深冷环路热管作为深低温区高效两相热传输系统，在地面和空间诸多工程实践中有着重要的应用。深冷环路热管传热能力及系统稳定性问题直接决定着热控系统热传输能力和运控性能。本文针对空间应用多重力场环境中深冷环路热管内部流动传热机理及系统失稳机制开展深入研究，以深冷环路热管系统级瞬态数值仿真和部件级冷凝传热数值模拟为主要研究手段，结合地面常重力实验和空间微重力飞行实验，深入分析深冷环路热管温度波动的规律、发生机制与条件，在此基础上提出相应的失稳抑制措施，为空间用深冷环路热管系统设计与在轨运控提供指导。

首先，从工程应用角度开展了气液两相热传输系统重力无关性表征与设计方法研究，确认了基于主导作用力机制的重力无关性准则可正确描述气液两相流重力无关条件，提出了针对气液 两相热传输管路及系统的重力无关性设计方法，将刻画重力无关临界条件的Bo数和Fr数准则转化为系统临界特征尺寸参数的计算与设计。此外，搜集和整理了不同重力条件下的气液两相流动摩擦压降的实验数据以及预测模型，评估了相应预测模型的预测精度及其对重力效应的表征能力；利用不同重力两相摩擦压降实验数据，在双流体同心环状流两相摩擦压降解析解基础上，采用遗传算法优化构建了一个显式计入重力效应的气液两相摩擦压降新模型，以满足空间应用系统设计中无法完全满足重力无关要求的情形对重力效应正确表征和高精度摩擦阻力预测的要求。

其次，基于深低温两相系统内部流动、传热及热力状态变化机理和深低温、微重力对两相系统热稳定性的影响机理分析，采用节点-网络法构建了深冷环路热管系统级瞬态仿真模型。与集中冷源式氖工质深冷环路热管地面超临界启动与运行实验数据以及SJ-20卫星搭载双冷板氖工质深冷环路热管地面和空间实验数据的详细比较发现，数值仿真结果与实验数据在时域和频域均具有优良的一致性，验证了模型对深冷环路热管超临界启动、稳态运行、瞬态变化以及微重力环境影响等方面均具有优良的预测能力。

第三，利用验证后的深冷环路热管系统级瞬态仿真模型，开展了典型参数影响下深冷环路热管运行性能的瞬态响应特性、扰动适应性的仿真分析，考察了热沉温度、充装压力、热负荷、寄生漏热等参数对系统超临界启动和运行性能的影响，从超临界启动成功的角度发现了最优充装压力的存在。

第四，从系统级和部件级数值仿真两方面，研究了重力对深冷环路热管运行性能的影响，揭示了重力影响下深冷环路热管系统表现出热管、热虹吸管和毛细蒸干（失效）等三种不同状态，揭示了三种状态发生机理并确定了相互间的分区边界；数值仿真了深低温工质管内冷凝流动与传热中的重力效应，分析了不同管径、质量通量及重力水平对氖工质冷凝流动过程中气液分布形态及传热特性的影响，揭示了深低温工质冷凝传热过程在不同重力条件下传热强化、传热恶化和重力无关三种状态的形成机理。

最后，通过深冷环路热管不稳定性实验数据和仿真结果分析，揭示了影响具有辅助回路的深冷环路热管系统稳定性的关键因素、影响模式及失稳机制，发现了深冷环路热管运行中的稳定运行、振荡衰减、振荡放大和周期振荡等四种运行状态特征；仿真分析了不同运行工况及系统结构参数对深冷环路热管系统温度振荡现象的影响，结合实验和仿真分析结果，提出了深冷环路热管失稳抑制方法。

Cryogenic loop heat pipes, as efficient two-phase heat transfer systems for ultra-low temperature regions, play a significant role in numerous terrestrial and spatial engineering applications. The heat transfer capability and system stability of cryogenic loop heat pipes directly determine the thermal transfer capacity and operational and control performance of thermal control systems. This paper conducts an in-depth study on the internal flow and heat transfer mechanisms of cryogenic loop heat pipes in the multi-gravitational field environment of space applications, as well as the system instability mechanisms. Employing system-level transient numerical simulations of cryogenic loop heat pipes and component-level numerical simulations of condensation heat transfer as the primary research methods, and combining terrestrial normal gravity experiments with space microgravity flight experiments, the paper thoroughly analyzes the patterns, mechanisms, and conditions of temperature oscillation in cryogenic loop heat pipes. Based on these findings, it proposes corresponding instability suppression measures, providing guidance for the design and in-orbit operational control of space-based cryogenic loop heat pipe systems.

