Effects Of Venturi Structural Parameters On The Absorption Fertilizer Performance

Water and fertilizer synchronization irrigation is a significant characteristic of drip irrigation, fertilization device is one of main devices in the drip irrigation system. In order to reasonably design venturi injector, provide theoretical basis, decrease the head loss of venturi injector and improve the absorption fertilizer ratio, based on the method of computational fluid dynamics (CFD),with the inlet diameter of 16mm,20mm,32mm and 50 mm, the numerical calculations of venturi injector were analyzed, the effects of venturi structural parameters such as throat contraction ratio, throat taper,inlet diameter, expansion section taper and throat length on minimum pressure,critical pressure,coefficient of head loss,absorption fertilizer ratio, the relationship between main structure parameters and coefficient of head loss,absorption fertilizer ratio was studied, value range of reasonable throat contraction ratio,throat taper,expansion section taper and throat length was also studied by sample test, and the major conclusion was obtained:(1) The flow stance index of venturi injector x was approximately 0.53, the flow stance index x was turbulence。The effects of structural parameters on the flow stance index of venturi injector x was comparatively small, the effects on the velocity coefficient was relatively large。While other structural parameters was in the same size, velocity coefficient k was invariant with the increase of the inlet diameter, k decreased with the increase of a, k increased with the increase ofλ1, the effects of inlet diameter was comparatively small。(2) Minimum pressure occurred in the throat inlet wall。When the pressure difference between inlet and outlet was too small, reverse flow of absorption fertilizer tube occured, minimum pressure occurred in the absorption fertilizer cavity wall。Minimum pressure and the pressure difference between inlet and outlet showed a linear relationship。While the pressure difference between inlet and outlet was too small, venturi injector appeared reverse flow of absorption fertilizer tube, caused redistribution of velocity and pressure, minimum pressure was not the throat inlet pressure, but was absorption fertilizer cavity wall pressure,ΔP-hmin curve of venturi injector was not line, but was broken line。 (3) Critical pressure increased with the increase of throat taper, decreased with the increase of inlet diameter, showed a parabola relationship with throat contraction ratio。With the increase of throat contraction ratio, critical pressure showed decrease trend firstly, when throat contraction ratio reached to 0.4-0.6 and reached to minimum, then showed increase trend。(4) Minimum pressure (vacuum) showed a linear relationship with throat contraction ratio and throat taper。During practical design process, the suitable pressure difference between inlet and outlet and appropriate throat contraction ratio were chosen according to different driving pressure, which caused bigger negative pressure。In order to obtain optimal negative pressure, throat taper should be appropriately shorten and throat contraction ratio should be properly increased。(5) When pressure condition can meet absorption fertilizer requirements, absorption fertilizer showed a positive correlation with throat contraction ratio, increased with the increase of throat contraction ratio。While the inlet pressure were determined, the bigger of the pressure difference between inlet and outlet, the more significant of this trend。While the pressure difference between inlet and outlet were determined, this trend was more obvious with the decrease of the inlet pressure。Absorption fertilizer and the pressure difference between inlet and outlet fundamentally showed a power function positive relationship, absorption fertilizer increased with the increase of pressure difference between inlet and outlet, the bigger of the throat contraction ratio, the more significant of this increase trend。(6) Exponential function can greatly depict the relationship between throat contraction ratio and absorption fertilizer ratio, power function can greatly depict the relationship between throat contraction ratio and head loss。When venturi injector was designed, throat contraction ratio was suggested to choose approximately 0.25。...