Numerical investigation of the Marangoni convection during the liquid column evaporation in microchannels caused by IR laser heating

Abstract

In this study, the photothermal effect of an infrared laser induced evaporation and Marangoni convection of a liquid column in microchannels is numerically studied. The volumetric Gaussian heat source is used to model the laser beam and the shear stress at the vapor–liquid interface due to the surface tension gradient is accounted. The results show that under the same laser spot position and laser power, the evaporation mass flow rate in the hydrophilic microchannel is greater than that in the hydrophobic microchannel due to the small thermal resistance. The direction of flow patterns in liquid column are totally different since the relative magnitudes of the horizontal and vertical temperature gradients are opposite for these two surfaces. The effects of the laser power and spot position are also studied. It is found that as the laser power increases, the evaporation mass flow rate, evaporation heat ratio and strength of the Marangoni convection are all increased because more heat can be generated. Regarding the laser spot position, the evaporation mass flow rate and evaporation heat ratio both decrease with increasing the distance between the laser spot and interface because of increased thermal resistance. Moreover, the laser spot position can change the Marangoni convection roll both by the direction and magnitude. The results obtained are helpful for the design and operation of the microdevices with the photothermal effect induced phase change.