随着能源利用领域的发展，电子器件、紧凑式换热器、航天飞行器等部件的集成度逐渐提高。为了解决高温部件的散热问题，流动沸腾技术被广泛应用于大功率设备热管理领域，采用多孔涂层和多孔材料可以进一步提高换热效果。对于微多孔结构中的流动沸腾过程，由于孔隙-喉道结构复杂、流体流动方向随机性大，多孔结构内气固液三相作用规律尚不明确，换热面存在液体蒸干、壁温飞升、材料烧毁等风险，同时相变过程受环境压力的影响及多孔与外部来流的耦合作用机理有待进一步认识。本文围绕以上研究难点开展了系统的研究。 为揭示多孔介质内束缚水的运移规律及对相变过程的影响，搭建了微观模型可视化实验系统，获得了孔隙内的气泡行为与相变的传热及压降特性，量化了相变过程中束缚水的运输形式。实验发现毛细效应引起的液桥和薄液膜流动对冷却液向高温壁面的输送起着重要作用，且多孔结构参数会显著影响液桥附着力及薄液膜流动能力。结合理论分析，设计出一种由六种孔喉尺寸构成的不规则多孔结构，该结构可以增强传热系数，降低流动阻力，进而提高系统运行的稳定性。 为研究运行压力及物性变化的影响，对传统多相混合物模型进行了改进，提高了模型的收敛性及准确性，以模拟低压条件下相变区的非等温传热过程，并比较了相变条件下局部热平衡和非热平衡假设的异同点。对飞行器相变发汗冷却过程开展数值模拟，研究了热负荷和外部压力变化影响下的温度场瞬态响应规律，分析相变发汗冷却过程中冷却失效的原因，并提出提升冷却效率的方法。 为理解相变时孔喉结构中毛细力对流体的抽吸补充作用，开展微观模型可视化实验，认识到多孔内由相变引起的毛细力可以驱动流体自发的流动。在一定范围内，随着热流密度的提升和孔隙尺寸的减小，多孔内流体的毛细流动逐渐增强。数值计算了不同多孔参数对毛细流动极限的影响规律，认为毛细流动在非均匀热流加热条件下具有较好的负荷适应能力，验证了该方法应用于航天热防护的可行性。 为理解多孔出流与外流耦合规律，借助可视化实验，研究了粒径和来流速度比的影响。进而建立了多孔区和外部流场的耦合界面条件，并对高马赫数飞行器的相变发汗冷却过程开展模拟，研究了飞行高度、攻角和马赫数对相变过程的作用机制。认识到外流会影响多孔表面的压力分布和冷却液在多孔结构中的流动与分配，同时相变生成的气体会在多孔表面形成气膜，进而降低外流施加在边界的热流密度。

With the development of energy utilization, the integration of electronic devices, compact heat exchangers, aerospace vehicles and other components have gradually increased. To solve the heat dissipation problem of high-temperature components, flow boiling is widely used to carry out thermal management for heating surfaces and devices, and the utilization of porous coatings and porous structures can further achieve heat transfer enhancement. However, for flow boiling in porous media, due to the complex pore-throat structure and the large randomness of the fluid flow distribution, the mechanism of interactions among different phases at pore-scale is insufficient and unclear, which is a challenge to avoid dryout, over-temperature accidents, and burning-down of the materials. Besides, understanding the effect of operating conditions and the coupling mechanism of external flow is important and needs to be further studied. This dissertation systematically studies the above difficulties: To reveal the role of trapped liquid and its influence on phase change process in micro-porous structure, a pore-scale investigation with micromodel was built to obtain bubble behaviors and characteristics of heat transfer and pressure drop during flow boiling inside the pores, and quantify the transport mechanism of trapped liquid. The experimental results showed that the liquid bridge and liquid film flow caused by the capillary effect play an important role to supply coolant to the heating surface, and the pore-throat parameters can significantly affect liquid bridge stability and thin liquid film flow rate. Combined with theoretical analysis, a designed porous structure with multiple throat sizes was proposed to enhance the heat transfer coefficient, reduce the flow resistance, and improve the reliability of the cooling system. To study the effect of operating pressures and physical property changes, the traditional phase change model was improved to simulate boiling process in porous media, which improved the model convergence and accuracy. The non-isothermal heat transfer process in the two-phase zone at low pressures was studied, and the difference between the local thermal equilibrium and the local thermal nonequilibrium hypothesis was analyzed. The model was applied to simulate phase-changed transpiration cooling for aircraft, studied the effect of non-uniform heat flux and low pressure on dynamic response of the temperature field, analyzed the reason of cooling failure of thermal protection, and proposed effective methods to remove vapor blockage and enhance cooling efficiency. To understand spontaneous flow process of fluid in porous structures by capillary effect, a pore-scale experiment was carried out with lab-on-a-chip method. It was revealed that the pore-throat structure can cause spontaneous capillary flow of fluid driven by phase change process, and the increase of heat flux and the decrease of pore size can improve capillary flow rate within a certain range. Numerical simulation discussed the effect of porous parameters on the limit of spontaneous capillary flow, and regarded this capillary flow has a promising load adaptability under non-uniform heating conditions, which verifies its feasibility in the field of aerospace thermal removal. To comprehend the interactions between two-phase outflow from porous media and free flow in external region, a pore-scale investigation was carried out to study the coupling effect of internal and external flows, and learn the influence of particle size and velocity ratio on the phase chang process. Based on the experimental results, a boundary condition to study the coupling effect between the porous zone and the external flow field was built, and the phase-changed transpiration cooling with high Mach number was simulated to study the effect of altitude, angle of attack, and Mach number. It was regarded that the external flow can affect the pressure distribution on the porous surface, and change the flow rate inside the porous structures. Besides, the gas film generated by the phase change can effectively reduce the heat flux imposed on the porous surface by the high-temperature external flow.