强迫对流条件下单颗粒水煤浆的加热、蒸发过程的研究

本文对强迫对流条件下单颗粒水煤浆的加热、蒸发过程进行了研究,建立了计算模型,计算结果与实验结果符合较好,因此可供工程上估算单颗粒水煤浆的加热时间和蒸发时间用.     

考虑液面凹陷时金属熔化与蒸发的数值研究

将关于液面凹陷的Young-Laplace方程与关于金属溶池的流体力学方程组及关于金属蒸发的ＢＧＫ方程联立求解，在给定的电子枪加热条件下，获得了熔池流场和温度场图像及金属蒸气密度、速度和温度分布.数值计算结果表明，随电子枪功率增加，金属的蒸发速率增加，蒸气的密度增大、温度降低而速度升高.与假设液面为平面的情况相比，考虑液面凹陷后求得的液面温度较低，金属的蒸发速率较小，并且这种差别随电子枪功率的增加而扩大.因此对于高功率电子枪加热金属蒸发，必须考虑液面凹陷的影响才能得到符合实际的结果. 关键词： 液面凹陷 Young-Laplace方程 熔池 金属蒸发     

蒸汽爆炸粗混合过程中的蒸发阻力模型

在蒸汽爆炸的粗混合过程中,由于液体的快速蒸发,高温金属液滴的周围会产生一层很薄的蒸汽膜,此时液滴周围的边界层流动与没有液体蒸发时有很大的不同,因此,常温情况下的小球在连续液体中运动时的通用阻力模型在这种情况下是不适用的．本文通过受力分析,考虑了高温小球受力的分布和表面蒸发对小球周围力的影响,从阻力的基本机理上分析了蒸发状态下小球的运动阻力,分别提出了高温颗粒穿过自由表面时与其在液体中运动时的蒸发阻力模型．分析表明,当小球温度高于2500 K,特别是在靠近自由表面的区域,由于小球表面液体蒸发而产生的蒸发阻力作用非常明显．分析指出,小球的入水初速、小球表面的液体蒸发速率以及汽膜厚度都是影响小球运动阻力大小的重要因素．     

颗粒与高频感应热等离子体流的迭代计算

用完全二维自洽模型计算等离子体的速度场与温度场，用颗粒轨迹模型计算颗粒的运动轨迹与加热历程，但在等离子体的连续、动量和能量控制方程中，增加一项由于颗粒直径、运动速度及能焓的变化而引起的源项，计及颗粒的运动与加热对等离子体的速度场与温度场的影响；在颗粒的运动轨迹与加热历程计算中，考虑流体阻力和热泳力对颗粒运动与加热的影响；并在等离子体的速度场与温度场和颗粒的运动与加热之间进行迭代计算。通过对铝颗粒与     

三维层流等离子体射流中陶瓷颗粒的运动与加热

本文对带载气-颗粒侧向喷射的三维层流等离子体长射流中陶瓷颗粒的运动与加热进行了模拟研究,并与忽略载气喷射影响时的结果进行了比较。模拟结果表明,侧向载气喷射所引起的三维效应对颗粒行为有明显影响,陶瓷颗粒在等离子体射流中加热时颗粒内部可能出现相当大的温差,取决于环境参数,陶瓷颗粒表面温度可以高于也可以低于中心温度。     

Cr_（75）（Fe_（0．67）Mn_（0．33））_（25）合金加外磁场穆斯

利用加外场穆斯堡尔效应对Ｃｒ７５（Ｆｅ０．６７Ｍｎ０．３３）２５合金的磁性进行了研究．结果表明该合金不是磁单相的．在温度约２７５Ｋ时合金中开始形成反铁磁相，其共存于一顺磁相．在１３３Ｋ下，该顾磁相转变成铁磁相，共存于反铁磁相二铁磁、反铁磁交换相互作用的竟争导至合金在２８Ｋ下重入自旋玻璃态．     

气液固三相流载气蒸发的抗垢性能

分析了化工设备换热面上碳酸钙碱性污垢生成及其影响因素,认为液体在加热壁面上的过热是导致碳酸钙碱性污垢沉积的重要原因,降低料液在加热壁面上的过热度可收到明显的防垢抗垢效果。在蒸发器加热管内引入少量的惰性气体(载气)与流态化固体颗粒,使之形成气液固三相流载气蒸发,可显著强化传热,降低料液在加热壁面上的过热度。以碳酸钙模拟工业硬水的实验结果表明,气液固三相流载气蒸发过程表现出明显的防垢抗垢效果,且具有一定的在线清洗作用。     

