共查询到20条相似文献,搜索用时 203 毫秒
1.
本文基于颗粒动理学理论建立了流化床中的欧拉双流体模型,采用了单气泡沿壁面运动物理模型,从颗粒分布特性、温度分布特性和瞬时传热特性三个方面对超临界水流化床和气固流化床的床层与壁面间传热特性进行了对比研究。研究表明,相同条件下,相对于气固流化床,超临界水流化床中气泡的直径和上升速度都较小;超临界水流化床中床层与壁面间的传热系数与颗粒浓度呈反相关关系,而对于气固流化床则是正相关关系;并且不同于气固流化床,超临界水流化床床层与壁面间传热系数在颗粒浓度较低处对表观速度变化比较敏感。 相似文献
2.
3.
基于欧拉-拉格朗日方法,考虑热解过程中挥发分的析出和颗粒体积的变化,以上海市常见的绿化树种香樟树的树枝为实验材料,对固定床中生物质颗粒热解过程中温度对传热特性的影响进行了详细研究,利用开源软件OpenFOAM获得了反应器内不同热解阶段不同温度范围内颗粒数的分布,给出了不同温度下的有效传热系数及不同传热方式所占的比例.结果 表明:热解温度越高,有效传热系数降低,固体颗粒的平均比热容也逐渐降低;同时热解温度越高,辐射的换热量占比越大,而对流提供的热量占比则不断下降. 相似文献
4.
5.
唐强宋赞杨仲卿刘川川 《工程热物理学报》2014,(6):1232-1235
采用实验的方法,在鼓泡流化床燃烧装置中研究了低浓度煤层气在床内的流动和燃烧特性,考察了床层温度、气体浓度、流化风速及床料颗粒特性等操作条件变化对甲烷转化率和燃烧产物的影响。研究表明:床层温度升高,甲烷转化率显著增加;增加流化风速及进气甲烷浓度,甲烷转化率减小;颗粒粒径增加,甲烷转化率增加;CO排放浓度随床层温度的升高先增加后降低,并在床层温度约850℃时达到其最大峰值,沿流化床轴向高度CO的排放浓度先增加后降低,呈钟型分布。 相似文献
6.
本文根据二维拟均相模型与二维非均相模型的等价条件建立了两种模型的传热参数之间的关系,所得结果适用于不存在床高效应的床层。根据本文的结果,只要用径向温度分布法测得床层的温度数据并反向拟合出二维拟均相模型中的传热参数,就可以在此基础上计算得到二维非均相模型中的传热参数,如此则为二维非均相模型的实际应用奠定了基础。 相似文献
7.
8.
针对在高温燃烧环境中的颗粒辐射传热问题,基于普朗克辐射定律,提出了用于高温颗粒辐射传热参数在线测量的辐射光谱法,根据高温颗粒可见波段辐射光谱随波长变化情况,通过参数拟合方法直接获得颗粒温度及辐射强度等辐射传热参数。为验证该方法测量准确性,搭建了高温黑体炉辐射测量系统,实验测量结果显示:温度测量值与设定温度相对偏差小于3%;辐射强度测量值与理论计算值相对偏差小于5%。以此为基础,设计了应用于高温燃烧环境下的颗粒辐射传热参数测量的水冷结构探针,并利用该探针开展了高温燃烧环境气固两相流200~1 100 nm波段辐射光谱测量,基于上述方法,直接获得了高温颗粒温度、辐射强度等辐射传热参数沿截面分布情况,有效剥离了高温气体对流传热的影响,为高温颗粒辐射传热研究提供数据支撑。 相似文献
9.
