Study On Flow And Heat Transfer Of Trapezoidal Convex Ribs And Concave Microchannels

With the rapid development of microelectronics,microelectromechanical systems(MEMS)and nanotechnology,the demand for miniature thermal management systems is also increasing.Traditional rectangular microchannels can no longer meet the heat dissipation requirements of these high-performance devices.Therefore,researchers set out to find new solutions to improve heat dissipation and reduce energy consumption.The trapezoidal convex-rib-cavity microchannel has the characteristics of high heat transfer efficiency,high surface area to volume ratio,compact structure,and light weight,and can be widely used in the fields of electronic heat dissipation,aerospace,biomedicine,and new energy.At present,there are few studies on trapezoidal convex-rib-cavity microchannels,and no in-depth analysis of the flow and heat transfer characteristics of the structural channel.Therefore,this paper uses numerical calculations to study the principle of enhanced heat transfer of trapezoidal convex-rib-cavity microchannels,and optimizes the channel structure through three aspects:structure,material,and cooling medium,and improves the heat transfer capacity of the channel.The specific research contents are as follows:(1)The flow characteristics and heat transfer performance of trapezoidal convex-rib-cavity microchannels were studied by numerical simulation.The analysis of the reasons for the enhanced heat transfer of the staggered trapezoidal convex-rib-cavity microchannels(MCCR-2)can be summarized as follows:the rib and cavity structure of the channel enhances the local disturbance of the fluid,which makes the fluid generate secondary flow in the microchannel and enhances the fluid flow;the shape of the channel groove has more heat transfer surfaces;the periodic arrangement of convex ribs and concave cavities can continuously break the boundary layer.This increases the flow disturbance and the convective heat transfer between the fluid and the wall,thereby improving the heat transfer performance of the channel.(2)75 groups of microchannels with different combinations of convex rib and concave cavity bottom thickness,inclination angle and bottom length were studied,and the effects of different bottom thickness,inclination angle and bottom length combination structures on channel flow and heat transfer were analyzed and compared.Through response plane fitting method(RSM),multi-objective genetic variation method(NSGA-Ⅱ)and k-means clustering method,the structure of the bottom thickness,inclination angle and bottom length of the convex rib and concave cavity of the channel is optimized,and different microchannels(bottom thickness,inclination,bottom length)optimal combined structural solution set and structural representative solution;a comprehensive dimensionless prediction model of six parameters(friction factor prediction model and thermal resistance prediction model)is obtained through nonlinear fitting,which can be trapezoidal The heat transfer design of convex-rib-cavity microchannel provides a reference.(3)A new trapezoidal convex-rib-cavity microchannel structure with staggered upper and lower layers(SMCCR-2)is proposed.The effects of different bottom-thickness ratios and layer-height ratios on the flow and heat transfer of the new microchannel structure were analyzed.The research shows that:with the increase of the bottom thickness ratio,the heat transfer performance and comprehensive performance of the channel are improved.In different layer height ratios(0,0.25,0.5,0.75,1),when the layer height ratio is 0.5,the overall channel performance is the best.(4)Applying nanoparticles to MCCR-2 and novel structure SMCCR-2 channels,it was found that the heat transfer performance of the microchannels could be significantly improved.The overall Nusselt number N_u and comprehensive evaluation factor PEC in the channel both increased with the increase of the nanometer volume fraction.When the volume fraction of nanoparticles is 3%and 6%,the comprehensive evaluation factors of MCCR channels are increased by 1.02-1.10 times and 1.10-1.19 times respectively;the comprehensive evaluation factors of SMCCR channels are increased by 1.01-1.08 times and 1.09-1.17 times respectively,and the heat transfer effect is improved obvious.(5)Porous materials were used as the channel sidewalls of MCCR-2 and SMCCR-2.It was found that the porous sidewalls can significantly reduce the channel pressure drop and improve the heat transfer effect of the microchannels.When the porosity of the porous material is 0.4 and 0.6,the channel resistance of MCCR-2 is reduced by 55.8%and 80.8%,while the overall Nusselt number N_u is increased by 76.7%and 96.3%;the MCCR-2 and SMCCR-2structures with porous side walls The PEC increased to 2.05～3.18 and 1.82～2.80,which improved the heat transfer performance of the channel.