半圆形粗糙元壁面颗粒沉积数值模拟研究

为研究半圆形粗糙元壁面对颗粒沉积的影响,分别采用雷诺应力模型（RSM）和离散相模型（DPM）求解流场与颗粒运动轨迹,并结合临界速度判别颗粒沉积的方法。通过构建不同半圆形粗糙元参数（e/D,p/e）的通风管道计算域,研究了1~10 μm颗粒沉积速度变化及沿气流方向颗粒的沉积趋势,分析了流场所引起的湍流变化对颗粒沉积的影响,与相同参数下的方形粗糙元壁面颗粒沉积特性进行了对比。同时,分析了粗糙元参数对颗粒沉积速度的影响。结果发现,半圆形壁面颗粒沉积速度小于同参数下的方形壁面颗粒沉积速度,这是由于半圆形壁面的回流区相对方形粗糙元更小,捕捉颗粒能力差,半圆形粗糙元流体附壁效应导致半圆形粗糙元拦截效率较低。当e/D=0.02,p/e=3时,颗粒沉积速度变化较大,但在其余参数下变化并不大。半圆形粗糙元壁面的迎风面是颗粒沉积的主要区域。     

LBE simulation of coherent vortex motion and heat transfer in jets of cross flow

Lattice Boltzmann equation method is used to simulate the coherent vortex motions and interactions and the heat transfer characteristics of jets in cross flow (JICFs) via TD2G9 model. After validation, the characteristics of cross flow under different Reynolds numbers are illustrated, including the mean profiles, the Reynolds stress tensor, the vortex and temperature fields, the temperature gradients near the walls, and the coherent correlation of vortex motions. The results show that the velocity profiles in JICF can be characterized by three basic regions, which are mainly caused by the mergence of JICF with the main flow. The temperature gradient near the walls can also be categorized by four basic regions, which are caused mainly by the impulse of JICFs too. Coherent vortex motions are found in JICF for Re = 3000, which are proved by strong periodic correlation of flow variables over a fixed area.     

卡尔曼滤波在极谱分析中的应用——Sn(Ⅳ)、Pb(Ⅱ)、In(Ⅲ)、Cd(Ⅱ)体系的同时测定

利用卡尔曼滤波（ＫＦ）技术，对互相干扰的Ｓｎ（Ⅳ）、Ｐｂ（Ⅱ）、Ｉｎ（Ⅲ）、Ｃｄ（Ⅱ）体系进行了定量测试研究。在５．００×１０５～３．００×１０４ｍｏｌ·Ｌ１的浓度范围内，各组分测试的相对误差为－４．０％～３．８５％。对大理石抛光粉管理样中的Ｓｎ（Ⅳ）、Ｐｂ（Ⅱ）进行了测定，结果与ＩＣＰＡＥＳ结果相符。回收率在９５．０％～１０４％之间。为保证ＫＦ的精度，使用了两个监控出口。数据说明效果良好     

Poly(ϵ‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ϵ‐caprolactone) triblock copolymers: Synthesis and self‐assembly in aqueous solutions

Nontoxic and biodegradable poly(?‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(?‐caprolactone) triblock copolymers were synthesized by the solution polymerization of ?‐caprolactone in the presence of poly(ethylene glycol). The chemical structure of the resulting triblock copolymer was characterized with ¹H NMR and gel permeation chromatography. In aqueous solutions of the triblock copolymers, the micellization and sol–gel‐transition behaviors were investigated. The experimental results showed that the unimer‐to‐micelle transition did occur. In a sol–gel‐transition phase diagram obtained by the vial‐tilting method, the boundary curve shifted to the left, and the gel regions expanded with the increasing molecular weight of the poly(?‐caprolactone) block. In addition, the hydrodynamic diameters of the micelles were almost independent of the investigated temperature (25–55 °C). The atomic force microscopy results showed that spherical micelles formed at the copolymer concentration of 2.5 × 10^?4 g/mL, whereas necklace‐like and worm‐like shapes were adopted when the concentration was 0.25 g/mL, which was high enough to form a gel. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 605–613, 2007     

Aggregation behavior of MPEG‐PCL diblock copolymers in aqueous solutions and morphologies of the aggregates

Poly(ethylene glycol)‐b‐polycaprolactone (MPEG‐PCL) diblock copolymers were synthesized via a ring‐opening polymerization of ε‐CL monomers with MPEG as an initiator. Their solubilities and apparent critical micelle concentrations (CMC) in aqueous solution were investigated as well as the determination of the micellar hydrodynamic diameter using dynamic light scattering (DLS). As PCL block length increased, the solubility and CMC decreased while diameters of micelles increased. The gel–sol transition behaviors were investigated using a vial tilting method. Aqueous solutions of copolymers undergo a gel to sol transition with increase in temperature when their polymer concentrations are above a critical gel concentration (CGC). The CGC of the copolymers and gel–sol transition temperature are influenced by the PCL chain length. The tapping mode AFM was performed by imaging the freeze‐dried deposits from the copolymer solutions on mica to investigate a process from free chains to micelles and to gel. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3406–3417, 2006     

Predicting kinetic parameters for coal devolatilization by means of Artificial Neural Networks

The chemical percolation devolatilization (CPD) model has been shown to represent the devolatilization process of different coals and heating conditions with good accuracy. However, its use in computational fluid dynamics is limited because of its relatively high computational cost. Here, an Artificial Neural Network (ANN) based model for predicting coal devolatilization kinetics is developed based on a database constructed with the CPD model for a wide range of coals and heating rates. The heating rates and the information of ultimate and proximate analysis are chosen as inputs of the ANN model to consider the effects of coal types and heating conditions on coal devolatilization; the outputs are the kinetic parameters for the two-step kinetic model. The learning, validation, and application results show that the proposed ANN model has a competitive prediction capability on both the total volatile release and release rates when compared with the CPD model, but has obvious computational efficiency advantages. Furthermore, the relative impact of the coal type and heating rate on each kinetic parameter for coal devolatilization is quantitatively evaluated through the Garson equation. It is found that the heating rate has the strongest effect on the pre-exponential factor, while the coal types show significant influence on the activation energy and final yield of the two reactions in the two-step model.     

Properties of Complex Oscillation of Solutions of a Class of Higher Order Linear Differential Equations

Let A(z) be an entire function with μ(A) 1/2 such that the equation f~((k))+A(z)f = 0, where k ≥ 2, has a solution f with λ(f) μ(A), and suppose that A_1 = A+h,where h■0 is an entire function with ρ(h) μ(A). Then g~((k))+ A_1(z)g = 0 does not have a solution g with λ(g) ∞.     

卡尔曼滤波伏安分析法同时测定钴(Ⅱ)、镍(Ⅱ)、锌(Ⅱ)

卡尔曼滤波（ＫＹ）用于解析互相干扰离子的Ｃｏ（Ⅱ）、Ｎｉ（Ⅱ）、Ｚｎ（Ⅱ）的伏安重叠峰。用该法对钢铁试样中的这些离子进行了测试，效果良好。设计了ＢＡＳＩＣ程序，将有关数据输入后，直接给出结果。为保证结果准确度，程序中设置了两个监控出口。