Experimental study of dispersed droplets in high-pressure annular flows

Local measurements were made in a droplet-laden vapor core in upward R-134a annular flow in a high aspect ratio vertical duct. These detailed measurem ents are unique in that they were performed at high pressures and low liqui d-to-vapor density ratios. Using a gamma densitometer, hot-film anemometer and laser Doppler velocimeter, profiles of void fraction, liquid droplet fr equency and droplet velocity were acquired across the narrow test section d imension. At relatively high pow's, the measured void fraction was highest near the wall, due to the thinning of the liquid film. The dir in the void fraction in rite vapor core at these flows suggests significant droplet ent rainment. The entrainment fractions for these refrigerant flows fall in the range measured for pressurized steam-water systems. The average drop size, calculated from direct measurements of void fraction, droplet velocity, an d frequency; compares favorably with previous experimental results from the literature. These data are useful for developing an improved understanding of practical two-phase flows, and for assessment of advanced nr two-fluid computer codes.