Vapor Chamber with Wickless Condenser - Thermal Diode

Abstract

The term "vapor chamber" has been used to describe a device that spreads heat, as opposed to the term "thermal diode" that has been assigned to a device technically designed to prevent heat flow along a specific direction. In this study, a vapor chamber with a wickless, wettability-patterned condenser is fabricated and tested. The device takes advantage of the phase-changing properties of water, inside a closed loop comprised of a classical wick evaporator opposing a wickless wettability-patterned condenser. The wettability pattern facilitates spatially-controlled dropwise and filmwise condensation, and provides an efficient way to transport the condensate with specially-designed wedge tracks using capillary forces. The vapor chamber can also act as a thermal diode if the wickless condenser has a higher temperature than the wick, thus blocking heat flow in the opposite direction. When the device is performing as a vapor chamber (VC), the working medium evaporates from the hot superhydrophilic copper wick and condenses on the cold wickless condenser. The condensed water returns to the hot side of the device from strategically-placed superhydrophilic wells on the condenser, where condensate droplets accumulate, grow and ultimately bridge between the evaporator and the condenser. However, when the device is performing as a thermal diode (reverse mounted), evaporation must be initiated on the wickless plate and condensation occurs on the opposing wick of the condenser. In this way, the fluid circulation in the device is choked and heat transfer is impeded. The device diodicity is tunable by changing the wettability pattern and can be adjusted as needed for different thermal applications. When the device operates as a VC, heat is effortlessly pumped out of the heat source; at the same time, the device blocks the undesirable heat backflow while working as a thermal diode. The present VC thermal diode apparatus could prove beneficial in a wide spectrum of thermal-management applications, such as aerospace, spacecraft, building materials, protection of electronics, packaging, refrigeration, thermal regulation during energy harvesting, thermal isolation, etc.