Magnetic Resonance Studies of sprays

喷雾是气体中液滴的动态集合，它可以通过将液体以非常高的速度喷射到气体中而“雾化”，即分解成微小的液滴。喷雾器用于在工业（涂层、清洁）和农业（浇水、输送养分、杀虫剂、杀虫剂）的表面上散布材料，也用于分散和混合液体与气体，应用于燃烧、采矿、消防、废物处理、化学、制药和食品工业。如果你的汽车使用汽油或柴油，你的汽车发动机效率是由燃料在燃烧室的雾化决定的。

Sprays are dynamic collections of droplets in gas that can be made by ejecting liquid at a very high speeds into a gas where it “atomizes”, i.e., breaks down to tiny droplets. Sprays are employed to distribute materials over surfaces in industry (coating, cleaning) and agriculture (watering, delivery of nutrients, pesticides, insecticides), and are also used to disperse and mix liquids with gases, with applications in combustion, mining, fire protection, waste treatment, chemical, pharmaceutical, and food industries. If your car runs on gasoline or diesel fuel, your car engine efficiency is determined by the atomization of the fuel in the combustion chamber. Sprays are also omnipresent in nature. Supercooled suspensions of water droplets in air, freezing rains, freeze upon impact with any surface, causing significant economic damage: the largest natural disaster in Canada was the Ice Storm of 1998, with $6 billion in damages and 120,000km of power lines downed due to excessive ice accumulation caused by freezing rains. These rains also cause damage on the seas and in the skies: they are extremely dangerous to aircraft due to rapid ice formation on aircraft surfaces. Many of sprays' properties are not well-understood because they can be quite difficult to measure. This project proposes new measurement techniques to study sprays using Magnetic Resonance Imaging (MRI), a modality commonly employed in clinics. MRI is a very powerful diagnostic tool due to its flexibility; you can make it sensitive to a wide range of chemical and physical parameters. Regular optical techniques use light to study sprays. This works well for well-separated droplets but fails close to the nozzle due to high amounts of liquid, and does not work at all inside spray nozzles because they are not transparent. MRI does not need a sample to be transparent because its signal comes directly from the sample bulk. We will develop new MRI sensitization techniques to study atomization processes and flows inside nozzles. The results, via a collaboration with spray technology experts, will lead to a better understanding of spray phenomena and more efficient uses of sprays. MRI will also be used to get a better understanding of freezing rains. Optical techniques are inefficient in measuring supercooled droplets' temperature and discriminating between frozen and unfrozen droplets. MRI signal, on the other hand, virtually disappears when water turns to ice and can also be sensitized to temperature changes and droplet speeds. These results will be useful for testing equipment to fight freezing rain on the ground, and in-flight icing hazards in aviation. Working on the project, students will gain useful research experience. Their skills in developing novel experimental approaches and designing new MRI techniques will be in demand in wide areas of Magnetic Resonance Imaging and materials science.