Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
STARTUP FLOW VISUALIZATION OF VISCOPLASTIC MATERIAL IN THE PRESENCE OF WALL SLIP
Submission Author:
Angel De Jesus Rivera Jimenez , PR , Brazil
Co-Authors:
Angel De Jesus Rivera Jimenez, Yamid José García Blanco, Eduardo Matos Germer, Admilson Franco
Presenter: Angel De Jesus Rivera Jimenez
doi://10.26678/ABCM.COBEM2021.COB2021-0599
Abstract
Viscoplastic materials are characterized by the presence of a critical stress value below which there is no flow, and a decrease of the apparent viscosity occurs when shear stress imposed is above this critical stress. Despite the complexity of viscoplastic materials, they are widely used in several industrials segments, such as polymer injection molding processes, food pumping, debris flow, cementing horizontal wells, and processes in the waxy crude oil industry. During shut down situations of the crude oil transportation caused by emergency or maintenance activities, the crude oil in rest exhibits a gel-like structure after a period of time. In order to restart the flow, high pressures are applied, which can cause risks of damage to the transport pipeline network and can compromise the operation. To prevent these risks, the pipeline dimensions are overestimated reflecting high infrastructure costs that sometimes make projects unviable. Therefore, an accurate prediction of the minimum pressure to restart the flow is necessary as an operational requirement. The objective of this experimental study is to investigate and visualize the startup flow of yield stress materials in the pipeline. The velocity profiles, the presence of plug structure and the solid-fluid transition are analyzed before and during the yielding of the fluid. For a better understanding of the flow dynamics of these materials, a test section of length 0.980 m with a circular cross-section of inner radius 0.011 m was attached to two reservoirs to control the inlet and outlet pressure. A 2D-Particle Imaging Velocimetry system is used as visualization setup. An aqueous ultrasound gel solution (25 wt%) is used as viscoplastic material. A previous validation stage was carried out using a glycerine solution as a Newtonian fluid. The validation test was performed in the laminar regime. The velocity profiles were compared with the analytical solutions for Newtonian fluid in a transient laminar flow regime. To verify the startup flow, constant pressure values were applied for a period of 600 seconds, and pressure measurements were obtained by pressure transducers located at the inlet and outlet of the test section. A relationship between the minimum startup flow pressure drop and velocity field evolution is observed. Also, the time required to restart the line blocked depends mainly on the applied pressure drop and the viscosity that decreases with time. Finally, it was observed that a slip velocity is presented during the restartup flow, which can be scaled as a power-law relation with the shear stress at the wall and the wall velocity gradient.
Keywords
Viscoplastic materials, Wall slip, PIV, Startup Flow
