Dropwise condensation in vapor chambers

Electronic devices continue to shrink in size while dissipating more heat. The size of the air cooled heat sinks required to remove this heat has increased while the size of the heat source has decreased. These trends have resulted in large conduction gradients across the base of the heat sinks, resulting in decreased thermal performance. A passive and reliable method of minimizing the spreading resistance in air cooled heat sinks is to embed a vapor chamber in the base of the heat sink. A vapor chamber is a two-phase heat transfer device that uses capillary forces to isothermally circulate a working fluid at saturated conditions. Provided that the vapor chamber is circulating fluid properly (within its capillary limit) the thermal resistance of the vapor chamber is limited by the evaporating and condensing processes in the vapor chamber. Much attention has been paid to the evaporating process since the heat flux of the evaporating process is generally many times higher than that of the condensing process. However, heat fluxes in the condensing regions of vapor chambers have risen to the point where they can´t be neglected. Described here is a novel method of improving the condensation performance in vapor chamber devices by using self-assembled monolayers to promote dropwise condensation. In other applications, dropwise condensation has been shown to improve the condensation heat transfer coefficient by an order of magnitude over the typical filmwise condensation surfaces found in vapor chambers. Presented here are condensation test data comparing the performance of filmwise and dropwise condensation surfaces in vapor chambers.