Experimental Research On Hydraulic Characteristics Of Low Pressure Drip Irrigation Lateral

Using the combining method of theoretical analysis and experimental, based on theanalysis of capillary inlet pressure, laying slope, hole spacing, laying length and other factors,studied the various factors influencing on irrigation uniformity、outflow characteristics、headloss and pressure distribution rule. Following results was obtained:1) Average flow under the same working pressure decreased with the increasing of layinglength, the average flow rate change is relatively slow with the increasing of laying length;increased with the increasing of the pressure head, and changed more intensely; increasedwith hole spacing increasing, and the rate of increase along with the increase of hole spacing,the largest orifice flow at hole spacing1.2m, the minimum orifice flow at hole spacing0.6m,smaller orifice flow differences between0.6m and0.9m.2) Drip irrigation laterals flow coefficient k increased firstly and then reduced afterlaying length increasing at hole spacing1.2m, the minimum flow coefficient at laying length40m; k reduced along with laying length increasing at hole spacing0.6m and0.9m. Flowregime exponent x increased firstly and then reduced after laying length increasing, and thehole spacing0.6m and1.2m, the maximum flow regime exponent x at laying length40m,while the hole spacing0.9m, the maximum flow regime exponent x at laying length30m.3) Under the same pressure head, irrigation uniformity along with capillary laying lengthincreasing showed a trend of decrease, the shorter the laying length, the better the irrigationuniformity. Under the same laying slope, irrigation uniformity showed a trend of increasingalong with the inlet pressure increasing. Irrigation uniformity firstly increased and thendecreased with the increasing of laying slope. when i changed in the range of-1‰~1‰,irrigation uniformity increased along with the laying slope increasing, the rate of increase islarger, and when i=1‰irrigation uniformity reached maximum. When i>1‰, irrigationuniformity decreased with the laying slope increasing, but reduced to a lesser extent.4) There was a big difference between the head loss using normal pressure formula andmeasured values, the measured values less than the theoretical values. And the ratio of themeasured values to calculated values using norms recommended formula decreased alongwith working pressure, and the ratio of approaching to1. Under low pressure conditions, regression analysis based on the ratio of the measured values to calculated value and inletpressure, head loss correction factor was obtained, better fitting correlation. When therequirements are not very precise calculations, using head loss formula on the basis of inletpressure can achieve the purpose of correction.5) According to the variable mass momentum equation, the establishment of pressurehead calculation formula about a drip irrigation perforated pipe at any point, using theformula to calculate the head loss at first hole section、the end section and any sections.6) According to the general formula for the head loss of micro-irrigation project, basedon orifice flow simplification of actual head line, the general equation of frictional head losswas worked out by using differential method. According to the energy equation, thecalculation formula of pressure head along the capillary, by comparing with the pressure headequation established on the basis of momentum equations, this simple model was rational, andthe method for determining the maximum allowable length was given under different slopes.