Study On Performance Parameters And Conditions Of Venturi Injector

Water and fertilizer synchronization irrigation is a significant characteristic of dripirrigation; fertilization device is one of main devices in the drip irrigation system. Venturiinjector is suitable for small drip irrigation system because of its simple structure, smallvolume, low cost, simple operation, uniform fertilization. Based on the hydraulics principle,the hydraulic performance was tested on Venturi injector of different structures. Theexperiment was conducted to study on the energy conversion relation for different featuresections, the influences of inlet and outlet pressure, flow velocity, and the coefficient of localhead loss on the negative pressure in the throat, the influences of the negative pressure in thethroat, inlet and outlet pressure, and inlet flow rate. And the major conclusion was obtained:（1）At present, the throat structure of Venturi injector is central symmetric, thecoefficient of local head loss is great. Now, the structure of Venturi injector was improved.Leave the throat diameter as is but change the structure that central symmetric to upwardeccentric, and the angle of shrink and magnification shall be reduced by half. In order to dothis, the coefficient of local head loss was decreased.（2）The throat negative pressure was no longer influenced by the inlet pressure headand the head loss increased sharply when the throat negative pressure reached the minimumvalue. The differences between the actual and the theoretical flow rate reflected the throatvacuum space size, the actual flow rate increased significantly and the kinetic energy in thethroat also increased being similar to a parabolic shape when the throat negative pressurereached the minimum value. The head loss (energy loss) increased sharply as the flow rateincreased when the water flowed through the Venturi injector. The more the inlet pressureincreased, the greater the energy loss. The starting pressure of the throat generating thenegative pressure increased and the flow rate was relatively large under non-free-outflowconditions. The inlet pressure and the flow rate under non-free-outflow conditions weresignificantly higher than that of free-outflow conditions based on the same negative pressure.（3）The generation of the negative pressure in the throat was related to inlet and outletpressure, with the increment of outlet pressure, higher inlet pressure was required to generatenegative pressure and reached the minimum. The negative pressure in the throat had asignificant linear negative correlation with inlet pressure. When the negative pressure reached the minimum value, the value of negative pressure was stable as the inlet pressure increases.Flow velocity had similar effects with pressure on the generation and dynamics of negativepressure. When the coefficient of local head loss was the same, at the same inlet pressure, thesame flow velocity had the same negative pressure, the greater the throat diameter, the greaterthe flow rate of the needed throat negative pressure to achieve the target; For the differentcoefficient of local head loss, the higher the value, the decrease speed was slower of negativepressure in the throat as the inlet pressure increased, the greater of the needed throat negativepressure to achieve the target.（4）The injection rate of Venturi injector increased with the increasing of the inletpressure and the inlet flow rate at the initial stage. When the injection rate reaches themaximum value, the injection rate was stable as the inlet pressure and inlet flow rateincreased; the injection concentration increased first, then decreased with the increasing of theinlet pressure and the inlet flow rate. The injection concentration reached the maximum valuethat was about12%~13%when the negative pressure reached the minimum value.（5）Pipeline design of Venturi injector in the drip irrigation system was improved. Theminimum inlet pressure needed and the formula of the critical velocity of the throat to achieveabsorbing fertilizer under different outlet pressures were put forward. On this basis, the paperhad come up with a method of reasonable selection of Venturi injector in the drip irrigationsystem, In order to ensure uniform of velocity, the paper present a new method about thepipeline design of Venturi injector in the drip irrigation system.