提高拉格朗日源相的计算稳定性：湍流与焦炭气化反应速率的耦合效应-

题目：湍流与焦炭气化反应速率的耦合效应
摘要：本文利用数值模拟方法研究了氧气/二氧化碳氛围中湍流对焦炭颗粒表明的非均相化学反应的影响，结果表明，对于Damköhler（Da数为湍流尺度与化学反应尺度的比值）较小的情况，湍流促进焦炭气化反应，这是由于湍流引起的颗粒与氧化剂之间的相对运动会增加碳颗粒表面的质量传递加。 但是，对于大的Damköhler数，由于粒子聚集，炭转化率大大降低。表面异相反应速率的减少的原因可能是：对于稠密颗粒群中的碳颗粒来说，由于颗粒群外部的碳颗粒消耗了氧气，氧气难以输运至颗粒群中心的颗粒。 同时，在颗粒群之间的空隙中存在高浓度的氧气，该氧气在输送到碳颗粒表面之前无法参与炭的气化反应。进一步，本文以一个简化的气体/颗粒反应系统为对象，基于直接数值模拟（DNS）数据，建立了湍流对非均相反应速率影响的模型。
关注点：
1.为了增加数值稳定性，使用了拉普拉斯扩散来扩散从粒子模型产生的源项，然后再将其添加到气相控制方程中：
2.粒径/网格尺寸比对气相化学反应有显著影响
图片摘要

Darmöhler数为0.1的情况下真实与理想均相反应速率之比随颗粒半径.网格尺寸之比的变化关系/Ratio of the real to the ideal homogeneous reaction rate for a constant Damköhler number of 0.1 over the ratio .

Title: Correlation effects between turbulence and the conversion rate of pulverized char particles
Abstract: The effect of turbulence on heterogeneous reactions on the surface of char particles embedded in a turbulent oxidizer, consisting of oxygen and carbon-dioxide, is in this work studied numerically. It is shown that for a small Damköhler number (Da), which is the ratio between a turbulent and a chemical time scale, the char conversion rates are somewhat increased by the turbulence. This is found to be due to the increased mass transfer rate to the char particle surface that is caused by the turbulence-induced relative velocity between the char and the oxidizer. For large Damköhler numbers, however, the char conversion rate is strongly reduced due to particle clustering. This reduction is explained by the fact that when particles are clustered in densely populated particle clusters, the transfer of oxygen to the particles in the centre of the clusters is reduced since the oxygen is consumed by the particles closer to the external surface of the cluster. At the same time, high concentrations of oxygen exist in the voids between the particle clusters. This oxygen cannot take part in the conversion of the char until it is transported to the char surface. The effects of turbulence on the heterogeneous reaction rates are furthermore modelled based on Direct Numerical Simulation (DNS) data for a simplified reacting gas particle system.
原文链接, CNF2017, IF 5.465
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