Magnetic resonance imaging of sonicated fluids

当将高强度的声音应用于流体时，会发生许多有趣的事情。例如，流体开始从声源流出，这被称为“声学流”。如果声音足够大，液体看起来就像是在沸腾，伴随着嘶嘶声和气泡。这就是所谓的“空化”，即液体中气泡的生长、振荡和破裂。空化气泡的快速坍塌会在气泡内产生非常极端的物质条件，类似于太阳表面的情况，温度高于5000K，发出光(声致发光)。有关空化气泡动力学的信息对于更好地理解和控制声诱导现象至关重要。强声混合流体并增强其在多孔介质中的传播，这对采油和地面修复非常重要。超声波引发的化学反应和空化气泡内的极端条件将带来新的化工产品和新材料。在我的发现奖申请中，我提出了利用强磁场测量和控制超声波效果的新方法。这项拟议的研究有两个主要组成部分。(1)超声物理效应的磁共振成像表征，如空化和乳化，以及这些效应如何改变流体在多孔介质中的传播。第二部分，(2)将开发控制单泡悬浮和声致发光的方法。对于单个气泡的声致发光，如果在地球上进行实验，气泡的崩塌永远不是对称的：浮力会改变气泡的动力学。有两种方法可以纠正这种影响：在太空中进行实验(美国国家航空航天局计划今年在国际空间站进行这样的实验)，或者找到一个可以补偿重力的力。我们将使用非常强的磁场梯度来进行补偿。

When a high-intensity sound is applied to a fluid, many interesting things happen. For example, the fluid begins to flow away from the sound source, which is called "acoustic streaming". If the sound is strong enough, the liquid looks like it is boiling, complete with hissing sounds and bubbles. This is called "cavitation", the growth, oscillation and collapse of bubbles in liquid. Very fast collapse of cavitating bubble creates very extreme conditions of matter inside the bubble, similar to those on the surface of the Sun, with temperatures above 5000K and emission of light (sonoluminescence). Information on cavitation bubble dynamics is crucial for a better understanding and control of sound-induced phenomena. Strong sound mixes fluids and enhances their propagation in porous media, which is important for oil recovery and ground remediation. Ultrasound-induced chemical reactions and extreme conditions inside cavitating bubbles will lead to new chemical products and novel materials.   In my Discovery grant application, I propose new methods of measurement and control of the effects of ultrasound, using strong magnetic fields. The proposed research has two principal components. (1) Magnetic Resonance Imaging characterization of physical effects of ultrasound such as cavitation and emulsification, and how these effects modify propagation of fluids in porous media. The second component, (2) will be the development of methods of to control single bubble levitation and sonoluminescence. For single bubble sonoluminescence, the bubble collapse is never symmetric if the experiment is performed on Earth: buoyancy will alter the bubble dynamics. There are two ways to correct for this effect: perform the experiment in space (such an experiment is scheduled by NASA for the International Space Station this year) or find a force that will compensate gravity. We will employ very strong magnetic field gradients for this compensation.