VENTURI TUBES WITH A 10.5 deg CONVERGENT ANGLE: DEVELOPMENT OF A DISCHARGE COEFFICIENT EQUATION

摘要

With gas production scenarios now frequently involving multiple gas fields, it is important that confidence in the measurements made by wet-gas meters is increased as this will ultimately help to increase the viability of marginal gas fields. There is an increasing desire to use Venturi tubes for wet-gas measurement, but to ensure accuracy in wet gas it is necessary to understand their behaviour in dry gas first. It was generally assumed until about eight years ago that the discharge coefficient at high Reynolds number in high-pressure gas would be constant and approximately equal to that obtained in water at Reynolds numbers greater than 2 X 10~(5). However, work carried out at NEL reported by Jamieson et al [1], data reported by van Weers et al [2], and subsequent work at NEL [3-7] showed that the performance of Venturi tubes in gas is very different from that in water. Some discharge coefficients in gas are greater than would have been expected by 3 per cent or even more. One factor which has an effect on how a Venturi tube performs is its internal shape. Work at NEL [8] showed that, of the designs evaluated, the optimum design was one with a convergent angle of 10.5 deg and sharp corners. This conclusion had been reached on the basis of 100 mm Venturi tubes; three Venturi tubes of this design of this diameter had been manufactured and tested [4,7]; so in the work described here it was desired to confirm those results with tests in larger and smaller Venturi tubes.