Hydrogen production rates of aluminum reacting with varying densities of supercritical water

April 2022
Keena Trowell, Sam Goroshin, David Frost, Jeffrey Bergthorson

Aluminum particles, spanning in size from 10 μm to 3 mm, were reacted with varying densities of water at 655 K. The density of the water is varied from 50 g L−1 to 450 g L−1 in order to understand the effect of density on both reaction rates and yields. Low-density supercritical water is associated with properties that make it an efficient oxidizer: low viscosity, high diffusion, and low relative permittivity. Despite this, it was found that the high-density (450 g L−1) supercritical water was the most efficient oxidizer both in terms of reaction rate and hydrogen yield. The 10 μm powder had a peak reaction rate of approximately 675 cmH23 min−1 gAl−1 in the high-density water, and a peak reaction rate below 250 cmH23 min−1 gAl−1 in the low- and vapour-density water. A decline in peak reaction rate with decreasing water density was also observed for the 120 μm powder and the 3 mm slugs. These findings imply that the increased collision frequency, a property of the high-density water, outpaces reduction in the reaction enhancing properties associated with low-density supercritical water. Hydrogen yield was minimally affected by decreasing the oxidizer density from 450 g L−1 to 200 g L−1, but did drop off significantly in the vapour-density (50 g L−1) water.

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