When integrating the gravity heat pipe with solar collector, namely solar gravity heat pipe (SGHP), the diameters of the evaporator and condenser are usually unequal, namely unequal diameter gravity heat pipe (UDGHP). Compared with the equal diameter gravity heat pipe (EDGHP), there are few studies focusing on operating pattern of the UDGHP. In this work, a numerical model for the UDGHP is firstly developed based on that of the EDGHP. Sensitivity analysis of the geometries of the evaporator and condenser, wall temperature, and working fluid on the filling and operating envelopes and the thermal resistance of the UDGHP is carried out under the criteria of local dryout and flooding limit. Particularly, comparisons between the UDGHP and EDGHP are simultaneously presented and discussed. The results reveal that the UDGHP has the expanded filling and operating envelopes and a smaller thermal resistance. Enlarging the inner diameter of the condenser, shortening the length of the evaporator, and raising the wall temperature can effectively improve the filling and operating envelopes and the heat transfer performance; lengthening the condenser improves the operating envelope and the heat transfer performance but shrinks the filling envelope. Variation patterns in the filling and operating envelopes and the thermal performance with different working fluids are disorders.

将重力热管与太阳能集热器集成时，即太阳能重力热管（SGHP），蒸发器和冷凝器的直径通常不等，即不等直径重力热管（UDGHP）。与等径重力热管（EDGHP）相比，关于UDGHP运行模式的研究较少。在这项工作中，UDGHP 的数值模型首先建立在 EDGHP 的基础上。蒸发器和冷凝器的几何形状、壁温、填充和运行外壳上的工作流体以及 UDGHP 的热阻的敏感性分析是在局部干涸和溢流极限标准下进行的。特别是，同时介绍和讨论了 UDGHP 和 EDGHP 之间的比较。结果表明，UDGHP 具有扩展的填充和操作包络线以及更小的热阻。加大冷凝器内径，缩短蒸发器长度，提高壁温，可有效改善充填和运行围护结构及传热性能；延长冷凝器可改善运行范围和传热性能，但会缩小填充范围。填充和操作范围的变化模式以及不同工作流体的热性能是混乱的。