Mechanism investigation and model assessment of methane flow condensation in minichannels based on numerical simulation

Abstract

Cryogenic refrigerants represented by methane differ significantly in thermophysical properties from working fluids at ambient temperature. Thus, examining their small-scale heat transfer and flow characteristics is essential for designing compact condensers within the cryogenic field. The numerical simulation of methane condensation in minichannels is conducted, and the process of phase-change mass and energy transfer is investigated by programming. Detailed condensation flow field information is obtained, and surface tension and gravity influences are elucidated. Synergy analysis indicates that the synergy near the tube wall still needs to be improved. Heat transfer performance is proved to be dependent on the relative significance of turbulence intensity and condensate film thickness. The tube inclination exerts a more noticeable influence on the condensation heat transfer for large diameters, which is supported by the dominance of gravity in the condensation heat transfer mechanism at larger diameters. At higher vapor quality and mass flux, the heat transfer enhancement governed by surface tension is more significant. The condensate at the bottom is mainly formed by the accumulation of condensate sliding off the tube top driven by gravity as the diameter increases, reducing the heat transfer region. The mass flux augments the frictional pressure drop more noticeably at high vapor quality. The prediction performance of empirical correlations is evaluated, and all the selected correlations underestimate the frictional pressure drop of methane. Moreover, the figure of merit analysis demonstrates that the pressure drop produced by diameter reduction is more substantial than heat transfer enhancement, suggesting the requirement to assess the pressure drop loss in practical applications.