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Title: An Improved Model For Venturi-Tube Overreading In Wet Gas
Author: Michael Reader-Harris, Emmelyn Graham
Source: 2009 North Sea Flow Measurement Workshop
Year Published: 2009
Abstract: Venturi tubes are commonly selected for the measurement of wet-gas flows. Reasons for this include their physical robustness to withstand erosion and the impact of liquid slugs at high velocities, familiarity with their use and the availability of standards for their use in dry-gas conditions. The presence of the liquid causes an increase in the measured differential pressure and results in the Venturi tube over-reading the actual amount of gas passing through the meter. This over-reading is usually corrected using available correlations derived from experimental data to determine the actual gas mass flowrate. This trend is observed in all differential-pressure meters. The flowrate of the liquid, which can be a combination of water and hydrocarbons, is normally determined by an external means such as from test separator data, tracer experiments or sampling etc. Information on the liquid flowrate and density is necessary to use the correlations. The correlations currently available for correcting the over-reading of Venturi tubes have been derived from a limited set of data and may only be suitable to cover restricted ranges of Venturi tube parameters, for example, a specific diameter ratio. Use of correlations outside the conditions used to define them can result in large errors in the calculation of the gas mass flowrate. This paper describes a new Chisholm/de Leeuw-type model for the over-reading, which covers a broader range of Venturi parameters such as diameter ratio and pipe diameter. The model also accounts for the behaviour of the over-reading with different liquids.

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