20吨钢锭轧制节能工艺

20t钢锭的轧制及轧后的冷却过程可建立起二维矩形数学模型,计算这个模型,得出了用热态初轧坯直接再轧制的可行条件,为轧钢厂系统节能提供了依据。     

Thermosolutal convective instability and viscous dissipation effect in a fluid-saturated porous medium

The combined effects of the double-diffusion and of the viscous dissipation on the convective instability in a fluid-saturated porous medium with a basic horizontal throughflow are investigated. A horizontal porous layer with an impermeable adiabatic lower wall and an impermeable isothermal upper wall is considered. The parallel boundary walls are assumed to have uniform, but unequal, concentrations of the solute. A linear stability analysis is carried out both numerically and by a first-order perturbation method. General disturbances having the form of oblique rolls are considered, reducing either to longitudinal rolls or to transverse rolls in the special cases of roll axes parallel or orthogonal to the basic flow direction, respectively. It is shown that the combined effects of viscous dissipation and mass diffusion may lead to the instability of the basic horizontal flow. Either the longitudinal rolls or the transverse rolls may be the preferred modes of instability depending on the value of the viscous dissipation parameter Ξ. The longitudinal rolls are the most unstable when Ξ < 61.86657.     

Growth and characterization of n-type polycrystalline silicon ingots

n-type polycrystalline silicon ingots were grown by directional solidification, and the grown ingots were sliced to wafers. The wafers were subjected to phosphorus gettering and hydrogen passivation. The minority carrier lifetimes of wafers before and after the processes were measured. The average lifetimes of the wafers after both the processes were improved by a factor of 2–3 times compared to those of as-grown wafers. The wafers were etched with a Secco solution to detect crystallographic defects. The effect of phosphorus gettering in the region where many etch-pits were observed is lower than that in the other region. On the contrary, the effect of hydrogen passivation in the region where many etch-pits were observed is higher than that in the other region.     

Thermosolutal Convection During Melting in a Porous Medium Saturated with Aqueous Solution

The thermosolutal convection in a porous medium saturated with an aqueous solution near the temperature of the density maximum is studied. The fixed temperatures applied to vertical walls include the density maximum. The formulation of the problem is based on the Darcy-Brinkman model and the density variation is governed by a nonlinear approximation. The equations are solved by a finite-volume method. The numerical model is validated through experimental results. We show that the nonlinear variation of the density influences strongly the flow structure and the heat transfer. The structures of this flow show that the density maximum generates a complex flow structure of two contrarotating cells of unequal importance.     

Thermosolutal convection from a discrete heat and solute source in a vertical porous annulus

Double-diffusive convection in a vertical annulus filled with a fluid-saturated porous medium is numerically investigated with the aim to understand the effects of a discrete source of heat and solute on the fluid flow and heat and mass transfer rates. The porous annulus is subject to heat and mass fluxes from a portion of the inner wall, while the outer wall is maintained at uniform temperature and concentration. In the formulation of the problem, the Darcy–Brinkman model is adopted to the fluid flow in the porous annulus. The influence of the main controlling parameters, such as thermal Rayleigh number, Darcy number, Lewis number, buoyancy ratio and radius ratio are investigated on the flow patterns, and heat and mass transfer rates for different locations of the heat and solute source. The numerical results show that the flow structure and the rates of heat and mass transfer strongly depend on the location of the heat and solute source. Further, the buoyancy ratio at which flow transition and flow reversal occur is significantly influenced by the thermal Rayleigh number, Darcy number, Lewis number and the segment location. The average Nusselt and Sherwood numbers increase with an increase in radius ratio, Darcy and thermal Rayleigh numbers. It is found that the location for stronger flow circulation is not associated with higher heat and mass transfer rates in the porous annular cavity.     

Segregation phenomena in large-size cast multicrystalline Si ingots

In cast multicrystalline silicon ingots impurity concentrations vary along the ingot height due to segregation phenomena during the directional solidification. It is expected that these concentrations are the highest at the top of the ingot which solidifies last. The bottom of the ingot which solidifies first, and which is longer in contact with the crucible floor is contaminated by solid state diffusion. As a consequence, lifetime (τ_n) and diffusion length (L_n) of minority carriers are the highest in the central part of the ingot and decrease strongly in the top as well as at the bottom. However, the impurity concentration is so high at the extremities of the ingot that additional solid state segregation phenomena occur at extended defects, which extract impurities from the adjacent grains. That is revealed at grain boundaries (GBs) by τ_n and L_n scan maps and also by the variation of the mobility of the majority carriers which cross GBs.     

