Solidification in the Presence of Natural Convection in a Hele-Shaw Cell - Selected Topics of Computational and Experimental Fluid Mechanics - page 361

2 Experimental Device and Visualization Methods

The experimental device where observations were made consists of a Hele-Shaw cell
formed by two 1mm thick glass plates with an area of 2.0 cm 2.0 cm. The plates

were separated 1mm by Nylamid pieces placed along the vertical walls of the cell
which provide mechanical support and thermal insulation. The upper horizontal wall
of the cell is a piece of copper that is physically in contact with the cold side of a
square thermoelectric device. The hot side of the thermoelectric is in contact with
a heat sink which is constituted by a container filled with pellets of solid CO 2 and
designed such that a mini fan blows the cold gaseous CO 2 product of the sublimation
to the upper wall of the Hele-Shaw cell. The illumination of the fluid inside the cell
is made through the lower horizontal wall which is made of a plexiglas piece that
acts as a light guide for three white light emitting diodes. The cell arrangement is
shown in the left panel of Fig. 1 . Small holes at the lower part of the vertical walls
connected to atmospheric pressure allow for the expansion of the working fluid as it
is cooled. The cell is fixed on a breadboard and aligned to a Microsoft, 960

×

540
pixels video camera that captures images at 15 fps (see the right panel of Fig. 1 ).
The resulting spatial resolution is 23 pixels per mm. Special care was required to
prevent water condensation from the ambient on the external walls of the cell since
this reduces the quality of the images, and may modify the boundary conditions on
the faces of the cell.
The working fluid is water with small (10

×

m in diameter) neutrally buoyant
hollowed glass particles in suspension. The temperature of the fluid inside the cell is
monitored with two thermocouples located near the top and bottom horizontal walls
as shown in Fig. 2 . The flow pattern and the position of the solidification front are
captured with the video camera and analyzed with the PIVLab software and image
processing tools. The maximum velocity observed is 0.8mm/s and the interrogation

µ

Fig. 1 Left Geometry and components of the Hele-Shaw cell. Right Experimental setup showing
the heat sink (solid CO 2 reservoir), and the position of the video camera