Insights into Enhanced Thermal Performance: Visualizing Diverse Flow Patterns in Fe3O4/Water Pulsating Heat Pipes

Abstract

Abstract This paper presents the outcomes of an experimental study employing flow visualization techniques to examine diverse flow patterns within closed-loop pulsating heat pipes (PHPs) utilizing Fe3O4/water as the working medium. A high-speed digital camera was employed to capture intricate flow patterns under various experimental conditions to gain a precise understanding of the operational mechanism of the PHP. The empirical findings demonstrated that in the evaporating segment of the PHP, the prominent flow pattern involved the oscillation of liquid slugs and vapor plugs, driven by the generation and expansion of bubbles through nucleate boiling. The results indicated a shift in the primary flow pattern of a closed-loop PHP employing Fe3O4/water. This transition progressed from a bubble flow accompanied by slug flow characteristics to an annular flow pattern. Additionally, the visualization study showed distinct flow patterns in the PHP’s evaporator, adiabatic, and condenser sections when Fe3O4/water was used with varying heat inputs. Notably, the oscillatory flow behavior of Fe3O4/water, the chosen working fluid, exhibited greater activity in comparison to water. This distinctive flow behavior contributed to achieving heightened thermal performance efficiency for the Fe3O4/water system, attributed to its faster attainment of the annular flow condition.