超临界压力碳氢燃料在细小圆管内的流动换热及动态结焦特性机理研究

Due to the increasing dynamic heat load of the hypersonic aerospace vehicle, taking efficient cooling approaches to maintain a sustainable and safety operation is essential. On the view of heat transfer theory, the cooling efficient could be improved substantially via decreasing the temperature of the cooling air for the high temperature component under the same environment and cooling structure. This proposal schedules taking aircraft fuel as the coolant to cool the hypersonic incoming flow and realize the sufficient cooling for high temperature components consequently by the pre-cooler. Based on this technology background, the proposal mainly focuses on two scientific issues for hydrocarbon flowing though the different surface treated miniature tubes at the supercritical pressure: 1), coking and suppression mechanisms; 2), coking influencing mechanisms on hydrocarbon heat transfer and flow resistance characteristics, carried out by the experimental and numerical approaches.. On the basis of the coking, heat transfer and flow resistance results, the coking forming mechanisms as well as its impacting law on heat transfer and flow resistance will be revealed to enrich the theoretical analysis for thermal-liquid-solid coupled scientific issues, leading to the significant academic value. Moreover, the corresponding mathematic models will be built as well based on the investigation data to supply the sufficient support for pre-cooler design and evaluate its integral performance reasonably in the schematic design process. Therefore, the potential benefits of this proposal will lead to extensive technology applications and considerable engineering value as well.

高超声速空天飞行器由于受到不断升高的气动热负荷，需要通过有效的冷却途径来确保发动机可靠、安全运转。从传热学角度出发，在环境条件和冷却结构不变的情况下，通过降低高温部件冷却流体温度，可以大幅提高其冷却效果。本项目拟利用飞行器自带燃料，通过预冷器来降低高声速来流温度，实现高热负荷部件的有效冷却。在该技术背景下，采用数值模拟和实验对比研究方法，针对超临界碳氢燃料在不同表面处理细小圆管内结焦及抑制机理和结焦沉积对流动换热特性影响机理两个科学问题开展研究，获取结焦、流动阻力和换热数据，准确揭示不同表面结焦形成机理及其对流动换热影响的作用过程和规律，从而丰富热流固耦合科学问题的理论分析，具有重要的学术价值。同时，建立相应的数学模型，为预冷器的设计提供有力支撑，实现在方案设计阶段对其整体效能进行合理预估和优化，具有广阔应用前景和重要的工程应用价值。

本项目以高超声速空天飞行器及其动力系统为潜在技术应用背景，重点围绕动力系统热负荷日益升高的技术要求，采用飞行器自带燃料降低高速气流温度和高温部件冷却气流温度的技术方案，开展超临界压力碳氢燃料在细小圆管内的流动换热及动态结焦特性机理研究，主要研究内容、重要结果和关键数据如下：. 1）受管内近壁区流体与主流间流体温差变化而导致的热物差异影响，管内换热在内壁温接近拟临界温度点时发生强化，并且在主流温度达到拟临界点时出现换热恶化。不同压力下燃油在相同无量纲温度点（Tb/Tpc）热物性变化速率不同，导致表面传热系数随压力的增大先升高后降低。管壁金属材料催化作用对热氧化结焦影响明显，且管内表面催化结焦加速了液体中非催化结焦在管壁上的附着，导致结焦总量增大。. 2）不同表面处理抑制了表面金属对燃油热氧化结焦的催化作用，使得800℃预氧化表面处理可在短时间内（1h）有效降低结焦总量，但随时间的延长（5h），预氧化管表面氧化层不断被弱酸性燃油腐蚀，催化结焦抑制作用减弱，管内结焦量增大；电解钝化处理在降低表面粗糙度的同时抑制了金属催化作用，限制了催化作用结焦的产生和液体内非催化结焦在管壁的附着，在实验范围内均表现出良好的结焦抑制效果。. 3）结焦沉积反应导致的结焦附着在短期（30min）内增加管壁粗糙度，管内换热强化，但随着时间的延长，管内结焦热阻增大。三种表面处理管在峰值点的结焦热阻变化趋势相同，结焦反应对材料表面粗糙度的影响会使管内流动阻力压降增大。结焦表面粗糙度的影响随结焦附着而减小，结焦层厚度对管内流通面积影响增大，导致管内流动阻力增大。电解钝化处理在实验范围内可以有效降低流动阻力压降。拟合得到了管内换热与流动阻力特性随结焦反应持续时间变化规律的经验关系式，并通过计算溶解氧消耗的空间反应和结焦速率的壁面反应，建立燃油氧化结焦简化模型。