Diffusion in Multi Component Mixtures

多组分混合物中的扩散

• 批准号: RGPIN-2015-05964
• 负责人: Saghir, Ziad
• 金额: $ 1.82万
• 依托单位: Ryerson University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=638707
• 关键词: Diffusion; Multi; Component; Mixtures

Thermal gradients are ubiquitous in human and industrial activities, and can induce a wide range of thermal transport phenomena, mass separation in multicomponent mixtures (thermodiffusion), or solute motion in solutions (thermophoresis). These phenomena are of practical interest in defining the composition of oil reservoirs, the replication and accumulation of short DNA fragments, or the design of microscale and nanoscale thermophoretic devices for the manipulation of small volumes of liquids or solutes in scales ranging from nano to micrometer. In subsurface hydrocarbon reservoirs, the temperature varies vertically and sometimes horizontally (i.e. there may be non-negligible horizontal gradients). Over time, some hydrocarbon components segregate towards the cold side and others towards the hot side of the reservoir due to thermodiffusion. Thermal segregation will also initiate molecular diffusion driven by concentration gradients and natural convection. As a result, it is crucial to determine the fluid compositional variation in the oil reservoir. Current models that are used in oil reservoir simulators are based on Fick’s law, which cannot account for these compositional interactions and the non-ideal behaviour of the species. The response of a suspension or a fluid mixture to a temperature gradient depends in a subtle and essentially unknown way on the molecular interactions. Understanding how these molecular interactions determine thermal transport is essential to advance the development of devices and processes of technological and industrial interest. An accurate molecular multicomponent diffusion model is needed to be able to predict this mechanism. We propose to measure experimentally these diffusion coefficients and introduce for the first time a molecular dynamics model combined with irreversible thermodynamic theory. Comparison between experimental and numerical results will help us develop an accurate molecular diffusion model. Such experimental measurements have been performed on board the International Space Station but sofar had a limited success in ground laboratory. This is due to the presence of convection, which creates mixing and therefore destroys the separation process. With a high cost and limited access to space experiment, an innovative experimental design to measure these diffusion coefficients in our laboratory for different average mixture temperature is proposed. This experimental approach requires a precise sample design to overcome the gravity effect (i.e. convection which leads to mixing). Succeeding in measuring the diffusion coefficients in laboratory will lead to an accurate molecular multicomponent diffusion model, which is in great needs in oil reservoir simulation.

热梯度在人类和工业活动中普遍存在，并且可以引起广泛的热传递现象，多组分混合物中的质量分离（热扩散）或溶液中的溶质运动（热泳）。这些现象在定义油藏的组成、短DNA片段的复制和积累或用于在从纳米到微米的尺度范围内操纵小体积液体或溶质的微米级和纳米级热泳装置的设计中具有实际意义。在地下碳氢化合物储层中，温度垂直变化，有时水平变化（即，可能存在不可忽略的水平梯度）。随着时间的推移，由于热扩散，一些烃组分朝向储层的冷侧分离，而另一些朝向储层的热侧分离。热分离也将引发由浓度梯度和自然对流驱动的分子扩散。因此，确定油藏中流体成分的变化至关重要。目前在油藏模拟器中使用的模型是基于菲克定律的，该定律不能解释这些成分相互作用和物种的非理想行为。悬浮液或流体混合物对温度梯度的响应以一种微妙的和基本上未知的方式取决于分子间的相互作用。了解这些分子间的相互作用如何决定热传递对于推动具有技术和工业意义的设备和工艺的发展至关重要。一个准确的分子多组分扩散模型是需要能够预测这种机制。我们建议实验测量这些扩散系数，并首次引入一个分子动力学模型结合不可逆热力学理论。实验结果与数值计算结果的比较将有助于我们建立一个精确的分子扩散模型。这种实验测量已经在国际空间站上进行，但在地面实验室中取得的成功有限。这是由于对流的存在，对流产生混合，因此破坏了分离过程。针对空间实验成本高、获取途径有限的问题，提出了一种在实验室内测量不同平均混合物温度下扩散系数的创新实验设计。这种实验方法需要精确的样品设计来克服重力效应（即导致混合的对流）。成功地在实验室中测定扩散系数，将有助于建立准确的分子多组分扩散模型，这在油藏模拟中具有重要的应用价值。