Experimental research of hydraulic performance on jet fertilizer applicator of SSQ series

Fertilizer device is essential to the precision fertigation technology. Most fertilizer equipment includes the pressuretanks, plunger pump of fertigation, Venturi injector, and self-pressure fertilizer device. A jet pump is widely used in theindustrial and agricultural production, because of its simple structure, and convenient operation without an external power. In the integration technology of water and fertilizer, the jet pump can serve as the function of Venturi injector. However, some jetfertilizer applicators with various types and sizes cannot meet the irrigation requirements of small pressure loss and large suction amount. In this study, 8 jet fertilizer applicators of SSQ series were tested according to the fertilization requirements of agricultural irrigationsystem, and subsequently their hydraulic performances were evaluated using the suction amount, and the pressuredifference between inlet and outlet. In terms of pressure difference, the working condition of a jet fertilizer applicator can be divided into 3 stages, including the no-injection, normal, and extreme stage. The results show that the suction amount of a jet fertilizer applicator increased with the increasing of pressure difference during the normal stage. The cavitation occurred, and the suction amount reached the maximum during the extreme stage. The 8 jet fertilizer applicators were achieved the optimal performance of injection, if the inlet pressure was higher than 0.20 MPa, where the maximum suction amount was found to be related to thecross-sectional area ratio of nozzle and throat. During the normal stage, the pressure difference of starting to inject or of themaximum efficiency was in positively linear relation with the inlet pressure. A theoretical linear equation with structural parameters was proposed to predict the relationship between pressure difference and inlet pressure, starting to inject, and the maximum efficiency, where most data derived from basic performance equation and pressure ratio, without considering theintercept. The slope mainly depended on the area ratio, and thereby it can be strongly related to the difference of pressure loss. In each inlet pressure, the maximum difference of pressure varied linearly with the increase of inlet pressure, where as, the cavitation was result in the large flow resistance during the extreme stage. The slope error of starting to inject was less than15%, and the average relative slope error of the maximum efficiency was 17% between regression model and relation formula, indicating that the relation formula had a good agreement with the experimental data. The prediction on thehydraulic performance of a jet fertilizer applicator can provide a sound theoretical basis for the design and application. Nevertheless, there were some assumptions when deriving this formula. It was assumed that the pressure was the same everywhere in thechamber between nozzle and throat. It also ignored the head loss in terms of the length of throat portion and diffuser portion. The derived relation formulas can be further improved in thefuture by considering the influences of extreme stage orcavitation.