Experimental study on dryout characteristics of steam-water flow in vertical helical coils with small coil diameters

Highlights: • Dryout characteristics in helical coils with small coil diameters are investigated. • A partial dryout phenomenon exists because of the geometry of helical coils. • The effects of flow parameters on dryout quality are discussed. • The effects of geometric parameters on dryout quality are analyzed. - Abstract: Helically coiled heat exchangers have been widely used in industrial applications. The goal of this study was to understand dryout characteristics of steam-water flow in vertical helical coils with small coil diameters. Experimental investigations were performed in helical coils of 12.5 and 14.5 mm inside diameters. The coil diameters were 180, 280 and 380 mm. Experimental results were presented for the effects of flow parameters and geometric parameters, tube diameter and coil diameter, on dryout characteristics in helically coiled tubes. The results indicated that a partial dryout region exists because of the geometrical characteristics of the helically coiled tube, and secondary flow has great influence on critical dryout quality. For flow parameters, increase in mass flux increases dryout quality and increase in heat flux or system pressure decreases dryout quality. Dryout characteristics are also significantly influenced by the geometric parameters. The dryout quality increases with increasing hydraulic diameter and decreasing coil diameter. None of the available dryout correlations in the literature are able to predict the dryout quality well in helical coils with small coil diameters under the investigated experimental conditions.