filter that renders high-frequency
velocity fluctuations ineffective in transporting heat.
Agriculture is the main user of water in Italy, as in most regions of the world. Particularly in Mediterranean regions, where it is more difficult to meet the agricultural water demand with conventional resources, wastewater reuse represents a viable option. Drip irrigation is particularly suitable for wastewater reuse because it minimises the health risks to farmers and product consumers due to contact with the wastewater. The performance of drip irrigation systems using wastewater is mainly limited by emitter clogging, and this discourages farmers from introducing it. The paper gives the results of experimental trials on the behaviour of six kinds of filters (gravel media, disk and screen) and four types of drip emitters (vortex and labyrinth) using five kinds of municipal wastewater that have not undergone previous advanced treatment. The performance of the emitters and filters tested depends on the quality of the wastewater: total suspended solids and organic matter content influence the percentage of totally clogged emitters, the mean discharge emitted, the emission uniformity coefficient, and the operating time of the filter between cleaning operations. Vortex emitters were more sensitive to clogging than labyrinth emitters. The gravel media filter guaranteed the best performance, but the disk filter, which is cheaper and simpler to manage, assured performance similar to that of the gavel media filter. The test showed the importance of the technology used in manufacturing disk filters. Screen filters were shown to be unsuitable for use with wastewater, with the exception of diluted and settled wastewater. The theoretical discharge of filters, suggested by the manufacturers for clean water, is not adequate for wastewater of the kind used in the trials (suspended solids greater than 78 mg/l and BOD5 more than 25 mg/l of O2). The operating times of the filters between cleaning operations, less than 1 h in most trials, suggest the use of automatic cleaning systems. The existing clogging risk classifications proposed for clean water can only be considered reliable for wastewater when labyrinth emitters and gravel or good quality disk filters (such as Arkal) are used; they are not adequate for vortex emitters or screen filters.
On the basis of picking up the structural feature parameters of labyrinth channels of drip irrigation emitters, the hydraulics performance experiments on integral labyrinth emitters were performed in order to summarize the design principle for labyrinth channels. The integral labyrinth emitters were made by means of utilizing rapid prototyping technique. Using multivariable linear regression, formulas of pressure versus flow and regression plots for different emitters were induced. The formulas of flow versus structural feature parameters were summarized based on the trapezoid unit, and those regression formulas were verified through experiments. The relationships among flow, pressure and cross-section dimension of this labyrinth channel were established. Furthermore, the effect of channel fabrication error on the flow rate of emitters was analyzed, which provided a basis for parameterized structural design and precision control in the fabrication of emitters.
In order to resolve the clogging problem of emitter from structure design and aiming at various kinds of small labyrinth channels of the drip irrigation emitters, the Computational Fluid Dynamics (CFD) was used to conduct the numerical simulation and visually reveal the flow behaviors in the labyrinth channels of emitters. The velocity field was measured by Laser Doppler Velocimeter (LDV) in hydrodynamic similarity experiment to verify the computational results. On this basis, the anti-clogging mechanism was analyzed. A main-route anti-clogging design method was proposed to optimize the structure in the stagnant areas in order to enhance anti-clogging performance of emitter channels. And it was verified through anti-clogging experiment.
In order to improve the reference of designing of anti-clogging ability of labyrinth channel emitter, the sand content and water and sand velocity distribution in the trapezoidal labyrinth channels were analyzed by CFD, the movement trajectories and velocity of solid particles in modified channel before and after tested by PIV. The phenomenon of a large number of solid particles concentrated on the surface near the upstream face and low velocity position of trapezoidal-channel emitters. When flow path is being modified, it is appropriate to increase the modification of the upstream face. Combined with the whole flow path and processing requirements, the downstream face may need not modified. Regarded the some one sand content distribution line as the borderlines of trapezoidal-channel to design the channel several times, after structural standardization and selecting the wide flow path, the position with high sand content can be canceled, and the better channel model is got. The method tested by CFD and PIV can keep the previous hydraulic performance before modification, and significantly improve the anti-clogging performance.
