Optimal Design Of Microchannel Heat Exchanger Structure Based On SLM Additive Manufacturing

With the continuous advancement of Microelectronics,Aerospace and other fields of technology,a variety of mechanical and electronic equipment turn from the direction of conventional scale to highly miniaturized,integrated direction,resulting in the unit volume of equipment heating power increases,the internal space is more and more compact,transfer of heat is also more and more difficult.Due to the large volume and low heat transfer efficiency of traditional heat exchanger,it is difficult to be applied in a relatively compact space.Therefore,micro-channel heat exchanger with small size,light weight and high heat transfer performance emerges at the historic moment.At present,micro-channel heat exchangers are generally manufactured by corrosion grooving and diffusion welding.However,the former can only manufacture conventional cross section channels,and the latter cannot avoid producing welds and additional thermal resistance.The selective laser melting(SLM)technology can realize the shaping of entities of arbitrary shape,forming parts with excellent mechanical properties and outstanding water tightness,so that the manufacturing of microchannel heat exchanger with more complex structure and more efficient performance becomes possible.Therefore,this essay designed and optimized the complex structure of microchannel heat exchanger through the finite element method,SLM additive manufacturing system was used to shape the model of microchannel heat exchanger,and the sample was tested on the thermal performance test platform,which provide a little reference value for the application of SLM additive manufacturing technology in the field of complex structure of microchannel heat exchanger.(1)In order to explore the influence of microchannel cross-section shape on the flow characteristics and heat transfer performance of the medium inside the microchannel.ANSYS Fluent software is used to analyze four kinds of microchannel models with circular,square,semicircle and ellipse sections.The heat transfer performance of each microchannel was evaluated by PEC evaluation method.The results show that under the same Reynolds number,the elliptical microchannel has the highest Nusselt number and the highest PEC factor,and has the best comprehensive heat transfer efficiency.(2)In order to further improve the comprehensive heat transfer performance of microchannels,the effects of the axial ratio k and hydraulic diameter D on the heat transfer and flow characteristics of the medium in the microchannels were studied.(3)On the basis of the determined optimal hydraulic diameter and axial ratio,the influence of screw pitch L and the number of sides on the heat transfer and flow characteristics of the medium in the microchannel was studied.The results show that when the Reynolds number is constant,the Nusselt number and the drag coefficient increase with the increase of pitch.The larger the number of tape sides,the stronger the heat exchange capacity and the larger the resistance coefficient.The PEC factor of the double-side tape is higher when the Reynolds number is 1000-2000,and the PEC factor of the single-side tape is higher when the Reynolds number is 3000-5000.(4)In order to make the flow distribution of the medium in the microchannel evenly distributed in multiple parallel channels,the influence of the deflector structure on the flow distribution characteristics of the medium was studied.Comparative analysis the flow distribution performance of the model without deflector,uniform aperture deflector —typeⅠ,uneven variable aperture deflector —type Ⅱ and uniform variable aperture deflector—type Ⅲ,The results show that the designed Ⅲ type deflector the flow distribution uniformity of the worst,the designed Ⅱ type deflector the flow distribution uniformity is best,relative to the condition under the condition of without deflector will not uniformity was reduced by 61.6% ～ 63%.The heat exchanger CAD model was pre-processed and imported into the additive manufacturing system for manufacture.After post-processing,the heat transfer coefficient was measured on the thermal performance experimental platform and compared with the simulation results of the overall heat exchanger,so as to verify the correctness of the numerical simulation method.Results show that the 5 groups of the experimental results of heat balance error range from 0.13% to 1.16%,conform to the standard which ‘JB/T10379-2002’ give on the basis of(ΔQ≤5%),the experiment method is correct,results are reliable,the simulation results deviation range from 0.75% to 1.61%,it is believed that numerical simulation method is correct.