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Journal of Drainage and Irrigation Machinery Engin
 
2013 Vol.31 Issue.1
Published 2013-01-25
article
Article
1 Analysis of flow in liquid jet pump—PartⅡ:Determination of dimensionless coefficients in theoretical model
WANG Yu-Chuan, CAO Shu-Liang, GAO Chuan-Chang, WANG Song-Lin
The relations of dimensionless coefficients, geometry parameters of crosssection and flow variables have been derived in a theoretical model of jet pumps. Those coefficients were determined by using numerical simulation of flow in the pump, and then their relationships with flow ratio were analyzed. It was indicted that the reaction force distribution coefficient c1 is nearly equal to the suction area ratio c at the best efficiency point; at the other flow conditions, however, two coefficients show significant difference. In fact, replacing c1 with c doesn′t cause a remarked error in theoretical prediction results. When the working fluid velocity keeps to be constant, the momentum correction coefficient k1 is independent of flow ratio, thus can be treated as a constant; the coefficient k2 shows a hyperbolic function against flow ratio, and asymptotically approaches to 1 as the flow ratio increases. The nozzle discharge coefficient 1 and suction chamber discharge coefficient 4 are constant in all the working conditions. The uniformity of velocity distribution in the diffuser inlet has a great influence on the diffuser velocity coefficient 3. The velocity correction coefficient at the throat 2 and the velocity correction coefficient 5 at the inlet to the nozzle of suction chamber decrease linearly as the flow ratio increases. They affect the results of theoretical model remarkably. The theoretical predictions show good agreement with the experiment results, confirming that the method proposed for determining the dimensionless coefficients is feasible and the model is reliable.
2013 Vol. 31 (1): 1-6 [Abstract] ( 2506 ) [HTML 1KB] [ PDF 5378KB] ( 1928 )
7 Pressure fluctuation characteristics of pumpturbine at pump mode
WANG Le-Qin, LIU Ying-Yuan, LIU Wan-Jiang, QIN Da-Qing, JIAO Lei
To study the hydraulic instability of a pumpturbine at the pump mode under different working conditions, the threedimensional, unsteady flow in the whole passage of the pumpturbine was conducted by using computational fluid dynamics softwareFluent under the optimal, low and high flow rate conditions. The pressure fluctuations were monitored respectively at the inlet of spiral casing, in the interface of runner and guide vanes, and in the space between head cover and runner, as well as in draft tube. The results show that a larger pressure fluctuation can be found in the interface of runner and guide vanes and in the space between the runner and head cover, while the pressure fluctuation is lower at the inlet of the spiral casing and in the draft tube. The pressure fluctuation is the smallest under the optimal condition; the larger the working condition deviates from the optimal one, the more considerable the fluctuation is. The dominant frequency of pressure fluctuation depends on the locations monitored. The dominant frequencies are integer multiples of the blade passing frequency and the runner rotational frequency in the interface of runner and guide vanes and in the space between runner and head cover, respectively. However, the dominant frequencies of the pressure fluctuation at the inlet of the spiral casing and in the draft tube are mainly related to lowfrequency components.
2013 Vol. 31 (1): 7-10 [Abstract] ( 3837 ) [HTML 1KB] [ PDF 1926KB] ( 2993 )
11 Effects of slotted blades on internal flow in centrifugal pump of low specific speed
LIU Wei, YUAN Shou-Qi, LI Xiao-Jun, PAN Zhong-Yong
To remedy the instability of internal flow in the impeller of a centrifugal pump of low specific speed at low flow rates, the impeller was redesigned to have slotted, then the flows in the pump with this kind of impeller and the original one were analyzed by using CFD codeFluent to identify effects of such blades on the internal flow and performance. It was shown that the pump head and total efficiency are a little increased at a lower flow rate as one slot was presented on every blade blades compared with the pump with the original impeller, but they are declined at a higher flow rate, suggesting the blade with one slot on it can improve the instability of internal flow in the impeller passages of centrifugal pumps of low specific speed at partial flow rates. In order to clarify influence of number of slots on the internal flow and the performance, an additional slot was made on every blade as well, and it was found that the instability of flow and efficiency are poorer against the case with one slot. It was confirmed that the slots on blades do improve the turbulence of flow in the impeller of a centrifugal pump of low specific speed at lower flow rates  point in some degree, however, that number of slots will affect the performance of the pump.
