Color schlieren deflectometry for characterization of crystal growth processes: KDP and lysozyme Anamika Sethia Gupta a , P.K. Panigrahi a,n , K. Muralidhar a , Rajive Gupta b a Department of Mechanical Engineering, Indian Institute of Technology, Kanpur 208016, UP, India b Department of Mechanical Engineering, Harcourt Butler Technological Institute, Kanpur, UP, India article info Article history: Received 18 June 2009 Received in revised form 30 November 2009 Accepted 17 December 2009 Communicated by J. de Yoreo Available online 28 December 2009 Keywords: A1. Interfaces A1. Mass transfer A2. Growth from solutions A2. Seed crystals B1. Lysozyme B1. Optical techniques abstract Color schlieren deflectometry is a technique that has great potential in terms of both quality and ease of implementation for the study of convection phenomena during crystal growth. The advantage stems from its non-intrusive and inertia-free nature. Application of this technique for crystal growth is not available in the literature and is the focus of the present work. The present study discusses the implementation of color schlieren deflectometry for characterization of KDP and protein crystal growth processes. The technique is evaluated both for qualitative visualization and as a tool for quantitative analysis. Crystal growth processes, in general, reveal complex transport phenomena. Solutal convection is present during KDP crystal growth while the protein crystal growth process includes both evaporation and condensation. The present study demonstrates the effectiveness of color schlieren technique for understanding these physical phenomena for both crystal growth processes. The color schlieren images are qualitatively compared with those from other optical techniques such as Mach–Zehnder interferometry, monochrome schlieren and shadowgraph techniques. The quantitative analysis procedure of color schlieren images is validated by using the Rayleigh–Benard convection experiment in a rectangular cavity. It is seen that the temperature profiles and the heat flux distribution in the Rayleigh–Benard experiment and concentration distribution during KDP crystal growth derived from color schlieren deflectometry match well with data reported in the literature. In the protein crystal growth experiment using lysozyme, evaporation of water from the droplet and its condensation on the reservoir surface followed by subsequent diffusion and complete mixing with the reservoir solution are clearly revealed from color schlieren deflectometry experiments. Overall, the present study establishes the color schlieren deflectometry as an attractive tool for characterization of crystal growth processes. & 2010 Elsevier B.V. All rights reserved. 1. Introduction Optical techniques are widely used for investigation of convective fields in many applications for both qualitative visualization and quantitative information. Some of the literature that focuses on crystal growth applications is discussed below. Mantani et al. [1] employed a Mach–Zehnder interferometer for the measurement of concentration gradients around a KDP crystal growing from its aqueous solution. Onuma et al. [2] described the use of a real-time phase shift interferometer for the measurement of concentration distribution around a growing as well as dissolving crystal. The authors calculated quasi-three- dimensional concentration profile around a sodium chlorate crystal by using the Abel transformation method. Shenoy et al. [3] presented a color schlieren approach for temperature field measurements in gas jets. Tanda and Devia [4] implemented the schlieren technique without the need for intensity measurements in the study of two-dimensional free convective heat transfer from heated plates and from vertical parallel channels to the surrounding fluid. A report on in situ monitoring and control of lysozyme concentration during crystallization in a hanging drop method was presented by Schwartz and Berglund [5] in which the authors used fiber optic Raman spectroscopy. Bredikhin et al. [6] proposed a technique based on optical schlieren method to investigate the growing crystal morphology of a KDP crystal under rapid growth conditions. Srivastava et al. [7] compared convection fields in air as well as in a water-filled rectangular cavity using interferometry, schlieren and shadowgraph. The study indicated that the schlieren and shadowgraph methods were more suitable for high temperature gradient applications. The above literature review indicates that monochrome optical methods such as interferometry and monochrome schlieren have been used for the study of thermal convection applications and the KDP crystal growth process. The application of color schlieren ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2009.12.043 n Corresponding author. Tel.: + 91 512 2597686; fax: + 91 512 2597408. E-mail address: panig@iitk.ac.in (P.K. Panigrahi). Journal of Crystal Growth 312 (2010) 817–830