Experimental investigation of a vapor chamber featuring wettability-patterned surfaces

Abstract Vapor-chamber heat spreaders are hermetically-sealed systems that rely on metal wicks to circulate a phase-changing liquid and spread heat more efficiently than solid-metal heat sinks. But metal wicks also impose capillary limitations due to their high pressure drop. Surface-wettability patterning does not pose the same limitations and, as shown in this work, could replace metal wicks in vapor chambers to transport the condensate faster and more efficiently. Combining the fast condensate transport characteristic of wettability patterning with the added advantage of domain-regulated dropwise condensation (DWC) and filmwise condensation (FWC) towards enhanced condensation performance, an intriguing hypothesis is explored here by incorporating surface-wettability patterning inside vapor chambers made of copper with and without wicking posts. Wettability patterns with different ratios of superhydrophilic (FWC-promoting) to hydrophobic (DWC-promoting) domains are explored and compared with a control case of unpatterned mirror-finish copper, all located on the condenser side. The heat-spreading capability of the devices from a heated spot of ~0.9 cm2 to an effective vapor chamber area of ~25.8 cm2 is tested at a horizontal orientation where gravity acts perpendicular to the vapor chamber plane and at a vertical orientation. The lowest thermal resistance achieved is 0.24 K/W at 87 W heat load (heat flux of 97 W/cm2) with a horizontally-placed vapor chamber that has a 0.5 mm-thick evaporator wick, a wettability-patterned condenser plate and no wicking posts. The work offers quantitative arguments for incorporating wettability patterning in vapor-chamber technology, and motivates further optimization towards achieving the full potential of this approach.