Fundamental study on micro-layer forming process in nucleate boiling: 1st year summary

by Mr Lubomir Bures (PSI)

Thursday 12 Dec 2019, 14:00 → 15:00 Europe/Zurich

OFLG/402 (Paul Scherrer Institut)

Nucleate boiling heat transfer is one of the most efficient modes of heat transfer under high heat-flux conditions. The mechanisms driving the process are still not sufficiently understood. One of the main uncertainties is the role of microlayer formation and evaporation in the overall dynamics of the phenomenon as well as its relation to the occurrence of the departure from nucleate boiling.

The microlayer is a layer of liquid with thickness less than several micrometres, which can form underneath vapour bubbles during nucleate boiling; its evaporation then contributes 15-50% of total mass transfer. In recent years, explicit simulation of microlayer has been made possible, thanks to the increasing available computational power and novel computational techniques. The role of wetting conditions is emphasised in the works related to the microlayer performed so far; at the same time, dynamic contact angle is profoundly affected both by the motion of the contact line and the presence of phase change. Nevertheless, only constant contact angle conditions have been hitherto considered, bringing uncertainty into the obtained results.

During the first year of the PhD project, a model for dynamic wetting in the presence of phase change has been developed. Its capabilities have been presented at a scientific conference. To increase the fidelity of the resolution of the phasic interface, the Volume-of-Fluid interface tracking method has been successfully implemented into the PSI-BOIL code and coupled to the existing sharp-interface phase change model. Its capabilities for diabatic flows have been verified using a set of 1D problems with very good agreement with analytical predictions. A preliminary 3D rising bubble calculation has indicated the capacity of the developed method to simulate non-trivial problems with respectable accuracy.

In this presentation, the results of the first year of this PhD project are presented, together with an outlook for the remainder of the project.