Date of Award:

5-2016

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Committee Chair(s)

Steven L. Barfuss

Committee

Steven L. Barfuss

Committee

Michael C. Johnson

Committee

Marvin W. Halling

Abstract

As the need to manage water resources increases, the ability to accurately measure use becomes crucial. In industry, measurement inaccuracies can cost either the
supplier or consumer large amounts of money or even result in a depleted resource. Generally, flow meters need a flow profile to be fully developed so to optimize
measurement accuracy.

In order to produce accurate measurements, most flow meters require a straight section of pipe immediately upstream of the meter. The straight pipe helps to develop the flow profile and produces flow conditions that are as ideal as possible. In many field installations, space restrictions lead to meters being installed with reduced straight pipe between a flow disturbance and the meter.

When describing the effect to a meters’ accuracy caused by a disturbance the term installation effects can be used. A flow disturbance can be anything that causes irregularities, swirls, eddies or turbulence to the flow profile including elbows, valves, and pumps. If any disturbance is placed upstream of a meter without enough straight pipe to fully develop an ideal flow profile, the meter may produce incorrect results.

Electromagnetic flow meters are referred to by several different names including: magnetic flow meter, mag meter or mag. The electromagnetic flow meter has grown in popularity in recent years as technology has improved and costs have decreased. Manufacturers commonly claim that their meters can produce highly accurate flow measurements, some as low as ±0.10%, with reduced upstream straight pipe requirements as low as 0 pipe diameters between a disturbance and the meter itself.

The results of this study provide quantified error associated with a partially closed butterfly valve on electromagnetic flow meter accuracy. The results show the effect of four valve openings (25%, 50%, 75%, and 100% open), at five locations downstream of the valve (1, 3, 5, 10, and 20 pipe diameters), and at two different meter orientations to the valve shaft. It was concluded in the study that twenty pipe diameters of length are required to produce accurate measurements (within the manufacturer’s specified accuracy) when a magnetic flow meter is installed downstream of a throttling butterfly
valve. Surprisingly, the largest effect to the meter’s accuracy unexpectedly occurred when the upstream butterfly valve was fully open and not when it was in a throttling position.

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