针对在高温燃烧环境中的颗粒辐射传热问题,基于普朗克辐射定律,提出了用于高温颗粒辐射传热参数在线测量的辐射光谱法,根据高温颗粒可见波段辐射光谱随波长变化情况,通过参数拟合方法直接获得颗粒温度及辐射强度等辐射传热参数。为验证该方法测量准确性,搭建了高温黑体炉辐射测量系统,实验测量结果显示:温度测量值与设定温度相对偏差小于3%;辐射强度测量值与理论计算值相对偏差小于5%。以此为基础,设计了应用于高温燃烧环境下的颗粒辐射传热参数测量的水冷结构探针,并利用该探针开展了高温燃烧环境气固两相流200~1 100nm波段辐射光谱测量,基于上述方法,直接获得了高温颗粒温度、辐射强度等辐射传热参数沿截面分布情况,有效剥离了高温气体对流传热的影响,为高温颗粒辐射传热研究提供数据支撑。 相似文献
10.
11.
Man Young Kim Ju Hyeong Cho 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(9):1607-1621
The radiative heat transfer between two concentric spheres separated by a two-phase mixture of non-gray gas and a cloud of particles is investigated by using the combined finite-volume and discrete-ordinates method, named modified discrete-ordinates method (MDOM), which integrates the radiative transfer equation (RTE) over a control volume and a control angle simultaneously like in the finite-volume method (FVM) and treats the angular derivative terms due to spherical geometry as the conventional discrete-ordinates method (DOM). The radiative properties involving non-gray gas and particle behavior are modeled by using the extended weighted sum of gray gases model (WSGGM) with particles. Mathematical formulation and final discretization equations for the RTE are introduced by considering the behavior of a two-phase mixture of non-gray gas and particles in a spherically symmetric concentric enclosure. The present approach is validated by comparing with the results of previous works including gray and non-gray radiative heat transfer. Finally, a detailed investigation of the radiative heat transfer with non-gray gases and/or a two-phase mixture is conducted to examine the dependence of the radiative heat transfer upon temperature ratio between inner and outer spherical enclosure, particle concentration, and particle temperature. 相似文献
12.
在气粒两相流动问题中,颗粒间以及气体与颗粒间的传热问题不可忽略.光滑离散颗粒流体动力学(SDPH)模型作为一种新的求解气粒两相流动问题的方法,已经成功应用于模拟风沙运动等问题.在此基础上,提出了SDPH方法的热传导模型,模拟了气粒两相流动问题中的热传导过程以及颗粒蒸发过程.首先引入各相的能量方程,利用有限差分与光滑粒子流体动力学一阶导数相结合的方法,处理各相内部热传导项中的二阶导数问题,基于气粒两相间温度差及对流换热系数计算颗粒与气体间的热传导量,推导得到了含热传导模型的气粒两相流SDPH计算方程组,模拟计算了圆盘形颗粒团算例及鼓泡流化床内部热传导算例,并与双流体模型计算结果进行对比,结果基本符合;其次利用离散液滴模型中的颗粒蒸发传质传热定律计算颗粒的蒸发过程,数值模拟了颗粒射流蒸发过程,并与离散颗粒模型结果进行对比,两者符合得较好,验证了该方法的准确性及实用性. 相似文献
13.
工业过程中粉体颗粒不可避免地会相互摩擦碰撞而荷电. 荷电颗粒的存在可能会危害正常的工业生产过程, 也可能对工业过程起促进作用. 因此, 荷电粉体颗粒及其特性受到了广泛的关注, 但目前对粉体颗粒的荷电机理依然缺乏透彻的了解, 尤其是在气固两相流动中的粉体颗粒荷电现象. 事实上, 工业中存在的粉体颗粒的运动都受到流体的影响, 是典型的气固两相流系统, 流体对粉体颗粒的作用使粉体颗粒接触的荷电现象变得更为复杂, 因此从两相流动的观点来研究粉体颗粒荷电的物理本质就显得越来越重要. 本文介绍了工业过程中的几种不同类型的粉体颗粒荷电行为, 回顾了颗粒的荷电机理与描述颗粒荷电的数学模型. 对于工业过程中颗粒的荷电现象及颗粒在多相流体中的动力学行为, 介绍了研究颗粒受流体影响时荷电特性的数值模拟方法. 本文旨在对粉体颗粒的荷电机理、应用以及研究方法进行梳理与探讨, 为正确认识工业过程中粉体颗粒的荷电现象并加以控制利用提供理论借鉴. 相似文献
14.
