High-resolution high-speed void fraction measurements in helically coiled tubes using X-ray radiography

Helical coil heat exchangers are known for their superior transfer, compactness and robustness against thermal expansion compared to systems with straight pipes. Due all these benefits, they became quite popular in the last few decades various industries such as pharmaceutical, chemical or nuclear. Generally, used a single-phase environment evaporation taking place on shell side. However, most of steam generator designs adopted advanced nuclear reactors, two-phase mixture flows upward within vertically oriented helical coils. In addition, physical phenomena inside tubes differ significantly from those pipes due inherent centrifugal torsion effects. To improve computational models predict hydraulic performance generators, experimental characterization identification different flow patterns coils essential. present paper, high-resolution measurements void fraction distribution an adiabatic air–water were conducted transparent helically coiled acrylic pipe by means high-speed X-ray radiography at ambient conditions. Various based features probability density function estimates, profiles over height cross-section temporal evolutions identify characterize regimes. A total 13 presented this classified into six regimes, namely: bubbly, plug, wavy, slug, slug-annular annular flow. The obtained regimes accordance regime characterizations transition criteria already reported literature.