Numerical analysis and experimental study of two-phase flow pattern and pressure drop characteristics in internally microfin tubes

Abstract

Microfin tubes with internal structures exhibit superior thermo-hydraulic performance, making them indispensable in systems such as air conditioning, chemical industry, and heat pumps. Despite their widespread application, research on microfin tubes has predominantly concentrated on single-phase flows. The heat transfer coefficient of phase change heat transfer is much higher than that of single-phase heat transfer. The higher heat transfer coefficient enables micro finned tubes using phase change heat transfer to significantly improve heat transfer efficiency while reducing equipment size. The understanding of gas-liquid two-phase flow characteristics is crucial for heat and mass transfer rates and pressure drop. This study examines the two-phase flow patterns and pressure drop characteristics within microfin tubes, considering variables such as two-phase Reynolds number (200≤Re ≤ 600), gas void fraction (0.3≤ζ ≤ 0.55), tube inner diameter (2.5≤d ≤ 5 mm), helix angle (0°≤β ≤ 36°), and microfin count (20≤Ns ≤ 60) through both experimental and numerical approaches. The findings reveal that the inlet Reynolds number and microfin count exert negligible effects on bubble dimensions and morphology. As the gas void fraction and helix angle increase, the gas-liquid interfacial profiles become more symmetric. The influence of changes in bubble length and gas void fraction on bubble velocity can be ignored. When the helix angle is 18°, friction resistance factor in the liquid column region is the minimum of 0.04. The friction resistance factor in the liquid column region decreases with the increase of two-phase Reynolds number and microfin count, and decreases with the decrease of gas void fraction and tube inner diameter.

Keywords

• Internally microfin tube
• Gas-liquid flow
• Bubble flow pattern
• Friction factor