2013 Vol. 31 (1): 11-14 [Abstract] ( 2193 ) [HTML 1KB] [ PDF 3957KB] ( 1787 )
15 Optimization of automobile pump based on CFD
SHI Wei-Dong, PEI Bing, LU Wei-Gang, WANG Chuan, LI Wei
The hydraulic design of an original model of the WP7 diesel engine cooling pump was optimized by solving the timeaveraged Navier-Stokes equations, the standard k-ε twoequation turbulence model and the multiphase flow model with CFD codeCFX. A structured hexahedral mesh has been generated for improving accuracy of numerical simulation. A comparison of fluid static pressure, turbulent kinetic energy and vapor volume fraction contours, hydraulic and suction performance was made between the original pump and optimized one. It was shown that the optimized pump not only exhibits obviously low turbulent kinetic energy and vapor volume fraction at the impeller entrance, but also has a better hydraulic and suction performance compared with the original impeller. The impeller with the blade leading edge that was properly extended into the impeller eye and with a certain inclined angle with respect to the pump shaft has an improved hydraulic and suction performance due to reduced shock losses at the leading ledges and more uniformed flow pattern at the impeller entrance, causing the head was raised by around 3.16 m and NPSHC was declined as low as about 1.10 m. Even thought the performance predicted by CFD has a certain difference from the experimental one,the variation tendency of them is consistent with each other.
2013 Vol. 31 (1): 15-19 [Abstract] ( 2327 ) [HTML 1KB] [ PDF 2710KB] ( 2227 )
20 Performance of parallel doublechamber valveless piezoelectric micropump with threeway diffuser/nozzle tube
DENG Zhi-Dan, LI Fu, HE Xiu-Hua, WANG Jian
The fluidstructure interaction (FSI) method was adopted to simulate the fluid flow in a valveless piezoelectric pump with threeway diffuser/nozzle tube, and then a comparison is made with the experiment results. As the 100 V excitation voltage is applied, the flow rate increases against increasing frequency (50~175 Hz); the maximum error of flow rate between FSI computation and experiment is 12%. At the frequency of 100 Hz the flow rate increases with voltage linearly. The experimental data confirmed such computed results, suggesting the FSI simulation method is feasible for this micropump. Moreover a parallel doublechamber valveless piezoelectric micropump with threeway diffuser/nozzle tube was designed to improve output flow rate and pressure of the traditional single chamber valveless piezoelectric pump. Effects of difference in phase of the two vibrators on flow rate in the doublechamber micropump were analyzed by the FSI method, and the transient flow rate plots in one circle were established under various differences of phase, eventually compared with those of the singlechamber pump. The results indicated the flow rate shows a little change with difference of phase in the parallel doublechamber micropump. However, a continuous fluid transport was realized in the doublechamber pump in one cycle, for example,as the difference of phase is 180°,the flow rate is 0367 mL/min, and as the difference of phase is 360°, the flow rate is 0.349 mL/min.
2013 Vol. 31 (1): 20-24 [Abstract] ( 2036 ) [HTML 1KB] [ PDF 2072KB] ( 1747 )
25 Comparison of internal flows in jet pump predicted by various turbulence models
ZHOU Ling-Jiu, YUAN Ling-Li
 In order to clarify the mixing process between the working fluid and the sucked fluid in a jet pump, several twoequation turbulence models (Standard k-ε, RNG k-ε, Realizable k-ε and SST k-ω model) and Large Eddy Simulation model were used to calculate 3D singlephase flow field in the pump, and the numerical results were compared with the experimental data. The results showed that the pressure ratio and efficiency obtained by LES model agreed well with the experimental data. All the above twoequation turbulence models overestimated the energy dissipation during the mixing process and the vortex structure in the mixing layer was not well predicted by them. Just the LES model, however, showed the coherent vortex structure in the mixing layer, which precisely reflects the transport of momentum and energy, and the mixing process between the working fluid and sucked fluid. Further the predicted characteristic curves by LES achieved better agreement with the experimental observations than those by the rest turbulence models. Then LES was chosen to simulate the internal flow of the jet pump at different flow ratios. The results showed that the mixing zone between the working fluid and the sucked fluid moved away from the throat to downstream with increasing flow ratio; consequently the core flow with high velocity is stretched along the axial direction and the axial velocity of the mixed fluid is also increased.
