(142w) Stereo-PIV Measurements of a Single Phase Flow in a Pipe Separator

Eyitayo A, AFOLABI and J.G.M LEE

School of Chemical Engineering and Advanced Materials,

University of Newcastle upon Tyne, Newcastle, UK.

     e-mail: e.a.afolabi@ncl.ac.uk

Today, cylindrical cyclones are recognised as an effective and economical alternative to the conventional vessel type separators in the Petroleum and Chemical industries. Cylindrical cyclone, also refer to as pipe separator is characterized as being simple to fabricate, low cost and robust separation devices with no moving parts.  Despite these advantages, the hydrodynamic flow behaviour within the cylindrical cyclone is found to be turbulent, highly anisotropic and multiphase in nature.  A 30-mm ID laboratory test facility of Gas-Liquid-Liquid pipe separator was designed, fabricated and installed. Although it was designed for the partial separation of a water-air-oil mixture at a higher water content and less than 10% oil content by volume, a single phase flow investigation using water was carried out to establish appropriate turbulence models before investigating the more complex Gas- Liquid-Liquid multiphase flow.

Stereoscopic Particle Image Velocimetry (S-PIV) was chosen for this study; because of the cyclone flow field is unsteady and highly three-dimensional with flow reversal. For each plane, the mean velocity fields and turbulence quantities were measured. The single phase flow experiment was run with a water flow rate of 196cm³/s. The outlets were restricted with rubber bungs such that the percentage water as a fraction of the inlet mass flow was 60% through the air outlet, 33% through water rich outlet and the balance through the oil rich outlet. The measurements were conducted for a turbulent water flow at three measuring planes along the vertical axis of the cyclone. The mean velocity fields were computed with Tecplot software by averaging a sequence of valid vector fields at each measurement location within the plane.

The experimental data presented in the form of contour and graphical plots for all the three axial positions are extracted along the y=0section in the separator. The velocity profiles shows greater fluctuations near the region of the inlet and this indicates higher mixing and separation. Then, the flow becomes more stable and less turbulent in other regions far away from the inlet.

At all axial positions, it is observed that the tangential velocity increases as we move away from the center of the tube, reaches a maximum and then drops close to the wall due to wall friction. In addition, the tangential velocity data shows a combination of a forced vortex near the center and a free vortex toward the wall of the cyclone. The swirl intensity decays as the axial distance from the inlet location increases. At the inlet section, forced vortex extends over 75% surface area of the separators’ plane and decreases to 67% and 50% at the planes below and above the inlet section respectively. However, free vortex occupies 50% surface area of the separators’ plane above the inlet and decreases as we move down the pipe separator axis. This means, surface area occupied by forced vortex decreases as we move away from the inlet section. However, free vortex increases as we move from the bottom to up the separator axis. A comparison of the tangential velocity profiles at three axial positions shows that the magnitude of the mean tangential velocity decreases as we move away from the inlet section towards the outlets.

The axial velocity fields shows two distinct regions, an upward flow near the center and a downward flow near the wall. Reverse flow occurs in the central region, and the magnitude of the reverse flow and the area occupied by it decreases as swirl decays. Axial velocity profiles at plane below the inlet reveals a combination of both downward and upward flow patterns at the wall and center of the tube respectively. However, at Z=295mm above the inlet, there is no negative axial velocity at all x-axis coordinates. This means, axial velocity is directed upwards at all x-axis. 

The radial velocity profiles show an irregular flow pattern of outward and inward directed flow pattern. The magnitude of the radial velocity decreases as the flow moves towards the outlets.