Forced Convection Heat Transfer Performance Analysis And Optimization Design Of Graded Honeycomb Structure Fabricated By Additive Manufacturing

Honeycombs exhibit fascinating mechanical properties in terms of strength,stiffness,and toughness.In addition,metal honeycomb with a single “easy flow” direction also appear particularly interesting for active cooling application,such as thermal protection system,engine combustion chamber wall and so on.The favorable properties of honeycomb materials strongly depend on their mesostructural topology.By changing the design parameters of the arrangement,shape,and dimensions of cell openings and walls,it is possible to realize a multi-functional co-design of load-bearing and heat dissipation,and provide an on-demand customized honeycomb structure.Additive manufacturing enables precise manufacturing of highly geometrically complex structures,providing support for the design of metallic honeycomb materials.The gradient design of structure is an important way to improve performance.However,the related research works on the graded metal honeycomb are all based on the numerical methods,which lacks proof by the reliable experimental data.In this paper,the graded and uniform honeycomb samples were fabricated by additive manufacturing,and a forced convection heat transfer experiment platform was built.The experimental and numerical study is carried out on the convective heat transfer performance of the graded and uniform honeycomb samples under the constant temperature and uniform heat flux conditions.And the influence of gradient ratios on the heat transfer performance of honeycomb structures is investigated.The experimental data verify the effectiveness of numerical methods for characterizing the heat transfer performance of honeycomb structures.The difference of heat transfer performance of three-dimensional graded honeycomb structure in different direction of fluid flow is studied by numerical simulation under constant temperature and uniform heat flux conditions.The main contents and results are given as follows:(1)Experimental and numerical study of forced convection heat transfer of graded metal honeycomb fabricated by additive manufacturing and validity of fast numerical methods.The graded and uniform honeycomb samples were fabricated by additive manufacturing,and the forced convection heat transfer experiment platform was built with copper plate thermostatic carrier.The overall pressure drop and the surface temperature of the upper and lower surfaces of the samples are directly measured under the different airvelocities.Results show that the experimental results of the samples are in good agreement with the numerical simulation results.The experimental results confirm that the new assumption that the fluid temperature of every individual channel is thought to be constant is reasonable,and the assumption of Constant Cross-sectional Fluid Temperature(CCFT)will lead to relatively large error.This work lays the foundation for further optimization design.(2)The optimization design of convective heat transfer performance of graded honeycomb structure considering additive manufacturing process.The previous works exhibit that the CCFT assumption would produce relatively large error for estimating the heat transfer rate of the graded metal honeycomb.So,it is necessary to re-discuss the graded honeycomb design.In this chapter,under the conditions of length,width,height,and flow rate,the honeycomb structure is re-discussed considering additive manufacturing process.The different design schemes of uniform honeycomb,linear graded honeycomb and three dimensional graded honeycomb are compared and analyzed.The results show that the optimization design of honeycomb structure in cross section can not significantly improve its heat transfer performance.The heat transfer performance of three-dimensional graded honeycomb structure in different direction of fluid flow is studied by numerical simulation under constant temperature condition,and the heat transfer performance has been greatly improved.(3)Performance analysis of forced convection heat transfer of graded metal honeycomb under uniform heat flux condition.Different boundary conditions correspond to different optimal designs.The above works mainly focus on graded honeycomb design under constant temperature boundary conditions.In this chapter,the forced convection heat transfer of graded honeycomb is studied by experimental and numerical method under uniform heat flux condition.The surface temperature of the lower surface of the samples are directly measured under the different air velocities.Results show that the experimental results of the samples are in good agreement with the numerical simulation results.At the same time,the heat transfer mechanism of graded honeycomb is revealed.In addition,The numerical simulation method is used to study the heat transfer performance of three-dimensional graded honeycomb structure in different directions of fluid flow.The results show that the equivalent heat transfer coefficient is similar under different direction of fluid flow,but the maximum temperature(temperature control effect)of the heating surface is quite different,in which the maximum temperature value of the heating surface of the three-dimensional graded honeycomb structure in A direction of fluid flow decreases by 21.23%.