Effects of pipe elbows and tube bundles on selected types of flowmeters

Abstract

This paper presents experimental results for the decay of pipe elbow-produced swirl in pipeflows and its effects on flowmeter measurement accuracy. Experiments include the decay of swirl produced by single and double elbow configurations for pipe diameter Reynolds numbers of 10 4 to 10 5 using water in a 50 mm diameter facility at NIST in Gaithersburg, MD. Results show that different types of swirl are produced by the different piping configurations. The swirl decay is found to be dependent on the type of swirl and the pipe Reynolds number. At high Reynolds number very long lengths of straight, constant diameter pipe are required to dissipate the single eddy type swirl that is produced by the two elbows out-of-plane configuration. Without flow conditioning, it is concluded that the specifications of upstream pipe lengths in the current flowmetering standards may not be sufficient to achieve the desired flow metering accuracy. Experimental results are also presented for the effects produced by tube bundle-type flow conditioners. These results show shifts in orifice meter discharge coefficients that are both positive and negative depending upon pertinent conditions. A range of orifice geometries, Reynolds numbers and meter locations are studied and explanations are put forth to explain these shifts. Results are also presented for a specific type of turbine meter. These show meter factor shifts that are also both positive or negative depending upon the type of swirl pattern entering this meter. An example is given in which the insertion of a tube bundle flow conditioner between a single elbow and the turbine meter produces a larger disturbance to the meter factor than would occur without the conditioner.