Sampling of High-Quality Wet Steam from Steam Mains Operating at 11·4 Bar Pressure

Abstract

A venturi device was employed to strip and entrain liquid from the wall of a 3 in (7·5 cm) diameter steam main prior to isokinetic sampling. By injecting heated water into dry steam the wetness fraction was controlled between 1 and 5 per cent. Venturi convergence half-cone angles of 20, 30, 40 and 50° were employed and steam flow rates varied from 360–730 kg/h (800–1600 1b/h). Observations were made of the distribution through the test section of static pressure, recovered temperature and film thickness (for pressure 3·8 bar (55 1b/in² absolute) only). Sampling across a diameter showed that under the most advantageous conditions the ratio, aggregate mass of entrained water: mass of injected water did not exceed 23 per cent. The optimum venturi half-cone angle lay between 40 and 50°. While capable of further development, the stripping-sampling principle seems unlikely to lead to significant improvements in wet steam sampling for quality.