浆态床法合成二甲醚的模拟研究

对于直接以合成气作为原料,使用Cu-Zn-Al和γ-Al2O3构成的双重催化剂、采用浆态床法合成二甲醚的反应体系,使用全混流反应器模型结合化学反应动力学进行模拟。组分方程使用超松弛迭代方法并结合C 编程进行求解,编制了计算机程序。通过模拟计算,讨论了压力、温度、空速、催化剂配比、反应气中不同氢碳比以及CO2含量对反应收率、DME选择性的影响,并讨论了在不同氢碳比下对CO转化率和CO与H2总转化率的影响,从而寻找合适的反应条件,为工业化生产提供参考。     

Early fault detection in gearboxes based on support vector machines and multilayer perceptron with a continuous wavelet transform

One of the research problems investigated these days is early fault detection. To this end, advanced signal processing algorithms are employed. The present paper makes an attempt at early fault detection in a gearbox. In order to evaluate its technical condition, artificial neural networks were used. Early fault detection based on support vector machines is a relatively new and rarely employed method for evaluating condition of machines, particularly gearboxes. The available literature offers very promising results of using this method. In order to compare the obtained results, a multilayer perceptron network was created. Such standard neural network ensures high effectiveness. The vibration signal obtained from a sensor is seldom a material for direct analysis. First, it needs to be processed to bring out the informative part of the signal. To this end, a wavelet transform was used. The presented results concern both a “raw” vibration signal and processed one, investigated for two neural networks. The wavelet transform has proved to improve significantly the accuracy of condition evaluation and the results obtained by the two networks are consistent with one another.     

On-chip glucose biosensor based on enzyme entrapment with pre-reaction to lower interference in a flow injection system

In this study, poly(3,4-ethylenedioxythiophene), PEDOT, was electropolymerized on a sensing chip to entrap glucose oxidase (GOD). The interdigitated array (IDA) electrode and microfluidic channel of the sensing chip was fabricated by photolithography. The IDA electrodes consist of two working electrodes in which one (WE1) was the enzyme-modified electrode and the other was a Pt (WE2) for eliminating noise effect. The microfluidic channel was formed on etched silicon by PDMS (poly(dimethylsiloxane)). In the flow injection analysis, a 0.7 V (vs. Ag/AgCl) was set on enzyme electrode to detect the catalytic product, H₂O₂, and the sensing signal was calibrated using the passed charge rather than the peak current. The linear relationship between the charges and the glucose concentrations, ranging from 1 to 10 mM, was obtained with a sensitivity of 157 μC cm⁻² mM⁻¹. Besides, the response time and the recovery time were about 15 and 35-75 s, respectively. In real human sample test, the error of single-potential and bi-potential were about 140% and 13%, respectively, comparing to the standard value, indicating that the WE2 can lower the interference effect in this system.     

The flow induced in a three layer stratified fluid by a submerged sink or source with stagnation points on the free surfaces

A boundary integral technique is developed to study the free surface flow of a steady, two-dimensional, incompressible, irrotational and inviscid fluid which is induced in both two and three layer stratified fluids in the presence of gravity by a submerged sink or source with stagnation points on the free surfaces. A special form of the Riemann–Hilbert problem, namely the Dirichlet boundary problem, is applied in the derivation of the governing non-linear boundary integral–differential equations which have been solved for the fluid velocity on the free surfaces and this involves the use of an interpolative technique and an iterative process. Results have been obtained for the free surface flow for various Froude numbers and sink heights in both two and three layer fluids. Further, we have also studied the critical Froude numbers for which no convergent solutions are possible for any larger values of the Froude number. We have found that the free surfaces are dependent on two parameters, namely the Froude number and the ratio of sink height to the thickness of either the middle layer in a three layer system and the bottom layer in a two layer system.