Evaporation enhancement for evaporative cooling systems

蒸发冷却系统的蒸发强化

• 批准号: RGPIN-2014-04197
• 负责人: MacDonald, Brendan
• 金额: $ 1.68万
• 依托单位: University of Ontario Institute of Technology
• 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=638412
• 关键词: Evaporation; enhancement; evaporative; cooling; systems

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.

冷却对于广泛的领域至关重要。目前，有两个领域的冷却对于实现性能和增长潜力至关重要：（1）微电子器件，其具有尺寸不断减小的组件，同时面临功率需求的增加和相应的散热需求，以及（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，其中大多数需要可能破坏环境的制冷剂。目前的技术无法满足不断增长的冷却需求，因此需要高效环保的技术。我们从自然中汲取高效冷却的灵感，人类的汗水就是使用蒸发液滴进行冷却的例子。蒸发可以通过利用在液体到蒸汽相变期间耗散的大量能量来提供非常有效的冷却。固着液滴由于其高的表面积与体积比而提供优于膜沸腾和池沸腾的优点，这有利于诸如蒸发的界面过程。利用固着液滴的蒸发冷却技术具有很大的潜力，然而，对蒸发过程和界面效应的作用仍缺乏充分的了解。更好地了解界面效应对蒸发的影响将有助于提高性能和效率，这在技术尺寸减小到微米和纳米尺度时尤为重要，界面效应变得更加重要。本研究计划研究称为Marangoni对流的界面效应，该界面效应是由液体-蒸汽界面处的表面张力不平衡引起的，并导致液滴内的流体流动。在某些情况下，马兰戈尼对流已经显示出显著增加蒸发速率，并且蒸发所需的大部分能量通过马兰戈尼对流沿着液滴的表面传输。增强的蒸发速率可用于改善冷却技术性能;然而，这种行为仍然知之甚少，并且基于液滴（尺寸、化学混合物）和基板材料的性质而波动。这项研究的目的是：（1）使用实验技术针对各种固着液滴尺寸、流体混合物和基底材料来量化Marangoni对流对蒸发速率的影响，（2）开发和验证蒸发过程的数学和数值模型，其包括Marangoni对流作为用于增加蒸发速率的方法的效果，及（3）应用研究结果，以开发具能源效益的蒸发冷却技术，并利用我们的模型进行设计及模拟。本研究计划旨在开发具能源效益、高容量及环保的蒸发冷却技术。使用现有技术冷却生活和工作空间对能源需求提出了很高的要求，特别是在发展中国家，但在加拿大温暖潮湿的夏季也是如此。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。我们将产生一个理解和量化的马兰戈尼对流的影响，在固着液滴的蒸发速率，这将是有价值的广泛的应用。这项研究将培养出精通热管理和能源领域的高素质人才，这对许多正在扩大的加拿大工业具有重要意义。