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首页> 外文会议>International Annual Conference of ICT >SELECTED OBSERVATIONS ON THE COMBUSTION OF CHARCOAL BRIQUETS UTILIZED FOR THE OUTDOOR PREPARATION OF FOOD. VII. ANALYSES OF THE SHRINKING CORE MODEL IN THE COMBUSTION PROCESS.
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SELECTED OBSERVATIONS ON THE COMBUSTION OF CHARCOAL BRIQUETS UTILIZED FOR THE OUTDOOR PREPARATION OF FOOD. VII. ANALYSES OF THE SHRINKING CORE MODEL IN THE COMBUSTION PROCESS.

机译：食品户外制备用木炭煤气燃烧的选定观察。 VII。燃烧过程中收缩核心模型的分析。

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This work represents a continuation of our investigation of charcoal briquet combustion, the first six parts of which were reported upon at the last two International Pyrotechnics Seminars held in the United States. A Weber-brand covered cooking kettle served as an assumed semi-batch reactor in which the chemical reaction was a batch of "Kingsford" charcoal briquets combusting in a stream of fresh air entering through inlet ports on the bottom of the kettle. We observed that a grey ash layer covers the surface of the briquets after they have become fully ignited, and at the termination of the combustion there is a significant amount of ash residue remaining. The glowing surface of the core gradually moves inward and the ash clings to the briquets in such a way that the original size remains rather constant. If not disturbed, the shape of the ash residue resembles that of the original briquet. This manuscript thus represents the seventh part of our report, and examines the applicability of a "Shrinking Core Model" to the combustion process. We consider two possibilities, viz., (1) that diffusion of oxygen through the ash layer is the controlling resistance, and (2) that chemical reaction at the surface of the core is controlling resistance. For the case of oxygen diffusion, we plotted the data points representing the Diffusional Conversion Function versus time for six individual experiments. The slope of such a curve is related to the diffusion coefficient D_e. We observed that in each test the slope increased as time progressed, which indicated that the diffusion coefficient was increasing. But data represented in previous parts of our investigation showed that the temperature in the kettle decreased with time. This meant that the diffusion coefficient should have been decreasing because data in the literature reveal that diffusivities decrease with temperature (in an Arrhenius-type relationship). Thus, this contradiction resulted in our conclusion that the mathematical analysis did not support a situation wherein diffusion of oxygen would be the controlling resistance in the charcoal briquet combustion. For the surface chemical reaction case, the slope of the Surface Conversion Function versus time is proportional to the First Order rate constant k_s. Here, plots of this conversion function for the same six experiments as above yielded very smooth linear regression correlations. The average value of the First Order rate constant was 0.1387 m/min. These results supported the conclusion that a First Order chemical reaction at the surface of the core was the controlling resistance in the charcoal briquet combustion. This manuscript concludes with a recommendation for the direct measurement of the combustion temperature of the briquets, in order to provide more realistic kinetics correlations and to further clarify the mechanism of the reaction.
机译：这项工作代表了我们对木炭压块燃烧调查的延续，这是在美国举行的最后两次国际烟火研讨会上报告的前六个部分。韦伯品牌覆盖的烹饪水壶作为假定的半批量反应器，其中化学反应是一批“金福”木炭砾石燃烧在进入水壶底部的入口端口的新鲜空气流中。我们观察到在完全点燃之后，灰色灰层覆盖了灰色的表面，并且在燃烧的终止时存在大量的灰分残余物。芯的发光表面逐渐向内移动，灰烬紧贴到砖块，使得原始尺寸保持相当恒定。如果没有受到干扰，则灰渣的形状类似于原始灰色。因此，该稿代表了我们报告的第七部分，并审查了“收缩核心模型”对燃烧过程的适用性。我们考虑两种可能性，viz，（1）通过灰分层扩散氧气是控制电阻，（2）芯表面的化学反应控制电阻。对于氧气扩散的情况，我们绘制了表示扩散转换函数与时间的数据点进行六个单独实验。这种曲线的斜率与扩散系数D_E有关。我们观察到，在每个测试中，随着时间的推移，斜率增加，这表明扩散系数正在增加。但是，在我们调查的前一部分中表示的数据表明，水壶中的温度随着时间的推移而降低。这意味着扩散系数应该减小，因为文献中的数据揭示了扩散性随着温度降低（在Arrhenius型关系中）。因此，这种矛盾导致我们的结论是，数学分析不支持其中氧气扩散是木炭压块燃烧中的控制电阻的情况。对于表面化学反应情况，表面转换函数与时间的斜率与第一阶速率常数Ks成比例。这里，与上述相同六个实验的这种转换功能的曲线曲线产生非常平滑的线性回归相关性。第一阶速率常数的平均值为0.1387米/分钟。这些结果支持结论，即核心表面的一级化学反应是木炭压块燃烧中的控制性。该手稿的结论是结束了推荐，用于直接测量燃气燃烧温度的推荐，以提供更现实的动力学相关性，并进一步阐明反应的机制。

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