Visualization of two-phase flow through microgrooved tubes for understanding enhanced heat transfer

Though widely used, questions remain as to the mechanisms by which micro-fin or microgrooved tubes enhance heat transfer performance. In this work, new experimental liquid film thickness profiles in adiabatic, air–water flow through clear tubes with 20 microgrooves at three different helix angles are presented. These results correlate well with the asymmetrical temperature measurements and heat transfer coefficients seen by previous investigators. Important observations include increased wall wetting for a given flow condition, decreasing influence of the grooves with increasing gas velocity, and a rotational redistribution of the liquid film by helical grooves, though without indication of a swirling behavior.