High-Flux and Stable Thin Film Evaporative Cooling from Fiber Membranes with Interconnected Pores

As the trend of miniaturization and increasing power density in electronic devices continues, thermal management is becoming a critical issue for performance, reliability, longevity, and energy environmental sustainability of the computing devices. Many devices possess power dissipation over 100 W cm^-2, such as light emitting diode chips (100 W cm^-2), power amplifier chips (500 W cm^-2), where traditional cooling techniques, i.e., single phase convection heat transfer or boiling, are insufficient. Evaporative cooling is promising for cooling high-power electronics, due to the large latent heat of liquid-vapor phase change compared to single phase, better stability, no hysteresis, and lower pumping power compared to boiling. It is well known that thin-film evaporation mainly occurs in a small portion of a liquid film (e.g. <1 μm thickness) where the triple phases, i.e., the (heated) solid, liquid, and vapor, converge. Therefore, high-flux evaporation often only occurs on porous structures with a large overall evaporating area. In the past decades, capillary-driven thin-film evaporation in nanoporous membranes has been investigated. However, earlier experiments on nanoporous membranes with isolated nanopores (e.g. anodized aluminum oxide) did not yield high critical heat flux (CHF) close to theoretical values and could not sustain stable operation for a long time, presumably due to clogging in the nanopores by inevitable defects and contaminants .

In this work, we propose and demonstrate an efficient evaporator using a fiber membrane with 3D interconnected pores, rather than isolated pores, as a remedy for the clogging and local hot spot issue the fiber membrane has interconnected pores for fluid (liquid and vapor) transport to more easily access spots inside it. We demonstrated the idea by conducting passive, capillary-driven thin film evaporation experiments on glass fiber membranes with interconnected micro- and nano- scale pores. All the membranes possess a high CHF over 200 W cm^-2 with water at 1 atm, with the highest observed CHF at about 800 W cm^-2. The membranes also demonstrated long-term continuous thin film evaporation at high flux. The superior liquid spreading capability of the fiber membrane with interconnected pores was further experimentally verified. The fiber membranes are low cost and scalable to manufacture, and mechanically flexible and strong. Our result suggests the suitability of using fiber membranes for thin film evaporation and future integration into high-flux electronic cooling devices such as evaporators and vapor chambers.