Vapor chamber with thermal diode and switch functions

Abstract

Strategically controlling heat flow will enable new functionality for future electronics and energy storage systems. Potential performance enhancements include confining and releasing heat in a predetermined fashion, heat flux shielding, or ensuring more isothermal operation. This article experimentally verifies operation of a vapor chamber that exhibits dual heat flux rectification and thermal switch functions. The sealed device comprises three internal layers: a sintered copper wick evaporator is saturated with a working liquid; a condenser is functionalized with a superhydrophobic coating to promote dropwise condensation of vapor; and a low-thermal-conductivity spacer between the two opposing surfaces establishes a fixed vapor gap. By properly controlling the internal environment of the chamber through precision charging, the boiling point of the working fluid at the evaporator surface is set to a desired temperature. During forward operation, vapor generated on the evaporator surface is condensed on the superhydrophobic surface in a dropwise mode; via the release of surface energy upon condensate droplet coalescence, liquid droplets jump back to the evaporator, completing the passive phase-change-based heat flow cycle. During reverse operation, where heat is applied to the superhydrophobic surface, there is no mechanism for liquid resupply to the surface, and heat is transferred by conduction/convection across the vapor gap. Experimental results indicate the vapor chamber operates as a thermal switch, yielding a difference in thermal conductance before and after reaching the boiling point. The device also exhibits heat flux rectification depending upon the direction (i.e., forward/reverse operation) of heat flow. The ratios of effective thermal conductivities in “on” versus ‘off’ modes, for switching and diode functions, are measured to be ∼18:1. Practical challenges with the current prototype and opportunities for performance enhancement are discussed.