Optimization of structural parameters and performance experiment of jet fertilizer injector based on numerical simulation

Abstract: Jet fertilizer injector is gradually emerging in the water and fertilizer integration equipment, owing to lower cavitation in the suction chamber and highly reliable performance than before. However, a large amount of fertilizer suction and low-pressure loss are still found in some jet fertilizer injectors. Structural parameters are also necessary to be optimized for the better performance of fertilizer absorption. Therefore, it is necessary to improve fertilizer absorption performance of jet fertilizer injectors, thereby meeting the demand of large fertilizer suction amount in the irrigation system under water and fertilizer integration. The different structural parameters in the throat of the jet fertilizer injector were therefore designed using the objectives of large fertilizer suction amount and high fertilizer absorption efficiency. In this study, a systematic optimization was performed on the structural parameters of a jet fertilizer injector. The objective parameters were then selected, including the contraction angle and diameter in the fertilizer suction chamber, while the diameter and contraction ratios of the throat. The amount and concentration of fertilizer suction, the discharge ratio of inlets, and the efficiency of fertilizer absorption were used to evaluate the absorption performance of the jet fertilizer injector. An optimum combination of structural parameters was obtained, according to the influence characteristics of four structural parameters on the four evaluation indexes using CFD numerical simulation. A new prototype was then manufactured under the optimal conditions using the 3D print technique. A field test was carried out to evaluate the fertilizer absorption performance of the new prototype under different inlet pressures. The results indicated that the average relative error of measured and simulated values for the inlet discharge, fertilizer suction amount, and outlet discharge were 4.25%, 10.12%, and 5.27%, respectively, showing a reliable performance of jet fertilizer injector. Four evaluation indexes (including fertilizer suction amount, inlet discharge ratio, fertilizer suction concentration, and fertilizer absorption efficiency) first increased then decreased in the simulation at the same inlet pressure, with the increase of contraction angle and diameter in the fertilizer suction chamber, and the diameter ratio of the throat. There was a peak value of fertilizer absorption performance. Specifically, the fertilizer suction amount increased gradually, whereas, the inlet discharge ratio, fertilizer concentration, and adsorption efficiency decreased significantly, with the increase of contraction ratio of the throat. In addition, the optimal combination of structural parameters was determined, where the contraction ratio of the throat was 0.2, the diameter ratio of the throat was 2.5, the diameter of the fertilizer suction chamber was 22 mm, the contraction angle of the fertilizer suction chamber was 80°, and the diameter of inlet straight pipe was 20 mm. Compared with the optimized jet fertilizer injector than before, the fertilizer suction amount and absorption efficiency increased ranging from 76% to 107%, and from 22% to 42% with the inlet pressure ranging from 0.15 to 0.30 MPa. The fertilizer suction amount and absorption efficiency increased 76% and 22%, respectively, when the inlet pressure was 0.30 MPa. Consequently, the higher performance of fertilizer absorption in the optimized jet fertilizer injector can widely be expected suitable for the irrigation under water and fertilizer integration with a large amount of fertilizer.