An Experimental Study of Fibre SuspensionFlows in Pipes using Nuclear MagneticResonance Imaging

Abstract: This study deals with fibre suspension flows through cylindrical pipes. Thepresent work aims at measurements of opaque flows, which are common inindustries. Nuclear magnetic resonance imaging (NMRI) and ultrasound velocimetryprofiling (UVP) were employed as non-invasive and optic-independenttools to measure the velocity profiles. As a first experiment, a paper-pulp suspensionflow through a sudden contraction and expansion was investigated.The results show the NMRI technique can be used to measure the stronglyunsteady flow such as separated regions though the MR signal is attenuateddue to the turbulence in the flow. The flow loop had however an insufficientinlet length which caused asymmetric profiles at the test section. As a secondexperiment, a flow loop which provided fully developed flows at the test sectionwas designed. After that, the velocity profiles of rayon-fibre and micro-spheresuspension flows were measured by the NMRI and the UVP independently.In principle, these two techniques measure the different velocities of the fibresuspensionflows, i.e. the velocity of the water and the fibre. In dilute suspensionflows, where the velocities of the two phases were assumed to be thesame, the velocity profiles were in good agreement. This shows the validityof the two measurement techniques. However, it should be pointed out thatthere is a limitation of the current UVP method for highly concentrated flows.The velocity profiles obtained by the UVP at high concentrations seems notto represent physics while the NMRI is not affected by the concentrations. Itis argued that the advances of the NMRI for the measurement of the highlyconcentrated flows.