Boiling in Microchannels: integrated design of closed-loop cooling system for devices operating at high heat fluxes

电子设备、微过程和制冷系统等各种行业中使用的小型设备的当前发展和未来趋势，对从小区域去除较高热负荷的需求日益增加。在某些情况下，除非提供足够冷却的问题得到解决，否则根本不可能进一步发展。因此，从空气到液体的过程，特别是流动沸腾，以传递产生的高热流是唯一可能的前进方向。蒸发冷却不仅可以转移这些负荷，还可以提供更高的温度均匀性，因为工作流体可以（在精心设计的系统中）处于恒定的饱和温度。由于金属和硅等物质的微加工技术的发展，考虑微通道流动沸腾过程成为可能。然而，在这些微型热交换器在工业上得到更广泛的应用之前，仍有一些基本的流体流动和传热相关问题需要解决。将研究的具体挑战-在本质上是基本的和实际的-包括流动不稳定和不均匀分布，这是系统流形和外部电路之间相互作用的结果。这些可能导致流动逆转和干燥在热交换器与随后的热传递率急剧下降。对基本物理现象及其与工业设计的相关性的理解是焦点之一，也是拟议研究的主要挑战之一。其他参数的影响，如进口过冷，这不仅与微热交换器本身有关，而且与整体设计有关，将通过使用金属和硅微通道与材料/表面特性一起解决。建议的工作将包括仔细接触详细的实验，测量相关参数，如局部热通量，温度和压力，结合流动可视化，通过工业上可用的和专门开发和制造的传感器。研究小组不仅将开发或调整先进的仪器，以便在这些小尺度上进行精确测量，而且还将开发新的三维数值工具，能够捕捉极端复杂的物理现象，例如三重线（蒸汽-液体-固体）。这些技术不仅有助于阐明当前的现象，而且可以在热流和生物医学流的类似研究中找到广泛的应用。该提案汇集了两个由工业界（Thermacore, Selex Galileo， Sustainable Engine Systems和Rainford Precision）支持的从事微加工/传感器和两相流工作的学者团队，以解决一些关键的基本挑战，这些挑战将使这种冷却方法得到更广泛的采用，从而满足当前和未来的行业需求。拟议的研究还将对节能和环境足迹产生更广泛的影响，例如，通过对世界各地的数据/超级计算中心进行更有效的热管理，可以减少能源消耗并重新利用原本会被拒绝的热量。

Current developments and future trends in small-scale devices used in a variety of industries such as electronic equipment and micro-process and refrigeration systems, place an increasing demand for removing higher thermal loads from small areas. In some cases further developments are simply not possible unless the problem of providing adequate cooling is resolved. The progression from air to liquid and specifically flow boiling to transfer the high heat fluxes generated is thus the only possible way forward. Evaporative cooling can, not only transfer these loads but also offer greater temperature uniformity since the working fluid can be (in a carefully designed system) at a constant saturation temperature. The consideration of microchannel flow boiling processes has been made possible by developments in microfabrication techniques both in metals and substances such as silicon. However, there still remain fundamental fluid flow and heat transfer related questions that need to be addressed before a wider use of these micro heat exchangers is possible in industry. The specific challenges that will be researched - both fundamental and practical in nature - include flow instabilities and mal-distribution which are the result of interaction between the system manifolds and the external circuit. These can lead to flow reversal and dry-out in the heat exchanger with subsequent drastic reduction in heat transfer rates. The understanding of the fundamental physical phenomena and their relevance to industrial designs is one of the focal points and constitutes one of the major challenges of the proposed research. The effect of other parameters such as inlet sub-cooling, which again relates not only to the micro-heat exchanger itself but also to the overall design, will be addressed along with material/surface characteristics through the use of both metallic and silicon microchannels. The work proposed will include carefully contacted detailed experiments measuring relevant parameters such as local heat flux, temperature and pressure combined with flow visualization through industrially available and purposely developed and manufactured sensors. The research teams will not only develop or adapt advanced instruments for accurate measurements at these small scales but also develop new three-dimensional numerical tools capable of capturing the extremely complex physical phenomena at, for example the triple-line (vapour-liquid-solid). These techniques will not only help elucidate the current phenomena but can find wide application in similar research, both in thermal and biomedical flows.The proposal brings together two teams of academics working both in microfabrication/sensors and two-phase flow supported by industry (Thermacore, Selex Galileo, Sustainable Engine Systems and Rainford Precision) to tackle some of the key fundamental challenges that will enable a wider adoption of this cooling method hence meeting current and future needs in the industry. The proposed research will also have a wider impact on energy conservation and environmental footprint trough, for example, more efficient thermal management of data/supercomputing centres around the world that can lead to a reduction in energy consumption and reuse of heat that would otherwise be rejected.