点阵结构热交换器激光增材制造及换热性能测定

Laser Additive Manufacturing and Heat Transfer Performance Measurement of Lattice Structure Heat Exchanger

采用激光粉末床熔化成形增材制造技术制备了具有点阵结构的316L不锈钢、TC4钛合金和铜合金三种不同材料的热交换器。采用微纳计算机断层扫描(CT)技术对制备成形后的点阵结构热交换器进行三维图形的重构,获得热交换面积的数值;测量了激光粉末床熔化成形的点阵结构热交换芯体的尺寸及表面粗糙度;使用由加热单元、流动水和热电偶组成的试验装置(水流量为0.5 L/min,入水口温度恒定为22℃,环境温度为25℃,加热单元的加热功率维持在400 W),对热交换器的换热性能进行了测定。测试结果如下:三种材料的热交换芯体尺寸均达到了150 mm×150 mm,尺寸精度控制在±0.1 mm,表面粗糙度(R_(a))小于10μm,热交换效率>1000 m^(2)/m^(3)。相比传统的具有相同芯体尺寸的热交换效率为875 m^(2)/m^(3)的板翅式热交换结构,三种材料的点阵热交换结构(具有相同点阵结构、尺寸、结构表面积和结构表观体积,未考虑材料的热物性参数)在热交换效率提高10%的情况下,体积减小了24.9%,质量减少了66.6%。

Objective Traditional radiators have a large volume,heavy weight,and low dissipation efficiency.Using the laseradditive manufacturing technology,the volume and weight of the heat sink with lattice structure significantly reduce under the same heat dissipation efficiency of the traditional radiator.Therefore,laser-additive manufacturing of heat sinks with lattice structures is a promising technology.In this study,three types of radiators with lattice structures are fabricated using laser-additive manufacturing technology with 316L,TC4,and B30 powder materials and compared with traditional radiators.Methods Based on the confirmation of the powder characteristics,the laser-forming process parameters of the 316L stainless steel,TC4 titanium alloy,and B30 copper alloy are investigated.Alloy specimens with different metallographic parameters are formed,and their internal metallurgical properties are analyzed.Process parameters with good forming quality are selected as optimized technological parameters.Previous studies have shown that the Kagome lattice has a good heat dissipation effect,and the central vertex of the Kagome lattice acts as a vortex generator,which disrupts the basic flow and causes stillness and separation of media.The complex flow behavior simultaneously strengthens the conduction of the wall and connecting rod.In this study,the size of the Kagome lattice is optimized for laser manufacturing.Using laser selective melting,lattice-structured heat exchangers are fabricated with 316L stainless steel,TC4,and Cu alloys.A three-dimensional image of the lattice structure is reconstructed using computed tomography(CT),the heat exchange area value of the structure is also calculated,the core body size and the surface roughness of the laser-selective manufactured lattice structure are measured,and a self-made device is used to evaluate the heat transfer performance of the heat exchanger.Results and Discussions The size of the three heat exchange cores with different materials reaches 150 mm×150 mm,the heat exchange efficiencies are all greater than 1000 m^(2)/m^(3)(Table 3),the dimensional accuracy is controlled within±0.1 mm,and the surface roughness is less than 10μm(Tables 5,6,and 7).Compared with the traditional plate-fin heat exchanger with a heat exchange efficiency of 875 m^(2)/m^(3),which has the same size as that of the heat exchange core,the volume and weight of the lattice heat exchange structure decrease by 24.9%and 66.6%,respectively(Table 4),and the heat exchange efficiency increase by 10%.However,because single cells used have the same size,the simulated heat exchange efficiencies of the three material lattice structures are the same,but the values measured by micro-nano CT 3D imaging are different.This study demonstrates that the simulated value,compared with the measured heat exchange efficiency of the TC4 alloy lattice structure heat exchanger,has the smallest deviation.The deviation between the simulated and actual heat exchange efficiency values is primarily caused by the difference between the actual value and digital model obtained by printing.Currently,TC4 alloy is the most mature material in laser-selective melting formation,and it has good adaptability to laser-selective melting formation;therefore,the component obtained by printing is closer to the digital model.For the B30 copper alloy,owing to the high reflectivity of the laser,high thermal conductivity,and other factors,the difference between its laser-manufacturing components and mathematical models is significant.The316L alloy case is intermediate between those of the TC4 and copper alloys.Conclusions In this study,based on the Kagome lattice,the size suitable of lattice cell structure for additive manufacturing heat exchangers is optimized.Compared to the traditional plate-fin heat exchange structure with a heat exchange efficiency of 875 m^(2)/m^(3),the volume and weight of lattice structure decrease by 24.9%and 66.6%,respectively,when the heat exchange efficiency is increased by 10%.The lattice-structured heat exchanger cores with316L stainless steel,TC4 titanium alloy,and copper alloy are prepared by laser-powder selective melting.The size of the heat exchange core reaches 150 mm×150 mm,and the heat exchange efficiency is greater than 1000 m^(2)/m^(3).The dimensional accuracy is controlled within±0.1 mm,and the surface roughness is less than 10μm.The lattice-structured heat exchanger achieves high performance and precision for all three different materials.The evaluation formula of the heat exchange efficiency should comprehensively consider the influence of physical parameters and other factors to improve further.