Experimental investigation of droplet propulsion driven by thermal power conversion
Droplet manipulation plays an important role in the field of microfluidics.Droplet propulsion driven via the Leidenfrost effect has received widespread attention.However,this method requires ultrahigh temperatures,leading to the consumption of a large amount of the working medium and low thermal power conversion efficiency.In this study,the droplet was driven by the thrust force generated by explosive boiling between the cold droplet and superheated wall,which was achieved through the partial boiling of the heat-transfer and superhydrophobic surfaces,to realize a low consumption of the working medium and high efficiency.The experimental system mainly consisted of two functional surfaces:A horizontal superhydrophobic surface and a vertical partial boiling heat-transfer surface.The partial boiling heat-transfer surface was arranged on both sides of the superhydrophobic straight channel.A regime map of the variation in the droplet oscillatory motion with the temperature of the vertical surface was established.In the partial boiling mode,the droplet was accelerated in one collision upon contact with the vertical surface.Moreover,the droplet oscillated between the two side surfaces,with an average impact frequency of 8.3 Hz,and the average motion speed reached 156.2 mm/s.The longitudinal motion of a droplet was observed on the straight orbit,and the peak values of its longitudinal offsets increased with decreasing droplet diameter.Gravity suppressed the droplet's longitudinal motion,while the tangential component of the thrust force promoted the droplet's longitudinal motion.The relative magnitude of the two forces determined the longitudinal oscillation dynamics of the droplet.Overall,this paper proposes a novel idea of cold droplet propulsion,which has application potential in the field of microfluidics.
droplet propulsionheat transfer modesdroplet dynamicsthermal power conversion
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