Micro heat and mass transfer by bubble-trains from the gas discharging at nucleation sites

Abstract

In this study consideration is given to the possibility of heat and mass transfer from the characteristic columnar bubble-trains observed when a diluted gas precipitates upon contact with nucleation sites at the surface of the container. Last impressive advances in micro/nanoscale surface modification start to allow the control -in number, roughness and spacing, of such nucleation sites and with this opening interesting and so far unexplored possibilities for heat and mass transfer. One of them is the kind of convection induced by bubble-trains when a supersaturated gas is discharging at nucleation sites clusters. Because the bubble generation from the nucleation sites is continuous, the bubble-trains are moving in a confined container, and because surfaces may be deliberately coated by design with such nucleation sites, then the constant upward ascent of the fluid entrained by the bubble train eventually set a convective loop driven by the bubble trains. This kind of convection -although expected to be rather small, nevertheless could be of potential interest for microelectronic applications and then it is worthy a first theoretical assessment in the mass and heat transfer enhancement attainable. Utilizing a simplified idealized two-dimensional geometrical model an expression for the upper limit in the Nusselt number was derived and comparison with natural convection performed.