Abstract:
Nucleate boiling is considered an efficient mechanism of heat transfer. Its applications
can be found in many industries including nuclear, processing, solar, power,
microelectronics and HVAC. However, applications of nucleate boiling are not
matured enough so that they can be implemented with safety. The utilization of boiling
for transferring heat has led to flow instability and flow reversals in nuclear reactors
and microchannels respectively. To avoid such incidents and pave a way for safe
commercial application of nucleate boiling, the physics behind nucleate boiling needs
to be elucidated completely. For this purpose, several mechanistic and empirical
models have been proposed after decades of research. But nucleate boiling depends on
range of parameters including surface properties, heat flux, nucleation density, fluid
properties and adopted applications. A comprehensive model which can incorporate
all these variables has not been proposed so far. Neither such perfect experimental
setups can be devised in near future which could depict the physics of the whole
phenomena with predictable accuracy. So, an alternative approach that could reveal
the physics behind nucleate boiling and provide a baseline for experiment is needed.
The advances and diversity in numerical simulation can help in understanding the
phenomenon of nucleate boiling. This study utilizes these advances and focuses on
numerical simulation of nucleate boiling. A 2-dimensional axi-symmetric domain is
considered for performing the simulation. Nucleation and thermal boundary layer
development process are bypassed. For this purpose, a hemi-spherical bubble and
linear thermal boundary layer are patched in domain. Source of mass and energy due
to phase change are implemented in governing equations through additional
subroutines written in C language. The accuracy of numerical model is assessed by
comparing the results of bubble shape, evolution of bubble contours and its size with
experimental datum in available literature. Relatively a good agreement is found in
shape and departure time except the size of the bubble, which is larger than the results
of experiment due to extensive evaporation at interface between the two phases. In
addition, an insight into temperature and velocity fields obtained from simulation are
analyzed which cannot be revealed by experimental results.
