Evaporation enhancement for evaporative cooling systems

冷却在许多领域都是至关重要的。目前，制冷对实现性能和增长潜力至关重要的领域有两个：(1)微电子设备，其组件尺寸不断减小，同时面临着电力需求和相应的散热需求的增加；(2)住宅和商业空间的空调，这与生产力和能源需求相关。有相对有限的冷却方法，其中大多数需要制冷剂，可以破坏环境。目前的技术跟不上日益增长的冷却需求，因此需要高效环保的技术。**我们从自然界中获取高效冷却的灵感，人类的汗液是利用蒸发液滴冷却的一个例子。蒸发通过利用液体到蒸汽相变过程中耗散的大量能量，可以提供非常有效的冷却。由于其高表面积与体积比，无柄液滴比薄膜和池沸腾具有优势，这有利于蒸发等界面过程。利用固体液滴的蒸发冷却技术有很大的潜力；然而，人们对蒸发过程和界面效应的作用仍然认识不足。更好地理解界面效应对蒸发的影响将导致性能和效率的提高，当技术的尺寸减小到微纳米尺度时，界面效应变得更加重要，这一点尤为重要。**本研究项目研究了一种被称为马兰戈尼对流的界面效应，它是由液-汽界面表面张力的不平衡引起的，并导致液滴内的流体流动。在某些情况下，马兰戈尼对流已被证明大大增加了蒸发速率，蒸发所需的大部分能量是由马兰戈尼对流沿着液滴表面传输的。提高蒸发速率可用于提高冷却技术性能；然而，这种行为仍然知之甚少，并且根据液滴的性质（尺寸，化学混合物）和衬底材料而波动。本研究的目的是：(1)利用实验技术量化马兰戈尼对流对蒸发速率的影响，包括不同大小的液滴、流体混合物和基材；(2)开发和验证蒸发过程的数学和数值模型，其中包括马兰戈尼对流作为增加蒸发速率的方法的影响；(3)通过生成设计并使用我们的模型进行模拟，将研究结果应用于开发节能蒸发冷却技术。**本研究项目旨在开发节能、高容量、环保的蒸发冷却技术。使用现有技术为生活和工作空间降温对能源需求提出了很高的要求，特别是在发展中国家，但在温暖潮湿的加拿大夏季也是如此。电子设备的冷却为新技术进入市场提供了机会，因为功率密度和性能受到组件过热的限制。我们将理解和量化马兰戈尼对流对固定式液滴蒸发速率的影响，这将对广泛的应用有价值。这项研究将培养出精通热管理和能源领域的高素质人才，这对许多正在扩张的加拿大工业具有重要意义。

Cooling is of critical importance for a wide range of fields. Presently, there are two fields where cooling is essential for realizing performance and growth potential: (1) microelectronic devices, which have components that are continually decreasing in size while facing an increase in power demands and corresponding need for heat removal, and (2) air conditioning for residential and commercial spaces, which is correlated with productivity and energy demand. There are relatively limited methods for cooling, most of which require refrigerants that can damage the environment. Current technology is not keeping pace with the rising cooling demands so there is a need for efficient and environmentally friendly technology.**We take our inspiration for efficient cooling from nature, where human perspiration serves as an example of using evaporating droplets for cooling. Evaporation can provide very efficient cooling by exploiting the large amount of energy dissipated during a liquid to vapour phase change. Sessile droplets offer advantages over film and pool boiling due to their high surface area to volume ratios, which are beneficial for interfacial processes such as evaporation. There is great potential for evaporative cooling technology using sessile droplets; however, there is still an inadequate understanding of the evaporation process and the role of interfacial effects. Better understanding of the influence of interfacial effects on evaporation will lead to improved performance and efficiency, which is especially crucial as technology decreases in size to the micro- and nano-scales where interfacial effects become more important.**This research program investigates an interfacial effect known as Marangoni convection, which is caused by an imbalance of surface tension forces at a liquid-vapour interface, and results in fluid flow within a droplet. In certain circumstances Marangoni convection has been shown to substantially increase evaporation rates and a majority of the energy required for evaporation is transported by Marangoni convection along the surface of a droplet. The enhanced evaporation rates can be used to improve cooling technology performance; however, this behaviour is still poorly understood and fluctuates based on the properties of the droplet (size, chemical mixture) and the substrate material. The objectives of this research are to: (1) quantify the influence of Marangoni convection on evaporation rates using experimental techniques for various sessile droplet sizes, fluid mixtures, and substrate materials, (2) develop and validate mathematical and numerical models of the evaporation process, which include the effects of Marangoni convection as a method for increasing the evaporation rates, and (3) apply the findings to develop energy efficient evaporative cooling technology by generating designs and performing simulations with our models.**This research program aims to develop energy efficient, high capacity, and environmentally friendly evaporative cooling technology. Cooling living and working spaces using current technology places high demands on energy requirements, particularly in developing countries, but also in warm and humid Canadian summers. Cooling in electronic devices presents an opportunity for new technology to enter the market since power density and performance are limited by the overheating of components. We will generate an understanding and quantification of the influence of Marangoni convection on evaporation rates in sessile droplets, which will be valuable for a broad range of applications. This research will produce highly qualified personnel who are proficient in the thermal management and energy fields, which are significant for many expanding Canadian industries.