SSQ系列射流施肥器水力性能试验研究

基于农业生产中水肥一体化技术的施肥要求，该研究对国内常用的SSQ系列射流施肥器进行了性能测试。以吸肥量、进出口压差等指标为研究目标进行了施肥器水力性能的分析和预测，推导了SSQ系列射流施肥器开始吸肥和吸肥效率最高时进出口压差与进口压力的关系公式。结果表明：在正常工作阶段，SSQ系列射流施肥器的吸肥量随进出口压差的增加而增大，在空化条件下达到极限工况；8种不同规格施肥器在进口压力超过0.20 MPa时才能充分发挥吸肥性能；正常工作阶段临界压差与进口压力关系公式的斜率与试验值的误差小于15%，斜率的大小主要受喉管截面和喷嘴出口截面的面积比影响；效率最高时压差与进口压力关系公式的斜率与试验值的平均相对误差为17%，验证了该关系公式的合理性。本文提出的SSQ系列射流施肥器水力性能预测公式可为同类产品的设计和应用提供参考。

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 pressure tanks, plunger pump of fertigation, Venturi injector, and self-pressure fertilizer device. A jet pump is widely used in the industrial 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 jet fertilizers with various types and sizes cannot meet the irrigation requirements of small head loss and large injection flow rate. In this study,8 jet fertilizers (SSQ series) were tested according to the fertilization requirements of agricultural irrigation system, and subsequently their hydraulic performances were evaluated using the injection flow rate, and the pressure difference between inlet and outlet. In terms of pressure difference, the working condition of a jet fertilizer can be divided into 3 stages, including the no-injection, normal, and extreme stage. The results show that the injection flow rate of a jet fertilizer increased with the increasing of pressure difference during the normal stage. The cavitation occurred, and the injection flow rate reached the maximum during the extreme stage. The 8 jet fertilizers were achieved the optimal performance of injection, if the inlet pressure was higher than 0.20 MPa, where the maximum injection flow rate was found to be related to the cross-sectional area ratio of nozzle and throat. During the normal stage, the pressure difference of starting to inject or of the maximum 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 the intercept. 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 than 15%, and the average relative slope error of the maximum efficiency was 17% between regression model and theoretical formula, indicating that the theoretical equation had a good agreement with the experimental data. The prediction on the hydraulic performance of a jet fertilizer 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 the chamber between nozzle and throat. It also ignored the head loss in terms of the length of throat portion and diffuser portion. The derived theoretical formulas can be further improved in thefuture by considering the influences of extreme stage or cavitation.