| The technology of gravitational flexible hose micro-irrigation is a kind of simple and practical saving irrigation technology in the inadequate economic technological condition. This technology is applied in an irrigation area that is a nature field. Making use of the micro-pressure head formed by irrigation channel, ground water levels and the natural gradient in the field, it is to achieve free irrigation through the micro-pressure hose irrigation systems constituted by the trunk, branch and capillary of tertiary hose or branch, capillary of secondary hose. The branch or capillary in the micro-pressure hose irrigation systems is a porous pipeline, there are many hole along which and the water freely flows through the holes at the same time. Capillary is the core and key of micro-irrigation technology for micro-pressure hose, and its flowing characteristic concerns with the factors such as work pressure head of the hose, diameter of the hose, length of the hose, drop-spacing, and drop diameter and the laying of pipelines slope and so on. Therefore, it is very necessary how to analysis the various affecting factors on characteristics for porous flow from the theoretical analysis, to establish the quantitative relationship with the corresponding experimental study on it, to provide the basis for engineering design, and at the same time to promote the development of the theory of the flow.This thesis aims at the problems existing in the actual production projects. The porous flow mechanism is discussed through a large number of field surveys, laboratory tests and theoretical analysis. The hydraulic performances of capillary in the micro-pressure hose on micro-irrigation systems are studied and analyzed in-depth. The major conclusions are drawn as followed:The comparison of the water flow capacity between the free flow to pipeline and the porous hose shows that, regardless of the factors such as the length of the hose, diameter of the hose, drop-spacing, and drop diameter and the laying of pipelines slope and so on how to change, the total flow of the porous hose will always smaller than the free flow without the porous hose. If the pipeline layout, plumbing materials, the diameter of pipeline and the work pressure head of the hose fixed, the total flow of discharging along the porous hose can be got by corresponding flow multiplied by a flux reduction coefficient of free flow without porous hose. According to the formula about the test data fitting the porous flux reduction coefficient, the formulas about total volume of porous hose and flow to the average single-hole are established. The results of the test data and engineering data showed that the formula results and the test results are quite identical. The results show that: with the increasing of the pressure-head and the diameter of the porous hose, the total flow and the average single-hole flow of the porous hose increase; with the increasing of the total laying length , the total flow of porous hose will increase, but the average single-hole flow of the porous hose will reduce; both the total flow and the average single-hole flow of the porous hose is linear with the laying of pipelines slope, they will increase when the laying of pipelines slope increase; the total flow of the porous hose will decrease when the drop-distance becomes smaller, but the average flow of the single-hole of the porous will increase when the drop-distance becomes larger.According to the law of momentum, in the conditions of laying only one slope along the porous hose, the variable mass of the flow of momentum equation, which has a variable exchanging coefficient and variable drag coefficient, had been established. At the same time, the porous distribution of power rate assumptions had been introduced in order to study the change law of the variable exchanging coefficient and variable drag coefficient. The momentum equation which was variable quality and variable coefficients was solved. The analytical solution of the variable mass momentum equation which has variable coefficients was given under the condition of uniform slope . The analytical solution has contained the components of the pressure, the gravity, the friction and the momentum, and reflected the various factors on the distribution of pressure along the porous hose. The analysis shows that the major force for the flow of a porous hose are the hydrodynamic pressure, gravity and friction, the three are interrelated and all have impacts on the porous flow. The verification results of predecessors and experimental data show that the analytical results of the calculation and the experimental results are identical.The head losses and the distribution of pressure head along the porous hose are demonstrated through the analysis, and the formula of the total head loss along the hose is got, and the method about the positions and sizes of the porous characteristic pressure heads is determined. The comparison of the energy formula and the momentum formula showed that the two methods after dimensionless can be transformed into the formula for the same form. At the same time, the theory that concerns the capillary hydraulics in micro-irrigation system neglected the velocity head is drawn on the basis of analysis. According to qualitative analysis about the changes of pressure heads of the porous-hose, the coefficient M for the characteristics of porous hoses is introduced. According to the coefficient M, three types of hoses are divided, such as short, medium and long porous hoses. The capillary in micro-irrigation system and micro-pressure porous hose in this paper are long porous hoses. The influences caused by some factors such as the laying of the hose, the imported pressure head, the diameter of hose and drop-distance on uniformity and head of the deviation are discussed. There is an optimum laying of the slope on the premise of the allowed flow deviation rate of the hose is pointed out. The situation of project application about micro-pressure hose irrigation technology is introduced, and calculating method on how to determine the laying of a reasonable length of hose is referred, and the appropriate laying length that meets required uniformity is given. With engineering example, the steps are designed for micro-pressure hose irrigation planning and design reference.The Porous discharge flow hose has been widely used in agriculture, water supply and drainage, ventilation, chemical and other fields. The paper aims at the porous micro-pressure hoses, on the basis of some results of previous studies, some theoretical analysis and experimental study on the capacity of the porous hose's discharge (flux), discharge principium, pressure distribution, the uniformity of flow discharge and the length of the laying or something are set out. Some common problems on the flow of the porous hoses are explained and made out from the point of theory. The results will have wide applicability, the important project value and theoretical significance. |
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