双边剪智能剪切控制功能的研发与应用

在宽厚板项目中,双边剪用来剪切钢板两个纵边,以达到厂家要求的钢板宽度。本文除了介绍宽厚板双边剪的系统配置及功能特点外,主要阐述智能剪切的自动控制。本着降本增效的原则,开发一种新的主传动控制模式,优化双边剪电机剪切程序,在钢板厚度满足设定条件的前提下,固定侧与移动侧各采用一组电机驱动剪刃,并且实现主从电机智能激活切换模式,以满足生产需要。经实践证明,优化后的控制系统不仅提高了生产效率,还实现了节能降耗、安全生产的目的。     

Three-dimensional modelling of Non-Newtonian fluid flow in a coat-hanger die

The three-dimensional model of isothermal flow of power-law fluid in a coat-hanger die has been developed using finite element method. The shape of coat-hanger die used in the present model was determined according to the previous analytical design equation which is based on one-dimensional flow model in the manifold and the slot. Because uniform flow rate across the die outlet is most important to achieve uniform thickness of extruded polymer sheet or film, flow rate distribution is mainly examined to determine the valid process condition for the design equation as the design parameters are changed. The effects of fluid property in terms of power-law index and process parameters not considered in one-dimensional design equation such as die inlet size and the presence of land were analyzed. Results show that the manifold angle is the most influencing design parameter on flow rate distribution. When the material of different power-law index from design value is processed, the change of power-law index affects the uniformity of flow rate appreciably.     

Shear rates investigation in a scraped surface heat exchanger

The electrodiffusion technique was performed in order to investigate the shear rate on a scraped surface heat exchanger. Microelectrodes were placed inside: the walls of the outer cylinder; the inlet and outlet bowls; the rotor and the blades. Highly viscous Newtonian fluid (Emkarox HV45 solutions) and non-Newtonian model fluid (aqueous solutions of CMC) were used. The electrodiffusion method allowed us to measure wall shear rates. Maximum shear rate was observed at the scraping surface and caused by blades scraping, high shear rate was also measured on the leading edge of the blades. In the other parts of the exchanger, shear rate remained low but the development of Taylor vortices completely modified the scraped surface heat exchangers behaviour inside the surface of the bowls. A dimensionless representation of the friction factor was established for the inner and outer wall surface of the exchanger.     

DAMPED OSCILLATIONS IN A BINGHAM PLASTIC FLUID

Stokes' second problem, the propagation and damping of waves into a semi-infinite fluid generated by harmonic oscillations of a flat pate on the surface, is solved for the simple Bingham Theological constitutive model. The solution reveals the existence of “windows” in the distance-time-stress space in which shearing is possible whereas outside these restricted regions no shearing can occur. Within these restricted regions the wave forms developed are exponentially damped, traveling waves which propagate from the excitation plane into the fluid and disappear along definitely prescribed boundaries determined by the yield condition. The most significant consequence of the existence of these “windows” of shear is that even very small yield stresses will radically modify the induced velocity wave patterns from that which would be expected based upon the classical Newtonian fluid solution of Stokes' second problem. At least in this physical setting, it is not necessary for shear to occur globally for motion to occur anywhere, as has been postulated in some recent studies of complex motions. Thus, the motion is consistent with a simple Bingham model which does possess a yield stress.     

二维参数化图形技术研究进展

近几年来，参数化图形技术得到了不断的发展。目前已有多种参数化图形方法及系统。这些参数化图形方法可分为３种，即变分几何法、几何推理法和过程法。主要介绍这３种方法的研究进展。     

窑尾高温风机调速装置选型及应用

本文从可靠性、经济性、技术先进性上论述了水泥熟料生产线窑尾高温风机调速装置的选型、内反馈高频斩波调速装置工作原理及运行情况。最后给出了实际节电效果。     

Combustion characteristics and flame stability at the microscale: a CFD study of premixed methane/air mixtures

A two-dimensional elliptic, computational fluid dynamics (CFD) model of a microburner is solved to study the effects of microburner dimensions, conductivity and thickness of wall materials, external heat losses, and operating conditions on combustion characteristics and flame stability. We have found that the wall conductivity and thickness are very important as they determine the upstream heat transfer, which is necessary for flame ignition and stability, and the material's integrity by controlling the existence of hot spots. Two modes of flame extinction occur: a spatially global type for large wall thermal conductivities and/or low flow velocities and blowout. It is shown that there exists a narrow range of flow velocities that permit sustained combustion within a microburner. Large transverse and axial gradients are observed even at these small scales under certain conditions. Periodic oscillations are observed near extinction in cases of high heat loss. Engineering maps that delineate flame stability, extinction, and blowout are constructed. Design recommendations are finally made.     

Transition of the flow in a symmetric channel with periodically expanded grooves

Transition of the flow in a periodically grooved channel is numerically investigated for periodicity indices m=1 up to 6 by assuming the two-dimensional and fully developed flow field, where m is defined as a number of grooves in which the flow repeats periodically. Critical Reynolds numbers for the onset of a self-sustained oscillatory flow from a steady-state flow are evaluated by numerical simulations. It is found that the bifurcations occur at the critical Reynolds numbers as a result of Hopf bifurcation, and a period in the streamwise direction of the oscillatory flow is twice as long as the groove pitch of the channel. In addition, flow visualization with the aluminum dust method is carried out to confirm the results obtained from the numerical simulations. The experimental results are in good agreement with the numerical ones.     

A NOTE ON THE REDUCED EFFICIENCY OF THE INDUSTRIAL CYCLONE

In this paper a theoretical investigation into the basis of the reduced efficiency of a conical cyclone is performed. By considering the flow in a region where viscosity is unimportant an analytical solution to the problem is obtained. From this model the performance of the cyclone is evaluated and this can be expressed in terms of three operating and design parameters. One of these parameters is the split ratio, that is the proportion of the volume of fluid entering the cyclone which goes to the underflow. It is demonstrated mathematically that the empirical formula for the reduced efficiency at present in common use is a very good absolute measure of the separating ability of a cyclone.     

Practical validation of the two-fluid model applied to dense gas-solid flows in fluidized beds

This paper discusses the simulation of bubbling gas-solid flows by using the Eulerian two-fluid approach. Predictions of particle motion, bed expansion, bubble size and bubble velocity in bubbling beds containing Geldart B particles are compared with experimental results and correlations found in the literature. In addition, gas mixing in a bed of Geldart A particles is investigated.An in-house code has been developed based on the finite-volume method and the time-splitting approach using a staggered grid arrangement. The velocities in both phases are obtained by solving the 2D Reynolds-averaged Navier/Stokes equations using a partial elimination algorithm (PEA) and a coupled solver. The k-ε turbulence model is used to describe the turbulent quantities in the continuous phase.In general, the model predictions are in good agreement with experimental data found in the literature. Most important observations are: the level of the restitution coefficient was found to be crucial in order to obtain successful results from 2D axisymmetric simulations of a system containing Geldart B particles. Bubble size and bubble rise velocities are not as sensitive to the restitution coefficient. The turbulence model is of outmost importance concerning gas mixing in a fluidized bed of Geldart A particles.From these numerical analyzes an optimized granular flow two-fluid model can be designed for the purpose of simulating reactive systems in fluidized bed reactors.