Pulsating heat pipes having non-planar layouts (i.e. three-dimensional layouts) are preferable to the planar geometries when both gravity-independency and compactness are needed. A multi-turn three-dimensional closed loop pulsating heat pipe is tested on ground with the aim of investigating the effects of gravity by means of a quantitative description of the working modes occurring during its operation at different orientations. The viscous effects are furthermore considered by varying the condenser temperature. The studied device is made of an annealed aluminium tube (inner/outer diameter: 3/5 mm), folded in 14 turns and partially filled with methanol (volumetric filling ratio: 0.5). The channels are externally coated with a black high-emissivity paint, thus allowing the measurement of the outer wall temperature in the whole adiabatic section by means of a high-speed medium wave infrared camera. The wall temperature and the fluid pressure are instead monitored by means of thermocouples and pressure transducers directly inserted in the fluid stream. The pulsating heat pipe global performance is first assessed by evaluating the equivalent thermal resistance for every test case, showing that the studied three-dimensional layout is independent of gravity at high power input levels, where the equivalent thermal resistance settles around 0.25 K/W for almost every orientation. The thermographic acquisitions are therefore post-processed to estimate the heat flux locally exchanged between the working fluid and the channels wall, and the resulting local wall-to-fluid heat fluxes are statistically reduced for the quantification of the observed working modes, i.e. pure conduction, start-up, intermittent flow and full activation. At high heat loads to the evaporator, the gravity-independent behaviour of the device is found to be promoted by full activations, i.e. when a regular fluid motion is perceivable in every branch within the adiabatic section. The flow modes are also identified, pointing out that the local heat transfer behaviour is capable of discerning fluid oscillations from net fluid circulations. All the qualitative and quantitative pieces of data are comprehensively presented to give further information regarding the device dependency on the orientation. To deeper investigate the link between local and global quantities, the equivalent thermal resistance is finally compared with the statistical coefficients provided by the local heat transfer analysis.

当需要重力独立性和紧凑性时，具有非平面布局（即三维布局）的脉动热管比平面几何形状更可取。多圈三维闭环脉动热管在地面上进行了测试，目的是通过定量描述其在不同方向运行期间发生的工作模式来研究重力的影响。此外，通过改变冷凝器温度来考虑粘性效应。所研究的装置由退火铝管（内/外径：3/5 mm）制成，折叠 14 圈并部分填充甲醇（体积填充比：0.5）。通道外部涂有黑色高辐射涂料，从而可以通过高速中波红外热像仪测量整个绝热段的外壁温度。壁温和流体压力通过直接插入流体流中的热电偶和压力传感器进行监测。首先通过评估每个测试案例的等效热阻来评估脉动热管的整体性能，表明所研究的三维布局在高功率输入水平下与重力无关，其中等效热阻稳定在 0.25 K/W 左右几乎每个方向。因此，对热成像采集进行后处理，以估计工作流体和通道壁之间局部交换的热通量，并且由此产生的局部壁对流体热通量在统计上减少用于观察到的工作模式的量化，即纯传导、启动、间歇流动和完全激活。在蒸发器的高热负荷下，发现装置的独立于重力的行为通过完全激活得到促进，即当在绝热部分内的每个分支中都可察觉到规则的流体运动时。还确定了流动模式，指出局部传热行为能够从净流体循环中辨别流体振荡。全面呈现所有定性和定量数据，以提供有关设备对方向依赖性的更多信息。为了更深入地研究局部和全局数量之间的联系，