Research On The Bubble Dynamic Characteristics In Y-junction Microchannels

In recent years,with the rapid development of microfluidic technology,the application of gas-liquid two-phase flow has aroused great concern.Bubble technologies are playing a remarkable role in biomedical science,chemical engineering,national defense and military and many other fields.Therefore,the study of bubble dynamics characteristics is of great significance for the effective use and control of bubble.In this paper,the effects of microchannel inlet and wall wettability on bubble dynamics were studied systematically by experiments.The main contents are as follows:Based on the Y mode,the 120° Y type microchannel was adopted,and the gas-liquid two-phase inlets were symmetrical.The process of bubble generation in the micro Y-junction was recorded by high speed camera system,and the influence of flow velocity,gas-liquid flow radio and channel size on bubble dynamics were emphatically invest:igated.The experiment results indicated that the cavitation formation mainly includes squeezing,trickle and transition,and the corresponding three flow regimes were slug flow,droplet flow and slug flow.With the increase of flow velocity,gas-liquid flow ratio or channel size,bubbles’ size increases.The formation period of cavitation decreases with the increase of flow rate and the decrease of gas liquid velocity ratio.The experiment was carried out using an asymmetric Y microchannel,the entrance angle of the micro channel is 30°,45°,60° and 75 °,respectively.Distilled water and 0.1%SDS aqueous solution were used as the continuous phase,and flowing together through the horizontal branch ports of the Y type micro channel.The air was used as the dispersed phase,entered through the other side of the Y type micro channel.The experiment results indicated that there are five main flow regimes:parallel flow,jet flow,slug flow,plug flow and droplet flow.The bubble size decreases with the increase of inlet angle.The surface tension decreases,which contributes to the formation of smaller volumes of cavitation,as well as the shortening of the cavitation generation cycle.The hydrophobic/superhydrophobic surfaces prepared by laser processing and self assembling technique were spliced to the micro channel as the microchannel wall through adhesive method.And Then,the moving process of the bubble in the wall with different wettability was captured by the high-speed camera system.The effects of flow velocity,wall wettability and channel size on the dynamic contact angle of cavitation were investigated.The experimental results showed that the stronger the hydrophobicity of the wall is,the larger the ratio of the dynamic contact angle is.With the increase of flow velocity,the dynamic contact angle and the ratio of the dynamic contact angle between the two sides of the wall decrease.The smaller the size of the channel is,the stronger the cavitation effect is.When the ratio of the dynamic contact angle is close to 1,with the increase of the channel size,the increasing amplitude of the dynamic contact angle ratio increases thereafter decreasing.