| dc.description.abstract | Pool boiling is an effective method used in many technical applications for a long
time. Its highly efficient heat transfer performance results from not only the convection
effect but also the phase change process in pool boiling. Pool boiling enhancement has
been studied in the past decade. However, the mechanisms of pool boiling has not yet
been fully understood because of the many parameters that affect its behavior including
the latent heat of vaporization, nucleation density, bubble and fluid motion, interaction at
the interface, and the physical properties of surface. Among the current studies, bubble
departure rate is viewed as one of the dominant factors that affect heat transfer.
This research considers the effect of bubble confinement on pool boiling. In the
study, confinement was achieved by placing a flat plate over heated surface. The flat
plate has a hole in the middle, and there is a gap between the flat plate and the heater.
The diameters of hole are 2 mm, 3 mm, and 4 mm; the gap distances are 2.3 mm, 3.6 mm,
and 5 mm. The heater consists of an indium-tin-oxide layer deposited on a silicon wafer. An IR
camera and high speed cameras are used to acquire the surface temperature distribution
and bubble image. By controlling the plate hole size and the gap distance, the effect of
confinement on heat transfer performance can be evaluated. Moreover, heat transfer
performance of pool boiling with three-2mm-holes plate was investigated and compared
with that of single-2mm-hole plate with the smallest gap size.
At the lower heat flux values, heat transfer enhancement in confined space was
experimentally observed. Surface temperature can be reduced by 4 °C at most. Results
indicate that higher bubble departure rate and coalescence effect might be the dominant factor for improving heat transfer performance in a confined space caused by induced shear flow. | en |
