Investigation on flow and heat transfer characteristics of phase change material slurry in twisted flat tubes

Against the backdrop of intensifying global energy supply-demand imbalances, enhancing energy utilization efficiency has become a critical challenge. As a phase change material with high energy storage density, ice slurry holds significant application value in HVAC systems. This research adopts the Euler-Euler two-fluid model to conduct a numerical investigation of the flow and heat transfer characteristics of ice slurry within twisted flat tubes. The analysis focuses on the effects of the straight section length ( W ) and the twist pitch length ( P ) of the twisted flat tube cross-section on flow patterns, resistance characteristics, heat transfer performance, and the ice particle phase change process. Results indicated that a helical secondary flow forms within the twisted flat tube, with its intensity increasing as both W and P decrease. The average friction factor ( f ) decreases with increasing flow velocity ( u ), increases with rising W and ice slurry volume fraction ( α ), and decreases with increasing P . The average Nusselt number ( Nu ) increases with rising W and u , decreases with increasing P , and shows a decreasing trend with increasing α . The concentration of ice particulates exhibits a monotonic decline along the streamwise path. Higher W values and lower P values promote the melting of ice particles. The comprehensive heat transfer factor ( PEC ) improves with larger W and smaller P , but declines with high α or excessive P . Finally, empirical correlations for f and average Nu are established, with prediction deviations controlled within ±10%, respectively. This study provides theoretical support for the structural optimization of twisted flat tube heat exchangers and the efficient application of ice slurry in thermal energy storage configurations.