Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.
The development of microelectronics is toward high
performance, high efficiency and yet small size. Thermal
management of microelectronics is of critical concern and
significant interest. Microchannel boiling is an advanced
cooling technology for high heat flux devices. The present
study explores heat removal capability of a two-phase natural
circulation loop with divergent microchannel evaporator. Our
previous studies revealed that a diverging cross section design
significantly could stabilize and enhance the heat transfer of
flow boiling. The temperatures at the inlet and outlet of both
evaporator and condensing units are measured to evaluate the
heat removal capability of the loop. Moreover, the pressure
changes through the downcomer and lower horizontal tube are
both measured to deduce the flow rate through the loop based
on the relationship between flow rate and pressure drop. This
study uses the high speed video camera to capture the flow
patterns in the evaporator and riser. The working fluid
employed in the present study is ethanol, as its boiling
temperature at atmospheric pressure is 78.4 ℃, which is below
the temperature limit of the most microelectronic materials. The
results show that the loop mass flow rate increases
monotonically with increasing the heating power of the
evaporator after boiling incipience. The current experimental
results indicate that the highest base heat flux could achieve is
about 105 kWm-2 with no sign of dry-out and it has great
potential to reach a higher heat flux. Moreover, it is found that
the loop instability appears at low heating powers after boiling
begins, while it can be suppressed if the input power is higher
than 20W. Indeed, the present two-phase natural circulation
loop with divergent microchannel evaporator demonstrates
stable circulation with high heat transfer capability.
