Chapter 8 - Pulp flow visualization using NMR imaging

Abstract

This chapter discusses the pulp flow visualization using nuclear magnetic resonance (NMR) imaging. The problems involved with visualizing pulp flow are those that arise while investigating the flow of most opaque materials, including suspensions. When using the most common flow visualization or measurement techniques, such as laser Doppler anemometry, opacity effectively limits the maximum concentrations at which the experiments can be performed. NMR imaging, on the other hand, is a non-invasive technique that, among other things, allows velocity measurement in systems where classical techniques are not suitable either because of opacity or the presence of a solid phase. This technique is explored to observe the flow of cellulose fiber suspensions undergoing steady pressure-driven flows in tubes. NMR imaging is based on the paramagnetic properties of the nuclei. Atomic nuclei are characterized by states that are inherently quantum mechanical in their behavior. In an NMR imaging experiment, signals are obtained by having radio frequency pulses and magnetic field gradient pulses interact with the spin system positioned in a static magnetic field.