Experimental study of two-phase frictional pressure drop of steam-water in helically coiled tubes with small coil diameters at high pressure

The pressure drop characteristics of helical coils are important to the design optimization of helically coiled steam generators. Single-phase and two-phase flow pressure drop characteristics have been experimentally investigated in coiled tubes of inner diameters of 12.5 mm and 14.5 mm. The helical diameters of the helical coils are 180, 280 and 380 mm and the system pressure range from 2 to 8 MPa. The effects of flow and geometry parameters on two-phase frictional pressure drop multiplier are discussed. For flow parameters, the two-phase frictional pressure drop multiplier decreases with higher system pressure and is insensitive to mass flux and heat flux. For geometric parameters, the two-phase frictional pressure drop multiplier is insensitive to the curvature ratio under the investigated conditions. Comparison with correlations reported in the literature is performed. A single-phase friction factor correlation and a two-phase frictional pressure drop multiplier correlation for helical coils with small coil diameters at high pressure are proposed and give good agreements with the experimental data.