Study of two-phase flow patterns and frictional pressure drop in helical and spiral coils

Experimental studies of flow pattern and pressure drop for air-water and R113 liquid/vapor flow in helical and spiral coils were conducted. Five test sections, namely, helical coils having a circular cross-section and three rectangular cross-sections of different aspect ratios, along with a circular cross-section spiral tube, were utilized in the study. Five sets of the flow pattern test data — helical coil vertical upflows for both air-water and R-113 in a circular cross-section tube, R-113 in a near-square cross-section tube, and spiral horizontal outward flow of both air-water and R-113 in a circular cross-section tube — are analyzed and compared with a modified Baker map, the Taitel & Dukler map, the Choe, Weinberg, & Weisman map, and the Uddin map. None of the maps are able to adequately predict both the helical and spiral coil test data. An empirical correlation of the slug-annular transition was developed for both helical vertical-up flow and spiral horizontal outward flow which gives good agreement with the test data. Three sets of the pressure drop test data — helical coil vertical upflows for both air-water and R-113 in a circular cross-section tube, and R-113 in a near-square cross-section tube — are analyzed and compared with homogenous and Lock hart-Martinelli models. All of them predict pressure drops only approximately in the slug and developing-annular flow regions. Empirical correlations were developed to calculate the critical Reynolds number and friction factors for R-113 helical coil vertical up-flow in both circular and near-square cross-section tubes.