Calibration of a Small Venturimeter for Wet Steam at Low Reynolds Number

Abstract

A device was required to measure the flow rate of steam through a small thrust bearing over the range 0–1·5 kg/h at pressures varying from 4·5 to 10 bar abs. and for steam quality varying from 0·75 dry to 100°C superheat. The ranges appeared to be outside those of existing instruments and not covered by existing design data for differential pressure devices; nor could the authors find any published work on the metering of wet steam at these low flow rates. Accordingly a 12·7-mm diameter venturimeter having an area ratio of 0·25 was made from stainless steel and has been calibrated for wet steam using a compounded differential U-tube manometer. The manometer and associated equipment is extremely simple and cheap to construct, and consists entirely of easily machined parts and standard pipe fittings. The results indicate that the discharge coefficient is very low and approximately a linear function of Reynolds number over the range tested.