  The ever-increasing need for power consumption in electronic devices, coupled
with the requirement for thinner size, calls for the development of efficient
heat spreading components. Vapor chambers (VCs), because of their ability to
effectively spread heat over a large area by two-phase heat transfer, seem
ideal for such applications. However, creating thin and efficient vapor
chambers that work over a wide range of power inputs is a persisting challenge.
VCs that use wicks for circulating the phase changing media, suffer from
capillary restrictions, dry-out, clogging, increase in size and weight, and can
often be costly. Recent developments in wick-free wettability patterned vapor
chambers replace traditional wicks with laser-fabricated wickless components.
An experimental setup allows for fast testing and experimental evaluation of
water-charged VCs with liquid-assisted cooling. The sealed chamber can maintain
vacuum for long durations, and can be used for testing of very thin wick-free
VCs. This work extends our previous study by decreasing overall thickness of
the wick-free VC down to 3 mm and evaluates its performance. Furthermore, the
impact of wettability patterns on VC performance is investigated, by carrying
out experiments both in non-patterned and patterned VCs. Experiments are first
carried out on a wick-free VC with no wettability patterns and comprising of an
entirely superhydrophilic evaporator coupled with a hydrophobic condenser.
Thereafter, wettability patterns that aid the rapid return of water to the
heated site on the evaporator and improve condensation on the condenser of the
vapor chamber are implemented. The thermal characteristics show that the
patterned VCs outperform the non-patterned VCs under all scenarios. The
patterned VCs exhibit low thermal resistance independent of fluid charging
ratio withstanding higher power inputs without thermal dry-outs.