2013 Vol. 31 (1): 25-30 [Abstract] ( 1713 ) [HTML 1KB] [ PDF 2007KB] ( 1953 )
31 Flexural deformation analysis of circular bimorph for piezoelectric pumps
SUN Xiao-Feng, YANG Zhi-Gang, SHAO Ze-Bo, DUAN Hao, JIANG Bin
The deformation characteristic of a circular piezoelectric vibrator in a piezoelectric pump needs to be analyzed theoretically in order to get precise change in volume of the chamber when the pump is in operation. The whole vibrator structure was divided into two substructures, namely the threelayer composite structure in the middle, which is composed of piezoelectric ceramic, metal substrates, and the external metal substrate structure. The volume change equation of the circular piezoelectric bimorph was derived under the fixed boundary condition based on the small deflection bending theory for the elastic thin plates. The analytical results indicated that the volume change of the bimorph is related to its geometry parameters, material property constants and the driving voltage. The displacements at the centre of the piezoelectric vibrator with 35 mm diameter copper substrate and 29 mm diameter bimorph were measured by using a noncontact laser measurement system when the vibrator was driven by different DC voltages, then they were compared with the above theoretical results to verify the equation proposed. It was confirmed that the analytical solutions are consistent with the measurements with an around 20% error. According to the equation above, if the single chamber of a piezoelectric pump is made of that piezoelectric vibrator measured, the predicted volume change of the pump will be nearly 128.81 mm3 and with 3 091 mL/min maximum output flow rate when the vibrator is driven by a sinusoidal voltage signal (110 V, 200 Hz).
2013 Vol. 31 (1): 31-35 [Abstract] ( 1917 ) [HTML 1KB] [ PDF 1846KB] ( 2388 )
36 Analysis and determination of critical nonsilting velocity of muddy water conveyance pipelines in Yellow River irrigation districts
HE Wu-Quan, CAI Ming-Ke, HE Xin-Ye, ZHANG Chen-Di
Sediment problem is the key factor that restricts the development of pipeline water conveyance irrigation engineering in Yellow River irrigation districts. In order to solve this problem, it is necessary to reasonably determine a critical nonsilting velocity of water conveyance pipelines in Yellow River irrigation districts. In doing so, a series of experiments on muddy water transport in pipelines were carried out by using four kinds of size of pipe diameter and six groups of sediment concentrations which were mixtures of water and various sand contents. Then influences of sand density, particle size, sediment concentration and pipe diameter on the critical nonsilting velocity were analyzed. The results showed that as the pipe diameter and sand density remain unchanged, the critical nonsilting velocity is increased with increasing sediment concentration. If the sediment concentration and sand density are kept constant, then the critical velocity is increased with increasing pipe diameter. The influence of sand density and particle size on the critical nonsilting velocity is also very obvious, especially for the sand particles with a size close to the upper limit of sand particle size (d90 or d95), which often deposit in the bottom of a pipe initially. Further, an empirical formula for calculating the critical nonsilting velocity was established based on the sediment suspension efficiency coefficient and the suspended sediment energy dissipation principal. The sediment suspension efficiency coefficient has been determined by the experimental data. It was confirmed that the maximum error is 2.958% between the predicted critical velocity and experimental one.
2013 Vol. 31 (1): 36-40 [Abstract] ( 2838 ) [HTML 1KB] [ PDF 1409KB] ( 2660 )
41 Fuzzy comprehensive evaluation model for pumping station buildings based on GAAHP
CAO Qiu-Lin, XU Wen-Ting
A comprehensive method for evaluating pumping station buildings safety was studied by using the standard genetic algorithm (GA), analytic hierarchy process(AHP) and fuzzy evaluation method so as to assess the buildings more precisely. Firstly, the numerical values for evaluating pumping station buildings safety were obtained and then a fuzzy comprehensive evaluation matrix was established by using the comprehensive integration method from qualitative to quantitative and by considering expert knowledge, inspection data and all other information. Secondly, the weight vector to evaluate index was determined with the standard genetic algorithm and AHP. Finally, the fuzzy comprehensive evaluation model was generated, through which a result of pumping station buildings safety evaluation could be worked out. For the buildings in Linhong west pumping station, the fuzzy comprehensive evaluation resultant vector is S=(0.313 6, 0.356 2.0.247 1,0.083 1); according to the maximum membership degree principle, Smax is 0.356 2, which corresponds to the 2nd commentsafe basically, thus the buildings in that station fall into the 2nd Class. This suggests that the buildings of that station meet the design standards and the safety requirements for operation as a whole. This conclusion is consistent with the one obtained by using usual evaluation methods, indicating the fuzzy comprehensive evaluation model is feasible.
