Enhancing the thermal effectiveness of beeswax-filled copper heat exchanger with multiple tubes and fins: A comparative analysis

This study experimentally evaluates the thermal behavior of a compact spiral/multi-tube heat exchanger incorporating beeswax as a natural phase change material (PCM), with particular emphasis on the effects of fin integration and heat transfer fluid (HTF) flow rate. The experimental findings indicated that the finned systems delivered improved thermal performance compared to unfinned counterparts. Notable reductions in charging and discharging durations were observed with the inclusion of fins. At 40 L/h, the finned heat exchanger (HX) reduced the charging time from 36 to 30 min and the discharging time from 66 to 56 min, corresponding to reductions of approximately 16.7% and 15.2%, respectively. As the HTF flow rate increased, the charging and discharging times decreased for both configurations. At 100 L/h, the charging time was reduced from 16 to 12 min and the discharging time from 36 to 28 min with the inclusion of fins, corresponding to reductions of 25.0% and 22.2%, respectively. Furthermore, thermal effectiveness during the charging phase ranged from 0.91 to 0.63 for the finned design, in contrast to 0.73 to 0.50 for the unfinned variant. Fins contributed to better thermal regulation by expanding the heat exchange surface and enhancing internal heat propagation within the PCM. Nonetheless, the benefits of fin integration were less pronounced at elevated flow rates, where convective heat transfer became more dominant. The comparison between the two HX configurations demonstrated that both the type of PCM and the direction of HTF flow significantly affected thermal storage and retrieval characteristics. Enhanced performance was particularly evident in the beeswax-filled HX at higher inlet temperatures and flow rates, despite the inherent thermal conductivity limitations of the natural PCMs. The compact spiral system allowed faster energy input but comparatively slower energy release, highlighting the importance of design consideration in thermal energy storage applications.