| Shrnutí: | Over the years, heat fluxes from high speed electronic devices are increasing at an
alarming rate and have now, reached levels where air and liquid cooling can no longer
handle. The use of two-phase cooling in thermosyphons has proven to be the potential
alternative in managing high heat loads. A thermosyphon system comprises a condenser,
an evaporator base simulating a heat dissipating electronic module and a coolant chamber.
The aim of this project is to investigate the effects of working fluid, graphite foam and
geometrical configuration on the heat transfer performance of a thermosyphon.
Two dielectric fluids, namely FC-72 and HFE-7000, were used and experiments
performed using the latter yielded lower wall temperatures due to its relatively lower
boiling point. However, the overall heat transfer coefficients of systems using FC-72
were significantly larger. Next, four graphite foams licensed under trade names POCO
and Koppers were used as heat sinks on the heated surface. Tests using the high density
HTC POCO foam showed the best results in achieving the lowest wall temperatures and
highest heat transfer coefficients at all heat fluxes. Kopper Foam Grade D1 performed the
worst. Results showed that the block foam heat sink performance was significantly better
than the finned foam. High speed image capturing of boiling processes was also carried
out to study the differences in bubble dynamics in different coolants, foams and
geometrical structures. In general, it is evident that bubble nucleation departure diameter and frequency play important roles in heat transfer performance of this two-phase system.
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