The use of super-long thermosyphons (TSs) is experimentally proved to allow a higher efficiency in extracting shallow geothermal energy. In this work, transient CFD (Computational Fluid Dynamic) simulation has been carried out for the super-long ammonia geothermal TSs, total length up to 54m, in order to understand their heat transfer behaviors for thermal performance optimization. The results show that due to the influence of hydrostatic pressure of liquid column, boiling initially starts at the liquid pool surface and then gradually moves downward in start-up. With the initial liquid-column height higher than 10m, the lower part of liquid pool in TSs would be throughout in quiescent state and make no contribution to heat extraction. At steady state, boiling zone in liquid pool shows a much higher heat transfer efficiency than that of partially-wetted area at the upper part of evaporator. Geothermal TS with 20% filling ratio of ammonia in evaporator, namely the initial liquid column height at 10m, has the best thermal performance under the simulation test conditions. For super-long geothermal TSs (>50m) using ammonia as working fluid, it is recommended to fill ammonia as much as possible, but the premise is that the initial height of liquid column must be controlled below 10m.

实验证明，使用超长热虹吸管（TSs）可以提高提取浅层地热能的效率。在这项工作中，已经对总长达54m的超长氨地热TS进行了瞬态CFD（计算流体动力学）模拟，以了解其传热性能以优化热性能。结果表明，由于液柱静水压力的影响，沸腾首先从液池表面开始，然后在启动时逐渐向下移动。当初始液柱高度高于10m时，TS中液池的下部将始终处于静止状态，并且对热量提取没有贡献。在稳定状态下 液体池中的沸腾区显示出比蒸发器上部的部分润湿区域更高的传热效率。在模拟测试条件下，蒸发器中氨的填充率为20％的地热TS（即初始液柱高度为10m）具有最佳的热性能。对于使用氨作为工作流体的超长地热TS（> 50m），建议尽可能填充氨，但前提是必须将液柱的初始高度控制在10m以下。