Bridging‐Droplet Thermal Diodes

Phase‐change thermal diodes effectively transport heat unidirectionally, but are currently constrained by either a gravitational dependence, a 1D configuration, or poor durability. Here, a novel bridging‐droplet thermal diode which uniquely bypasses all of these existing constraints is developed. The diode is comprised of two opposing copper plates separated by an insulating gasket of micrometric thickness; one plate contains a superhydrophilic wick structure while the other is smooth and hydrophobic. In the forward mode of operation, water evaporates from the heated wicked plate and condenses on the hydrophobic plate. The large contact angle of the dropwise condensate enables bridging across the gap to replenish the wicked evaporator, providing sustained phase‐change heat transfer. Conversely, in the reverse mode, the heat source is now on the hydrophobic plate, resulting in dryout and excellent thermal insulation across the gap. An orientation‐independent heat transfer ratio (i.e., diodicity) as high as 85 was measured.