欧姆加热共蒸镀法制备Y-Ba-Cu-O超导薄膜

我们首次利用欧姆加热共蒸镀的方法制备了的超导薄膜．目前得到的结果是：起始转变点温度９８Ｋ；零电阻温度６５．８Ｋ；转变宽度ΔＴｃ为３２Ｋ．在同一块薄膜样品上，还发现了明显的电导各向异性。经过几次冷热循环后，由于样品表面结霜和吸水，样品的超导电性出现了退化现象．     

微波场对Co／La2O3上的甲烷部分氧化制合成气的影响

考察了微波场对Ｃｏ／Ｌａ２Ｏ３上的甲烷部分氧化制合成气的催化活性及产物选择性的影响，为揭示微波场与物质之间的相互作用规律进行了有意义的探索，结果表明，微波辐照下的反应有如下特点；在达到相同的ＣＨ４转化率时，微波活化方式下催化剂床层温度远比常规加热低得多，且产物中Ｈ２和ＣＯ选择性明显高于后者，微波活化方式的优越性还表现为：当微波加热的温度等于或高于１０７３Ｋ时，甲烷的转化率高达９９．３％以上，Ｈ２Ｏ     

自由流区近壁蒸发及未蒸发颗粒的热泳分析

本文给出了自由分子流区作用在壁面附近蒸发及未蒸发颗粒上的热泳力的分析结果.分析中气体分子在壁面和颗粒表面处均假定为部分镜反射和部分漫反射.分析表明,作用在近壁颗粒上的热泳力不仅依赖于气体中的温度梯度,还和气体的压力以及壁面与气体温度比有关.颗粒表面的温度和镜反射分数对作用于未蒸发颗粒的热泳力没有影响,但明显影响作用于蒸发颗粒的热泳力.研究表明,近壁效应及蒸发对颗粒热泳的附加影响是不容忽视的.     

Peculiarities of heat transfer in water droplets with a solid inclusion during heating in a high-temperature gas medium

A physical model and a mathematical model of heat transfer in the conditions of inhomogeneous (with a solid inclusion—a carbon particle) liquid droplet evaporation while moving through high-temperature (800–1500 K) gases are formulated. Numerical investigations were performed using, as an example, a spherical inhomogeneous water droplet during heating in the air medium. The most probable mechanism of phase transitions in a water–carbon particle–heated air system is considered (the initial droplet size, radius, varied in the range from 0.5 mm to 1.5 mm, the inclusion radius was 0.1–1 mm). It has been found that in certain conditions, besides water evaporation from the outer (free) droplet surface, intensive vaporization is possible at the liquid–solid inclusion interface. Conditions of realization of these phase transitions in inhomogeneous water droplet–high-temperature gas medium systems are identified.     

The properties of the nonequilibrium LaB6 surface resulting from field evaporation

The nonequilibrium surface of single-crystal lanthanum hexaboride needles and its modifications are studied with a time-of-flight atomic probe. The surface is obtained by room-temperature field evaporation. The mass spectra of field evaporation shed light on the surface composition at the needle tip immediately after tip etching, corrosion in residual gases, intense cleaning by field evaporation, and the relaxation of the nonequilibrium surface by heating to 1250 K. Conditions for the breakdown of an oxide film on the tip surface and for obtaining the mass spectra of field evaporation for stoichiometric or lanthanum-enriched pure LaB₆ single crystals are discussed.     

On energy transfer and generation of an electric current in the vicinity of an electrode dipped in an electrolyte and strongly heated by a current passing through it

Processes occurring when a metal electrode dipped in an electrolyte is heated by intense evaporation of the electrolyte are considered in terms of a physically rigorous model. Based on the Onsager principle of least energy dissipation rate in nonequilibrium processes, the fractions of thermal energy that are spent on heating and evaporating the electrolyte and on heating the vapor are found. The energy is released within the vapor-gas sheath when an electric current flows between the electrode and electrolyte surface. It is found that the electrolyte vapor temperature exceeds 1300 K. Analytical expressions are derived for the vapor-gas sheath thickness, the electrolyte vapor pressure, and the velocity of the vapor escaping the discharge zone. It is shown that field evaporation of thermally activated negative ions from the electrolyte surface cannot provide an electric current with densities found in experiments but is responsible for the generation of free electrons near the electrolyte surface. These electrons arise when the ions decay via collisions with excited molecules.     

