Catalytic modification of conventional SOFC anodes with a view to reducing their activity for direct internal reforming of natural gas

When using natural gas as fuel for the solid oxide fuel cell (SOFC), direct internal reforming lowers the requirement for cell cooling and, theoretically, offers advantages with respect to capital cost and efficiency. The high metal content of a nickel/zirconia anode and the high temperature, however, cause the endothermic reforming reaction to take place very fast. The resulting drop of temperature at the inlet produces thermal stresses, which may lower the system efficiency and limit the stack lifetime. To reduce the reforming rate without lowering the electrochemical activity of the cell, a wet impregnation procedure for modifying conventional cermets by coverage with a less active metal was developed. As the coating material copper was chosen. Copper is affordable, catalytically inert for the reforming reaction and exhibits excellent electronic conductivity. The current density–voltage characteristics of the modified units showed that it is possible to maintain a good electrochemical performance of the cells despite the catalytic modification. A copper to nickel ratio of 1:3 resulted in a strong diminution of the catalytic reaction rate. This indicates that the modification could be a promising method to improve the performance of solid oxide fuel cells with direct internal reforming of hydrocarbons.     

时滞与界带

基于分析结构力学提出的界带分析方法,将子结构间的分界面延拓为有一定宽度的分界带/分界域,从而可以用于分析计算结构的非局部效应.分析动力学中存在弹性时滞积分问题,在理论方面仍存在许多有待明确的问题.通过分析结构力学与分析动力学间的模拟关系,可将界带分析方法用到弹性时滞积分问题中去,基于辛体系建立相应的分析计算方法.数值算例验证该套理论算法的可行性,也为进一步开展深入研究打下了理论基础.     

Research on residual stress inside Fe-Mn-Si shape memory alloy coating by laser cladding processing

The stainless Fe-Mn-Si shape memory alloy (SMA) coating was prepared on the surface of AISI 304 stainless steel. The principal residual stress measured by the mechanical hole-drilling method indicates that the Fe-Mn-Si SMA cladding specimen possesses a lower residual stress compared with the 304 stainless steel cladding specimen. The mean stress values of the former and the latter on 10-mm-thick substrate are 4.751 MPa and 7.399 MPa, respectively. What’s more, their deformation values on 2-mm-thick substrate are about 0° and 15°, respectively. Meanwhile, the variation trend and the value of the residual stress simulated by the ANSYS finite element software consist with experimental results. The X-ray diffraction (XRD) pattern shows ε-martensite exists in Fe-Mn-Si SMA coating, which verifies the mechanism of low residual stress. That’s the γ→ε martensite phase transformation, which relaxes the residual stress of the specimen and reduces its deformation in the laser cladding processing.     

椭圆余弦波的位移法分析

为研究线性浅水波理论的适用范围,基于位移浅水波方程的椭圆余弦波解,计算在不同水深h、波高η0和波长L条件下,非线性椭圆余弦波与线性余弦波的相对差。数值计算结果表明：η0/h越小或h/L越大,浅水波的非线性效应越弱;当η0≤0.42h且η0L2/h3≤5.34－12.85η0/h时,非线性椭圆余弦波与线性余弦波的相对差小于0.05,可满足工程需要。     

铸铁缸套表面石墨含量对抗拉缸性能的影响

目的研究铸铁缸套表面石墨含量对抗拉缸性能的影响规律。方法基于贫油试验方法,对铸铁缸套表面石墨含量分别为0.18%、1.27%、2.13%、3.92%、4.66%、5.88%的铸铁缸套进行抗拉缸试验。试验过程记录抗拉缸时间,使用扫描电子显微镜(SEM)观察缸套的表面形貌并分析成分。结果铸铁缸套表面露出石墨,可以有效延长其抗拉缸时间。随着表面石墨含量的增加,抗拉缸时间呈现先增加后降低的趋势。当表面石墨含量达到4.66%时,抗拉缸时间为8 h,为表面无石墨缸套的9.6倍。结论铸铁缸套表面露出的石墨起到储油和固体润滑剂的作用,可以显著改善配对副的抗黏着性能;另一方面石墨作为软质相,含量过高时,缸套整体承载能力反而减弱,容易发生拉缸。     

Optimum Duty Cycle of Unsteady Plasma Aerodynamic Actuation for NACA0015 Airfoil Stall Separation Control

Unsteady dielectric barrier discharge(DBD) plasma aerodynamic actuation technology is employed to suppress airfoil stall separation and the technical parameters are explored with wind tunnel experiments on an NACA0015 airfoil by measuring the surface pressure distribution of the airfoil.The performance of the DBD aerodynamic actuation for airfoil stall separation suppression is evaluated under DBD voltages from 2000 V to 4000 V and the duty cycles varied in the range of 0.1 to 1.0.It is found that higher lift coefficients and lower threshold voltages are achieved under the unsteady DBD aerodynamic actuation with the duty cycles less than 0.5as compared to that of the steady plasma actuation at the same free-stream speeds and attack angles,indicating a better flow control performance.By comparing the lift coefficients and the threshold voltages,an optimum duty cycle is determined as 0.25 by which the maximum lift coefficient and the minimum threshold voltage are obtained at the same free-stream speed and attack angle.The non-uniform DBD discharge with stronger discharge in the positive half cycle due to electrons deposition on the dielectric slabs and the suppression of opposite momentum transfer due to the intermittent discharge with cutoff of the negative half cycle are responsible for the observed optimum duty cycle.     

开孔碳纤维层合板层间应力分析

针对具有典型铺设角 的开孔碳纤维层合板, 采用三维有限元数值模拟方法, 分析了在单向拉伸载荷作用下孔边附近的层间应力, 讨论了界面层参数对层间应力的影响, 详细给出了典型铺设角之间层间应力的分布规律和最大层间应力产生的位置。结果表明: 对于相同铺设角的界面层, 沿厚度方向的位置影响层间应力的大小, 但不影响分布趋势; 而铺层顺序(如 或 )对层间应力的大小和分布趋势影响则较小。最大层间正应力产生于 的界面层, 位于与拉伸方向成90°的位置, 是外加拉伸应力的51%; 最大层间剪应力产生于 的界面层, 最大层间环向剪应力位于与拉伸方向成74°的位置, 是外加拉伸应力的64%; 而最大层间径向剪应力位于与拉伸方向成66°的位置, 是外加拉伸应力的25%。      

A parametric study of Trombe walls for passive cooling of buildings

Air movement in a naturally-ventilated room can be induced through the use of a solar chimney or Trombe wall. In this work Trombe walls were studied for summer cooling of buildings. Ventilation rates resulting from natural cooling were predicted using the CFD (computational fluid dynamics) technique. The renoramlization group (RNG) k-ε turbulence model was used for the prediction of buoyant air flow and flow rate in enclosures with Trombe wall geometries. The CFD program was validated against experimental data from the literature and very good agreement between the prediction and measurement was achieved. The predicted ventilation rate increased with the wall temperature and heat gain. The effects of the distance between the wall and glazing, wall height, glazing type and wall insulation were also investigated. It was shown that in order to maximize the ventilation rate, the interior surface of a Trombe wall should be insulated for summer cooling. This would also prevent undesirable overheating of room air due to convection and radiation heat transfer from the wall.