Computer Vision Analysis of a Melting Interface Problem with Natural Convection - Visual Computing: Scientific Visualization and Imaging Systems - page 208

12.1 Introduction
Currently, digital images have widespread use in many applications. The increase
in its use is mostly because much of the information that humans get from the
world is by observing images, whether in their daily life, walking down the street,
watching television, reading books, or in professional and scientific applications.
In the last case, there are many data obtained from the analysis of photographs,
spectrograms, thermal imaging, etc.
Computer Vision employs artificial systems that can extract information from
digital images. It involves image acquisition, processing, and analysis.
As presented, Computer Vision techniques can offer support in many areas [ 1 - 4 ].
Images produced by experimental tests can be better understood through these
techniques. In this work, image-processing techniques will be applied to better
understand the behavior of a phase-changing material in the presence of natural
convection. The analysis of this kind of problem has received increasing research
attention and it is important for energy storage systems, thermal environment
control, crystal growth processes, and other engineering applications. This study
deals with the melting of a pure substance in the presence of natural convection in a
rectangular enclosure due to a horizontal thermal gradient.
Several numerical and experimental studies have been reported in the literature
concerning the problem of melting or solidification in the presence of convection.
Examples of experimental studies can be found in the works of Wolff and Viskanta
[ 5 ] and Bénard et al. [ 6 ]. In numerical analyses, the works of Kim and Kaviany [ 7 ],
based on the Finite Difference method, and the works of Sparrow et al. [ 8 ], which
pioneers in solving phase change problems by the Finite Volumes method, can be
mentioned. Gobin and Le Quéré [ 9 ] performed a comparison exercise about
melting with natural convection. This work applies different numerical procedures
and models to a simple phase change problem.
Some fluids exhibit maximum density near their freezing points. In such case,
the problem becomes even more complex because the hypothesis that the density
varies linearly with temperature cannot be applied. This phenomenon occurs with
water near 4 C at atmospheric pressure, which is a temperature often found in
several technological applications and in nature. Numerical and experimental
works involving maximum density and thermal natural convection can be found in
the literature, such as in the work of Lin and Nansteel [ 10 ] and Bennacer et al.
[ 11 ]. Braga and Viskanta [ 12 ] and Kowalewsky and Rebow [ 13 ] analyzed the
effect of maximum density in water solidification in a rectangular cavity. Tsai et al.
[ 14 ] presented a numerical work about the effect of maximum density on laminar
flows in tubes with internal solidification, involving mixed convection. A simple
model of water freezing in a differentially heated cavity is used by Yeoh et al. [ 15 ].
This work is motivated by the need to gain a more complete understanding of
the heat transfer process during the solid-liquid phase change that occurs with
natural convection and maximum density.