Research The Nano Flows And Heat Transfer In Micro-channels Of Cross-section Shapes

With the rapid development of industrial science theory and technology,the problem of high heat flux density,especially in microscopic areas,has become increasingly severe.For example,microelectronic systems and high-speed mechanical narrow areas have raised higher heat transfer requirements.The micro-channel heat dissipation technology with strong potential for heat dissipation in small areas has attracted much attention.Many researches at home and abroad have verified that relying on micro-channel heat dissipation has a strong potential for heat dissipation in micro-zones under high heat flux density.On the other hand,due to the addition of solid nanoparticles in the base fluid,the nanofluid cooling liquid enhances the heat transfer efficiency of the base fluid based on the Brownian motion of the particles and thus enhances the thermal conductivity.There are many theoretical and engineering achievements in the application of nanofluidic cooling fluids to microchannels at home and abroad.However,there are few reports on the effect of the cross-section shape on the heat transfer and flow of nanofluidic cooling fluids in microchannels.1.The theoretical forming of wire cutting manufacturing technology was analyzed and discussed using wire cutting precision manufacturing technology.The feasibility of fabricating different microchannel structures by wire cutting is obtained.The influence of cutting speed on manufacturing forming is studied.Finally,the forming effect of rectangular microchannels and triangular microchannels is better.Finally,the mathematical model of triangle,rectangle,trapezoid,circle and elliptical microchannel is established and analyzed,which provides the basis for the simulation and experimental analysis.2.Using the simulation analysis technology,the microchannel cross-section shapes are triangular,rectangular,trapezoidal,circular and elliptical microchannels.The calculation results show that under the same initial conditions,the initial velocity is 2m/s,and the rectangular channel has the best fluidity.Under the research conditions,the average flow velocity is 2.77m/s;the triangular channel has the most fluidity.Poor,the average flow velocity is 2.47m/s;the trapezoidal channel has the best heat transfer characteristics,the heat transfer characteristics of the rectangular microchannel are very close to the trapezoid,the highest temperature difference of the measured point is 0.91%,and the heat transfer characteristics of the triangular microchannel are the worst.Finally,it is concluded that different microchannel structures and different section size parameters have a great influence on the Poiseu number and Nusselt number,and the reliability of the mathematical model is also verified.3.the stability of the four nanofluidic cooling fluids was investigated by static experiments.The cooling fluids were Cu-H20,CuO-H2O,Al-H20 and Al2O3-H2O nanofluids.The experiment was compared in three stages,initial state,10 days and 20 days.Photographs of nanofluids in three phases were recorded separately.It was found that there were different degrees of precipitation at 20 days,but A1203-H20 nanofluids Coolant stability is best.At the same time,the thermal conductivity,viscosity and boiling point of four kinds of nanofluids were studied respectively.After comprehensive determination,the optimal stability of A1203-H20 nanofluid cooling liquid was selected as the cooling medium in this paper.4.the A1203-H20 nanofluid cooling liquid with a volume fraction of 1.5%was used as a cooling medium and applied to the microchannel under test with rectangular cross section.The heat dissipation performance and pressure were measured on the self-built heat exchange test bench.The results show that the difference between the average surface temperature of the microchannel and the liquid average temperature decreases as the flow rate increases.For example,when the flow rate is 2m/s,the average temperature difference is 15.46℃ when the flow rate is 3m/s Yes,at this time the average temperature difference is 12.45℃,the cooling effect is increased by 19.5%;at the same time,the pressure difference between inlet and outlet is also increased,for example,when the flow rate is 3m/s,the pressure difference between inlet and outlet is 2050Pa,when the flow rate is At 4m/s,the differential pressure at the inlet and outlet is 3020Pa,and the pressure loss is increased by 47.3%.The average temperature difference between the rectangular microchannels in the simulation and the variation trend of the inlet and outlet pressure differentials are within the tolerance range.Through this actual measurement experiment,the computer simulation results are verified,and a follow-up engineering nanofluid cool:ing fluid is applied to the microchannel,and a cross-sectional shape of the channel is selected to provide an experimental data reference.5.On the basis of the previous study,a rectangular microchannel heat sink with different depth and width ratio is designed.It is found that the higher the depth and width ratio,the better the flow uniformity and the better heat transfer effect.Compared with the conventional channel,the rectangular microchannel has a better heat transfer effect.