Heat transfer augmentation using collapsible tube-induced pulsating flow

This study investigates the enhancement of heat transfer rates using a simple passive pulsation mechanism facilitated by a collapsible tube (CT). A comparative analysis between the collapsible tube and a rigid tube is conducted at various Reynolds numbers ($Re$) to understand the impact of pulsation on the thermal and flow characteristics. The results show that the CT-induced pulsation significantly enhances the heat transfer rate, with an observed increase ranging from 70% to 50% at lower $Re$ (581 to 1597) with a corresponding Strouhal number ($Sr⪆0.2$). However, the enhancement diminishes at higher $Re$ beyond 1597, characterized by a lower pulsation frequency ($Sr⪅0.15$), reducing from 44% at $Re$ = 1742 to 23% at $Re$ = 2323, as compared to the rigid tube case. Additionally, the thermohydraulic performance index (TPI) is assessed to quantify the efficiency of heat transfer rate relative to pressure losses in the collapsible tube system. Proper Orthogonal Decomposition (POD) analysis is employed to extract key flow structures and characterize the pulsation dynamics. The POD results reveal that the dynamic behaviour of the collapsible tube introduces energetic intermittent coherent structures in the flow field, which are absent in the rigid tube case, contributing to enhanced mixing and more efficient heat transfer. These findings suggest that employing a collapsible tube offers a practical strategy for significantly improving the heat transfer rate in various engineering applications without the need for complex active control systems.