Numerical Simulation Of Droplet Migration In Micro-channel Under Periodic Temperature Boundary Conditions

In this thesis,Front Tracking Method(FTM)is used to establish a coupled heatflow model for droplets in microchannels.Due to the advantages of accurately describing the droplet surface,the migration phenomenon of droplets has been deeply studied.Firstly,the numerical simulation of the motion state of the droplet under the periodic temperature fluctuation is carried out,and the basic evolution law of the motion state of the droplet under the periodic temperature boundary is found.The results show that there is a velocity separation point at the initial stage for different amplitudes.After the separation point,the droplet velocity is positively correlated with the amplitude,and the amplitude is proportional to the maximum velocity that the droplet can reach.Under different angular frequencies,the lower the input angular frequency,the greater the vibration velocity the droplet can reach.And the time for the droplet to reach the maximum velocity decreased with the angular frequency.For different phase offset angle temperature inputs,the maximum velocity that the droplet reached decreases sequentially with the increase of the phase offset angle in the case of the same sign phase offset angle less than 1/4 of the cycle.For the reverse phase offset angle,with the increase of the reverse phase offset angle,the maximum velocity that the droplet reached decreases in turn.The smaller the Re number,the greater the maximum migration velocity that the droplet migration reached.And at the same time,the point at which the droplet velocity begins to separate will be correspondingly advanced.The droplet migration phenomenon of droplets under a given temperature field was studied in this thesis.The given temperature field influenced the droplet migration only in the early stage of droplet migration.With the increase of time,the droplet will have velocity separation in the first 1/4 cycle,and the reverse acceleration of different waveforms is different.The maximum velocity in the reverse direction that a droplet reached is related to a given periodic amplitude.The effect of motion migration on droplet varied with temperature level.If the level of temperature is higher than the given temperature field,the droplet will keep increasing its velocity after reaching the separation point.Otherwise,the droplet velocity is slowly reduced to reverse motion.Corresponding research was carried out on the Pr number of the droplet itself.It was found that the droplet with a larger Pr number had more obvious movement when the motion state was controlled by temperature changes.The droplet with large Pr is more sensitive even if small change in the temperature field.Four different periodic waves(square wave,sine wave,triangle wave and sawtooth wave)acting on droplet migration were investigated.It is found that the vibration amplitude and power density of the droplet have numerical relationship from large to small which is a square wave,sine wave,triangle and sawtooth wave in order under different input waveforms with the same input amplitude and frequency.Secondly,the difference in the input amplitude will also lead to the difference in the maximum amplitude of droplet motion under the same waveform.It shows a significant linear function relationship for droplet motion and a significant quadratic function for power spectral density under different waveforms.The difference relative to the input frequency will lead to the difference between the maximum movement amplitude of the droplet and the movement frequency of the droplet itself.When the frequency of the input temperature waveform increases,the maximum movement amplitude that the droplet can reach decreases.And the frequency of the droplet increases with the input temperature waveform increases.The power spectral density function of the droplet decreases with the increase of the frequency,and the frequency of reaching the extreme value increases.This characteristic holds true for the four selected waveforms,but does not have a certain functional relationship.In conclusion,the numerical simulation of the thermocapillary migration phenomenon of a single droplet in a temperature field is carried out in this paper.The relevant conclusions about the migration of a droplet in a fluctuating temperature field are obtained.It has theoretical reference significance for engineering technology applications such as biopharmaceuticals and cell culture.