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Title: Swirling Flow Through Venturi Tubes
Author: Jeff Gibson, Michael Reader-Harris
Source: 2007 South East Asia Flow Measurement Conference
Year Published: 2007
Abstract: There is an increasing desire to use Venturi tubes for wet gas measurement, but to ensure accuracy in wet gas, their behaviour in dry gas must also be understood. Work carried out at TUV NEL reported by Jamieson et al 1, data reported by van der Weers et al 2, and further work have shown that the performance of Venturi tubes in gas at high Reynolds number is very different from that in water due to the static-hole error effect. Some discharge coefficients in gas are greater than would have been expected by 3 per cent, or even more. Another factor which has an effect on how a Venturi tube performs is its internal shape, and work has shown that, of the designs evaluated, the optimum design was one with a convergent angle of 10.5 and sharp corners 3,4. It exhibited more predictable behaviour than the design recommended in ISO 5167 5,6. Differential-pressure flowmeters are known to be affected by upstream disturbances such as valves and bends, and the next stage in evaluating the suitability of the new design for industrial gas flow measurement was to investigate its installation requirements. Computational Fluid Dynamics (CFD) was used to compute the effect of upstream bends on Venturi tubes with convergent angles of 10.5 and 21 for comparison with experimental data. Two cases were modelled: a single bend and an out-of-plane double bend. The results of the single bend models have been reported previously in Reader-Harris et al 7 and TUV NEL report 2005/225 8. The focus of this paper is on the results of the double-bend and further examination of the effect of swirl on discharge coefficient, C, using the axisymmetric approximation comparison is drawn between the results of single- and double-bend cases where appropriate.

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