Experimental investigation of the ice-melting behavior of a fractal microtube bundle heat exchange element

The continuously increasing power density and transient heat loads in compact electronic systems pose challenges for thermal management, underscoring the need for effective thermal energy storage devices that can serve as thermal buffers. In this study, a monolithic cast three-dimensional fractal microtube bundle (FMB) heat exchange element was developed to promote ice melting. The tested element integrates 16 branched microtubes sharing a common inlet and outlet, and each branch has an inner diameter of 0.9 mm and a wall thickness of 0.165 mm. The results show that increasing the flow rate from 20 to 100 ml/min significantly accelerated melting, reducing the complete melting time of ice layer. During the melting plateau, the average heat transfer rate generally increased with flow rate, although the enhancement became less pronounced at higher flow conditions. Increasing the inlet temperature from 16 to 23°C markedly improved the thermal performance, with the average heat transfer rate during the melting plateau increasing from approximately 7.4 W to 13.1 W. The pressure drop increased nonlinearly with flow rate. The fitted experimental correlation of pressure drop was used as the primary reference because it better represents the realistic hydraulic behavior of the actual device. Additional discussion based on baseline comparison and numerical analysis indicates that the thermal advantage of the fractal design should not be interpreted as a purely conduction driven geometric effect. Instead, its performance should be understood from a combined perspective involving distributed heat transfer, natural convection, hydraulic penalty, flow uniformity, and manufacturability. The present results provide experimental and mechanistic support for evaluating the performance of a single FMB heat exchange unit under the tested conditions.