In the process of preparing quantum dots in droplet-based microreactors,the perfluoropolyether oil as the continuous phase and the dispersed phase will change the motion behavior of droplets and affect the heat and mass transfer of the reaction due to the large density difference.The effects of the relative direction of buoyancy and flow and the two-phase flow on the dynamic behavior of the droplet were studied by using coaxial microchannels.The results show that the axial symmetry of the flow field in the horizontal droplet is affected by the buoyancy force,and the coaxiality of the droplet decreases to 0％in the early stage of shedding.By adjusting the relative direction of flow and buoyancy,droplet coaxiality stabilized to 100％at a low continuous phase flow rate(Qc=1.514 ml/min),but at a high Qc(3.666 ml/min)the droplet coaxiality(96.8％)decreased by only 3.2％.By adjusting the two-phase flow rate,the droplet size can be controlled within 537-980 μm.Based on the mechanism of promoting and inhibiting the horizontal/upward and downward droplet by buoyancy,the droplet size prediction model is established with the deviation less than±10％.The experiment elucidates the effect of buoyancy on droplet behavior in microchannel and provides guidance for the design of droplet based microreactor.
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