Research On The Effect Of Solid-liquid Interface Interaction On Microscale Flow And Heat Transfer

With the development of science and technology,the miniaturization of research objects has become an important trend in the development of natural science and engineering technology.The laws of microscale flow and heat transfer are different from those of conventional scales.The development and application of microflow systems have put forward urgent demands for the study of microscale flow and heat transfer laws.In this paper,focusing on the effect of solid-liquid interface interaction on microscale flow and heat transfer,a systematic study was carried out using a combination of theoretical analysis,numerical simulation and experimental research.The main research contents of the paper include:The apparent viscosity of the liquid near the wall is theoretically studied.Based on the theory of intermolecular interaction and the wetting theory,an apparent viscosity model of liquid near the wall is established.Affected by the solid-liquid intermolecular interactions,the viscosity of the liquid near the hydrophilic wall is greater than that in the bulk region,while the viscosity of the liquid near the hydrophobic wall is smaller.The stronger the solid-liquid intermolecular interactions,the stronger the wettability of the interface,and the greater the difference between the apparent viscosity of the liquid near the wall and the bulk viscosity.At the same time,the apparent viscosity of the liquid changes as the distance from the wall increases.The laminar flow characteristics of liquid through microchannels is theoretically and numerically studied.Based on the apparent viscosity model of liquid near the wall,the classical N-S equation is improved.On this basis,the influence of solid-liquid interaction and channel size on microscale flow characteristics is analyzed.The results show that the flow resistance in the hydrophilic microchannel is greater than the classical theoretical value,while the flow resistance in the hydrophobic microchannel is smaller than the classical theoretical value,and the Poiseuille number is no longer a constant and its value is affected by the interface wettability and channel size.When considering the solid-liquid interactions,the deviation between the microflow characteristics and the conventional theory becomes larger as the wettability increases,and decreases as the hydraulic diameter of the channel increases.When the hydraulic diameter of the channel is large enough,the effect of solid-liquid interaction on flow can be ignored.The single-phase convective heat transfer characteristics of liquid in microchannels is theoretically and numerically studied.Based on the apparent viscosity model,the convective heat transfer model for microtube is improved.On this basis,the effects of solid-liquid interaction and channel size on microscale convective heat transfer characteristics are analyzed.The results show that the average Nusselt number of microscale convective heat transfer is no longer a constant,and decreases with the increase of solid-liquid interaction.When the surface of the microchannel is hydrophilic,the Nusselt number is smaller than the conventional theoretical value;while when the microchannel,the Nusselt number is greater than the conventional theoretical value.The effect of solid-liquid interactions on microscale convective heat transfer decreases as the hydraulic diameter of microchannel increases.The laminar flow and heat transfer characteristics of liquid through microchannels are experimentally studied.A microscale flow and heat transfer experimental system is established to study the effects of wettability and channel size on microscale flow and heat transfer.The flow experimental results show that the flow resistance in the microchannel is larger than that predicted by the classical flow theory,the Poiseuille number is no longer a constant and is larger than the theoretical value,and decreases as the Reynolds number increases.The deviation between the experimental results and the classical theory is related to the wettability and the channel size.The stronger the wettability,the larger the deviation,and the larger the hydraulic diameter of the channel,the smaller the deviation,which are consistent with the theoretical analysis results.The proposed apparent viscosity model is validated by the experimental data.The theoretical value of the mass flow rate corrected by the apparent viscosity model is in good agreement with the experimental results,which verifies the validity of the proposed apparent viscosity model.The results of heat transfer experiments show that the average Nusselt number of the fully developed heat segment in the microchannel is significantly smaller than the traditional theoretical value,and is no longer a fixed value,but increases with the increase of the Reynolds number.When the channel size is the same,the Nusselt number becomes larger as the flow velocity increases.In addition,the Nusselt number also becomes larger as the channel feature size increases.Therefore,the flow state and channel feature size are important factors affecting the convective heat transfer in the microchannel.The influence of microchannel geometric characteristics on flow characteristics is studied numerically and experimentally.Firstly,the influence of the aspect ratio of the rectangular channel,the angle of the apex angle of the isosceles triangle and the channel parameters of the isosceles trapezoid on the flow characteristics are analyzed by numerical simulation.It is found that the larger the aspect ratio of the rectangular microchannel,the greater the resistance of the flow resistance,and the greater the influence of the wettability on the flow.When the apex angle of the triangular microchannel changes,the effect of wettability on the flow is substantially unchanged.The effect of wettability on the flow in the trapezoidal microchannel decreases as the angle of the upper corner increases.Secondly,the flow experiments in two kinds of materials(quartz glass and steel)micro-tubes were carried out,and the influence of surface roughness on micro-scale flow characteristics was analyzed.The experimental results show that the flow frictional resistance in the micro-circular tube increases with the increase of the Reynolds number,and the rough surface will cause the flow resistance to become larger.As the diameter of the tube increases,the ratio of the surface roughness to the tube diameter becomes smaller,the effect of roughness on the flow was gradually weakened.No early transition was found in the experiment.