A Study of Flow Downstream of a T-Junction and the Implications of its Effect (In Crude Oil Flow) on Water Droplet Size and Distribution

A laser Doppler anemometer (LDA) is used to measure velocity profiles and turbulence levels of water flow in the first few diameters downstream of a T-junction. The ‘vertical’ limb of the T-junction is half the diameter of the ‘horizontal’ limb, one end of which is blanked off. Flow passes from the smaller into the larger tube and LDA measurements of axial and tangential velocity components are conducted in the larger tube up to 3.75 diameters downstream of the T-junction at Reynolds numbers of 10.5 × 10⁴ and 7.42 × 10⁴. The pipe geometry is a commonly occurring configuration in crude oil pipelines and is of interest because of its possible ability to break up and mix water droplets to an extent sufficient for accurate grab sampling. LDA measurements of r.m.s. velocity fluctuations give information on the level of turbulent diffusivity and hence the maximum size of droplets that can be present in crude oil flow in the same geometry. A novel mathematical technique is used to interpolate between LDA measurements of mean velocity and to calculate the radial component of mean velocity. The three-dimensional velocity distributions thus formulated are used to predict water droplet concentration profiles downstream of the T-junction using the Segev approach—that is by solving numerically a differential equation for concentration of a contaminant under conditions of turbulent diffusion. Results are compared with field measurements in a similar geometry.