Research On Influence Laws Of The Operating Water Pressure On Hydraulic Properties Of Drip Emitters

Drip irrigation is one of the most effective technologies to solve the problem of water scarcity for modern agriculture. However, the clogging problem of drip emitter and the high cost seriously limited the real application of drip irrigation. By the support of some projects such as the State 863 Major Project of China:to research and manufacture the laboratory experiment platform for testing the comprehensive hydraulic performance of drip emitters was researched and manufactured, and the evaluation methodology and theory for the anti-clogging ability of drip emitter were established; to reveal the influence laws of the operating pressure on the flow regime and the anti-clogging ability through the strengthened clogging experiments, and explained the root cause of the operating pressure on the emitter clogging. Based of all above researches, to design and invented a new kind of drip irrigation system using dynamic operating pressure, and the anti-clogging ability of this system was emphatically studied by using the sthengthened clogging experiment.In the aspect of hydraulic performance testing platform and evaluation methods:to construct the laboratory hydraulic performance testing platform; to establish the rapid assessment method of the anti-clogging ability of drip emitters; to define the computational method of clogging rate on condition that the drip emitter was partially clogged; and to modify the calculating formula of the uniformity; the strengthened clogging experiments of three new kinds of drip emitters were carried out, and the change law of clogging rate and uniformity was systematic analyzed. In the aspect of the effect of operating pressure on the flow regime:to conduct the experiments of testing discharge of six kinds of drip emitters under 21 groups of operating working pressure; to calculate the discharge exponent for different groups of operating pressure according to the experiments; and to analyse the influence law of operating pressure on the discharge exponent for different kinds of drip emitters; further, to calculate the average velocity and the Reynolds number, and the result shows that the Reynolds number ranges between 20 and 1800, the critical Reynolds number is far less than that of conventional scale when the water flow inside drip emitter channel turns to full turbulent.In the aspect of the effect of operating pressure on the anti-clogging ability: to conduct the strengthened clogging experiments of seven kinds of drip emitters under eight different groups of operating pressure; to analyse the influence law of operating pressure on the emitter anti-clogging ability, and to reveal the root cause of the influence law of operating pressure on the emitter anti-clogging ability from the aspect of average velocity; when the average velocity is larger than 1.25m/s, solid particles are difficult to deposite inside emitter channel, and to decrease emitter discharge; when the average velocity is less than 1.25m/s, the pressure compensation emitter with bigger discharge and the drip emitter with vortex flow will have strong anti-clogging ability.In the aspect of drip irrigation using dynamic operating pressure:to carry out multi kinds of dynamic operating pressure kinds by using technologies of automatic control and frequency conversion; to conduct experiments of discharge-pressure and sthrengthened clogging under dynamic operating pressure; to analyse influence laws of dynamic operating pressure model and amplitude on the emitter discharge and the anti-clogging ability; the result shows that the dynamic operating pressure has obvious "lagging" phenomenon which makes the emitter discharge is smaller than that of equivalent operating pressure; and the strengthened clogging experiment shows that the dynamic operating pressure can significantly decrease the degree of emitter clogging, and the anti-clogging ability of drip emitters is strongest when the amplitude of the dynamic operating pressure is 4mH2O.In a word, this paper concerns on the laboratory hydraulic performance testing platform, the method and theory of rapid evaluation of drip emitter anti-clogging ability, the influence law of the operating pressure on flow regime and anti-clogging ability, and invents a new kind of drip irrigation system using dynamic operating pressure which has stronger anti-clogging ability, the research results will provide significant theoretical basis and technical guidances for new-type emitters development and selections of drip irrigation technic.