IR laser induced phase change behaviors of the NaCl solution in the microchannel

Abstract

With the promising potential in non-contact fluid manipulation, the photothermally induced phase change along with the interfacial behaviors have been frequently applied in various microfluidic devices. The property of the working fluid greatly affects the photothermal conversion and thus phase change behaviors. For this reason, the IR laser induced phase change of the NaCl solution in the microchannel was visually studied and compared with distilled water in this work. Experimental results indicated that the NaCl solution exhibited the distinct phase change behaviors. The existence of dissolved ions could weaken the photothermal conversion, leading to lowered temperature rise and evaporation rate as compared to the distilled water. In particular, different from the distilled water, the condensed droplets were formed at the region relatively far away from the evaporating interface due to lower evaporation rate. No coalescence between the condensed droplets and liquid slug was observed. Besides, the effects of the NaCl concentration, laser power and spot position were also investigated. It was found that higher NaCl concentration resulted in lower temperature rise and evaporation rate. With the increase of the input laser power and the decrease of the distance between the laser spot and the interface, the temperature rise and evaporation rate could be improved. The obtained results can be further applied in the design and operation of the microfluidic devices based on the photothermally induced phase change.