Interaction of Participating Medium Radiation with Thermosolutal Convection—A Critical Appraisal

The present study addresses the interaction effect of participating media radiation with the onset of double‐diffusive convection in a square enclosure. Vertical walls are imposed with constant temperature and concentration, and the horizontal walls are impermeable and adiabatic. The boundaries of the enclosure are diffuse‐gray, and the enclosed fluid isotropically scatters, emits, and absorbs thermal radiation. Numerical simulations have been performed for both aiding and opposing buoyancy conditions. The buoyancy ratio has been varied to simulate the effect of buoyancy driven flow and compositionally driven flow, along with transition of flow between the above. Optical properties like opacity of medium, scattering albedo, Planck number, and wall emissivity have been varied to depict their influence on flow and heat transfer. The modified MAC method is used for the solution of convective transport equations. Gradient dependent consistent hybrid upwind scheme of second order (GDCHUSSO) is used for the discretization of the convective terms. The discrete ordinate method, with S8 approximation, is used to solve the radiative transport equation. The parametric results are provided in graphical and tabular form. Flow lines, isotherms, and isoconcentration contour maps are provided to bring clarity in the understanding of the momentum, heat, and solute transport phenomenon. The stabilization effect of thermal radiation at critical buoyancy ratio for buoyancy opposed flow is observed. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21108     

Soot formation characteristics and PAH formation process in a micro flow reactor with a controlled temperature profile

A micro flow reactor with a controlled temperature profile was examined with regard to its capabilities to investigate soot formation characteristics of rich methane/air mixtures and the formation process of polycyclic aromatic hydrocarbons (PAHs) of rich acetylene/air mixtures. In the experiment for a methane/air mixture, four kinds of flame and soot responses to equivalence ratio (1.5–4.5) and inlet mean flow velocity (5–40 cm/s) were observed: soot formation without a flame; a flame with soot formation; a flame without soot formation; and neither a flame nor soot formation. Soot formation was observed at high equivalence ratio and low flow velocity. Sooting limits depending on equivalence ratio and flow velocity (residence time) were successfully identified by the present micro flow reactor. To investigate the PAH formation process, the micro flow reactor was employed for a rich acetylene/air mixture at equivalence ratios of 4, 5 and 6 at an inlet mean flow velocity of 2 cm/s and gas sampling experiments were conducted at temperatures from 600 to 1000 K. Temperature dependence of mole fractions of benzene, styrene, naphthalene, phenanthrene, indene, acenaphthylene and biphenyl was successfully obtained and larger PAHs such as pyrene and coronene were not observed in this study. One-dimensional computation with the ABF 2.99 mechanism predicted a benzene mole fraction three times higher than the experimental result. The modification of the ABF 2.99 mechanism using recent benzene reactions greatly improved the prediction of the benzene mole fraction. The rate of production analysis was carried out and PAH formation in the micro flow reactor was investigated in detail.     

Effect of flow rate conditions on bubble formation

An experimental study has been carried out on bubble generation by means of air injection through an orifice submerged in water. An orifice, drilled in an hydrophobic horizontal plate and a radius a = 1 mm, have been used to investigate the effect of the flow rate working conditions on the bubble formation process; a wide range of volumetric gas flow rates (2.0 × 10 ? Q ? 1.8 × 10⁴ mm³/s) has been used, including different chamber volumes before the injection orifice.Two volumetric gas flow rates are apparent: the one into the experimental setup, which could be assumed as a constant, and a higher one into de bubble through the injection orifice; there is a first and significant time step with zero gas flow through the orifice. This drives to two different working conditions, named: constant volumetric gas flow rate, when both flow rates are equal, and non-constant volumetric gas flow rate, when both flow rates are different. First, a short experimental study, for constant volumetric gas flow rate, is presented; it represents a link between both working conditions. The main part of the work are devoted to non-constant volumetric gas flow rate and, it showed that the experimental data can be reduced approximately to a single bubble volume/flow rate relationship, as in the case of constant volumetric gas flow rate, if the properly scaled volumetric gas flow rate is used. Finally a simplified model, to estimate this proper volumetric gas flow rate, is presented and checked experimentally.     

