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Title: Effect Of Liquid On Orifice Meter Measurement Accuracy In Low Pressure Air
Author: R.K. Mcbrien
Source: 1999 International Symposium on Fluid Flow Measurement
Year Published: 1999
Abstract: The effects of small amounts of entrained water on orifice metering of low pressure air flows (58 kPaa) has been examined for a 101 mm, 0.61 beta ratio (b) orifice plate at an orifice flow Reynolds number of 1.3x105 . Using orifice flow correlations developed for dry gas flow 1, a measurable meter shift (MS) in predicted flow rate from dry gas conditions was observed for water to air mass ratios (z) ranging from 0.22% to 5.9 %. All observed shifts were positive, with some reaching a maximum and then decreasing as z was increased to greater values. The shifts were not as expected based on previous studies reported in the literature. It was found that the MS could depend on the location of the orifice temperature measurement in some circumstances (i.e. upstream or downstream of the meter). The unexpected MS trends were due to evaporation of the water when the air entering the test section was unsaturated. This was evident form the different trends observed in measured flow temperatures upstream and downstream of the orifice plate. Such trends should be used as an indication that phase change is occurring. These results illustrate the importance of accounting for phase change between the liquid and gaseous states of gas/liquid mixtures to properly characterize metering errors that may occur with orifice meters.

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