Wick-free vapor chamber featuring laser-textured surfaces: A new paradigm for ultra-thin high-efficiency heat spreaders

The advent of high power-density devices in both electronics and battery systems has re-invigorated interest towards vapor chambers (VCs) and heat pipes for effective heat dispersal. Furthermore, miniaturized, thinner VCs -although attractive for the electronics industry- become inefficient, as the thermal resistances of wick-lined VCs rise with decreasing thickness. Surface-engineered components allow wickless VC operation (by harnessing capillary forces to circulate the working fluid) and can mitigate the shortcomings of wick-lined VCs. However, the working principles of wickless VCs across different operational regimes and varying design geometries remain unchartered. Herein, we develop a numerical model for a wick-free VC (WFVC) comprising a uniformly hydrophobic condenser and a uniformly superhydrophilic evaporator. The model is validated against experimental data obtained with a custom-made, liquid-cooled wick-free VC, whose surfaces were fabricated by laser processing. The numerical model produces insights into thermal performance for variations in condenser-surface wettability, fluid charging ratio, and VC thickness, while offering critical design guidelines as well as predictions for the onset of thermal dry-out. The work further establishes that wick-free VCs can overcome the limitations faced by traditional ultra-thin vapor chambers (UTVCs) when the vapor-gap thickness declines to similar to 0.3 mm or lower. The thermal resistance of such WFVCs decreases monotonically with decreasing vapor-space gap. This aspect makes the WFVC more pertinent for cooling of miniaturized high-energy-density electronics and battery systems, which require compact VCs with thinner vapor-space gaps. A benchmarking study further attests to the potential and superior performance of ultra-thin WFVCs (Critical heat-flux, 432 W/cm(2)) as compared to wicklined VC designs.