Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.
Multiphase flow and heat transfer in mini/microspaces are
of significant interest for thermal management applications,
where the latent heat of phase change offers an efficient method
to dissipate large heat fluxes in a compact device, such as a heat
spreader or a heat pipe. However, a significant challenge for the
implementation of microscale phase change heat spreader is
associated with micro/nano flow instabilities due to insufficient
micro/nano bubble removal, leading to local liquid dry-out
which severely limits the heat removal efficiency. This work
will conduct a review on the challenges and opportunities that
surfaces with micro/nanostructure patterned wettabilities.
Bubble dynamics, fluid flow and heat transfer caused by the
micro/nanostructure patterned surfaces will be reported and
discussed. The effects of micro/nanostructure patterned
surfaces on flow generation under a vapor bubble in a
microchannel under very low Reynolds number will be
demonstrated. The effects of wettability patterned surfaces on
nucleation pool boiling and flow boiling heat transfer processes
will be described. Bubble formation, breakup and departure are
visualized and measured. Wettability patterned
micro/nanostructure surfaces are manufactured on glass wafers
and copper surfaces, respectively. Different surface hexagonal
pattern size will be used. Indium Tin Oxide (ITO),
Fluoroalkylsilanes (FAS) and Copper Oxide (CuO) will be used
for glass and copper surfaces, respectively. It is found that
bubble dynamics and pool boiling performance are enhanced
significantly on smooth and flat surfaces combining hydrophilic
and hydrophobic patterns in comparison with a hydrophilic
surface. A micro/nanostructured heat spreader with
asymmetrical wettability patterns will be demonstrated.
