Experimental Study On Directional Transport Of Droplets On The Microarray Structure Surface At High Temperature

Directional transport of droplets is a common phenomenon in nature and People's Daily life.It is widely used in many fields of industrial production,such as microfluidic control,energy saving transmission of liquid,biomedical diagnosis,water collection in dry areas,the boiling heat transfer and drag reduction.Although great progress has been made in the directional transport of droplets at room temperature,it is extremely difficult to transport droplets at high temperature due to the complex phase transition process.The directional high speed transport of droplets on surface at high temperature is realized by designing the oblique ridge array structure and the oblique hole array structure.The paper has obtained the following research results:(1)The micron scale oblique ridge array structure is manufactured on the stainless steel substrate by the wire cutting finishing technique.Then,the motion characteristics of the approximately statically released droplet on the oblique ridge array surface at high temperature of 300 ~ 480? are experimentally studied.It finds the droplets present a unidirectional self-propelling motion opposite to the oblique ridge.The effects of sample surface temperature,ridge tilting angle and ridge height on the directional transport velocity of droplet on the oblique ridge array surface at high temperature are also studied further.The experimental results show that the directional transport velocity of droplet decreases with the increase of temperature on the same sample surface under the film boiling mode.At the same temperature,the transport speed of droplet is the fastest on the sample with a ridge tilting angle of 30°,and the maximum horizontal speed was about 46cm/s.When the ridge tilting angle increases,the maximum horizontal velocity of droplet directional transport decreases.When the ridge height increases,the maximum horizontal velocity of droplet directional transport remains unchanged.Finally,the model of droplet directional transport is established,and the formula for calculating the initial instantaneous acceleration of droplet directional transport is obtained through theoretical analysis,and the relationship between each parameter and the initial instantaneous acceleration and the maximum horizontal velocity is explained.(2)The micron scale oblique hole array structure was fabricated by laser etching on the surface of pure aluminum.The experiment of droplet movement is carried out on the oblique hole array surface at a temperature of 280 ~ 450?.In the experiment,the droplet releasedalmost statically showed the unidirectional self-propelled movement in the same direction as the oblique hole.However,the droplet impacting on the sample surface at a certain initial velocity shows the phenomenon of unidirectional bouncing motion in the same direction as the oblique hole.The effects of sample surface temperature,hole tilting angle and Weber number on the directional transport velocity of droplet on the oblique hole array surface are also studied further.It is found that when the surface temperature of the sample increased,the directional transport velocity of droplet first increases and then decreases.When the temperature is constant,the directional transport velocity of droplet increases with the increase of the hole tilting angle.In addition,an appropriate increase of the Weber number can greatly increase the directional transport speed of droplet in the low Weber number range.The research in this paper has certain guiding significance for the design of surface directional moving droplet at high temperature.