Numerical investigation of flow and thermal performance in straight and convergent–divergent vortex tubes using CFD

Abstract This study investigates the flow characteristics and thermal performance of Straight Vortex Tubes (SVTs) and Convergent–Divergent Vortex Tubes (CDVTs) under identical operating conditions using computational fluid dynamics (CFD). A three-dimensional model with compressed air as the working fluid was simulated using the finite volume method and the RNG k–ε turbulence model. Grid independence was verified to ensure numerical reliability. Results show that while the straight tube (0°/0°) configuration achieves the highest instantaneous temperature separation (ΔT ≈ 48 K), its performance is highly sensitive to geometric variations and deteriorates with changes in diameter and length. In contrast, the CDVT with fixed 10° convergent and 6° divergent angles demonstrates superior cold outlet temperature reduction and vortex stability for shorter tube lengths (90–130 mm), where compactness and robustness are critical. These findings highlight that geometric modifications do not universally maximize ΔT but provide enhanced stability and efficiency in constrained geometries, offering valuable insights for designing compact, energy-efficient vortex-based cooling systems.