Development of Correlations for Pressure Drop in Vertical Helical Tubes with Non-Boiling Two-Phase Air/Water Flow: An Experimental Study

Helical tubes have a tightly wrapped construction that is very efficient and provides excellent stability for managing two-phase flows. They also exhibit good thermal performance. With the increasing use of two-phase flows in helical tubes across many applications, it is crucial to further investigate the thermal and entropic characteristics of these flows in those helical tubes. This work aims to explore the hydrodynamic characteristics of helical tubes experimentally. The study tested different coil tube sizes by passing a two-phase air/water flow through them. To achieve this goal, a vertical helical tube with varying coil sizes is used. Water and air are specifically guided into the helical pipe, with the water and air mixture flowing downward and upward after being thoroughly mixed in a mixing chamber. The primary variable assessed is the pressure decrease. The collected experimental findings are evaluated to develop a correlation for pressure loss, with multiple linear regression being the primary focus of this work. The results indicate that decreasing the coil diameter results in reduced pressure drop in downward flow and increased pressure drop in upward flow. The maximum pressure drop ratio is around 1.25 in a downward flow and 1.63 in an upward flow. The highest pressure drop value is about 352 mbar for the coil of 100 mm diameter in downward flow and 541 mbar for the coil of 180 mm diameter in upward flow.