When there are obstructions in a pipe and there is insufficient straight run to deliver a fully developed flow profile to the thermal flow meter, a flow conditioner can recreate an optimum profile.
A flow meter’s performance is dependent upon the flow profile of the media entering the instrument. The desired flow profile is referred to as a fully developed flow profile where the profile is symmetrical in the pipe, and the center line velocity, when in turbulent flow, is 1.2 times the average velocity. This flow profile will naturally develop with sufficient straight run; a distance of 15 to 25 pipe diameters downstream of a single elbow is typically sufficient.
Longer lengths of straight run are recommended for various upstream flow obstructions. Table 1 gives recommended amounts of straight run for different flow obstructions commonly encountered. Downstream distances are not as critical as upstream distances; a distance of generally 5 pipe diameters is adequate for most piping configurations.
In some installations the pipe layout does not permit this amount of straight run. In these cases the straight run recommendations can be reduced by using Sage’s flow conditioning plates or flow conditioner.
Built in Flow Conditioning
In some designs such as Sage’s in-line flow body, the flow conditioning is designed and built into the thermal mass flow meter. In these cases the upstream distances ahead of the flow body shown in the table should be maintained.
These dimensional relationships are used in Sage Metering’s calibration facility. Installing the flowmeter utilizing these same dimensions will provide the expected and repeatable flow profile at the sensors.