Final Report Summary - COOLING TECHNIQUE (Elaboration of an evaporative cooling technique with shear-driven liquid films)
The principal technological goal of the project was to elaborate an advanced evapourative cooling technique with shear-driven liquid films, which can be applied for cooling of a broad range of equipment with intense local heat eneration (high power electronics including space electronics devices, solid-state laser light sources, high power light-emitting diodes, radio frequency systems,...). The proposed research was aimed at achieving a fundamental understanding of the parameters and factors enabling high heat transfer rates in such a system.
Evapouration of drops is an efficient way to cool a heated surface by latent heat of evapouration when the drop changes phase. On the other hand, liquid drop is a simplest object to study the triple liquid-gas-solid contact line. The problem of the contact line is very important for a number of phenomena in the domain of fluid mechanics and heat transfer. Although there is a lot of investigations on contact line in the literature, there are only a few performed under different gravity conditions and uder intensive heating from the substrate.
In the project, the dynamics of contact line in a growing sessile liquid drop was studied under gravity level from 0 to 20 g. The experiments were conducted during ESA parabolic flight campaigns and also in the ESA large diameter centrifuge. Eleven different smooth and rough surfaces were used, with different contact angles (CA) and contact angle hysteresis (CAH). For the first time, the spreading of a sessile drop under the effect of gravity has been observed on surfaces with low CAH. For surfaces with high CAH, the contact line was pinned while CA adjusted for different gravity. Good agreement was obtained between the experiment and theoretical modelling. The dynamic advancing CA was found to increase with the gravity level.
Using the shadow technique, an experimental study of the evapouration of a liquid drop on different substrates with micro and nano coating, has been performed. It has been found that, depending on the substrate CAH, there are several possible scenarios of the drop evapouration dynamics. On substrates with small CAH, the evapouration rate increases with time and at the last stage can be several times the initial value.
From fundamental point of view, the results obtained contribute to basic knowledge of the problem of heat transfer. From practical point of view, they may eventually lead to creation of a new practical cooling technique with broad area of applications in the marketplace.
Evapouration of drops is an efficient way to cool a heated surface by latent heat of evapouration when the drop changes phase. On the other hand, liquid drop is a simplest object to study the triple liquid-gas-solid contact line. The problem of the contact line is very important for a number of phenomena in the domain of fluid mechanics and heat transfer. Although there is a lot of investigations on contact line in the literature, there are only a few performed under different gravity conditions and uder intensive heating from the substrate.
In the project, the dynamics of contact line in a growing sessile liquid drop was studied under gravity level from 0 to 20 g. The experiments were conducted during ESA parabolic flight campaigns and also in the ESA large diameter centrifuge. Eleven different smooth and rough surfaces were used, with different contact angles (CA) and contact angle hysteresis (CAH). For the first time, the spreading of a sessile drop under the effect of gravity has been observed on surfaces with low CAH. For surfaces with high CAH, the contact line was pinned while CA adjusted for different gravity. Good agreement was obtained between the experiment and theoretical modelling. The dynamic advancing CA was found to increase with the gravity level.
Using the shadow technique, an experimental study of the evapouration of a liquid drop on different substrates with micro and nano coating, has been performed. It has been found that, depending on the substrate CAH, there are several possible scenarios of the drop evapouration dynamics. On substrates with small CAH, the evapouration rate increases with time and at the last stage can be several times the initial value.
From fundamental point of view, the results obtained contribute to basic knowledge of the problem of heat transfer. From practical point of view, they may eventually lead to creation of a new practical cooling technique with broad area of applications in the marketplace.