钢锭零能少氧化均热轧制的研究

根据计算机的辅助分析,采用新的钢锭传搁、注后强制水冷却、垫铁脱模等工艺后,入炉钢锭的热焓已超过开坯轧制需要,利用普通均热炉代替钢锭保温车,可完全依靠到钢锭自身潜热与显热进行均热。对不同锭型与钢种采用经试验的最佳时间均热后再轧制,收与保温车均热钢锭直接轧制相同的效果。     

BP人工神经网络在钢铁生产过程信息流分析中的应用

钢铁企业生产过程的信息流蕴藏着丰富的生产工艺规律。BP人工神经网络广泛用于信息流分析中,将其概括为四个方面:过程状态参数预测、产品性能参数预测、能耗信息预测和原材料参数优化。分别介绍相关研究和应用工作,指出应用流程中存在的不足,并给出规范流程。最后给出某大型钢铁企业新区焦炉单元的日能耗预测实例,验证了BP人工神经网络在钢铁生产过程信息流分析中的作用和应用流程的有效性。     

Effect of creep deformation on Z phase formation in Gr.91 steel

Abstract

In order to make clear the effect of creep deformation on Z phase formation in Gr.91 steel, creep interrupted tests were performed for 10?000, 20?000, 30?000, 50?000 and 70?000 h at 600°C under 70 MPa. The time to rupture was 80?736·8 h at 600°C under 70 MPa. Z phase was observed in the vicinity of prior austenite grain boundaries in the grip and gauge portions after creep deformation for 10?000 h and more. Number density of Z phase particles increased with increasing creep time in the grip and gauge portions. The number densities of MX carbonitrides particles in the grip and gauge portions clearly started to decrease after 30?000 h corresponding to increase in number density of Z phase. In the gauge portion, the number density of MX carbonitrides particles was almost the same as that of Z phase particles after creep rupture, meaning that a large number of MX carbonitrides particles were disappeared. The number density of Z phase particles in the gauge portion was 2·5 times of that in the grip portion after creep rupture. This indicates that creep deformation promotes the Z phase formation.     

Thermosolutal transport and macrosegregation during freeze coating of a binary substance on a continuous moving object

The process of freeze coating of a binary substance on a continuous moving plate is investigated theoretically. A comprehensive model describing the momentum, heat, and mass transport in the freeze-coating system has been developed that accounts for the coupling between the macroscopic and microscopic aspects of the process. The problem is formulated using the single-domain approach and the governing equations are solved by the finite difference method. Effects of various controlling parameters on the freeze-coat thickness and the macrosegregation pattern have been determined. It is found that macrosegregation could be important in the freeze-coating process. As the distance from the surface of the plate is increased, the solid species concentration considerably decreases, reaching a minimum value and rising toward the ambient concentration. The macrosegregation pattern appears to be most sensitive to the equilibrium partition ratio. As the latter is increased, the difference between the solid and liquid species concentrations tends to decrease, leading to a substantial reduction of macrosegregation within the freeze coat.     

Enhancement and suppression of ice formation around isothermally cooled cylinders in convective water flow

To enhance and suppress ice formation around isothermally cooled cylinders in convective water flow, circular fins and heat conductor plates are used, respectively. The heat conductor plates are positioned around each cylinder with some clearance. In the present experiment, the cooled cylinders had a staggered alignment. The experimental results show that the present analytical method for cooled cylinders with fins and heat conductor plates is useful for predicting ice volume under the conditons in which the cooled cylinders are not completely linked by ice in a steady-state condition. It is found that ice accumulation with fins is significantly enhanced compared to that without fins. It is also shown that use of cylinders with the heat conductor plates is effective for suppression of ice formation. © 1998 Scripta Technica, Heat Trans Jpn Res, 26(7): 419–434, 1997     

