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Fertigation is an important feature of drip irrigation, fertilization device is drip irrigation system is one of the main device. To design Venturi fertilization is reasonable to provide a theoretical basis, lower venturi fertilization is the head loss increase of fat absorption ratio, this paper application calculate fluid dynamics CFD software, respectively, the inlet diameter to 16mm, 20mm, 32mm and 50mm, Wen mound inside the tube The Venturi fertilization is carried out numerical calculation and analysis, the study of the structural parameters (pipes shrink than, contraction section taper, inlet diameter expand the segment tapers pipe length) minimum pressure in the tube, the critical fat absorption pressure head loss coefficient, the ratio of fat absorption, the main structure parameters and the head loss coefficient of fat absorption ratio relationship, and sample test, initially identified reasonable pipes shrink ratio, shrink segment taper expanding segment the taper and pipes length take range of values, and made the following main conclusions: (1) Venturi tube flow state index of approximately 0.53 x tube flow regime is turbulent. Changes in the structural parameters of the venturi tube flow state index x is smaller, the flow rate coefficient k. When the other structural parameters are the same, the velocity coefficient k with the increase of the inlet diameter and the same k value decreases as α increases, k value is increased with increasing of λ1, the inlet diameter of its influence small. (2) The the fertilization tube Venturi minimum pressure in the ring wall at the inlet end of the pipe. When the import and export of the pressure difference is too small, leading to suck fat pipe backflow occurred when the minimum pressure in the tube of fat absorption chamber wall. Venturi tube minimum pressure with the import and export of the pressure difference is linear. Import and export pressure difference is too small, the Venturi fertilization is the mouth of a stream of fat absorption phenomena, caused by the flow rate, pressure redistribution, the minimum pressure within the tube the throat inlet end pressure, but to suck fat cavity wall pressure, Venturi fertilization is △ P ~ hmin relationship curve is not a straight line, but the broken line. (3) critical pressure differential with the contraction section taper increases increases with the inlet diameter increases and decreases, and shrinkage ratio of the secondary parabolic relationship with the contraction ratio increases, the critical pressure differential was less first small trend, after the contraction ratio of 0.4-0.6 between minimum and then tended to increase. (4) The minimum pressure (vacuum) in the tube and the throat contraction ratio, the contraction conicity linear relationship. Suitable Visual pressure difference in the actual design process, selected according to different driving pressure, and select the appropriate shrinkage ratio, makes it easier to form a large negative pressure should be properly reduced in order to obtain the negative pressure in the optimum tube, the taper of the contraction section throat segment, an appropriate increase contraction ratio. (5) When the pressure conditions to meet the requirements of fat absorption, the absorption amount of fertilizer pipes contraction than the positive correlation between the absorption amount of fertilizer increases with the pipes contraction ratio increases, when the inlet pressure is determined, the import and export of the pressure difference the greater this tendency is more obvious when the outlet pressure differential fixed, as the inlet pressure decreases and this tendency is more significant. Of fat absorption amount of pressure difference between the import and export of basic positive correlation between the power function of fat absorption amount with the import and export of the pressure difference increases with increasing pipe contraction than the larger, the more significant increasing trend. Exponential function (6) can be described in better the pipes shrinkage ratio and the relationship between the ratio of fat absorption, can be well described by a power function pipes shrinkage ratio and the relationship between the head loss. Design Venturi fertilization, it is recommended that the Venturi fertilization is pipes contraction than 0.25 should choose.
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