Effects of Particle Size and Particle Size Distribution on Heat Dissipation of Heat Pipes with Sintered Porous Wicks

Permeability and capillary pressure are the two main characteristics that are frequently referenced in discussing the performances of the sintered wick in a heat pipe. These properties are closely related to the copper powder used. To investigate the effect of mean particle size and particle size distribution on these two properties and the resultant heat dissipation, three gas-atomized Cu powders with different particle sizes, 65, 92, and 128 μm, were examined. The results of thermal performance show that the coarse powder was favorable due to its larger pore size and lower sintered density, which was attributed to the heavier water vapor formation from its high intrinsic oxygen content and the hydrogen atmosphere. The data also showed that powders with narrower particle size distributions result in better thermal performance than those with wide distributions. Since the explanation of the heat dissipation based on the permeability and capillary pressure was not satisfactory, a new method, using capillary speed along with porosity, was applied. This method was shown to be more effective and more practical in evaluating the influence of powder characteristics on the heat dissipation performance of sintered porous wick structures.