Simultaneous multiparameter measurement of NaCl solution liquid film based on absorption spectroscopy technique

In the seawater desalination falling-film evaporation process, the formation of crystallization on the outer surface of the evaporator tube is closely related to multiple parameters, such as liquid film thickness, temperature, and concentration (mass fraction). Therefore, high-precision quantitative analysis of these parameters is essential for providing data support to optimize evaporator design, effectively preventing the formation of crystallization on the outer surface of the evaporator tube, and improving the evaporation rate during the seawater desalination falling-film evaporation process. In this study, NaCl solution is used as the research subject, and a new method for simultaneous multiparameter measurement of NaCl solution liquid film based on absorption spectroscopy is proposed. The measurement accuracy of this method is verified using a self-made standard device. The results show that the average relative deviations of the measured liquid film thickness, temperature, and concentration from the known values are 5.30 %, 0.10 %, and 3.30 % respectively. In addition, by combining a high-speed camera with a thermal imager, the evaporation process of NaCl solution liquid films on a horizontal quartz glass plate was studied under different temperatures (298.00 K, 303.00 K, 308.00 K, and 313.00 K) and varying initial concentrations (5.00 %, 10.00 %, 15.00 %, and 20.00 %). The results indicate that both the volume change rate and concentration change rate of the NaCl solution liquid film increase with the rise in liquid film temperature, while they decrease with the increase in initial concentration.