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On the refractive index of sodium iodide solutions for index matching in PIV


Refractive index matching has become a popular technique for facilitating applications of modern optical diagnostic techniques, such as particle image velocimetry, in complex systems. By matching the refractive index of solid boundaries with that of the liquid, unobstructed optical paths can be achieved for illumination and image acquisition. In this research note, we extend previously provided data for the refractive index of aqueous solutions of sodium iodide (NaI) for concentrations reaching the temperature-dependent solubility limit. Results are fitted onto a quadratic empirical expression relating the concentration to the refractive index. Temperature effects are also measured. The present range of indices, 1.333–1.51, covers that of typical transparent solids, from silicone elastomers to several recently introduced materials that could be manufactured using rapid prototyping. We also review briefly previous measurements of the refractive index, viscosity, and density of NaI solutions, as well as prior research that has utilized this fluid.

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  • Abdulagatov IM, Zeinalova AB, Azizov ND (2006) Viscosity of aqueous electrolyte solutions at high temperatures and high pressure. Viscosity B-coefficient. Sodium iodide. J Chem Eng Data 51:1645–1659

    Article  Google Scholar 

  • Adrian RJ, Westweel J (2011) Particle image velocimetry. Cambridge University Press, Cambridge

    Google Scholar 

  • Averbakh A, Shauly A, Nir A, Semiat R (1997) Slow viscous flows of highly concentrated suspensions—part I: laser-Doppler velocimetry in rectangular ducts. Int J Multiph Flow 23(3):409–424

    Article  MATH  Google Scholar 

  • Budwig R (1994) Refractive index matching methods for liquid flow investigations. Exp Fluids 17(5):350–355

    Article  Google Scholar 

  • Chen RC (1991) Experimental and numerical studies of solid–liquid multiphase flow in pipes. PhD Dissertation, Case Western Reserve University

  • Chen RC, Reese J, Fan LS (1994) Flow structure in a three-dimensional bubble column and three-phase fluidized bed. AIChE J 40(7):1093–1104

    Article  Google Scholar 

  • Goldsack DE, Franchetto RC (1977) The viscosity of concentrated electrolyte solutions. I. Concentrated dependence at fixed temperature. Can J Chem 55:1062–1072

    Article  Google Scholar 

  • Goldsack DE, Franchetto RC (1978) The viscosity of concentrated electrolyte solutions. II. Temperature dependence. Can J Chem 56:1442–1450

    Article  Google Scholar 

  • Hong J, Katz J, Schultz MP (2011) Near-wall turbulence statistics and flow structures over 3D roughness in a turbulent channel flow. J Fluid Mech 667:1–37

    Article  MATH  Google Scholar 

  • Jiang J, Sandler S (2003) A new model for the viscosity of electrolyte solutions. Ind Eng Chem Res 42:6267–6272

    Article  Google Scholar 

  • Kacperska A, Taniewska-Osinska S, Bald A, Szejgis A (1989) Influence of ionic association on the B coefficient of the Jones–Dole equation for NaI in water-tert-butyl alcohol mixtures at 26 °C. J Chem Soc Faraday Trans 85:4147–4155

    Article  Google Scholar 

  • Lengyel S, Giber J, Holderit J, Tamas J (1964) Study of viscosity of aqueous alkali halide solutions. J Acta Chim Hung 40:125–143

    Google Scholar 

  • Narrow TL, Yoda M, Abdel-Khalik SI (2000) A simple model for the refractive index of sodium iodide aqueous solutions. Exp Fluids 28(3):282–283

    Article  Google Scholar 

  • Northrup MA, Kulp TJ, Angel SM (1991) Fluorescent particle image velocimetry: application to flow measurement in refractive index-matched porous-media. Appl Opt 30(21):3034–3040

    Article  Google Scholar 

  • Okumra M, Yuki K, Hashizume H, Sagara A (2005) Evaluation of flow structure in packed-bed tube by visualization experiment. Fusion Sci Technol 47(4):1089–1093

    Google Scholar 

  • Parker J, Merati P (1996) An investigation of turbulent Taylor–Couette flow using laser doppler velocimetry in a refractive index matched facility. J Fluids Eng Trans ASME 118(4):810–818

    Article  Google Scholar 

  • Shida S, Kosukegawa H, Ohta M (2011) Development of a methodology for adaptation of refractive index under controlling kinematic viscosity for PIV. In: Proceedings of the ASME, Colorado USA

  • Stoots C, Becker S, Condie K, Durst F, McEligot D (2001) A large-scale matched index of refraction flow facility for LDA studies around complex geometries. Exp Fluids 30:391–398

    Article  Google Scholar 

  • Talapatra S, Katz J (2012) Coherent structures in the inner part of a rough-wall channel flow resolved using holographic PIV. J Fluid Mech 711:161–170

    Article  MATH  MathSciNet  Google Scholar 

  • Uzol O, Chow YC, Katz J, Meneveau C (2002) Unobstructed particle image velocimetry measurements within an axial turbo-pump using liquid and blades with matched refractive indices. Exp Fluids 33(6):909–919

    Article  Google Scholar 

  • Wiederseiner S, Andreini N, Epely-Chauvin G, Ancey C (2011) Refractive-index and density matching in concentrated particle suspensions: a review. Exp Fluids 50(5):1183–1206

    Article  Google Scholar 

  • Wildman DJ, Ekmann JM, Kadambi JR, Chen RC (1992) Study of the flow properties of slurries using the refractive index matching technique LDV. Powder Technol 73(3):211–218

    Article  Google Scholar 

  • Wu HX, Miorini RL, Katz J (2011) Measurements of the tip leakage vortex structures and turbulence in the meridional plane of an axial water-jet pump. Exp Fluids 50(4):989–1003

    Article  Google Scholar 

  • Yousif MY, Holdsworth DW, Poepping TL (2011) A blood-mimicking fluid for particle image velocimetry with silicone vascular models. Exp Fluids 50:769–774

    Article  Google Scholar 

  • Yuki K, Okumura M, Hashizume H, Toda S, Morley NB, Sagara A (2008) Flow visualization and heat transfer characteristics for sphere-packed pipes. J Thermophys Heat Transf 22(4):632–648

    Article  Google Scholar 

  • Zaytsev ID, Aseyev MA (1992) Properties of aqueous solutions of electrolyte. CRC Press, Boca Raton

    Google Scholar 

  • Zerai B, Saylor BZ, Kadambi JR, Oliver MJ, Mazaheri AR, Ahmadi G, Bromhal GS, Smith DH (2005) Flow characterization through a network cell using particle image velocimetry. Transp Porous Media 60:159–181

    Article  Google Scholar 

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We thank Cao Zhang and Dr. Yury Ronzhes for their help during the measurement, Robert Blakely for lending us the circulator bath, and Dr. Jiarong Hong for useful discussions.

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Correspondence to Joseph Katz.

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Bai, K., Katz, J. On the refractive index of sodium iodide solutions for index matching in PIV. Exp Fluids 55, 1704 (2014).

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  • Refractive Index
  • Particle Image Velocimetry
  • Rapid Prototype
  • Couette Flow
  • Polyvinyl Acetate