THE INFLUENCE FACTORS OF MICRO-DROPLET FORMATION IN T-JUNCTION MICRO-FLUIDIC CHIP

The effective droplet diameter, generation location and generation frequency of droplets in two-phase flow are important reference factors for quantitative and structural improvement of experimental reagents. Based on the two-phase flow theory, the level set method is used to track the fluid interface between continuous phase and dispersed phase. The effects of wall contact angle of fluid, channel width ratio and main pipe length ratio on the droplet formation frequency, diameter and generation location under different velocities are investigated in this paper. The results show that: Four Typical flow patterns are mainly captured: stratified flow, slug flow, dripping flow and bubbly flow. Among them, the dripping flow pattern is widely distributed, which is the most common flow pattern in the stable droplet formation, as long as the velocity ratio is large enough (η≥3.0) and can be generated at different capillary numbers. The differential pressure is the main generating factor of slug flow, while the dripping flow and bubble flow are mainly formed by the joint action of differential pressure, viscous shear stress and interfacial tension. The larger ratio of dispersed phase velocity, the higher droplet formation frequency, the smaller diameter of droplet and the farther droplet formation location. The larger contact angle, the larger droplet formation frequency and the smaller droplet diameter. However, the influence of contact angle on droplet formation frequency and size is limited, but the influence of contact angle on droplet formation location is farther, especially when contact angle θ_w ≥ 160°, the droplet formation location curve tends to converge. When the flow velocity ratio was constant, the channel width ratio promoted the droplet formation frequency, size and location increased with the increase of the channel width ratio. The range of channel width ratio \lambda =0.3 ~ 0.55 is the stable range for droplet formation at different flow velocity ratio. The main channel length ratio ψ=15 is the critical point of the droplet generation location, and the droplet formation position is stable right here. The formation location of droplet is greatly affected by the contact angle, main channel length ratio and channel width ratio. The larger the contact angle and main channel length ratio are, the larger the on-way resistance along the channel and the higher the pressure are, the earlier the formation location is. The larger the channel width ratio is, the formation location of droplets is further and further away from the intersection.