Emitter with tooth-labyrinth paths was main research subject. The distribution law of sand content and hydraulic performance of emitter were analyzed by CFD (computational fluid dynamics) two-phase simulation technology firstly. The optimal design method of labyrinth paths was proposed that the lesser isoline of sand content was regarded as the borderline of labyrinth paths. According to the results of two-phase CFD simulation on the optimal structure, the sand content of labyrinth paths by optimized was more uniform than before, the phenomenon of a large number of solid particles concentrated on the surface near the entrance and exit of labyrinth paths was basically eliminated, the anti-clogging performance of emitter was significantly improved. Secondly, based on optimized structure, a standardization optimized structure was designed, the prototype structure emitters and the standardization optimized emitters were produced by mould. Finally, hydraulic performance of tooth-labyrinth paths and distribution of sand were tested by combined CFD simulation and period clogging experiment. Accuracy of sand distribution with CFD simulation was tested with short period clogging experiment. The results showed that the emitter by anti-clogging optimal design with the lesser isoline of sand content as the borderline of labyrinth paths maintained the previous excellent hydraulic performance, its anti-clogging performance was significantly improved from prototype structure, the life was twice as prototype structure.
Computational Fluid Dynamics (CFD) techniques have been used for the design and improvement of many hydraulic devices over the past several years. The use of CFD in microirrigation emitters is new but it could be a powerful tool for emitter manufacturers. A study of the flow behaviour through an in-line emitter labyrinth has been carried out and is present by the authors. A laminar flow condition was assumed inside the emitter due to a low Reynolds number (lower than 1500 in all cases). The influence of the grid was taken into account using a finer mesh, but its use shows that there was no influence on the final results. The mathematical model developed for this paper shows a good correlation with the empirical results of the emitter testing carried out in the laboratory. These results show that the mathematical model has a very good agreement with the experimental data and it could be used for improving the design of microirrigation emitters through changes of the inside geometry of the emitters.
The aim of this research was to compare the evolution of head loss in disc (130 μm) and non-woven synthetic fabric filter media used to filter the water in drip irrigation systems. Two forms of treatment of the irrigation water were carried out: one with a chemical product (chlorine) and the other with none. The research used two different filter media: two for each treatment together with a fertigation technique with organic products in both types of treatment. The chemical treatment of the irrigation water was done by chlorination, in which the source of chlorine was sodium hypochlorite. Water from an open reservoir was used, in which a drip irrigation module was installed. The temporal variation in water quality over one year was analyzed, taking into consideration the physical, chemical, and biological parameters of water that can cause clogging problems in emitters. The results showed that, in irrigation water, the pH and iron chemical parameters presented an average risk of clogging, and the hydrogen sulfide parameters presented a high risk. The performance of the filters was analyzed by comparing the concentrations of the effluent on the disc and non-woven synthetic fabric filters in relation to the efffluent's physical and biological parameters. An attempt was made to follow head loss evolution in relation to the volume filtered by the filters so as to make a comparative analysis. It could be seen that the evolution of head loss was more significant and quicker with the non-woven synthetic fabric filter than with the disc filter. The level of clogging in the emitters was calculated by means of a uniform distribution index. The test area using the non-synthetic woven fiber filter presented the smallest level of clogging and the greatest water distribution index. © 2008 American Society of Agricultural and Biological Engineers.
The coupling of large eddy simulation (LES) with statistical turbulence models, i.e. Reynolds-Averaged Navier–Stokes (RANS) models, is arguably the main strategy to drastically reduce computational cost for making LES affordable in a wide range of complex industrial applications. The present paper presents a coherent review of the various approaches proposed in the recent literature on this topic. First, basic concepts and principal strategies highlighting the underlying ideas are introduced. This culminates in a general scheme to classify hybrid LES/RANS approaches. Following the structure of this novel classification, a larger number of individual methods are then described and assessed. Key methods are discussed in greater detail and illustrated with examples from the literature or by own results. The aim of the review is to provide information on how to distinguish different methods and their ingredients and to further the understanding of inherent limitations and difficulties. On the other hand, successful simulation results demonstrate the high potential of the hybrid approach.
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.
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.
An integral 3D numerical model based on the structural characteristics of the emitter with arc labyrinth channels was constructed to simulate the relationship between flow rates and pressure heads as well as the flow field distribution in the small channels by computational fluid dynamics (CFD). Meanwhile, the emitter prototypes fabricated by stereolithography technology were used in the flow rate experiments. The calculation results obtained revealed turbulence model can supply a better agreement with the experimental data than laminar flow model under pressure ranges of 40–160 kPa. Most pressure losses are occurred in labyrinth channels and the losses within each arc unit are constants under different inlet conditions. In addition, laser-Doppler velocimetry (LDV) was employed to measure the flow fields of the magnified model with a magnifying scale of 15:1 according to the channel structure of the emitter, and the measured velocity distribution in the cross-section is in good agreement with calculation results. It was found that reversed flow happened near the upper fringe of the flow path, and that in the longitudinal symmetric plane mainstream velocity regions and low velocity regions could be observed clearly. The vortexes of different sizes were developed in low velocity regions, which may be one of the reasons leading to channel clogging.