2013 Vol. 31 (1): 41-45 [Abstract] ( 2508 ) [HTML 1KB] [ PDF 1410KB] ( 1890 )
46 Dynamic characteristics of axial flow check valve
YANG Guo-Lai, WU Guo-Guo, LIU Xiao-Xiong, CAO Wen-Bin, XU Min-Ying
The unsteady fluid flow caused from the moving disc in an axial flow check valve was numerically simulated by means of the computational methods and flow physical models available in CFD codeFluent. The disc regularly instantaneous movement was realized by the dynamic mesh technique and UDF (user defined function) in Fluent. The transient pressure and velocity were obtained during a period of the disc being closed by means of unstructured mesh, the standard k-ε turbulence model. Those transient characteristic curves have been measured experimentally as well, and exhibit good agreement with the predicted ones, suggesting the numerical simulation method is reliable. Moreover, such dynamic characteristic curves were calculated in the valves in various nominal diameters and external forces and their influences have been identified. Those results will play a critical role in investigation into water hammer effect in the axial flow check valve, and might be useful for check valve design in engineering projects.
2013 Vol. 31 (1): 46-49 [Abstract] ( 3074 ) [HTML 1KB] [ PDF 1981KB] ( 2578 )
50 simulation and experimental study on submersible selfaspirating aerator
ZHU Rong-Sheng, LI Xiao-Long, SHI Wei-Dong, LIU Ling-Ling, WANG Tao
An openstyle impeller with radial blades and an opentype diffuser were designed according to the performance specifications of a submersible selfaspirating aerator to investigate the fluid flow in the aerator, and their threedimensional models have been generated in CAD codeUG. The turbulent flow through the aerator was simulated by means of CFD softwareAnsysCFX with a multiplephase turbulence flow models, and the simulated results were analyzed and confirmed by related experimental observations. The simulated results showed that when the submersed depth of the aerator was increased to 6.5 m from 2.5 m, the flow patterns in the aerator experienced three changes, such as chaos, smooth and chaos again, accordingly the lowest pressure zone appeared, disappeared and reappeared as well. The experimental data exhibited that when the submersed depth of the aerator was increased to 6.5 m from 2.5 m, the air in the suction pipe got the highest velocity of 4.25 m/s at the 3.5m submersed depth. A similar air velocity in the suction pipe was achieved too. This suggests that predicting performance of aerator by means of CFD method is feasible.
2013 Vol. 31 (1): 50-55 [Abstract] ( 3015 ) [HTML 1KB] [ PDF 5650KB] ( 1765 )
56 scheme of MRT lattice Boltzmann method for viscous fluid flow
YANG Fan, SHI Xu-Ming, GUO Xue-Yan, CHEN Tie-Jun, WU Yu-Lin
In the last 20 years or so, there has been rapid progress in developing the lattice Boltzmann method (LBM) for solving a variety of fluid dynamic problems. Compared with the single relaxation time (SRT) collision model, the multiple relaxation time (MRT) one has better computational stability. In order to obtain a high resolution near a solid body, a multiblock scheme is developed for the MRT lattice Boltzmann method. The interface conditions are derived to make sure the continuity of mass, momentum and stresses across the interface between any two blocks can be satisfied. Further a temporal interpolation at an interface is also performed to ensure information at correct time level to be used. For validation the numerical simulations of the unsteady flows past a circular cylinder at Re=100 was carried out. It was showed that the spatial oscillations in the regions with large velocity or pressure gradients such as stagnation point are suppressed in a great deal with increasing grid resolution, and the predicted drag and lift coefficients agree well with the benchmark data.
2013 Vol. 31 (1): 56-60 [Abstract] ( 2390 ) [HTML 1KB] [ PDF 2420KB] ( 2057 )
61 Analysis of temporal and spatial variation of nitrogen in fieldditch system of small agricultural watershed
ZHANG Zhan-Yu, CHEN Jing-Jing, ZHANG Wen-Xiang, SI Han
A typical agricultural small watershed in summer season in Lishui county, Nanjing city was specified as a study model to explore the temporal and spatial variation trend of nitrogen in the small watershed. The temporal and spatial variation of soil nitrogen in the watershed was investigated by insitu observation, indoor laboratory analysis and statistics regression, eventually the distribution characteristics of nitrogen concentration in the drainage ditch were clarified. It was turned out that the profiles of three forms of soil nitrogen content against time show some differences, namely, the total soil total nitrogen content gets the maximum at a time instance, but both the soil nitrate nitrogen and ammonium nitrogen are subject to a steady decrease and the maximum declines are 37.1% and 60.9%. In the central area of the watershed the soil total nitrogen content is the highest, meanwhile the total nitrogen in the southern area is higher than that in the northern part. The averaged concentrations of the total nitrogen, nitrate nitrogen and ammonium nitrogen are 3.54, 0.81,0.59 mg/L in the drainage ditch during summer. In water migration process in the ditch, the concentrations of three forms of nitrogen at the outlet of the ditch are always higher that those at the entrance.
