科创中国

Supercavitation in the diesel nozzle increases the instability of droplets in part due to the two-phase mixture,while the effect of cavitation bubbles on the instability of drops is still unclear.In order to investigate the breakup of cavitation bubbles within the diesel droplet,a new mathematical model describing the disturbance growth rate of the diesel bubble instability is developed.The new mathematical model is applied to predict the effects of fluids viscosity on the stability of cavitation bubbles.The predicted values reveal that the comprehensive effect of fluids viscosity makes cavitation bubbles more stable.Compared with the viscosities of air and cavitation bubble,the diesel droplet's viscosity plays a dominant role on the stability of cavitation bubbles.Furthermore,based on the modified bubble breakup criterion,the effects of bubble growth speed,sound speed,droplet viscosity,droplet density,and bubble-droplet radius ratio on the breakup time and the breakup radius of cavitation bubbles are studied respectively.It is found that a bubble with large bubble-droplet radius ratio has the initial condition for breaking easily.For a given bubble-droplet radius ratio(0.2),as the bubble growth speed increases(from 2 m/s to 60 m/s),the bubble breakup time decreases(from 3.59μs to 0.17μs)rapidly.Both the greater diesel droplet viscosity and the greater diesel droplet density result in the increase of the breakup time.With increasing initial bubble-droplet radius ratio(from 0.2 to 0.8),the bubble breakup radius decreases(from 8.86μm to 6.23μm).There is a limited breakup radius for a bubble with a certain initial bubble-droplet radius ratio.The mathematical model and the modified bubble breakup criterion are helpful to improve the study on the breakup mechanism of the secondary diesel droplet under the condition of supercavitation.

校长更替是常见的教育现象和社会现象.而校长更替问题,是指因校长更替工作低效、失误、失败、无效而造成的教学士气低迷、领导愿景模糊、教育质量下降等组织发展的停滞、错乱.我国目前的中小学校长更替问题,主要表现为校长更替的理念缺失、频率紊乱、方式单一以及身份认同与文化传承的困难.未合理筹划校长更替、未重视校长更替过程的有效管理、未统筹安排校长更替的后续工作及未系统思考校长更替,是导致中小学校长更替问题的主因.应对中小学校长更替问题的措施主要有:加强对校长更替的规划设计,平衡权责关系加强情感交流,改善校长更替的后续工作,以及推行可持续领导.

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