窄缝通道对流-热辐射耦合传热特性及其颗粒沉积行为的研究

The technology of narrow channel is of great significance for the improvement of EGR (Exhaust Gas Recycling) technology. Fundamental research on heat transfer characteristics of combined convection and radiation, behavior of particle deposition in narrow channel is conducted. The specific content includes: .The heat transfer characteristics of combined convection and radiation is accurately predicted with the help of the basic test and theory analysis combined with numerical simulation. The effects of narrow channel topological structure, working medium physical properties and channel material on combined convection and radiation will be studied. The influence of the structure for dividing the area on medium flow rate and pressure distribution is clarified. The evolution of the development process for the secondary flow is obtained in the passage. And the mechanism of heat transfer enhancement is revealed in narrow channel. On this basis, the mathematical model of particle deposition is acquired in narrow channel on the condition of combined convection and radiation. Moreove, it implements accurate prediction for the particle deposition rate, deposition distribution, deposition thickness and deposition morphology. The inherent law of mutual influence is revealed between the process of particle deposition distribution and heat transfer, flow in narrow channel. In the project, a method was put forward for comprehensive problem analysis and solving of gas-solid two phase flow on the condition of combined convection and radiation in complex structure of narrow channel. This project will be help for the upgrade of the EGR technology, control of exhaust emission and atmosphere pollution control.

管体窄缝通道技术是EGR技术变革升级的关键。项目对管体窄缝通道对流-热辐射耦合传热特性及其颗粒沉积行为进行了基础科学研究。具体内容包括：通过基础实验、理论分析结合数值模拟的方法，实现了窄缝通道内对流-热辐射耦合传热和流动特性的准确预测，明确了窄缝通道拓扑结构，介质物性，通道材质对热辐射-对流耦合传热的影响规律，阐明了管体窄缝分区数量对各区介质流量、压力分布等因素的影响关系，获得了通道内二次流的演变发展过程，揭示了窄缝通道强化传热的机理；并构建了热辐射-对流耦合传热条件下，管体窄缝通道内颗粒沉积的数学模型，实现对颗粒沉降速度、沉积分布、沉积厚度、沉积形态的准确预测，探明了颗粒沉积过程与通道中流动、传热之间相互影响的内在规律。项目研究为对流-热辐射耦合传热条件下，结构复杂的窄缝通道内，气固两相流综合问题的分析和解决提供了一定的思路，并有助于EGR技术升级和控制尾气排放，为大气治理贡献一份力量。

雾霾对人类健康和社会经济造成严重的危害。柴油车排放的尾气是雾霾形成的重要因素。我国中轻型柴油车尾气后处理技术占主流的是“冷却的EGR+DOC/DPF/POC（冷却的废气再循环+柴油氧化催化器/柴油颗粒过滤器/颗粒氧化催化器）”技术路线，简称EGR路线。.实现冷却EGR技术的关键装置就是EGR冷却器，部分废气经EGR冷却器冷却后，回到燃烧室。然而，面对未来排放更高标准，EGR冷却器仍有诸多严重缺陷。EGR率提升，致使通过EGR冷却器处理的废气流量、温度、烟尘颗粒量将大幅增加。由于其自身体积极小，且所处空间受限，因此管体窄缝通道技术随之引入提升散热性能。但是，在发动机高负荷条件下，流经EGR冷却器的部分高温废气热辐射作用显著，并且因其芯体中窄缝通道的高效散热致使通道内温度梯度加大，热泳沉降加剧，造成尾气中细颗粒更易沉积，甚至通道堵塞，导致EGR系统失效，从而威胁发动机安全。.本课题的研究目标是通过理论分析、数值模拟和实验验证相结合的方法，建立了准确预测周期性扩缩窄缝通道中的总体传热系数和阻力系数的对流-热辐射耦合传热数学模型；明确管体窄缝分区数量对各区介质流量、压力分布等因素的影响关系，揭示通道的数量、横截面形状、内切圆直径对通道内流动与传热特性的影响机理，并建立温度、压力分布模型，指导对管体通道的合理分区；察明了周期性扩缩窄缝通道结构内强化传热的机理，准确获取大量内部二次流信息，尤其是在不同的扩缩节点结构诱导下，主、次通道内流体混合相互作用的二次流发展的演变形态；建立热辐射作用下周期性扩缩窄缝通道内颗粒的沉积行为及其对传热的影响的数学模型，阐明颗粒大小、沉降速度、沉积分布、沉积厚度、沉积形态与通道中流动、传热之间的内在规律。.本课题从解决EGR冷却器面临的技术难题角度出发，提炼出基础科学问题，研究成果将有助于EGR技术的变革升级，控制柴油机尾气排放，为大气污染治理贡献一份力量。