Evaporation of a particle into chemically reactive carrier gas

After a general discussion and classification of physicochemical processes contributing to aerosol particle formation, evaporation of a particle into chemically active carrier gas is studied in more detail. The vapor flux from the particle surface is shown to increase if the carrier gas contains components reacting with the evaporated molecules. A method for determining the chemical correction to the Maxwell formula for evaporated flux is proposed. The correction to the heat balance of the evaporation process due to heat production by the chemical reaction is considered. The temperature of the particle is found to depend on the total evaporated flux, specific heat of the reaction, and the latent heat of evaporation. Main results are listed in the concluding part of the paper.     

深空环境下液滴辐射相变过程分析模拟

太空中固体粒子比液体粒子对航天器危害性大,计算液滴相变时间和温度变化对评估粒子危害性有重要意义.本文建立了太空环境下液滴辐射相变模型,分析了三种相变凝固模型,估计了水滴蒸发量,考虑了太阳辐射对液滴温度变化的影响,分别计算了水和氧化铝液滴的温度变化.结果表明:液滴粒径越小液滴冷却速率越大,三种相变凝固模型的相变时间差别较小;水滴蒸发比例均大于10%,其蒸发量不可忽略;水滴受太阳周期性辐射时,其温度在50 K至266 K之间周期性振荡变化.     

Investigation of the third heat transfer crisis on a vertical surface

The process of development of the third heat transfer crisis for vertical orientation of the heating surface was studied experimentally. Experiments were carried out with acetone under the conditions of saturation for the pressures in the working volume from 20 to 28 kPa. In all experiments, the third heat transfer crisis was preceded by propagation of evaporation front along the heating surface. The threshold values of heat flux densities, above which a stable vapor film is formed on the whole heating surface, are lower for vertical orientation of this heating surface than for the horizontal one. Data on the threshold heat flux densities and overheating before boiling-up were obtained. Above these values, formation of evaporation fronts was observed. The range of operation parameters corresponding to formation of the sites of unstable film boiling on the heating surface after boiling-up was determined.     

3D problem of heat and mass transfer at the ignition of a combustible liquid by a heated metal particle

A nonlinear nonstationary 3D problem of heat and mass transfer at gas phase ignition of a combustible liquid spread on the surface of a solid body by a metal particle heated to a high temperature is solved. This is done within the framework of a model taking into account the heat conduction and evaporation of the liquid, the diffusion and convection of the combustible vapors in the oxidizer medium, the crystallization of the ignition source, the kinetics of the processes of evaporation and ignition of liquids, the dependence of the thermophysical characteristics of the interacting substances on the temperature, and the moisture content of the oxidizer—air. The dependences of the ignition delay time of the liquid on the temperature and sizes of the heating source are established. Limiting values of the temperature and particle sizes at which the ignition conditions take place are determined. The influence of the air humidity on the inertia of the process being investigated is analyzed. A comparison of numerical values of typical parameters of the process under investigation for 2D and 3D models is performed.     

Zn/ZnO纳米颗粒的表面声子Raman散射

Ｚｎ／ＺｎＯ纳米颗粒的表面声子Ｒａｍａｎ散射许建峰黄亚彬莫育俊（河南大学物理系开封４７５００１）ＲａｍａｎＳｃａｔｅｒｉｎｇｆｒｏｍＳｕｒｆａｃｅＰｈｏｎｏｎｓｉｎＺｎ／ＺｎＯＮａｎｏｐａｒｔｉｃｌｅｓＸｕＪｉａｎｆｅｎｇ，ＨｕａｎｇＹａｂｉｎ，Ｍｏ...     

Silicon nano-wires fabricated by thermal evaporation of silicon wafer

Thin silicon nano-wires (SiNWs) with a diameter of 10–20 nm were fabricated by a simple thermal evaporation of silicon wafer at 1523 K. The gold produced by an electrochemical method was covered on the wafer surface as catalyst. It was found that the SiNWs are amorphous and its Raman peak shifted down maybe due to the effect of laser heating and quantum confinement. Finally, a temperature gradient growth model is suggested to explain the growth direction of SiNWs.     

The High-Temperature Evaporation of Water Droplets in a Gaseous Medium

Technical Physics - The results of experimental investigations of the processes of water droplet evaporation upon heating in a gaseous medium at temperatures of 500–1100 K have been...