Calibration of flowmeters in superheated and wet steam

The vapour mass fraction (dryness fraction) of wet-steam flows such as those encountered in the steam main of a power or process plant will rarely be less than 90. In flowmetering of high-quality saturated steam, the moisture content in the steam is allowed for by correcting the mass flow indicated by the steam flowmeter. Although there are a number of different ways of correcting the mass flow for water content, there is still doubt as to the methods used. In the work reported in this paper, three types of flowmeter were calibrated: first in superheated steam and then in an equilibrium wet-steam mixture to determine their wet-steam correction factors. The correction factors were found to be dependent on the types of flowmeter. For consistency with recommended practice, the method recommended by the 'Shell Flowmetering Engineering Handbook' (Ed. G. W. A. Danen, McGraw-Hill, 1985) can be used universally with reasonable accuracy provided a high-efficiency separator is placed upstream of the steam meter to increase the dryness fraction to above 95. © 1992