【作者】 梁森森；

【导师】 施明恒；

【作者基本信息】 东南大学 ， 工程热物理， 2006， 硕士

【摘要】 含内热源可燃多孔介质普遍存在于我们的日常生活中，研究这类多孔介质内部的温度分布，找出其自燃规律，防止其储存和运输过程中自燃现象的发生，将其安全性定量化具有重要的现实意义。本文从热自燃理论出发，以煤粉、弹药为研究对象，对可燃多孔介质内部的热传导过程进行了全面系统的分析；数值模拟了这类典型介质内部的温度分布及影响因素，并实验验证了数值模拟所采用的模型的正确性。 由于微观结构的复杂性，目前对具有化学反应的可燃多孔介质内微观热量传递过程的研究仅局限于定性的分析。本文首先介绍了热自燃理论以及化学反应过程的动力学规律，分析了活化能、指前因子、反应热等化学动力学参数对温升的影响。 多孔介质的自燃着火现象可简化为一含内热源项的非稳态传热过程，本文在一定的简化条件下获得了内热源恒定时一维直角坐标、一维柱坐标、一维球坐标模型的解析解。由于解析解包含无穷级数，不能清晰的表达出温度变化趋势，又采用近似拟合法求得一维平板形煤粉堆积床内部的温度随时间和空间的分布曲线。 实际情况下内热源项均随温度发生变化，本文建立了以煤粉为研究对象的可变内热源一维直角坐标下的传热模型，获得了其内部的温度变化趋势。计算结果表明，内热源强度随温度变化时温度上升速率逐步加快，煤粉处于危险情况。计算了球形煤堆在夏季高温和冬季低温两种不同环境温度下内部温升情况。 模拟了二维柱坐标下弹药填充床内部的温度分布，分析了内热源项的变化规律，求解了环境温度对弹药内部温度变化的影响。比较了有限长和无限长圆柱形填充床内部温度分布，结果表明无限长圆柱内部最高温度上升速率比有限长圆柱温升快，按照无限长圆柱计算将是最坏的散热情况，这样的计算结果将具有更好的安全保证。弹药的型号不同，其化学动力学参数就不相同，内部的温升过程就不相同。活化能反映化学反应对所需要的能量输入大小，活化能越低反应越容易发生。指前因子大代表分子碰撞的几率大，温度上升就快。一般来讲，最危险的放热反应系统是具有低活化能且反应热很大的系统。计算表明，单基弹药内部最高温度比双基内部最高温度上升的快。讨论了对流换热系数、堆积尺寸、孔隙率等对弹药内部最高温度的影响。得出对流换热系数越小，堆积床外径越大、堆积越紧密，弹药内部最高温度上升的越快，越容易发生自燃着火。 实际弹药温升非常缓慢，在全尺寸上进行自燃过程的实验研究需要较长的时间，而且实验条件难以控制。在本项研究中，采用一小尺寸实验药粉填充床来代替实际弹药。实验采用恒壁温条件，测量结果表明壁面温度越高，弹药达到自燃的时间越短；实验测出的弹药内部最高温度变化趋势与同一壁面温度下数值模拟结果基本一致。 本文的研究结果，对建立符合实际存贮情况的可燃多孔介质传热模型具有很好的参考价值!更多还原

【Abstract】 This dissertation deals with the spontaneous combustion and ignition behavior of porous media stack. Combustible porous media with inner heat source is ubiquitous in our daily life. Research on such porous media’s inner temperature distribution, finding out the spontaneous combustion disciplinarian, avoiding self-ignite during the deposit and transportation and supervising the media’s security have very important meanings. This article bases on heat self-ignite theory, using coal and ammunition as investigate objects, systemically analyzed the heat exchange process in the combustible porous media. And it numerically simulates such representative media’s inner temperature distribution and the influence factors. Using experiment’s results validate the model’s validity used in the simulation at the end of this paper.Because of the microstructure’s complexity, the research on microcosmic transfer process with chemistry reaction in combustible porous media just limited in qualitative analysis at present. This paper introduces heat self-ignite theory and dynamics disciplinarian of chemistry reaction process at first, analyzes the influence of chemistry dynamics parameter (such as activation energy and frequency gene and reaction heat, etc) to temperature ascend.The self-ignite phenomenon of porous media can be predigested into an unsteady heat transfer process with inner heat source. In this paper, we obtained the theory results under Cartesian coordinate, pole coordinate and sphere coordinate with invariable inner heat source. However, the accuracy results always contain infinite series and they can’t express the temperature trend clearly.In practice the inner heat source changes along with the temperature. In this paper using coal parameter to establish Cartesian coordinate heat transfer model with changeable inner heat source and acquired inner temperature change direction. The simulation results show that when inner heat source changing with temperature, the inner heat ascend velocity increases gradually and coal is in danger circumstance. Spherical coal stack’s inner temperature distribution in high temperature circumstance (like summer) and in low temperature circumstance (like winter) are simulated in this paper.Then, ammunition stack’s temperature distribution under two dimensional poles coordinate is simulated, inner heat source’s change is analyzed, and environment temperature’s influence is calculated in the paper, compared finite and infinite long columelliform stack’s inner temperature distribution. The result shows that the highest temperature ascendance in infinite long column quicker than that in finite column. So using infinite long column to calculate is the worst emanate heat circumstance. Such results have the best safety guarantee. Different ammunition type have different chemistry dynamics parameters, and the temperature ascend process in ammunition is different. Activation energy reflects the needed input energy in chemistry reaction. The lower the activation energy is, the easier the chemistry to react. The bigger the frequency factor is, the bigger the collide odds between molecule is. Then the temperature will goes up quickly. Generally speaking, the most dangerous exothermic reaction system is such that has low activation energy and high frequency factor.Convection heat exchange coefficient, stack size and porosity’s influence to the highest temperature in porous media are also discussed in this paper. The results show that the smaller the convection heat exchange coefficient, the bigger the stack size and the smaller the porosity is, the quicker the temperature ascends in porous media and the easier to combust.In real ammunition temperature ascend is very slow. So spontaneous combustion experiment study with full size will take very long time, and the experimental condition is hard to control. In this paper using a small size experiment drug stack to instead of real ammunition experimented under constant wall temperature. The measure results show that the higher the wall temperature is, the shorter the ignite time. The experimental measure results about the highest temperature change in ammunition almost consistent with numerical simulation results under the same condition.更多还原