碳纤维改性热塑性树脂研究进展

主要从碳纤维对材料的力学性能、耐热性、电学性能以及材料的耐磨性能等方面的影响对碳纤维在聚丙烯(PP)、聚氯乙烯(PVC)、聚碳酸酯(PC)、尼龙(PA)、聚苯硫醚(PPS)、聚醚醚酮(PEEK)等热塑性塑料改性中的应用进行了综述,并对碳纤维在热塑性树脂中的应用前景进行了展望。采用双螺杆挤出法制备碳纤维增强热的塑性高分子复合材料具有非常广阔的应用前景。     

酸碱理论在现代有机反应的应用

酸碱理论是一个重要无机化学理论,在无机化学中有着重要的作用,同时在有机化学中也有着广泛的应用。本文简单介绍了现代酸碱理论的发展,简单概述了几个在有机化学中常用的酸碱理论:酸碱质子理论、酸碱电子子理论、软硬酸碱理论。同时简要讲述酸碱质子理论、酸碱电子子理论在有机反应中的应用,以及在某些有机合成方面的应用实例。     

A Mathematical Study for Laminar Boundary‐Layer Flow,Heat, and Mass Transfer of a Jeffrey Non‐Newtonian Fluid Past a Vertical Porous Plate

In this article, we investigate the nonlinear steady‐state boundary‐layer flow, heat and mass transfer of an incompressible Jeffrey non‐Newtonian fluid past a vertical porous plate. The transformed conservation equations are solved numerically subject to physically appropriate boundary conditions using a versatile, implicit finite‐difference technique. The numerical code is validated with previous studies. The influence of a number of emerging non‐dimensional parameters, namely, Deborah number (De), Prandtl number (Pr), ratio of relaxation to retardation times (λ), Schmidt number (Sc), and dimensionless tangential coordinate (ξ) on velocity, temperature, and concentration evolution in the boundary layer regime are examined in detail. Furthermore, the effects of these parameters on surface heat transfer rate, mass transfer rate, and local skin friction are also investigated. It is found that the velocity is reduced with increasing Deborah number whereas temperature and concentration are enhanced. Increasing λ enhances the velocity but reduces the temperature and concentration. The heat transfer rate and mass transfer rates are found to be depressed with increasing Deborah number, De, and enhanced with increasing λ. Local skin friction is found to be decreased with a rise in Deborah number whereas it is elevated with increasing λ. And an increasing Schmidt number decreases the velocity and concentration but increases temperature. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21111     

Effect of Newtonian Heating and Thermal Radiation on Heat and Mass Transfer of Nanofluids over a Stretching Sheet in Porous Media

Laminar boundary layer slip flow from a stretching surface in a nanofluid‐saturated homogenous, isotropic porous medium is studied numerically. A Newtonian heating boundary condition in the presence of thermal radiation is incorporated and a Darcy model utilized for the porous medium. The model used for the nanofluids include the effects of Brownian motion and thermophoresis. A group theoretical analysis is conducted to generate similarity transformations. The governing transport equations are nondimensionalized and rendered into a set of coupled similarity ordinary differential equations using similarity transformations. The transformed equations are then solved using the Runge–Kutta–Fehlberg fourth‐fifth order numerical method with shooting technique. It is shown that the physical quantities of interest depend on a number of parameters. The results are presented in tabular and graphical forms. Comparison of the present numerical solutions with published work shows very good agreement. The study finds applications in high‐temperature nanotechnological materials processing.     

An electrical network for the numerical solution of transient mhd couette flow of a dusty fluid: Effects of variable properties and hall current

The Network Simulation Method (NSM) has been used to study the variations with velocity of suction, hall effect, Reynolds and Hartmann number, particle concentration and Eckert number on the unsteady MHD Couette Flow and heat transfer of a dusty and electrically conducting fluid between parallel plates in the presence of an external uniform magnetic field and uniform suction and injection. The solutions are obtained with the network model proposed and the electric circuit simulation program PSpice. The fluid is acted upon by a constant pressure gradient and an external uniform magnetic field is applied perpendicular to the plates. Due to the presence of uniform suction and injection, the Hall Effect is not dismissed. The NSM is applied to solve the steady-state and transient problems of flow and heat transfer for both the fluid and dust particles. This method requires only discretization of the spatial co-ordinates, while time remains a real continuous variable. Velocity and temperature are studied for different values of the viscosity and magnetic field parameters and for different particle concentrations and upper wall velocities.     

冷蚀检验在连铸坯质量控制中的应用实践

介绍了武钢第二炼钢厂通过采用冷蚀检验对连铸坯质量进行监控，确保了连铸机的运行状况，铸机精度，二次冷却系统，电磁搅拌系统以及铸坯内部的组织形态和结构等要素处于良好的受控范围。保证了多品种和高难品种钢生产的要求。     

Effect of Different Packaging Methods on Quality and Shelf Life of Fresh Reindeer Meat

The impact of different packaging methods [vacuum, modified atmosphere packaging (MAP) (60% CO₂ and 40% N₂) and MAP + CO₂ emitter] on the quality of fresh reindeer meat (M. semimembranosus) stored at 4°C for 21 days was investigated. Colour and odour of the meat, drip loss, pH, microbial content, antioxidant capacity and cooking loss were measured. The MAP + CO₂ emitter resulted in prolonged microbial shelf life compared with vacuum and MAP without CO₂ emitter as lower level of total viable counts was detected after 13 and 17 days. Samples stored with CO₂ emitter also had lower drip loss. Samples stored in vacuum had significant lower L*‐value, higher a*‐value and lower intensity of freshness (odour and colour) compared with those stored in MAP and MAP with CO₂ emitter. However, MAP with a gas‐to‐product volume ratio of 1 : 1 seems to be too low in quality preserving. Increased partial pressure by adding a CO₂ emitter improved bacterial inhibition compared with vacuum and traditional MAP. Copyright © 2014 John Wiley & Sons, Ltd.     

Application of differential transform method to unsteady free convective heat transfer of a couple stress fluid over a stretching sheet

In the present article, the transient rheological boundary layer flow over a stretching sheet with heat transfer is investigated, a topic of relevance to non‐Newtonian thermal materials processing. Stokes couple stress model is deployed to simulate non‐Newtonian characteristics. Similarity transformations are utilized to convert the governing partial differential equations into nonlinear ordinary differential equations with appropriate wall and free stream boundary conditions. The nondimensional boundary value problem emerging is shown to be controlled by a number of key thermophysical and rheological parameters, namely the rheological couple stress parameter (), unsteadiness parameter (), Prandtl number (Pr), buoyancy parameter . The semi‐analytical differential transform method (DTM) is used to solve the reduced nonlinear coupled ordinary differential boundary value problem. A numerical solution is also obtained via the MATLAB built‐in solver “bvp4c” to validate the results. Further validation with published results from the literature is included. Fluid velocity is enhanced with increasing couple stress parameter, whereas it is decreased with unsteadiness parameter. Temperature is elevated with couple stress parameter, whereas it is initially reduced with unsteadiness parameter. The flow is accelerated with increasing positive buoyancy parameter (for heating of the fluid), whereas it is decelerated with increasing negative buoyancy parameter (cooling of the fluid). Temperature and thermal boundary layer thickness are boosted with increasing positive values of buoyancy parameter. Increasing Prandtl number decelerates the flow, reduces temperatures, increases momentum boundary layer thickness, and decreases thermal boundary layer thickness. Excellent accuracy is achieved with the DTM approach.