2013 Vol. 31 (1): 61-65 [Abstract] ( 1556 ) [HTML 1KB] [ PDF 2252KB] ( 1735 )
66 Remote farmland irrigation monitoring system based on wireless sensor networks
YU Xiao-Qing, WU Pu-Te, HAN Wen-Ting, ZHANG Zeng-Lin
A remote irrigation monitoring system, in which soil moisture monitoring, pump and electromagnetic valve control and data remote management are integrated, was designed to realizes automatic control on irrigation for saving water. In the system, the wireless sensor network nodes were developed with the 433 MHz core frequency to accomplish a real-time monitoring for soil temperature and moisture in farmland. Base stations were built based on ARM9 microprocessor S3C2410, where the operation of pumps and electromagnetic valves was controlled by comparing with the stored thresholds in the database. The remote realtime monitoring of irrigation system was conducted through GPRS wireless transmission, and the Citect configuration software was used in the remote monitoring center for the data and HMI (humanmachine interface) management. In the application, four groups of wireless sensor nodes were chosen. The soil temperatures and moistures in 25 cm depth were acquired by the system in the 30 min data sampling interval. The operation of the pumps and valves in the base stations was controlled according to the soil information just obtained. This information was also transmitted to the remote monitoring center through the GPRS wireless network. It was showed that the system is flexible in use, low power consumption and with a friendly HMI. It can better meet the demand on application of farmland irrigation remote monitoring.
2013 Vol. 31 (1): 66-69 [Abstract] ( 3166 ) [HTML 1KB] [ PDF 2323KB] ( 1946 )
70 Simulated effects of texture and rooting depth on soil moisture sensor placement
FAN Jun, WANG Quan-Jiu, WANG Yu-Ning
Soil water dynamics and balance under various rooting depth and soil texture were simulated by the Hydrus-1D model to investigate the effects of soil texture and rooting depth on sensor depth in soil profile, and the simulated results were validated by experimental efforts. It is concluded that the soil texture and distribution of plant root has significant influence on the sensor depth.  Soil moisture sensor should be buried at 5 cm under sand soil for plants with shallow roots (10 cm), while those should be buried at 20 cm depth for rooting depth of 30 cm.As for loam soil, sensor placement locates in the one third to two third rooting depth is best. Shallow sensor placement could increase irrigation frequency and deep sensor placement could results in plant water stress. The complex results were achieved under fine soil and plants with deep roots, therefore, field observation should be done for the buried depth of sensor in soil profile. In conclusion, it is useful to guide sensor placement by simulation for sand and loam soil, but it is not suitable for clay soil. Optimum sensor placement should be adjusted according to plant water requirement which affected by plant species. More detailed researches should be focused on the situations that sensor buried depth affected by nonuniform irrigation and temporal and spatial variations of plant roots.
2013 Vol. 31 (1): 70-74 [Abstract] ( 2291 ) [HTML 1KB] [ PDF 1307KB] ( 1897 )
75 Influence of irrigation and drainage mode on water requirement content and fruit yield of tomato cultivated in rainshelter
SHAO Guang-Cheng, 蓝Jing-Jing , TONG Dao-Bin, CHEN Chang-Ren, ZHANG Chao-Bo
 In order to realize watersaving, good quality and high yield of tomato in Southern China, the influence of irrigation and drainage mode on water demand and fruit yield under rainshelter condition was studied. The results showed that the soil moisture reduces steadily with time in various deficit irrigations, and it drops off more quickly when the underground pipes are in the depth of 0.8 m than that when the pipes in the depth of 0.6 m; however, the moisture curves against time don't show a significant difference in those cases. The evapotranspiration of tomato was quite different at three growth stages of tomato, namely, it declines in the following subsequence of the growth stage, blossoming and fruitsetting, fruit maturing and harvest, seedling; moreover, the daily evapotranspiration usually shows a rising trend with growth of tomato. The ranges of daily evapotranspiration for tomato are 1.07-2.71 mm/d in seeding stage, 1.60-3.09 mm/d in blossoming and fruitsetting period, and 1.78-3.35 mm/d in fruit maturing and harvest period for the different irrigation and drainage modes and under the rainshelter cultivation condition. The tomato fruit yield is reduced, but the wateruse efficiency and irrigation water use efficiency are increased with decreasing irrigation amount in the same drainage depth of underground pipes. These outcomes can provide a reference for selection of irrigation and drainage mode to realize watersaving, good quality and high yield of tomato under the rainshelter cultivation condition in Southern China.
