Capillary Performance of Bi-porous Al Fabricated Using Space Holders with Different Sizes

Capillary pressure (△Pcap) and fluid permeability (K) of porous media are important for heat transfer devices including loop heat pipes. In general, smaller pore sizes enhance capillary pressure but decrease permeability. To solve this trade-off relationship, introducing bi-modal pore size distributions is promising. In the present study, the capillary performance of bi-porous Al fabricated using NaCl space holder particles with two different sizes (approximately 400 μm and 40 μm) was evaluated and compared with that of mono-porous Al. Increasing the porosity (from 60% to 80%) of mono-porous Al with large pores around 400 μm enhanced the permeability but decreased the capillary pressure. By contrast, increasing the fraction (from 0% to 20%) of small pores (around 40 μm) led to the enhancement of both permeability and capillary pressure in bi-porous Al with a constant large-pore fraction of 60%.