Shumei Ren

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

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.

Hydraulic Characterizations of Tortuous Flow in Path Drip Irrigation Emitter

At present, the tortuous emitter has the most advanced performances in drip irrigation. But the theories and methods for designing its flow path have been strictly confidential and the researches on the function of practical guidance have seldom been published. Seven types of most representative tortuous emitting-pipes currently used in agricultural irrigation regions of China were chosen for investigating the geometric parameters of the flow path by means of combining high-precision microscope and AutoCAD technology. By the measurement platform developed by the authors for hydraulic performances of emitters, the free discharge rates from the 7 types of emitters were measured at 9 pressure levels of 1.5 m, 3.0 m, 5.0 m, 7.0 m, 9.0 m, 10.0 m, 11.0 m, 13.0 m and 15.0 m. Then the discharge-pressure relationship, manufacturing variation coefficient, average velocity on the cross-section of flow path and the critical Reynolds number for the flow regime transformation within the paths were analyzed in detail. The results show that both pressure-ascending work pattern and pressure-descending work pattern have some impacts on the discharge rates of tortuous emitters, but the impact level is not significant. The target pressure could be approached by repetitive applications of the two work patterns during pressure regulation. The operation under low pressures has some impacts on the hydraulic performances of emitters, but the impact level is also not significant. The classical model of the discharge-pressure relationship is suitable for the pressure range of 1.5 m –15.0 m. The Reynolds number for fluids within the 7 types of tortuous emitters ranges from Re =105 to Re =930. The critical Reynolds number for the flow regime transformation is smaller than that for the routine dimension flow path. The variation coefficient of emitter discharge rates is slightly fluctuating around a certain value within the whole pressure range.

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

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.

Impact of Simulated Irrigation with Treated Wastewater and Saline-Sodic Solutions on Soil Hydraulic Conductivity, Pores Distribution and Fractal Dimension

Irrigation with treated wastewater which has the characteristics of higher salt content, larger sodium adsorption ratio (SAR), and more organic matter and suspended particles can cause the deterioration of the soil environment. Ordinary water, treated wastewater, and saline-sodic solutions with SAR = 3, 10 and 20 (mmolc·L− 1)0.5, respectively, were used as five irrigation water types, and the changes of soil saturated hydraulic conductivity (K s), soil pores distribution, and soil pores single fractal dimension (D m) were studied after simulated irrigation for 1 and 2 years with simulated irrigation systems, which consisted of soil bins and simulated evaporation systems. The results showed that soil K s in the following descending order: CK > SAR3 > WW > SAR10 > SAR20, and the adverse effects on soil K s caused by suspended solid particles and dissolved organic matter might play a more significant role than sodium in treated wastewater. The 0-5 cm soils had a smaller single soil pore area but larger pores quantity after simulated irrigation, the distribution of soil pores which was irrigated with treated wastewater had a smaller change compared with saline-sodic solutions treatments, and it showed the soil pores structure binary image was an effective method to analysis soil pores distribution. Soil D m increased after simulated irrigation, and the smallest was the soil simulated irrigation with treated wastewater for 1 year, because the plugging and filling of suspended particles and dissolved organic matter in treated wastewater made the soil pores well distributed, but the soil D m did not increase with increasing of SAR levels in irrigation waters. The relative SAR levels irrigation to soils and soil K s had a good linear correlation relationship, while the relationship between soil D m and the relative SAR levels irrigation to soils was very complicated. The soil D m which calculated from soil binary images could not well reflect the hydraulic conductivity of saturated soil. Irrigation with treated wastewater had a greater effect on soil K s than soil D m, comparing with saline-sodic solutions which had the similar SAR value. It was suggested that the future research should consider both the horizontal and vertical directions of soil D m to well reflect the soil K s.

The Vulnerability Assessment Method for Beijing Agricultural Drought

Drought is a major disaster which Beijing agricultural systems faced with, build drought warning mechanism we need in-depth analysis the causes and mechanism of the drought to provide a basis for scientific disaster reduction and prevention. VAM vulnerability assessment method, selected 15 factors represent drought exposure, sensitivity and adaptive capacity, based on improved analytic hierarchy process to determine the weight of each factors, use K-means clustering algorithm to generate the drought vulnerability index system of research district. Draw vulnerability zoning map based on ArcGIS.

