CFD evaluation of pipeline gas stratification at low fluid flow due to temperature effects
AbstractIt has been found through experiments at Southwest Research Institute that temperature
differences between the gas and wall of the pipe through which the gas is flowing can
greatly influence the gas flow in the pipe line and give different velocity magnitudes at
the top and bottom half of the pipe. The effect on the flow is observed to worsen at low
fluid flow and high temperature differences. This effect has been observed by ultrasonic
flow meters which measure the chord average gas velocity at four heights across the pipe.
A significant variance in chord averaged velocities is apparent at these conditions. CFD
analysis was performed. Low flow velocities of 0.1524 m/sec, 0.3048 m/sec and 0.6096
m/sec and temperature differences of 5.5oK, 13.8oK and 27.7oK were considered. When
these conditions were imposed onto the three different geometries, it was seen that the
heating caused increased errors in the ultrasonic meter response. For the single elbow and
double elbow pipe configurations, the errors were below 0.5% for constant wall
temperature conditions but rose to 1% for sinusoid varying wall temperature conditions.
The error was seen to increase as the axial velocity became more stratified due to
momentum or temperature effects. The case of maximum error was noted for the double
elbow geometry with sinusoid wall temperature condition where a swirl type of flow was
noted to create localized velocity maxima at the center of the pipe. This part of the pipe
was barely touched by the ultrasonic meter acoustic path giving maximum error of 1.4%.
A thermal well was placed in the path of the gas flow in the pipe to observe the
temperature response on the surface of the thermal well. It was noted that the thermal
well surface temperature differed by 1.4% for most cases with gas velocity below 0.6096