Fundamental Research On Heat Transfer Characteristics Of Microchannels Based On Additive Manufacturing

Efficient cooling technology is the key to ensuring the normal operation of hotend components such as turbines and combustion chambers in aeroengines.In-tube flow heat transfer and jet cooling are two common cooling forms for the hot end parts of aeroengines.However,the existing cooling technology can no longer fully meet the requirements of future aeroengine cooling,and it is impossible to achieve great material temperature resistance in the short term.In the case of breakthroughs,it is extremely necessary to continue research on new cooling structures in combination with new manufacturing methods.In this paper,combined with the development trend of microchannel cooling technology and additive manufacturing technology in the field of aeroengines,the lattice Boltzmann method is used to numerically simulate the internal flow heat transfer characteristics and jet cooling efficiency of additive manufacturing microchannels.Before conducting the research,the micro-channel heat transfer test was first conducted by building a test bench.In the research of the internal flow heat transfer characteristics of the additive manufacturing microchannel,the surface morphology of the actual additive manufacturing object is obtained by scanning the electron microscopy system.Then combined with the fractal theory,four types of circular crosssection tube models were obtained,real tube,smooth tube,fractal interpolation tube and cantor set tube,triangle and rectangular cross-section tube models are also obtained.The equivalent diameter of the microchannel tube model was 100μm～1000μm.Then the convective heat transfer characteristics of air in different microchannel tube models were numerically simulated,and the Reynolds number Re ranged from 80 to 640.The influence of microchannel surface morphology construction method,relative roughness,Reynolds number,and microchannel cross-sectional shape on the heat transfer characteristics of microchannels was studied.The results showed that surface morphology is a factor that cannot be neglected in convective heat transfer in microchannels,the larger the relative roughness,the better the heat transfer,and the heat transfer performance of the real scanning tube was 2.22%higher than that of the smooth tube under the same conditions.The fractal theory can be used to construct the surface morphology of microchannels.However,the fractal interpolation model can more accurately reflect the actual shape than the Cantor set model under the same number of iterations.The heat transfer performance of the fractal interpolation model differs from the real scan topography by 0.03%,while the heat transfer performance of the Cantor set model differs from the real scan topography by 1.88%.In the microchannel,as the Reynolds number increases,Nusselt number will no longer be a constant,but has an increasing trend.For microchannels of circular,triangular,and rectangular cross-sections with the same equivalent diameter,the microchannels with circular cross-sections have the best internal flow heat transfer performance,followed by microchannels with rectangular cross-sections,and micro-channels with triangular cross-sections are the worst.In the research on the cooling efficiency of the additive manufacturing microchannel jet,by importing the measured actual morphology of the additive manufacturing microchannel into the model,the geometric models with different jet apertures,number of holes,different morphologies and different incident angles were constructed.Through numerical calculation,the influence of microchannel jet hole diameter,additive manufacturing printing direction,blowing ratio and incident angle of microchannel jet hole on the cooling efficiency of microchannel jet was explored.It was found that,under the same cooling air volume,replacing the large jet holes with smaller and more number of uniformly distributed jet holes can make the cooling gas more evenly distributed near the wall,which can improve the cooling efficiency and at the same time avoid Localized high temperature appears on the wall.Under the same cooling air volume,the jet cooling efficiency decreases slightly with the increase of the angle between the microchannel and the printing direction.The increase of the blowing ratio in jet cooling can bring more cooling air,which can effectively avoid local high temperature on the wall surface,but it will also reduce the diffusion and adhesion of the cooling air near the wall surface and reduce the cooling efficiency.Under the same cooling air volume,the jet cooling efficiency tends to decrease with the increase of the incident angle.