Firstly, from the perspective of engineering applications, research on the characterization and design methods of gravity independence for gas-liquid two-phase heat transfer systems was carried out. It was confirmed that the gravity independence criterion based on the dominant force mechanism could accurately describe the gravity independence conditions of gas-liquid two-phase flows. A gravity independence design method for gas-liquid two-phase heat transfer pipelines and systems was proposed, transforming the Bo and Fr number criteria, which characterize the gravity-independent critical conditions, into the calculation and design of system critical characteristic scale parameters. In addition, experimental data on gas-liquid two-phase flow frictional pressure drop under different gravity conditions and prediction models were collected and organized. The prediction accuracy of these models and their capability to characterize gravity effects were evaluated. An explicit gas-liquid two-phase frictional pressure drop model accounting for gravity effects was developed using genetic algorithms based on the analytical solution of two-phase frictional pressure drop in concentric annular flows and experimental data on two-phase frictional pressure drops under different gravity conditions. This model meets the requirements for accurate representation of gravity effects and high-precision frictional pressure drop prediction in space application system designs that cannot fully satisfy gravity independence requirements.

Secondly, based on the analysis of the internal flow, heat transfer, and thermodynamic state change mechanisms in cryogenic two-phase systems, and the impact mechanisms of cryogenic and microgravity on the thermal stability of two-phase systems, a node-network method was used to construct a transient simulation model of the cryogenic loop heat pipe system. Detailed comparisons between the numerical simulation results and experimental data from ground supercritical startup and operation experiments of centralized cold source type neon cryogenic loop heat pipes, as well as ground and space experimental data of dual cold plate type neon cryogenic loop heat pipes carried by the SJ-20 satellite, showed excellent consistency in both time and frequency domains. This verified the excellent predictive capability of transient model for supercritical startup, steady-state operation, transient changes, and the impact of microgravity environments on cryogenic loop heat pipes.

Thirdly, using the validated transient simulation model of the cryogenic loop heat pipe system, transient response characteristics and disturbance adaptability of cryogenic loop heat pipe operational performance under typical parameter influences were analyzed. The effects of parameters such as heat sink temperature, charged pressure, heat load, and parasitic heat leak on the supercritical startup and operational performance of system were investigated. The existence of an optimal charged pressure for successful supercritical startup was identified.

Fourthly, the impact of gravity on the operational performance of cryogenic loop heat pipes was studied from both system-level and component-level numerical simulations. It was revealed that under the influence of gravity, cryogenic loop heat pipe systems exhibited three different states: heat pipe, thermosyphon, and capillary dry-out (failure), with the mechanisms of these states and the boundaries between them being identified. The gravitational effects in the condensation flow and heat transfer of cryogenic working fluid in pipes were numerically simulated, analyzing the impact of different pipe diameters, mass fluxes, and gravity levels on the gas-liquid distribution patterns and heat transfer characteristics during neon condensation flow. The mechanisms of heat transfer enhancement, heat transfer deterioration, and gravity independence in cryogenic condensation heat transfer under different gravity conditions were revealed.

Finally, through analysis of experimental data and simulation results on the instability of cryogenic loop heat pipes with auxiliary loop, the key factors, impact modes, and instability mechanisms affecting the stability of cryogenic loop heat pipe systems were revealed. Four operational state characteristics were discovered: stable operation, damped oscillation, amplified oscillation, and periodic oscillation. Simulation analysis of the effects of different operational conditions and system structural parameters on the temperature oscillation phenomena in cryogenic loop heat pipe systems was conducted. Combining experimental and simulation analysis results, methods for suppressing instability in cryogenic loop heat pipes were proposed.