Towards a Thermal Optimization of a Methane/Steam Reforming Reactor

Plug-flow reactors are very common in methane/steam reforming applications. Their operation presents many challenges, such as a strong dependence on temperature and inlet composition distribution. The strong endothermic steam reforming reaction might result in a temperature drop at the inlet of the reactor. The strong non-uniform temperature distribution due to an endothermic chemical reaction can have tremendous consequences on the operation of the reactor, such as catalyst degradation, undesired side reactions and thermal stresses. One of the possibilities to avoid such unfavorable conditions and control thermal circumstances inside the reforming reactor is to use it as a fuel processor in the solid oxide fuel cell (SOFC) system. The heat generated by exothermic electrochemical SOFC reactions can support the endothermic reforming reaction. Furthermore, the thermal effects of electrochemical reactions help to shape the uniform temperature distribution. To examine thermal management issues, a detailed modeling and corresponding numerical analyses of the phenomena occurring inside the internal reforming system is required. This paper presents experimental and numerical studies on the methane/steam reforming process inside a plug-flow reactor. Measurements including different thermal boundary conditions, the fuel flow rate and the steam-to-methane ratios were performed. The reforming rate equation derived from experimental data was used in the numerical model to predict gas composition and temperature distribution along the steam reforming reactor. Finally, an attempt was made to control the temperature distribution by adopting locally controlled heating zones and non-uniform catalyst density distributions.     

基于神经网络的叶绿素含量精细测量建模方法研究

活体植物叶片叶绿素含量SPAD值易受叶片厚度、水分等影响,提出了基于多参数神经网络建模的叶绿素含量精细反演方法。通过测量叶片在中心波长分别为650,940和1 450 nm光照射下的透过率,获得叶片的SPAD值和水分指数WI(water index),同时用数字螺旋测微仪测量相应的叶片厚度并用分光光度法测得其叶绿素含量。利用建模集样本分别建立SPAD值与实测叶绿素含量之间的单参数模型和基于BP神经网络的WI、厚度及SPAD值与实测叶绿素含量之间的非线性模型。利用这两种模型分别计算获得验证集样本的叶绿素含量预测值,对预测值和实测值进行了相关分析和相对误差的分析。实验以340个三种不同植物叶片为样本,用以上方法进行了分析。结果表明,利用BP神经网络建模后,每种植物样本的叶绿素含量预测精度都有不同程度的提高,尤其对于叶片厚度值较大的样本,效果更为明显。数据显示所有混合样本平均相对误差绝对值由单参数模型的7.55%降低到5.22%,实测值与预测值的拟合决定系数由0.83提高到0.93。验证了利用多参数BP神经网络模型可以有效地提高活体植物叶绿素含量预测精度的可行性。     

脉冲放电弧光等离子体演示仪

介绍了一种脉冲放电弧光等离子体演示仪.该设备内置的测量电路可以直接显示放电电压、电流的大小和放电的持续时间,放电电流也可以通过附带的感应线圈来测量;结合光栅光谱仪,可以测出发光光谱,进而求出等离子体的温度、密度等参数.     

环形激波绕射、反射和聚焦流场的间断有限元模拟

采用间断有限元方法对环形激波在圆柱形激波管内绕射、反射和聚焦流场进行了数值模拟。将二维守恒方程的间断有限元方法发展到轴对称Euler方程,并对环形激波绕后台阶流动进行了数值计算。计算结果表明,采用间断有限元方法能够有效地捕捉运动激波在圆柱形激波管内传播的复杂流场结构;在聚焦点附近,数值解具有较大的梯度变化,表明该方法对间断解具有较强的捕捉能力,在聚焦点附近不会产生振荡或抹平间断现象。     

Solid-State NMR Studies of Polysaccharide Systems

Summary: Two polysaccharide systems were studied by solid-state NMR methods: (i) Chitin/glucan complexes. The ¹³C NMR spectra have shown that in samples isolated from the mushroom Pleurotus sp., the glucan content was always higher in stems than in pilei. While carbonyl lineshape in complex isolated from Aspergillus niger mycelium shows similar hydrogen bonding as in neat chitin, a significantly higher amounts of hydrogen bonding between carbonyl groups of chitin and hydroxy groups of glucan was found in complexes isolated from Pleurotus sp. (ii) Biodegradable starch/polycaprolactone (PCL) blends. From the relaxation times T₁(H) and T_1ρ(H) it follows that blends starch/PCL, starch/ester oligomers and starch formate/ester oligomers are phase-separated even on the scale 20–110 nm. On the contrary, starch formate/PCL blend is phase-separated on the scale 1–9 nm but homogeneously mixed on the scale 20–90 nm. Therefore formylation of starch significantly improves its miscibility with PCL.     

Rayleigh-Taylor不稳定性的Runge-Kutta间断有限元模拟

 采用发展后的间断有限元方法,对Rayleigh-Taylor不稳定性进行了数值模拟。在计算中采用Level-Set方法进行界面追踪,用虚拟流体方法（Ghost Fluid Method,GFM）对界面附近物理量进行等压装配。对两个典型的Rayleigh-Taylor不稳定性算例的数值研究结果表明,采用该方法计算含有接触间断的多介质流体力学问题是有效的,在交界面附近不出现伪振荡,具有较高的分辨率。     

Double folding model calculation applied to fusion reactions

The interaction potential between a spherical and a deformed nucleus is calculated within the double-folding model for deformed nuclei. We solve the double folding potential numerically by using the truncated multipole expansion method. The shape, separation and orientation dependence of the interaction potential, fusion cross section and barrier distribution of the system ¹⁶O+¹⁵⁴Sm are investigated by considering the quadrupole and hexadecapole deformations of ¹⁵⁴Sm. It is shown that the height and the position of the barrier depend strongly on the deformation and the orientation angles of the deformed nucleus. These are quite important quantities for heavy-ion fusion reactions, and hence produce great effects on the fusion cross section and barrier distribution.     

绿色化学与创造性教学

绿色化学的创造性教学具有现实的可行性和必要性,且绿色化学与创造性教学存在着很好的结合点。探讨了在绿色化学教学中贯彻创造性教学的原则和方式及其对培养高素质有创造性人才的意义。     

双时间步方法的应用分析

对双时间步方法隐式迭代的稳定性、启动问题、子迭代初值和收敛性准则进行分析.一般认为,双时间步的真实时间步长是基于精度,而不是稳定性的基础上给定,因此真实时间步长可以取得很大,但对VonNeumann稳定性分析表明,对于子迭代采用隐式的算法,稳定性的要求对真实时间步有限制.并通过对Sod激波管问题的计算,验证该分析.     

Reconstructing Reliable Powder Patterns from Spikelets (Q)CPMG NMR Spectra: Simplification of UWNMR Crystallography Analysis

Spikelets NMR spectra are very popular as they enable the shortening of experimental time and give the possibility to obtain required NMR parameters for nuclei with ultrawide NMR patterns. Unfortunately, these resulted ssNMR spectra cannot be fitted directly in common software. For this reason, we developed UWNMRSpectralShape (USS) software which transforms spikelets NMR patterns into single continuous lines. Subsequently, these reconstructed spectral envelopes of the (Q)CPMG spikelets patterns can be loaded into common NMR software and automatically fitted, independently of experimental settings. This allows the quadrupole and chemical shift parameters to be accurately determined. Moreover, it makes fitting of spikelets NMR spectra exact, fast and straightforward.