Experimental investigation on sintered porous wicks for miniature loop heat pipe applications

A miniature loop heat pipe (mLHP) is an efficient two-phase heat transfer device based on capillary pumping effects within a porous wick that provides the driving forces for flow circulation. Several properties of the porous wicks, including capillary pressure, permeability and thermal conductivity are influential design factors in determining the mLHP thermal performance under a set of specific operating constraints. This study presents the fabrication and characterization of sintered porous wicks to be employed in mLHPs which address the thermal management of high power density desktop computers, workstations, and servers. Specifically, the mLHP under consideration must be able to dissipate a high flux of ∼28 W/cm2 and reject it to a remote area at a distance of 500 mm, while the operating temperature of the electronic chip is maintained below 70 °C. To accomplish this task, it is determined theoretically that the wick must have a capillary pressure between 25 kPa and 35 kPa and a permeability in a range of 10−13 to 10−14 m2 if water is used as working fluid. The thermal conductivity must also be less than 10 W/m °C. To manufacture wicks possessing these properties, a single step, low temperature sintering method in gravitational field was used with an isothermal sintering and active cooling process. The main goal was to increase the capillary pressure, while having minimal impact on permeability. Multiple sets of sintering conditions were explored. The properties of interest were then investigated experimentally in order to verify that the prepared wicks meet the design constrains discussed above.