RESUMO
Gallium liquid metal is one of the promising phase change materials for passive thermal management of electronics due to their high thermal conductivity and latent heat per volume. However, it suffers from severe supercooling, in which molten gallium does not return to solid due to the lack of nucleation. It may require 28.2 °C lower temperature than the original freezing point to address supercooling, leading to unstable thermal regulation performance along fluctuations of cooling condition. Here, gallium is infused into porous copper in an oxide-free environment, forming intermetallic compound impurities at the interfaces to reduce the activation energy for heterogeneous nucleation. The porous-shaped gallium provides ≈63% smaller supercooling than that of the bulk type due to large specific surface area (≈9,070 cm2 per cm3) and high wetting characteristics (≈16° of contact angle) on CuGa2 intermetallic layer. During repetitive heating-cooling cycles, porous-shaped gallium consistently shows propagation of crystallization at even near room temperature (≈25 °C) while maintaining stable performance as thermal buffer, whereas droplet-shaped gallium is gradually degraded due to partial-supercooled state. The findings will improve the responsive thermal regulation performance to relieve a rapid increase in temperature of semiconductors/batteries, and also have a potential for energy storage applications.
RESUMO
A membrane with selective wettability to either oil or water has been utilized for highly efficient, environmentally friendly membrane-based oil-water separation. However, a predictive model, which can be used to evaluate the overall separation performance of the membrane, still needs further development. Herein, we investigate three separation performance parameters, that is, separation efficiency, liquid intrusion pressure, and mass flux in particular, as a function of pore geometry and liquid properties using metallic meshes whose surface wettability is modified by scalable spray coating. We show that the prepared membrane exhibits a separation efficiency over 98% below the intrusion pressure, while the intrusion pressure increases with the decrease of pore size of the membrane. Particularly, we develop a semi-empirical model for the mass flux through the membrane. As application examples of our performance analysis, we successfully predict the separation time for one-way and two-way gravity-driven separation of the oil-water mixture, the decrease of the mass flux due to membrane fouling, and the maximum allowable separation capacity of the given membrane. This work can help to design optimal membrane-based oil-water separation systems for actual industrial applications by providing a selection guideline for separation membranes.
