Magnetic resonance imaging (MRI) is a non-invasive and non-optical measurement technique, which makes it a promising method for studying delicate and opaque samples, such as foam. Another key benefit of MRI is its sensitivity to different nuclei in a sample. The research presented in this article focuses on the use of MRI to measure density and velocity of foam as it passes through a pipe constriction. The foam was created by bubbling fluorinated gas through an aqueous solution. This allowed for the liquid and gas phases to be measured separately by probing the 1H and 19F behavior of the same foam. Density images and velocity maps of the gas and liquid phases of foam flowing through a pipe constriction are presented. In addition, results of computational fluid dynamics simulations of foam flow in the pipe constriction are compared with experimental results.
We have recently introduced a methodology to determine the average velocity and flow behavior index of laminar pipe flow of a power-law fluid using simple magnetic resonance (MR) techniques. In general, MR techniques are noninvasive and capable of working on optically opaque fluids. Knowledge of the average velocity and flow behavior index provides the information needed to reconstruct the flow velocity profile. However, as the flow velocity increases, the flow will begin to develop turbulence. For pipe flow of a particular fluid, the velocity profile is flatter in the center of the pipe at turbulent flow rates compared with laminar flow. An effective flow behavior index can approximate the time-averaged velocity profile, as the Reynolds number increases, as a fluid transitions from laminar to turbulent flow. Here, we show the results of testing the utility of such a simplification in monitoring that transition. For the present study, Reynolds numbers ranged from approximately 490 to 6800, which corresponds to flow rates of 200 to 2750 ml/min and average velocity of 5 to 80 cm/s. We found that visual inspection of the data would be sufficient to determine the state of the flow. With some external knowledge of the flow rate, the shape of the time-averaged velocity profile and eddy diffusivity can be estimated (and potentially also an average fluid particle acceleration).
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