2013 Vol. 31 (1): 75-80 [Abstract] ( 1834 ) [HTML 1KB] [ PDF 1337KB] ( 1905 )
81 Water movement characteristics in hydrophobic soils between two emitters of trickle irrigation
LI Yi, GUAN Bing-Yi
The variation of wetting front and the characteristics of soil moisture distribution were studied and compared for the hydrophobic and hydrophilic soils by means of indoor water infiltration experiment in which two emitters of trickle irrigation is put 30 cm apart and at 0.41 mL/min flow rate. The experimental results indicated that all the wetting fronts are relatively smooth and take a quarterellipse shape regardless of if these wetting fronts originated from the two emitters meet each other or not for the hydrophilic soil; the horizontal wetting front was longer than the vertical one, and the times for the two wetting fronts to meet each other are 1 270 and 279 min, corresponding to wettable Lou and salinealkaline soils,respectively. For the hydrophobic soil, however, the wetting fronts are not so much smooth, and they move forward faster in some directions than in the others; and the times for the two wetting fronts to meet each other are 40 and 210 min,corresponding to hydrophobic Lou and salinealkaline soils, respectively. The relationship between wetting front position and time at various conditions can be described by a logarithmic or power function, their regression coefficients are over 0.86. All the relations of the horizontal and vertical wetting fronts to time yield a logarithmic function in the interface plane of two wetting fronts, the corresponding regression coefficients are more than 0.98. For the loess soil, soil water content contours in the vertical profile, which was through and beneath the emitter origin, are very uniform and the wetting surfaces are mostly like circles. The water content contours in the interface plane are less uniform than those in the vertical plane, but they are still more regular than those for the salinealkaline soil. The water content distributions in various depths are much stochastic and spatially heterogeneous for both hydrophobic soils. In general, water movement in loess hydrophilic soils are more regular than in salinealkaline hydrophilic soils; and because of the unstable flow in hydrophobic soils, the water movement in hydrophobic soils is less regular than in hydrophilic soils. The obtained results might be useful for applying some saving water irrigation techniques into hydrophobic soils irrigation.
2013 Vol. 31 (1): 81-86 [Abstract] ( 1940 ) [HTML 1KB] [ PDF 9964KB] ( 1399 )
87 Variation characteristics of soil water diffusivity in greenhouse soil
ZHENG Zi-Cheng, LI Ting-Xuan, LI Wei
In order to clarify the change of soil water diffusivity and achieve better management of greenhouse soil and fertilizer as well as combat the secondary salinization of the soil, the variation characteristics of soil water diffusivity in 0<h≤60 cm depth greenhouse soil were studied by using the horizontal soil column method. The results showed that the soil water diffusivity varies from 0.02 to 378 cm2/min in that soil. The soil water diffusivity depends on the depth of soil. For example, the highest soil water diffusivity occurs in 20 cm<h≤40 cm soil layer, while the lowest in 40 cm<h≤60 cm layer. Meanwhile, the soil water diffusivity in every layer in the greenhouse soil is higher than in the open field soil. The relationship between soil water diffusivity and soil water content in every soil layer was an exponential function, and the correlation factor is in significance level (P<0.01). The relationship between Boltzmann parameters and soil volumetric water content in every soil layer presents a quadratic function. In 0<h≤20 cm soil layer, when the volumetric water content is greater than 043 cm3/cm3, Boltzmann parameters of the greenhouse soil are less than the open field soil; however, when the volumetric water content was lower than 0.43 cm3/cm3, Boltzmann parameters of the greenhouse soil are greater than the open field soil. In 20 cm<h≤60 cm soil layer, Boltzmann parameters of the greenhouse soil are all greater than the open field soil.
2013 Vol. 31 (1): 87-92 [Abstract] ( 2567 ) [HTML 1KB] [ PDF 1776KB] ( 2176 )
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