Bulk NMR Measurements of Spray Dynamics

Spray systems present unique challenges for fluid mechanics research due to their complex dynamics. Non-optical techniques such as synchrotron X-rays and magnetic resonance imaging (MRI) are promising measurement avenues for non-invasive studies of opaque or enclosed sprays. Previous MRI studies of sprays employed sophisticated pulse sequences possible only with an MRI scanner. In this work, we explore the potential of simple bulk NMR techniques, pulsed-field-gradient (PFG), time-of-fight (TOF), and dynamic magnetic resonance scattering to investigate spray dynamics in three distinct regions. A variable recovery delay was employed to filter signal contributions based on velocity. The PFG measurements of mechanical dispersion are the first of their kind to our knowledge, yielding dispersion coefficients in the range of 10^–4–10^–3 m²/s. Velocity measurements successfully detected velocities surpassing 30 m/s near the nozzle, with the flow slowing down to several m/s downstream. These techniques show potential for investigating spray dynamics and simple gradient requirements making them suitable for portable NMR applications and in situ measurements.