【作者】 周伟；

【导师】 汤勇；

【作者基本信息】 华南理工大学 ， 机械制造及其自动化， 2010， 博士

【摘要】 随着世界经济的飞速发展,人类面临的能源危机、环境污染问题日益严重,新能源的研究开发与利用必将成为解决该问题最为有效的技术途径。以低碳醇为燃料的制氢微反应器可为燃料电池等微小型电子装置提供安全可靠的在线氢源,从而引起世界各国研究者的广泛关注。本文以切削法加工的金属纤维为原材料,利用固相烧结技术形成多孔金属纤维烧结板,并将其作为催化剂载体构造一种新型甲醇水蒸气重整制氢微反应器,取得了显著的制氢性能。主要研究内容如下:1.金属纤维的切削加工成形及微结构表征采用车削加工和刨削加工两种成形方法获得不同形貌的金属纤维,并系统研究加工参数对金属纤维及其表面结构的影响规律。采用多齿车削加工的连续型铜纤维表面具有丰富的微结构,其尺度变化范围在30μm以下;当量直径可达100μm以下,截面形状为近似矩形或三角形;在800oC温度下保温30分钟后,纤维内部拉长变形的晶粒由于再结晶而生成等轴的细晶粒。2.金属纤维烧结板的烧结成形及工艺参数优化以铜纤维为原料,利用固相烧结技术在800~1000oC烧结温度下形成多孔金属纤维烧结板和定向金属纤维烧结板。在多孔金属纤维烧结板中,存在纤维长度的接触连接和纤维之间的交错连接两种结合方式,烧结过程中容易形成牢固的烧结颈,从而实现纤维之间的冶金结合。研究烧结工艺对其成形过程的影响规律,烧结温度对其成形具有重要影响,而烧结时间则影响不大。3.多孔金属纤维烧结板的结构与性能研究在单向拉伸与压缩实验过程中,多孔铜纤维烧结板都先经历短暂的弹性变形阶段后迅速进入拉伸破坏或压缩密实变形阶段,在整个变形过程中没有屈服阶段出现。不同孔隙率的多孔铜纤维烧结板表现出良好的均匀传热特性,在高孔隙率的条件下仍具有较高的热导系数。通过改变流速的方法,研究气体通过不同孔隙率的多孔铜纤维烧结板的压降特性,并对停留时间进行了测试。4.多孔金属纤维烧结板的几何模型和传输特性的数值模拟在GAMBIT软件中,建立基于立方孔单元结构的三维立体模型来描述多孔铜纤维烧结板的几何特征。通过改变孔隙率大小和入口流速,利用FLUENT数值模拟流体在多孔铜纤维烧结板中的流速和温度分布及压降特性。在70~90%的孔隙范围内,孔隙结构对入口流速具有显著增强作用,但孔隙率大小对流速分布影响不大。压降随流速的增加而逐渐增加,随孔隙率的增加而呈迅速减小的趋势。5.金属纤维烧结板载体结构的甲醇重整制氢微反应器利用两层浸渍的方法进行催化剂负载,通过超声波水浴振动实验,系统研究孔隙率和负载质量对催化剂负载强度的影响规律。采用改变反应空速和反应温度的方法,分析不同孔隙率和制造工艺参数条件下形成的多孔铜纤维烧结板的催化反应性能。在还原氛围条件下在800oC温度下烧结形成80%孔隙率多孔铜纤维烧结板,由于其具有三维网状结构和大比表面积,获得最优制氢反应性能。与商用不锈钢纤维烧结板进行对比分析,采用多孔铜纤维烧结板作为载体的甲醇水蒸气重整制氢微反应器,在甲醇转化率,氢气流速,重整气流速等方面都明显优于商用不锈钢纤维烧结板,H2选择性可达98%以上,产生的氢气可输出18W的功率。更多还原

【Abstract】 With the rapid development of world economy, energy crisis and environmental pollution is two growing problems for human society. Development and utilization of new energy gives the most effective way to solve these problems. In recent years, microreactors for hydrogen production fueled by hydrocarbons successfully provided the on-line hydrogen source for PEMFC. Therefore, microreactors exhibit a promising way to provide hydrogen for microelectronics powder equipment. In this dissertation, a novel porous metal fiber sintered felt (PMFSF) has been produced by the solid-state sintering of copper fibers fabricated using the cutting method. A methanol steam reforming microreactor for hydrogen production is constructed using the PMFSFs as catalyst support, which demonstrates good performance in hydrogen production. Main research results are as follows:1. Cutting process of metal fiber and microstructure characterizationTurning and planing process are employed to produce metal fibers with different morphologies. The effect of machining parameters on metal fibers and their surface structure in turning and planing process is studied. The continuous fine copper fibers have a lot of microstructures on the surface, with the scale of below 30μm; the equivalent diameter is less than 100μm, and the cross-section shape is approximate rectangle or triangle; after sintering at 800oC for 30 min, the extended and deformed grains in copper fibers regenerate equiaxed grains due to internal crystallization.2. Sintering process of PMFSF and optimization of sintering parametersA novel PMFSF and oriented linear metal fiber sintered felt have been produced by the solid-state sintering of copper fibers at the sintering temperature of 800~1000oC. After sintering process, there are two kinds of sintering joints present in the PMFSF: fiber-to-fiber surface contact and crossing fiber meshing. In sintering process, sintering joints can be easily formed so that the metallurgy union between fibers is completed. The effect of sintering parameters on the forming process of PMFSF is studied . The sintering temperature has a significant influence on the sintering process of PMFSF, but the holding time does not.3. Structure and performance of PMFSFIn uniaxial tensile and compressive test, the PMFSF first has a short stage of elastic deformation, and then rapidly enter into tensile fractures or compression dense deformation, without allowing yielding stage to take place. The PMFSF has excellent heat transfer properties, and show a good thermal conductivity, even in high porosity condition. In addition, pressure drop characteristics is studied when the gas pass through the PMFSF. While, the residence time for gas in the PMFSF with different porosities is tested and anlyzed.4. Geometry model of PMFSF and numerical simulation of transport propertyUsing GAMBIT software, the three-dimensional model of cell-based cubic pore structure is established to describe the PMFSF. When the fluid pass through the PMFSF, the velocity and temperature distribution as well as pressure drop characteristics are shown by the numerical simulation using FLUENT under different porosity sizes and inlet velocities. At the porosity of 70~90%, the pore structure has significantly enhanced the inlet velocity, but the porosity don’t influence the velocity distribution greatly. Pressure drop is increased gradually with increasing inlet velocity, and is rapidly decreased with increasing porosity.5.Methanol reforming microreactor for hydrogen production with PMFSF as catalyst supportThe two-layer impregnation method is employed to coat catalyst on the PMFSF. The effect of the porosity and mass of catalyst on the loading intensity is studied by the ultrasonic water bath vibration method. Moreover, the effect of the porosity and manufacturing parameters for the PMFSF on the performance of methanol steam reforming microreactor is studied by varying the gas hourly space velocity and reaction temperature. The PMFSF sintered at 800oC in the reduction atmosphere shows remarkable superiority in reaction performance for hydrogen production, owing to its three dimensional reticulated structure and superior specific surface area. Comparing with commercial stainless steel fiber sintered felts coated with equal mass of Cu/Zn/Al/Zr catalyst, obvious advantages are observed in methanol conversion, reformate gas flow rate and H2 production rate when the PMFSF is used as catalyst support. The H2 selectivity can reach 98%. The developed methanol steam reforming microreactor can generate hydrogen enough to provide a power output of 18W for a fuel cell.更多还原