The effect of surface tension on flow condensation in vertical small-diameter tube

The effect of surface tension on flow condensation in vertical small tube with inside diameter of 1-5 mm is compared with that of gravity and shear stress in different gravity environments at low Reynolds number, which is less concerned in former studies. The present study indicates that surface tension is the most important factor affecting flow condensation, but it is weakened by shear stress as decreasing tube diameter in a microgravity environment. In a normal gravity environment, body force is the dominant effect that is weakened by shear stress as decreasing tube diameter, while the effect of capillary pressure drop due to surface tension is enhanced. The work will be helpful in understanding the characteristics of heat pipe or capillary pumped loop (CPL) at low Reynolds number.