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Journal of Flow Visualization and Image Processing
SJR: 0.161 SNIP: 0.312 CiteScore™: 0.1

ISSN Print: 1065-3090
ISSN Online: 1940-4336

Journal of Flow Visualization and Image Processing

DOI: 10.1615/JFlowVisImageProc.2012004720
pages 347-369

SINGLE LENS-BASED SCHLIEREN MICROSCOPE FOR INVESTIGATION OF THREE-DIMENSIONAL BUOYANCY-INDUCED CONVECTIVE FLOW FIELDS

Atul Srivastava
Department of Mechanical Engineering, Indian Institute of Technology Bombay, Powai – 400076, Mumbai, India
Katsuo Tsukamoto
Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, 6-3, Aramaki Aoba, Sendai, Miyagi, 980-8578, Japan
K. Murayama
Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, 6-3, Aramaki Aoba, Sendai, Miyagi, 980-8578, Japan

ABSTRACT

The present work describes the development and application of a single lens-based schlieren microscopic system for imaging of buoyancy-induced convective fields and subsequent determination of three-dimensional temperature and/or concentration fields. The system differs from the conventionally employed schlieren method in a way that in contrast to a collimated beam of light in conventional methods, the developed optical system employs a diverging beam of light to scan the area of interest. The usage of the diverging beam of light shifts the rear focal plane of the microscopic objective lens, which also acts as the magnifying lens, by a finite distance outside its body without the need of any extra lens pair arrangement. This configuration enables the use of only a single microscopic objective lens for focusing the light beam onto a knife edge and/or a color filter placed at its rear focal plane to get the desired schlieren cut-off. The appli-cability of the proposed method has been demonstrated by imaging the buoyancy-induced convection currents around a sodium chlorate (NaClO3) crystal growing from its aqueous solution in the free-convection regime in situ. Monochrome as well as rainbow schlieren images of the convective fields have been recorded using a knife edge and a rainbow filter placed at the rear focal plane of the objective lens.
A detailed quantitative analysis of the monochrome schlieren images has then been carried out to determine the path-averaged concentration profiles in the growth chamber. Subsequently, principles of tomography have been employed to determine the three-dimensional distribution of the concentration field around the growing crystal. Results have been presented in the form of monochrome and rainbow schlieren images recorded using the developed optical setup, path-averaged salt concentration distribution as deduced from the microscopic monochrome schlieren images, and local concentration distributions at various horizontal planes above the growing crystal using the principles of tomography. A comparative study of the results obtained using the proposed method has also been carried out against the results of the standard microscopic inter-ferometry tomography to establish the accuracy of the results and an overall good match is to be seen in the two approaches.


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