Experimental Study of Human Exhaled Breath-Like Humid Air Condensation on a Surface-Modified Aluminum in a Rectangular Flow Channel

Abstract Water vapor extraction from human exhaled breath is critical for breath analysis, enabling lower humidity interference in volatile compound sensing and separate analysis of exhaled breath condensate. Thus, any condenser surface must support efficient vapor extraction and condensate collection from high-humidity breath samples. This study investigates the effect of aluminum surface modification on water vapor extraction and condensate collection from humid air simulating exhaled breath in a 110 × 40 × 5 mm rectangular flow channel. Aluminum surfaces were modified via alkali etching and anodization to achieve superhydrophilicity (contact angles: 15.6 deg ± 2.5 deg and 12.9 deg ± 1.13 deg) and further treated with perfluorooctyltriethoxysilane to obtain superhydrophobicity (contact angles: 154.3 deg ± 1.9 deg and 165.5 deg ± 1.1 deg). Surface modification did not significantly affect bulk heat and mass transfer within 28–36 °C and 95% relative humidity, and the data agreed with the comsol model within 15% for temperature and 20% for water vapor concentration. Droplet growth behavior differed between treatments, where alkali-treated surfaces exhibited pinned droplets with larger departure diameters (2.061 ± 0.319 mm), while anodized surfaces had smaller, unpinned droplets (0.351 ± 0.151 mm). Under gravity-driven collection, superhydrophilic surfaces outperformed superhydrophobic ones, with anodized superhydrophobic surfaces showing the lowest collection efficiency.