Research On Morphology Of Oscillating Droplet On Horizontal Surface

The phenomenon of droplet colliding with surface is quite common in life,such as rain drop landing on lotus leaf,inkjet printing,internal combustion engine directly spraying fuel into the combustion chamber and so on.In addition,it is also common in other fields,such as the spraying of pesticides and irrigated farmland in agriculture,the horizontal falling film evaporation of sea water desalination process and spray coating technology in chemical industry and so on.Therefore,the study of phenomenon of droplet impacting on solid surface not only has an important scientific value for the enrichment and development of multiphase hydrodynamic theory and heat and mass transfer theory.For the static morphology of a single droplet deposited on horizontal solid wall,it is studied from two aspects of experimental and theoretical derivation in paper.In the experiment,the camera is used to get the static droplet image,and the outline of droplet morphology in image is extracted captured by software Image-Pro-Plus.In terms of theory,two static theoretical models of semi-ellipsoidal and spherical segment droplet are established.According to the force analysis of droplet microelements,the static equilibrium equation of droplet is deduced,so the spreading radius and height of droplet can be calculated by using the dichotomy method.Afterwards,the two theoretical results are compared with experiments in order to determine the experimental conditions and accurate theoretical model.For the morphology of single oscillating droplet on horizontal solid wall,it is simulated the process of droplet impacting flat wall and reaching equilibrium state in paper.The effects of different parameters(contact angle,initial radius,impacting velocity,dynamic viscosity and surface tension coefficient)on the oscillation process are investigated.And the changing rules of the oscillation period,spreading radius,height,amplitude of spreading radius and height and time required to achieve static state are analyzed with each parameter.At the same time,the variations in internal flow field of droplet is analyzed.It is found that the oscillatory motion of internal flow field is not synchronized in different parts of droplet.It is also studied the static shape of a large droplet with different initial shapes(height/radius = 0.8,1.2,and 2.0)colliding with horizontal surface in paper,then the results that the final shape cannot be affected on different initial shapes of droplet.