Test facilities

Diagnostic techniques


Boiling flow in microchannels

micro nano engineering


Flow instabilities pose a major concern for flow boiling in micro-channels. Large pressure fluctuations arise due to the rapid evaporation and growth of vapor bubbles following nucleation, often resulting in reverse flows. Stability control of the flow boiling process is, therefore, crucial in implementing micro-channel cooling devices and to allow further miniaturization. Despite instabilities during flow boiling have been studied extensively in large diameter tubes, similar studies in micro-channels are sparse and are mainly based on linear and non-linear stability analysis, which, in turn, cannot be validated due to the lack of extensive experimental data under stable boiling conditions.

Methods have been currently suggested to stabilize flow boiling in micro-channels based on the introduction of a flow constrictor at the entrance of the channel or the introduction of artificial nucleation sites on the channel wall. On the other hand, hydrophobic surfaces have been reported to tend to trap air when the liquid enters the channel, hence providing more active nucleation sites, while experimental studies confirm that wettability affects heat transfer characteristics in the micro-channel and that an improvement in wettability leads to more efficient heat transfer.

In our work, we consider to artificially alter surface wetting properties to stabilize the nucleate boiling flow. Systematic investigations will be conducted making use of structured surfaces and of proper cooling liquids, which, in turn, allow improve pump requirements and, therefore, to consider additional implementation of cavities together with pressure drop elements.