液体性质对气泡雾化液滴不稳定性的影响

为了改善气泡喷嘴雾化性能,利用基于液滴统计学的理想雾化理论模型研究了液体性质对气泡雾化液滴不稳定性的影响.同时,采用高速摄影技术分析了气泡喷嘴内部气液两相流动及喷口雾化状况,探究了雾化液滴产生不稳定现象的根本原因.实验结果表明,气泡喷嘴雾化本身具有不稳定性,且雾化下游场中不同粒径的液滴均表现出不稳定性.当喷嘴内部气液两相处于气泡流时,喷口处单个气泡的破裂可导致雾化下游场中液滴不稳定;当气液两相处于过渡流时,单个气泡、液体以及较长气柱交替流经喷口会造成气泡雾化液滴不稳定;当气液两相处于环状流时,液桥现象的存在致使雾化下游场液滴不稳定.增加牛顿流体的黏度或者降低非牛顿流体剪切变稀的强度能够有效降低雾化液滴的不稳定性.

Influence of liquids properties on unsteadiness of droplet in effervescent sprays

In order to improve the atomization performance of an effervescent atomizer,the influence of fluid properties on the unsteadiness of droplets in effervescent sprays was investigated by using the ideal spray theory model based on the droplet statistics.Gas-liquid two-phase flow pattern in nozzle and the atomization near the discharge orifice were analyzed by the high-speed photography to explore the root cause of droplets’ unsteadiness.The experimental results show that the effervescent atomization is an inherently unsteady process and the droplets with all sizes in the downstream of effervescent sprays exhibit unsteady behavior.When the gas-liquid two-phase flow in nozzle belongs to the bubble flow,the rapidly expanding bubbles can induce the unsteadiness of the droplets.When the gas-liquid two-phase flow belongs to the intermittent flow,the alternate flow of a single bubble,liquid and a long gas column through the jet can lead to the unsteadiness of the droplets.In addition,the presence of liquid bridges in annular regime can also cause the unsteadiness of the droplets.The increase of the viscosity of the Newtonian fluid and the reduction of the shear-thinning strength of the non-Newtonian fluid can reduce the level of spray unsteadiness.