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首页> 外文期刊>International Journal of Heat and Mass Transfer >Flame shapes and burning rates of spherical fuel particles in a mixed convective environment
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Flame shapes and burning rates of spherical fuel particles in a mixed convective environment

机译：混合对流环境中球形燃料颗粒的火焰形状和燃烧速率

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In this work, experimental and numerical investigations of spheres burning in a convective environment have been carried out. In the numerical simulations, transient axi-symmetric Navier-Stokes equations along with species and energy conservation equations are solved using a finite volume technique based on non-orthogonal semi-collocated grids. A global single step reaction involving two reactants, two products and one inert species together with an Arrhe-nius rate equation has been used to model kinetics. For the sake of comparison, an infinite rate chemistry model has also been attempted. The density of the mixture has been evaluated from ideal gas equation of state. Thermo-physical properties like thermal conductivity and viscosity have been evaluated using the Chapman-Enskog description of binary gas mixtures. Specific heats and species enthalpies have been evaluated using piece-wise polynomials of temperature. The burning of isolated spherical particles in a mixed convective environment at atmospheric pressure has been simulated for various particle sizes, free-stream velocities and ambient temperatures. The numerical predictions have been compared with experimental results obtained using the porous sphere technique and the agreement is found to be good. Correlations have been developed for the critical Reynolds number at which transition from the envelope to wake flame occurs and also for the mass burning rates at sub-critical or super-critical Reynolds number regimes. It is observed that, at higher ambient temperatures, transition to wake flame is delayed to a higher critical Reynolds number value. The infinite rate chemistry model predicts flame shapes and mass burning rates with reasonable accuracy in the sub-critical Reynolds number regime, but it fails to predict transition to wake flame shape. For analyzing transition phenomena, a finite rate chemistry model is required.
机译：在这项工作中，对流环境中燃烧的球体进行了实验和数值研究。在数值模拟中，使用基于非正交半共置网格的有限体积技术求解了瞬态轴对称Navier-Stokes方程以及物种和能量守恒方程。涉及两种反应物，两种产物和一种惰性物质以及阿雷尼乌斯速率方程的全局单步反应已用于动力学建模。为了进行比较，还尝试了无限速率化学模型。混合物的密度已根据理想的气体状态方程进行了评估。已使用Chapman-Enskog对二元混合气体的描述对热物理性质（如导热系数和粘度）进行了评估。使用温度的分段多项式评估了比热和物质的焓。对于各种粒径，自由流速度和环境温度，已经模拟了在大气压下混合对流环境中孤立球形颗粒的燃烧。将数值预测与使用多孔球技术获得的实验结果进行了比较，发现一致性很好。对于临界雷诺数和从次临界或超临界雷诺数状态下的质量燃烧速率，已经建立了相关性，该临界雷诺数发生从包络线到尾焰的转变。可以看出，在较高的环境温度下，向尾焰的过渡被延迟到较高的雷诺临界值。在亚临界雷诺数体系中，无限速率化学模型可以合理的精度预测火焰形状和质量燃烧速率，但无法预测到唤醒火焰形状的转变。为了分析过渡现象，需要使用有限速率化学模型。

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