BOIL-MODE-ON is set within the context of a continuous miniaturisation of electronics components resulting in an ever increasing power density request. All of that energy is turned into heat to be dissipated through dedicated thermal management systems. The ability to dissipate these large amounts of heat while keeping the operating temperatures below prescribed thresholds is becoming critical to many applications ranging from integrated circuits, to X-ray medical equipment, and airplane avionics.
Classical air or liquid cooling methods have become inadequate for the most demanding recent applications. These limitations have spurred the transition from single-phase cooling solutions to two-phase thermal management systems. The heat transfer coefficient attainable can be dramatically enhanced by the use of two-phase systems employing boiling. The basic underlying idea is simple: nucleate vapour bubbles in the liquid in contact with the hot surface and take advantage of the latent heat of evaporation associated with boiling. Its implementation, however, faces a number of challenges, hindering the transition from laboratory research to commercial products.
The most fundamental difficulty is represented by the intrinsically multiscale nature of the boiling phenomenon: the large-scale features of the process — like the overall heat transfer, the flow pattern and the total pressure drop — are in fact strongly influenced by the small-scale characteristics such as the frequency of bubble nucleation, their size, and the release rate from the hot surface. Probably, the most elusive subprocess of boiling heat transfer, and nonetheless the most influential, is the boiling inception, namely, the very first stage of bubble formation, occurring at sub-micron length scales. The bubble nucleation rates (i.e. the number of bubbles formed per unit time and surface area), their spatial distribution on the hot surface, and the mean first passage times (i.e. the time to be awaited to observe a nucleation event), are necessary quantities in most of the semi-empirical models of boiling heat transfer, but difficult to be accessed via experiments.
BOIL-MODE-ON met the urgent need of a synergic effort on developing suitable theoretical models, specialised numerical simulations and accurate experiments, to make a real breakthrough on the understanding of the detailed mechanisms underlying the boiling inception at hot surfaces. The aim of the project is to investigate two of the major controlling mechanism of the nucleate boiling onset process: 1) the wetting properties of the hot surface; 2) the gas content dissolved in the liquid. The quantitative prediction of these effects is a daunting task, and remained an open problem before BOIL-MODE-ON.