An improved canopy transpiration model and parameter uncertainty analysis by Bayesian approach

In this paper, an improved canopy transpiration (Ec) model that considered the unidirectional influence of soil evaporation on Ec was presented by extending Penman-Monteith model for increasing accuracy of modelling in sub-humid regions, and a Bayesian approach was used to fit the transpiration model to half-hourly transpiration rates for the 14-year-old cherry (Prunus avium L.) orchard collected over 4-month period and probabilistically estimated its parameters and prediction uncertainties. The probabilistic model was extended by adding a normally distributed error term, and the Markov chain Monte Carlo simulation method was used to determine the posterior parameter distributions. Seasonal variation of the Ec was analyzed by the experiments of Sap Flow method in Sijiqing Orchard in Beijing, north of China. The result showed there were larger uncertainties of the parameter and transpiration. The average value of parameters was used for the model, and long series data from simulated value of the model were compared with the measured data, and it showed that the improved transpiration model possessed high accuracy.

Characteristics of E. japonicus stomatal conductance under water-deficit stress using a nonlinear Jarvis modified model

Abstract Stomas are important gateways in the photosynthesis and transpiration of plant leaves. The stomatal size directly influences the photosynthetic and transpiration rates. However, the stomatal size is closely related to environmental factors. This study aimed to reveal the response principle between the leaf stomatal conductance of Euonymus japonicus and related environmental factors under water stress using pot experiments. The present paper introduced the difference between the leaf and air temperatures ( Δ T ) based on the Jarvis model, as well as established the improved Jarvis model between stomatal conductance and environmental factors. After optimizing the model parameters by the least-square method, the parameters were verified by the crossing method. An artificial neural network model was then introduced and compared with the former two. The results showed that the simulation results of the improved Jarvis model were better than those of the Jarvis and artificial network models. Compared with the Jarvis model, the improved Jarvis model had RMS and MRE errors that were at least 65% smaller, as well as a correlation coefficient ( R 2 ) that was at least 10% higher. The improved Jarvis model simulation results were more uniformly distributed than the Jarvis model on both sides of the 1:1 regression line. Therefore, under a water stress condition, the improved Jarvis model is more appropriate to use in simulating the stomatal conductance relationship of E. japonicus with environmental factors.

Effects of Reclaimed Water and C and N on Breakthrough Curves in Sandy Soil and Loam

Long-term irrigation with reclaimed water may change soil physical properties and solute transport rate due to C and N in reclaimed water and the particularity of reclaimed water. Ordinary water, reclaimed water and mixed water which added C and N into reclaimed water were used as background water, then potassium bromide was added to background water and mixed them into three kinds of solutions whose bromide concentrations were all 0.5 mol/L, then soil column breakthrough experiments were conducted. The results showed that bacteria quantity increased both in sandy soil and loam after soil column experiments, and bacteria quantity in sandy soil and loam were all in the following descending order: breakthrough solution using mixed water as background water, breakthrough solution using reclaimed water as background water, and breakthrough solution using ordinary water as background water. However, fungi quantity had no significant difference. Cumulative infiltration in sandy soil and loam can be properly described by power function and logarithm function, respectively. The amount of cumulative infiltration in sandy soil and loam in the same infiltration time were all showed a descending order as: breakthrough solution using ordinary water as background water, breakthrough solution using reclaimed water as background water, and breakthrough solution using mixed water as background water. Breakthrough curves can be well described by CXTFIT 2.1 code, it can be seen from the values of V and D that reclaimed water and the addition of C and N made solute transport more difficult in soils and increased diffusion coefficient, and these impacts were greater on loam than sandy soil. Reclaimed water and the added C and N increased soil bacteria, complicated soil pore system, and decreased soil hydraulic conductivity.

Effect of Different Nitrogen Fertilizers with Reclaimed Water Irrigation on Soil Greenhouse Gas Emissions

In order to investigate the effect of using different nitrogen fertilizer with reclaimed water irrigation on the emissions of soil greenhouse gases (CO2 and N2O), plot experiments were conducted using clean water and reclaimed water combined with different nitrogen fertilizer (urea, ammonium sulfate, slow release fertilizer) for irrigation. No significant differences in CO2 and N2O emission flux was observed between the treatments irrigated with clean water and ones with reclaimed water. The soil CO2 emission flux had no significant relationship with the application of nitrogen fertilizer, whereas the soil emission flux increased significantly as applied with nitrogen fertilizer. The N2O emission flux reached its maximum in 2-5 days after irrigation.

Analysis of Soil Water Wetting and Dynamics in Trace Quantity Irrigation

Compared with ordinary subsurface drip irrigation the trace quantity irrigation has some new features which will provide water according to the demand of the crops and continuous supply right and small amount water to the root of crops slowly, so the flow and moisture distribution is different from others and this Soil box experiments was used to study it. the result shows that when the trace quantity irrigation tape was buried into the soil the flow is approximately 53% of it in the air and the moisture distribution is divided into three kinds according to the depth.