A multiscale study of single-loop pulsating heat pipes: the effects of nanostructured surfaces, macro-geometrical design, and orientation configuration

This thesis investigates the single-loop pulsating heat pipe (SLPHP), the fundamental unit of a multi-turn pulsating heat pipe (PHP), with the dual objectives of enhancing its thermal performance and elucidating the underlying physics. While SLPHP devices offer greater geometric simplicity and predictability than their multi-turn counterparts, they typically exhibit lower heat-transfer efficiency. To address this, the present work adopts a bottom-up approach, connecting nanoscale phase-change phenomena to device-level design and operation. At the nanoscale, non-equilibrium molecular dynamics (MD) simulations are used to examine liquid–vapor transitions within engineered nanostructures, including parallel, looped, and cross nanowalls, as well as a random rough surface. These simulations reveal the competing roles of interfacial potential energy and atomic mobility in film boiling dynamics. At the macroscale, a novel triple-diameter SLPHP (TD-SLPHP) is designed, fabricated, and tested. Experimental results demonstrate that this configuration outperforms both regular and dual-diameter designs at moderate to high heat inputs. Furthermore, numerical simulations are employed to optimize its internal diameters. Finally, a systematic experimental study distinguishes the effects of frontal and sagittal inclination on a regular SLPHP, clarifying orientation-dependent behaviors that were previously unaddressed in the literature. Through this multiscale investigation, spanning from the nanoscale to the macroscale, this thesis delivers new strategies for enhancing SLPHP performance and provides a clearer understanding of their operational mechanics. Last but not least, I wish to express my sincere gratitude to Professor Bozzoli and Professor Cattani for their invaluable guidance and support throughout my PhD journey. Their insights and encouragement were essential to the completion of this work.