Detailed modeling of soot formation in a partially stirred plug flow reactor

The purpose of this work is to propose a detailed model for the formation of soot in turbulent reacting flow and to use this model to study a carbon black furnace. The model is based on a combination of a detailed reaction mechanism to calculate the gas phase chemistry, a detailed kinetic soot model based on the method of moments, and the joint composition probability density function (PDF) of these scalar quantities.Two problems, which arise when modeling the formation of soot in turbulent flows using a PDF approach, are studied. A consistency study of the combined scalar-soot moment approach reveals that the molecular diffusion term in the PDF-equation can be closed by the IEM and Curl-type mixing models. An investigation of different kernels for the collision frequency of soot particles shows that the influence of turbulence on particle coagulation is negligible for typical flame conditions and the particle size range considered.The model is used as a simple tool to simulate a furnace black process, which is the most important industrial process for the production of carbon blacks. Despite the simplifications in the modeling of the turbulent flow reasonable agreement between the calculated soot yield and data measured in an industrial furnace black reactor is achieved although no adjustments were made to the kinetic parameters of the soot model. The effect of the mixing intensity on soot yield and different soot formation rates is investigated. In addition the influence of different operating conditions such as temperature and equivalence ratio in the primary zone of the reactor is studied.     

Theoretical and technological aspects of flow batteries:Shunt current formation and control

全钒液流电池(VFB)的电堆由若干单电池叠合在一起组成,通过公共流道和电解液分配管路连通多个单电池,电堆内部的电势差引起电解液中的离子定向迁移,形成旁路电流导致能量损耗.本文分析产生旁路电流和能量损耗的电堆结构机制,利用等效电路模型计算电堆内部旁路电流的分布,提出抑制和减小旁路电流的措施.通过设计合理的电解液流动管路,能够有效减缓旁路电流的影响,减小充电/放电循环过程的电荷损失,提高储能过程的能量效率.     

Experimental investigation of frost formation on a parallel flow evaporator

This paper experimentally studied the frosting process of a folded–louvered-fin, parallel flow microchannel evaporator in a heat pump central air-conditioning system under three conditions, in which three open states of two capillaries were adopted. Surface temperature distribution on evaporator was measured by 16 thermocouples buried on the leeward side. Mesoscale frost formation processes on its front view surface for three different test conditions were observed using a Charge Coupled Device (CCD) camera. The results showed that the surface temperature distribution on the parallel flow evaporator was uneven and initial frost formation generally started on some partial surface areas of the louvered fins whose surface temperature was lowest after the heat pump system running 6 min later under conditions B and C, while the evaporator began to frost after 8 min under condition A. The non-uniform surface temperature distribution caused by the unequal distribution of the refrigerant flux in the flat tubes’ microchannels resulted in uneven distribution of frost. The ice crystals distribution and frost thickness in frost period could be obtained by the digital image processing method in which the initial pictures were converted into binary image. The results indicated that in a thin layer near fins’ surface, ice crystals had relatively high occupancy rate in the frost growing period and full growth period; the occupancy rate of ice crystals decreased almost linearly with the increasing of the frost thickness (frost height), where the decreasing rate in the frost full grown period was less than that in the frost growing period (in 0.1 mm frost thickness condition, the occupancy rate of ice crystals decreased to 58% in the frost growing period, while in the frost full grown period occupancy rate of ice crystals decreased to 90%; and in 0.25 mm frost thickness, they were 0%, 45% respectively). Furthermore, it can be found that the frost thickness increased as the time increasing and then finally reached maximum values of 0.3 mm, 0.35 mm, and 0.32 mm respectively at three conditions.     

Effects of internal radiation on heat flow and facet formation in Bridgman growth of YAG crystals

Internal radiation, in the crystal and the melt, is investigated using the P₁-approximation for the Bridgman growth of YAG crystals. Its effects on the interface shape and facet formation are illustrated through three-dimensional simulation. The P₁-approximation is first validated by a one-dimensional solution. Further comparison for axisymmetric cases with the rigorous calculations by Brandon and Derby [J. Crystal Growth 121 (1992) 473] is performed for opaque melt, and reasonable agreement is obtained for optical distance being <1 cm. The no-slip Rosseland model also gives a reasonable prediction in the interface shape; however, interface position and facet size are over predicted due to the poor approximation in the thermal gradients at the interface. Furthermore, melt transparency introduces radiation heating from the hot zone to the interface. Accordingly, the interface concavity is reduced with the increasing optical distance of the melt.