Abstract: Gas-liquid precipitation reactions in terms of a spray exist widely in energy, chemical, and environmental engineering. In this paper, a rainbow refractometry-based method is used to measure the reaction process of these spray-based gas-liquid precipitation reactions in a non-intrusive way. Rainbow refractometry can simultaneously provide information on thermochemical and physical properties of droplets. A global rainbow measurement system was built to characterize a CO₂ absorption reaction. Rainbow signals of spray droplets of Ca(OH)₂ solutions before and after CO₂ absorption were recorded and processed. Results indicated that the average refractive index of saturated H₂O-Ca(OH)₂ solution was 1.335 69, which accorded with the Abbe measurement. After the absorption reaction, the refractive index of droplets decreased to 1.335 17 which is close to that of water. The reaction extent was therefore reflected in the change of the refractive index of droplets. An extra experiment of CO₂ absorbed by Ba(OH)₂ solutions was conducted. The refractive index of droplets decreased with the reaction process, which acted well as an evolution indicator of the reaction. A heat transfer analysis of the reaction was also carried out. Due to the high heat dissipation performance of fine droplets, the temperature increase in the measurement volume was estimated to be less than 0.61 K, which has almost no effect on the measured results. The rainbow refractometry-based method shows good potential for in-situ characterization of a gas-liquid precipitation reaction.

彩虹折射法对喷雾气液沉淀反应的原位表征

[1]Gao X, Huo W, Luo, ZY, et al., 2008. CFD simulation with enhancement factor of sulfur dioxide absorption in the spray scrubber. Journal of Zhejiang University-SCIENCE A, 9(11):1601-1613.

[2]Gao X, Guo RT, Ding HL, et al., 2009. Absorption of NO₂ into Na₂S solution in a stirred tank reactor. Journal of Zhejiang University-SCIENCE A, 10(3):434-438.

[3]Haghnegahdar MR, Rahimi A, Hatamipour MS, 2011. A rate equation for Ca(OH)₂ and CO₂ reaction in a spouted bed reactor at low gas concentrations. Chemical Engineering Research and Design, 89(6):616-620.

[4]Letty C, Renou B, Reveillon J, et al., 2013. Experimental study of droplet temperature in a two-phase heptane/air V-flame. Combustion and Flame, 160(9):1803-1811.

[5]Li H, Rosebrock CD, Wriedt T, et al., 2017. The effect of initial diameter on rainbow positions and temperature distributions of burning single-component n-alkane droplets. Journal of Quantitative Spectroscopy and Radiative Transfer, 195:164-175.

[6]Lohner H, Lehmann P, Bauckhage K, 1999. Detection based on rainbow refractometry of droplet sphericity in liquid– liquid systems. Applied Optics, 38(7):1127-1132.

[7]Nussenzveig H, 1969. High-frequency scattering by a transparent sphere. II. Theory of the rainbow and the glory. Journal of Mathematical Physics, 10(1):125-176.

[8]Ouboukhlik M, Saengkaew S, Fournier-Salaün MC, et al., 2015a. Local measurement of mass transfer in a reactive spray for CO₂ capture. The Canadian Journal of Chemical Engineering, 93(2):419-426.

[9]Ouboukhlik M, Godard G, Saengkaew S, et al., 2015b. Mass transfer evolution in a reactive spray during carbon dioxide capture. Chemical Engineering & Technology, 38(7):1154-1164.

[10]Promvongsa J, Vallikul P, Fungtammasan B, et al., 2017. Multicomponent fuel droplet evaporation using 1D global rainbow technique. Proceedings of the Combustion Institute, 36(2):2401-2408.

[11]Quan X, Fry ES, 1995. Empirical equation for the index of refraction of seawater. Applied Optics, 34(18):3477-3480.

[12]Rosebrock CD, Shirinzadeh S, Soeken M, et al., 2016. Time-resolved detection of diffusion limited temperature gradients inside single isolated burning droplets using rainbow refractometry. Combustion and Flame, 168:255-269.

[13]Roth N, Anders K, Frohn A, 1990. Simultaneous measurement of temperature and size of droplets in the micrometer range. Journal of Laser Applications, 2(1):37-42.

[14]Saengkaew S, 2005. Study of Spray Heat Up: on the Development of Global Rainbow Techniques. PhD Thesis, Rouen University, Rouen, France.

[15]Saengkaew S, Charinpanitkul T, Vanisri H, et al., 2006. Rainbow refractrometry: on the validity domain of Airy’s and Nussenzveig’s theories. Optics Communications, 259(1):7-13.

[16]Saengkaew S, Charinpanitkul T, Vanisri H, et al., 2007. Rainbow refractrometry on particles with radial refractive index gradients. Experiments in Fluids, 43(4):595-601.

[17]Saengkaew S, Godard G, Blaisot J, et al., 2009. Experimental analysis of global rainbow technique: sensitivity of temperature and size distribution measurements to non-spherical droplets. Experiments in Fluids, 47:839-848.

[18]Song F, Xu C, Wang S, et al., 2016. Measurement of temperature gradient in a heated liquid cylinder using rainbow refractometry assisted with infrared thermometry. Optics Communications, 380:179-185.

[19]van Beeck J, Riethmuller M, 1996. Rainbow phenomena applied to the measurement of droplet size and velocity and to the detection of nonsphericity. Applied Optics, 35(13):2259-2266.

[20]van Beeck J, Giannoulis D, Zimmer L, et al., 1999. Global rainbow thermometry for droplet-temperature measurement. Optics Letters, 24(23):1696-1698.

[21]Verdier A, Santiago JM, Vandel A, et al., 2016. Experimental study of local flame structures and fuel droplet properties of a spray jet flame. Proceedings of the Combustion Institute, 36(2):2595-2602.

[22]Whitaker S, 1972. Forced convection heat transfer correlations for flow in pipes, past flat plates, single cylinders, single spheres, and for flow in packed beds and tube bundles. AIChE Journal, 18(2):361-371.

[23]Wilms J, Weigand B, 2007. Composition measurements of binary mixture droplets by rainbow refractometry. Applied Optics, 46(11):2109-2118.

[24]Wu X, Wu Y, Saengkaew S, et al., 2012. Concentration and composition measurement of sprays with a global rainbow technique. Measurement Science and Technology, 23(12):125302.

[25]Wu X, Jiang H, Wu Y, et al., 2014. One-dimensional rainbow thermometry system by using slit apertures. Optics Letters, 39(3):638-641.

[26]Wu X, Li C, Jiang H, et al., 2017. Measurement error of global rainbow technique: the effect of recording parameters. Optics Communications, 402:311-318.

[27]Yu H, Xu F, Tropea C, 2013a. Optical caustics associated with the primary rainbow of oblate droplets: simulation and application in non-sphericity measurement. Optics Express, 21(22):25761-25771.

[28]Yu H, Xu F, Tropea C, 2013b. Simulation of optical caustics associated with the secondary rainbow of oblate droplets. Optics Letters, 38(21):4469-4472.

[29]Zhao Y, Qiu H, 2006. Measurements of multicomponent microdroplet evaporation by using rainbow refractometer and PDA. Experiments in Fluids, 40(1):60-69.

[30]Zumdahl, SS, 2009. Chemical Principles. Houghton Mifflin Company, Boston, USA.