脂溶性农药旋动射流混合机理与混药器流场数值模拟

Swirling Jet Mixture Mechanism of Fat-soluble Pesticides and Numerical Simulation of Mixer Field

摘要:

以研究脂溶性农药和水的混合均匀性为目的，试验验证了传统射流混药器结构对脂溶性农药在线混合的局限，提出旋动射流混合机理以增加工作液和混合液的旋度，根据该机理设计的旋动射流混药器采用螺旋弯曲收缩管、起旋器和在扩散管中加入固定导叶等方式，增加工作液的卷吸能力、掺混作用。经过数值仿真，采用容积分数分布均匀性评判指标来判断混合效果，结果表明，喷嘴出口处面积加权平均均匀性指数γa为0.9989，截面上药液容积分数最大值与最小值的差值很小，整个截面上的药液分布一致，旋动射流混药器结构设计能够保证出口位置处脂溶性农药与水的均匀混合。

Abstract:

To characterize jet mixture profiles for inline injection of pesticides, twophase flow fields in conventional mixing chambers were investigated under various test conditions. The twophase flow was formed with water mixed with either a watersoluble liquid or a fatsoluble liquid (silicon oil). Test results illustrated that there were limitations for the conventional mixers to obtain uniform mixtures with the fatsoluble pesticide. To overcome these limitations, a new mixing device based on the swirling jet mechanism was conceived and developed to improve the mixture uniformity of water and the fatsoluble pesticide. The swirling jet mixer consisted of a spiral curved shrink tube, a diffuser and a guide vane to accelerate the twophase flow spiral movement and blend the two liquids. A computational fluid dynamics program (Fluent) was used to simulate the flow field inside the swirling jet mixer to optimize its design. The mixture uniformity was evaluated by introducing the uniformity index γa, representing that the two liquids were blended homogenously as γa was 1. Simulated results showed that the γa was 0.9989 across the entire cross sections inside the mixer, confirming uniform mixture profiles with the new mixer design. 〖JP3〗Therefore, the new swirling jet mixer would solve the nonuniform mixture problem associated with conventional mixers and could significantly improve the inline injection technology to reduce pesticide waste.