Wake galloping energy harvesting in heat exchange systems under the influence of ash deposition

Abstract

Since the fluid flows in heat exchange systems contain hydrokinetic energies, flow-induced vibration (FIV) energy harvesting technology can be potentially applied to collect electrical energy. Different from the applications in traditional scenarios, cylinder bluff bodies implemented in the heat exchange systems will inevitably suffer from ash deposition. This study proposes a wake galloping energy harvester to be used in heat exchange systems and focuses on investigating the effects of different ash deposition types on the energy harvesting performance. According to different ash deposition types, bell-shaped and horn-shaped cylinder bluff bodies are designed to consider the ash deposition effect. Wind tunnel experiments are conducted to investigate the performance of the wake galloping piezoelectric energy harvester (PEH) with different upstream ash deposit cylinders, at various space distances and under different wind speeds. The experimental results reveal that compared to the horn-shaped cylinder, the bell-shaped cylinder is more beneficial for energy harvesting. Among all tested cases, the optimal configuration is determined: the upstream cylinder is attached by bell-shaped ash deposition; and the space ratio between the upstream and the downstream cylinders is 1.5. The threshold wind speed of the optimal configuration is reduced and the maximum voltage output is improved by over 111%. It is learned that the two types of upstream ash deposit cylinders can both cause the quenching phenomenon to deteriorate the performance of the energy harvester. Guidelines based on the experimental results are provided to avoid the occurrence of the quenching phenomenon. Computational fluid dynamics (CFD) studies are conducted to reveal the underlying mechanisms to explain the experimental results. The CFD results corroborate that different ash deposit cylinders produce different wake vortices and the flow pattern changes with the space distance, which determines the dynamic response of the downstream cylinder.