Surface evaporation enhancement using porous metasurfaces: 3-D multiscale, open-system wick evaporators

Abstract

In open-system water-vapor production by direct heat supply, wick evaporators are promising for efficient use of the supplied heat. However, designing a suitable wick structure for achieving high evaporator performance had proven challenging. Here, novel, high-performance porous metasurfaces (unit-cell based capillary structures) are designed, fabricated and tested, using sintered copper powder. In addition, the wicks optimized for yet higher performance are presented. Vertically placed wicks are partially submerged in a pool of water, while heated through a copper substrate by Joule heating. The baseline wick is a monolayer wick, and three different particle diameters (78, 100, and 130 μm) are used. The next variations are bilayer wicks which improve the particle packing and the maximum capillary pressure. The most improvement is achieved by adding strips of capillary arteries (1 mm thick and 1 mm wide, with an interartery gap of 1 mm) on the monolayer. These unit-cell based 3-D porous metasurfaces allow for tailoring the surface design to achieve an optimal thermal-hydraulic performance. Analyses of the wick capillary-viscous dryout limit and the extended-surface heat transfer predict the performance of the fabricated wicks under the test conditions. Overall, an evaporation efficiency of unity and an evaporation enhancement by 50% are recorded.