Improving Direct Air Capture of Carbon Dioxide with Geometry-induced Instability

Many proposed systems for removing carbon dioxide directly from the atmosphere rely on wall bounded, low-Reynolds-number flows, thereby suffering from poor rates of mass transport. Incorporating geometric wall textures (grooves transverse to the flow) can give rise to flow instabilities that may improve mass transfer with low additional cost in system pumping power. In channel flow geometries, prior numerical simulations indicate that the flow becomes unstable at a critical Reynolds number of order 100; the resulting secondary flow is predicted to exhibit stable waves reminiscent of Tollmien-Schlichting modes. We report experimental measurements in a channel with one wall textured by spanwise grooves placed periodically in the streamwise direction. We examine instability onset and the resulting secondary flow as a function of the channel aspect ratio. Additionally, 2D and 3D simulations of the early transition process are presented for groove patterns with differing periodicity.