MRI measurements of sprays
- 1. University of New Brunswick, Physics, Fredericton, Canada
- 2. Spraying Systems Co., Spray Analysis and Research Services, Wheaton, IL, United States
Fundamentally, sprays are defined as dynamic collections of droplets dispersed in a gas [1] and are used in many industrial and agricultural applications such as: manufacturing processes, fuel injection, painting, and crop protection. Furthermore, "Sprays are among the most intellectually challenging and practically important topics in fluid mechanics" [2] and provide a complex environment for improved understanding and research.
A quantitative measurement is essential for understanding processes of spray formation and dynamics. There exists a wide range of measurement techniques to characterize sprays, from gravimetric to laser Doppler anemometry to X-rays, which provide detailed information on spray characteristics in the "far-nozzle" region (>> 10 diameters of the nozzle). However, traditional methods are limited in their ability to characterize the "near-nozzle" region where the fluid may be inside the nozzle, optically dense, or incompletely atomized.
Magnetic Resonance Imaging presents potential as a non-invasive technique that is capable of measuring visually inaccessible fluid in a quantitative fashion. In this work, MRI measurements of the spray generated by ceramic flat-fan nozzles (Spraying Systems Co.) were performed. A wide range of flow speeds in the system (0.2 - >30 m/s) necessitated short encoding times. A 3D Conical SPRITE [3] and motion-sensitized 3D conical SPRITE were employed, with 0.47x0.3x0.3 mm voxel resolution. The signal from water inside the nozzle was well-characterized, both via proton density and velocity measurements. 28+/-4.7 m/s speeds were measured outside the nozzle, with images corresponding to expected flat-fan spray patterns up to 3 mm away, the droplet formation region. Integration over this region showed a steady signal loss with distance, as the liquid atomized into droplets.
The results demonstrate the potential of MRI for measuring sprays in areas inaccessible by other means, leading way to an experimental corroboration of spray formation models.
[1]. ASTM E1620 - 97(2012). Standard Terminology Relating to Liquid Particles and Atomization
[2]. T.D. Fansler, S.E. Parrish. Meas. Sci.Technol. 26 (2015) 012002.
[3]. M.Halse et al JMR (2003) 219-229.