Although Large Eddy Simulations (LES) have demonstrated their potential in simple academic combustion chambers, their application to real gas turbine chambers requires specific developments and validations. In this study, three specific aspects of such chambers are discussed: multiple inlets, multi-perforated plates and film cooling. LES are used in an industry-like chamber and results are compared with predictions provided by Reynolds Averaged Navier–Stokes (RANS) simulations and experimental measurements. Multi-perforation is handled using a simplified effusive wall law while film cooling makes use of low resolution influx conditions (‘coarse LES’). Experimental results are well reproduced and qualitatively improved when compared to RANS predictions. LES results underline the potential of the approach for industrial use.
The most serious problem in trickle irrigation is clogging of emitters or applicators. Recommendations and guidelines are presented for preventive maintenance which include water filtration, chemical treatment, pipeline flushing, and field inspection. A suitable type, size, and capacity of a filtration unit is required. Chemical treatment should be considered in terms of theory and field research on the reclamation and prevention of emitter clogging. Proper procedures for the flushing and field inspection of trickle irrigation systems are also essential. Because water quality is of primary importance in the design and operation of this maintenance program, a tentative water-classification system was developed to establish criteria by evaluating the clogging potential of a trickle irrigation water source.
The effect on emitter clogging of four filtration systems (sand, screen, disc and a combination of screen and disc filters) and six emitter types placed in laterals 87 m long, using two different effluents with low suspended solid levels from a wastewater treatment plant, was studied for 1000 h. Four of the emitters were molded and welded into dripline wall, two of them being pressure-compensated and the other two non-pressure-compensated. The other two emitters, both pressure-compensated, were inserted into thick wall. Emitter clogging was affected mainly by emitter type, location along the lateral and the interaction between these two factors. Differences among emitters with larger clogging were only observed at the end of dripline. Two molded and welded emitters showed the worst performance: one non-pressure-compensated with the lowest passage section, and the other pressure-compensated that, after 800 h working at higher dripline flow and particle load, experienced an important decrease in flow rate. Only with the effluent that had a higher number of particles, did the filter and the interaction of filter and emitter location have a significant effect. Emitters placed after screen and sand filters showed the largest flow rates at the lateral ending, even though only sand filtration significantly reduced turbidity and suspended solids. Emitters protected by a disc filter experienced the largest flow rate reductions.
Agricultural irrigation equipment-emitter technical specifications and test methods
- Gb Standards
GB standards, GB/T 7187-1997 (1997) Agricultural irrigation equipment-emitter technical specifications and test methods
Impact of emitter clogging on hydraulic characteristics in micro-irrigation: field Evaluation
- A A Ghaemi
- S T Chieng
Ghaemi AA, Chieng ST (1998) Impact of emitter clogging on hydraulic
characteristics in micro-irrigation: field Evaluation. In: Proceeding of the Canadian Sherbrooke, Qubec, pp 162-171
The flow path design, and flow characteristics test and numerical simulation of fractal flow path in emitter
- Y K Li
Li YK (2005) The flow path design, and flow characteristics test and
numerical simulation of fractal flow path in emitter. China Agricultural University, Beijing (Chinese with English abstract)
The test for the movement characteristics of water and particles in drip irrigationemitter
- H S Sun
Sun HS (2014) The test for the movement characteristics of water and
particles in drip irrigationemitter. China Agricultural University,
Beijing (Chinese with English abstract)
The test for the movement characteristics of water and particles in drip irrigationemitter
- G Salvador
- J Arviza
- F Bralts
Salvador G, Arviza J, Bralts F (2004) Hydraulic flow behaviour throngh
an in-line emitter labyrinth using CFD Techniqued. ASAE/CSAE
Annual International Meeting. Fairmont Chateau Laurier, The
Westin, Government Centre Ottawa, Ontario
Sun HS (2014) The test for the movement characteristics of water and
particles in drip irrigationemitter. China Agricultural University,
Beijing (Chinese with English abstract)