Study On Bubble Dynamic Behavior And Mechanism Of Enhanced Heat Transfer Under EHD

Based on the self-developed VOF+LS+SPP method,the motion and deformation of a perfect dielectric bubble,as well as their influences on the heat transfer performance,in the direct-current(DC)and alternating-current(AC)electric fields are investigated.Firstly,in order to accurately simulate the perfect dielectric bubble dynamic behaviors in the electric field,a coupled volume-of-fluid,level set and smoothed physical parameter(VOF+LS+SPP)method based on the commercial software FLUENT is first presented.In this method,the LS function is applied to compute the surface tension force accurately and obtain the smoothed physical parameters(SPP)near the interface.The accuracy of this method is verified by comparing with the VOF method,VOF+LS method and other methods in the literature.For the studied case,the VOF+LS+SPP method not only obtains the grid-independent solutions,but also has very high precision with a maximum deviation of 7%.Secondly,the perfect dielectric bubble dynamics in the gravitational and uniform electric fields are systematically investigated by VOF+LS+SPP method.Simulation results show that the electric Bond number has a much greater effect on bubble dynamic behaviors than the permittivity ratio.The effect of electric field on the rising and deformation of bubbles is almost the same for different Morton numbers.The change of Morton number hardly influences the increase rate of bubble Reynolds number and the change rate of maximum bubble horizontal cross section caused by electric filed force.However,the electric field has a different effect on the rising and deformation of bubble for different Eotvos numbers.With the increase of Eotvos number,the electric field force has a decreasing effect on the change rate of maximum bubble horizontal cross section and the increase rate of bubble Reynolds number.Finally,the dynamic behaviors of a perfect dielectric bubble attached to the wall under the effect of cosine AC electric field are simulated by the VOF+LS+SPP method.The effects of different angular frequency and voltage on the bubble deformation and detachment are analyzed.Results show that the cosine AC electric field is beneficial to the bubble detachment from the wall at a low electric potential comparing with the DC electric field.When the voltage remains unchanged,the bubble detachment time decreases with the increase of angular frequency at first.Once the angular frequency exceeds the optimal value,the bubble detachment time increases with the increase of angular frequency.However,the bubble will not detach from the wall when the angular frequency is higher than a certain value.For the different applied voltage,the angular frequency has a different effect on the bubble detachment time.With the voltage increasing,the bubble can detach from the wall at a wider angular frequency range and with a shorter period of time,which contributes to achieving the heat transfer enhancement.