Análise do efeito da compressibilidade no reinício do escoamento de fluido tixotrópico

Abstract

The objective of this work is to analyze the compressibility influence on start-up flows of a thixotropic fluid, using also two simpler fluid models: Newtonian and Bingham plastic. The problem is formulated as a horizontal opened pipeline filled with a steady fluid, which may be submitted to a constant pressure or flow rate in order to start-up. Two models are evaluated: a compressible and an incompressible one. The governing equations of the problem are solved numerically by computational algorithms, written in FORTRAN and MATLAB. The models parameters are fit to rheometric test results of an oil from the pre-salt brazillian region. For newtonian fluids, the compressibility effects are attenuated by the imposition of a pressure ramp on the pipe inlet, while for Bingham fluids, these ramps are not so efficient. For the thixotropic fluid, higher elasticities and lower equilibrium times minimize the compressible effects for a constant pressure on the pipe inlet. For a constant flow rate, for a thixotropic fluid, higher elasticities also minimize the compressible effects, and lower equilibrium times accelerate the start-up process, while also decreasing the pressure peak.