Study on the Influence of Axial Geometric Variations in the Hot-End Tube on Energy Separation Effects in Maxwell Structured Tubes

Maxwell structure tube is a special case of vortex tube, and the vortex tube is a further technical derivative of the Maxwell structure tube. Research on the vortex tube helps to gain a deeper understanding of the hot and cold separation phenomenon generated during the rotation of airflow, a process that involves the intersection of fluid mechanics and heat and mass transfer. This study systematically investigates the axial geometric variations of the hot-end tubes in Maxwell structured tubes (a type of special vortex tube) through computational fluid dynamics (CFD) simulations, thermodynamic analysis, and experimental testing. The focus is on analyzing their impact on energy separation and flow characteristics, aiming to enhance overall separation efficiency. At a lower cold mass fraction (e.g., 0.2), the temperature difference increases and energy separation is enhanced; at a higher value (e.g., 0.7), the separation effect weakens. Experiments show that the bulge section regulates tangential velocity and radial pressure gradient, thereby affecting separation efficiency. In a comparison of typical parameters, ( the ratio of the radius to the length of the waist drum)=3 yielded the best results, followed by =4.8, while =2.4 performed worst, indicating that a compromise design is key to enhancing performance. Additionally, discrepancies exist between experimental and simulation results, with CFD predictions for hot-end separation slightly underestimating measured values, suggesting that numerical methods still require optimization in turbulence modeling and boundary condition settings.