Phase-change thermal diodes effectively transport heat unidirectionally, but are currently constrained by either a gravitational dependence (thermosyphons), a one-dimensional configuration (liquid-trap heat pipes), or poor durability (jumping-droplet vapor chambers).  Here, we develop a novel bridging-droplet thermal diode which uniquely bypasses all of these existing constraints. Our diode is comprised of two opposing copper plates of dimensions 101 mm × 101 mm, separated by an insulating gasket of micrometric thickness; one plate contains a superhydrophilic wick structure with pillars of dimensions 100 µm × 100 µm × 600 µm, while the other is smooth and features a hydrophobic coating. In the forward mode of operation, the heat source is located on the back face of the wicked copper plate, such that water evaporates from the 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 across the chamber. Conversely, in the reverse mode of operation the heat source is now on the hydrophobic plate, resulting in catastrophic dryout and excellent thermal insulation across the gap. The resulting heat transfer ratio (i.e. diodicity) was orientation-independent and could be as high as about 50.


Bridging-Droplet Thermal Diodes

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
Paper Proceedings: https://asmedigitalcollection.asme.org/ICNMM/ICNMM2020/volume/83693

Fluids Engineering Division Summer Meeting
Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2020/volume/83716

HT-ICNMM2020 - Virtual Conference, SHTC - Virtual Conference, FEDSM2020 - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.