Simulation on the dynamic flow and heat and mass transfer of a liquid column induced by the IR laser photothermal effect actuated evaporation in a microchannel

The photothermal effect induced evaporation in microchannels is a typical phenomenon in optofluidics, which greatly affects the performance of this type microdevice. In this study, the dynamic flow and heat and mass transfer characteristics of a liquid column induced by an IR laser with the wavelength of 1550 nm in a microchannel is numerically studied. The results show that the Marangoni convection is caused by the non-uniform temperature distribution arising from a local heating source of the IR laser. The intensity of the Marangoni convection is weak at the beginning because the spontaneous evaporation is dominant. With the laser heating going on, the intensity of the Marangoni convection becomes strong and then weak again due to the competition between the photothermal effect and increased vapor pressure. It is also found that the heat transfer coefficient at the interface and Biot number decrease with the laser heating time because the increased vapor pressure in the gas phase resists the evaporation. Due to the same reason, although the evaporation mainly relies on the spontaneous evaporation at the beginning, the evaporation rate is the highest and then gradually decreases with the laser heating time and finally becomes relatively stable. Correspondingly, the mass transfer coefficient at the interface is also gradually decreased with the laser heating time. Besides, the effects of the laser power and air humidity are also studied. It is shown that the evaporation rate increases with increasing the laser power and decreasing the air humidity.