近场辐射引起的能量交换可以比远场辐射高若干个数量级.本文计算了SiC和Cu两种球形颗粒的近场辐射换热,发现当颗粒间距非常小时,辐射换热会大大强化.颗粒直径、颗粒间距以及颗粒的介电常数是决定近场辐射换热大小的重要因素,而颗粒温度对近场辐射换热的影响较小. 相似文献
15.
L.H. Liu 《Journal of Quantitative Spectroscopy & Radiative Transfer》2003,76(2):225-234
The transient radiative heating of particle polydispersions initially at uniform temperature is numerically analyzed. Due to the different radiative heating characteristics between particles, the temperature evolution of particle changes with particle diameter. To take local thermal nonequilibrium between particles into consideration, the particles are discretized into several size groups. The radiative transfer equation in particle polydispersions and the transient energy equation for each particle group are solved by the discrete ordinates method and an implicit finite difference method, respectively. The effects of the standard deviation of particle diameter and the emissivity of particle surface on the thermal evolution of particle polydispersions are analyzed. The results show that, omitting thermal nonequilibrium of particles will result in significant errors in the calculation of radiative heat transfer, especially when the nonuniformity of particle diameter is large. 相似文献
16.
V. M. Gremyachkin E. P. Mazanchenko 《Russian Journal of Physical Chemistry B, Focus on Physics》2010,4(6):963-968
The diffusive-kinetic model of porous carbon particles gasification is developed. The model considers the processes of heat
and mass transfer both inside the porous particle and above it. Analysis of the model shows that heat and mass transfer have
an influence to the gasification process to a marked degree. Gasification of carbon particle by carbon dioxide is impossible
if particle temperature is lower about 850 K because concentration of carbon dioxide at the particle surface becomes lower
than its equilibrium concentration. The rate of the carbon particle gasification is determined as a function of the porous
particle internal surface area for different pressures and furnace temperatures. 相似文献
17.
圆管内潜热型功能流体对流换热的实验研究 总被引:10,自引:1,他引:9
本文实验研究了由正十四烷和尿素甲醛树脂制成的相变微胶囊和水混合组成的潜热型功能流体流过等热流圆管时的对流换热特性。相变微胶囊的加入可以显著增强流体与壁面间的对流换热,显著降低壁面温度和流体温度;在融化段对流换热系数呈增加分布,流体和壁面温度各自基本稳定在相应的温度值。强化对流换热的效果主要在融化段,并随流体中相变微胶囊浓度的增大而增强,也随R-eynolds数的增大而增强。 相似文献
18.
Functional nanocrystals are widely considered as novel building blocks for nanostructured materials and devices. Numerous
synthesis approaches have been proposed in the solid, liquid and gas phase. Among the gas phase approaches, low pressure nonthermal
plasmas offer some unique and beneficial features. Particles acquire a unipolar charge which reduces or eliminates agglomeration;
particles can be electrostatically confined in a reactor based on their charge; strongly exothermic reactions at the particle
surface heat particles to temperatures that significantly exceed the gas temperature and facilitate the formation of high
quality crystals. This paper discusses two examples for the use of low pressure nonthermal plasmas. The first example is that
of a constricted capacitive plasma for the formation of highly monodisperse, cubic-shaped silicon nanocrystals with an average
size of 35 nm. The growth process of the particles is discussed. The silicon nanocubes have successfully been used as building
blocks for nanoparticle-based transistors. The second example focuses on the synthesis of photoluminescent silicon crystals
in the 3–6 nm size range. The synthesis approach described has enabled the synthesis of macroscopic quantities of quantum
dots, with mass yields of several mg/hour. Quantum yields for photoluminescence as high as 67% have been achieved. 相似文献
19.