Thermal performance and visualization of dual-diameter channel pulsating heat pipes additively manufactured through stereolithography

As two-phase passive heat transfer devices, pulsating heat pipes (PHPs) have attracted widespread research interest for their potential to enhance heat dissipation and contribute to energy-efficient thermal management. This study experimentally assesses the thermal behavior and flow-characteristics of PHPs fabricated using Stereolithography (SLA) additive manufacturing technology. The investigation focuses on PHPs with dual-diameter channels, also called non-uniform channels, in three configurations: 2-turn center-heated, 10-turn center-heated, and 10-turn end-heated. Experiments were performed in vertical and horizontal orientations using acetone, except in one test with deionized (DI) water for performance comparison. For baseline comparison, tests were also conducted on uncharged PHPs. Results reveal that 2-turn PHP failed to initiate startup in the horizontal orientation, while all 10-turn PHPs started successfully, emphasizing the importance of increasing turns, even with a capillary-enhanced dual-diameter channel. The 10-turn center-heated PHP demonstrated orientation-independent operation with the lowest thermal resistance of ∼4.7 K/W, slightly outperforming end-heated cases. With DI water, the 10-turn PHP reached 121 °C evaporator temperature at 38.5  W. Flow visualization was conducted to capture fluid movement throughout the PHP channels for 10-turn PHPs in both orientations, revealing differences in flow stability, oscillation amplitude, and liquid distribution, particularly emphasizing the influence of initial fluid distribution on startup in vertical orientations. Evaluation of effective thermal conductivity indicates conventional methods overestimate it for polymer-PHPs by disregarding axial-conduction through heat sources and sinks. A refined methodology is proposed for improved accuracy. These insights pave the path for optimizing polymer-based PHPs for thermal management applications requiring low-mass, low-cost, or electrically insulating solutions.