Ne Nieck Benes

Inhibition of nonlinear acoustic cavitation dynamics in liquid CO2

The authors present a model to study ultrasound-induced cavitation dynamics in liquid carbon dioxide (CO(2)), which includes descriptions for momentum, mass, and energy transport. To assist in the interpretation of these results, numerical simulations are presented for an argon cavity in water. For aqueous systems, inertia effects and force accumulation lead to a nonlinear radial motion, resulting in an almost adiabatic compression of the cavity interior. The simulations for liquid CO(2) suggest that transport limitations impede nonlinear cavitation dynamics and the corresponding temperature rise. Consequently, in liquid CO(2) the ultrasound-induced formation of radicals appears improbable.

Grace: Development of Silica Membranes for Gas Separation at Higher Temperatures

This chapter discusses the development of silica membranes for gas separation at higher temperatures. Using a polymeric gel solution route, tubular micro-porous silica membranes showing high hydrogen permeance and high gas selectivities are prepared. Silica membranes are coated on top of steam-stable γ-Al 2 O 3 intermediate membranes inside a high-quality tubular support. Tube ends are coated with glass giving a gastight changeover between support and membranes. Single dead-end gas permeance measurements performed at temperatures > 300 °C and 4 bar pressure difference showed hydrogen fluxes >1.10 −6 mol m −2 s −1 Pa −1 while H 2 /CO 2 permselectivity under these conditions is 80–100. H 2 /CO 2 selectivity increases up to 200 with decreasing pressure down to 1 bar. Membranes are shown to be thermally stable for at least 2000 h at temperatures between 200 and 400 °C. Preliminary water-gas-shift experiments are performed at temperatures above 250 °C and showed higher than equilibrium CO conversion.