The on-going trend towards increasing device performance while shrinking device size often results in escalating power densities and high operating temperatures. High operating temperatures may lead to reduced reliability and induced thermal stresses. Therefore, it is necessary to employ new and innovative thermal management techniques to maintain a suitable junction temperature at high power densities. For this reason, there is interest in a variety of liquid cooling techniques. This study analyzes a composite material heat sink. The heat sink consists of a very large number of small cross-section fins fabricated from carbon pitch fibers and epoxy. These carbon pitch fibers have a high thermal conductivity along the length of the fin. It is expected that the longer length will result in more heat transfer surface area and a more effective heat sink. This experimental study characterizes the thermal performance of the carbon-fiber heat sink in a two-phase closed loop thermosyphon using FC-72 as the operating fluid. The influence of heat load, thermosyphon fill volume, and condenser operating temperature on the overall thermal performance is examined. The results of this experiment provide significant insight into the possible implementation and benefits of carbon fiber heat sink technology in two-phase flow leading to significant improvements in thermal management strategies for advanced electronics. The carbon fiber heat sink yielded heat transfer coefficients in the range of 1300-1500 W/m2 K for heat fluxes in the range up to 3.2 W/cm2. Resistances in the range of 0.20 K/W – 0.23 K/W were achieved for the same heat fluxes. Condenser temperature and fill ratio did not show a significant effect on any of the results.

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