Magnetic Resonance Studies of sprays

喷雾是气体中的液滴的动态集合，可以通过将液体以非常高的速度喷射到气体中而产生，在气体中，液体被雾化，即分解成微小的液滴。喷雾用于在工业(涂层、清洁)和农业(浇水、输送养分、农药、杀虫剂)的表面分布材料，也用于分散液体和混合气体，应用于燃烧、采矿、消防、废物处理、化学、制药和食品工业。如果您的汽车使用汽油或柴油，那么您的汽车发动机效率取决于燃烧室中燃料的雾化程度。喷雾在自然界中也无处不在。过冷的水滴悬浮在空气中，冻雨，在与任何表面接触时冻结，造成重大经济损失：加拿大最大的自然灾害是1998年的冰暴，冻雨造成过多的冰层积聚，造成60亿美元的损失和12万公里的电线倒塌。这些降雨还对海洋和天空造成损害：由于飞机表面迅速结冰，它们对飞机极其危险。喷雾的许多特性还没有被很好地理解，因为它们可能很难测量。该项目提出了使用磁共振成像(MRI)研究喷雾的新测量技术，这是临床上常用的一种方式。由于其灵活性，MRI是一种非常强大的诊断工具；您可以使其对广泛的化学和物理参数敏感。常规光学技术使用光来研究喷雾。这对分离良好的液滴很有效，但由于液体量高而无法靠近喷嘴，而且由于喷嘴不透明，在喷嘴内部根本不起作用。磁共振成像不需要样本是透明的，因为它的信号直接来自样本体积。我们将开发新的MRI敏化技术来研究雾化过程和喷嘴内的流动。通过与喷雾技术专家的合作，这些结果将使人们更好地理解喷雾现象，并更有效地使用喷雾。核磁共振也将被用来更好地了解冻雨。光学技术在测量过冷液滴的温度以及区分冻结和未冻结液滴方面效率低下。另一方面，当水变成冰时，磁共振信号几乎消失，也可以对温度变化和液滴速度敏感。这些结果将有助于测试设备，以对抗地面冻雨和航空飞行中的结冰危险。在这个项目上，学生们将获得有用的研究经验。他们在开发新的实验方法和设计新的MRI技术方面的技能将在磁共振成像和材料科学的广泛领域中得到需求。

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.