The ability of a rapid supercritical extraction (RSCE) process implemented in an industrial hot press to produce silica aerogel monoliths (AMs) with properties suitable for use in fenestration products was investigated. The effects of hot-press processing parameters such as press force and heat-up and cool-down rates on the size (area) and quality (presence of cracks and optical flaws) of the AMs produced, and on the manufacturing cycle times required to produce them, were studied. AMs of 14 × 14 × 1.27 cm were produced in a 6.5 h RSCE process using a laboratory scale (267 kN) hot press. Evacuated window prototypes were prepared by packaging aerogels in the interspaces of a double-glazing system under vacuum. The aerogels were found to have high translucency (>80% transmittance) in the red portion of the visible spectrum. The double-glazing evacuated aerogel windows were found to have thermal resistivity of 1.21−1.55 K·m 2 /W.

Aerogels offer a potential alternative to noble metals that could reduce both the cost and environmental impact associated with catalytic converter production. The environmental impact of the production of aerogel catalysts could be further reduced by using a rapid supercritical extraction (RSCE) technique, which reduces the time and solvent waste associated with aerogel preparation. Alumina aerogels, which have shown activity in catalyzing exhaust processing reactions, were prepared using an epoxide-assisted gelation technique with RSCE processing in a contained mold in a hydraulic hot press. Samples were characterized by FTIR, XRD, SEM, EDX, nitrogen adsorption porosimetry and pycnometry. Solvent characterization by GC-MS headspace analysis shows that excess propylene oxide and chloropropanol products of an irreversible epoxide ring-opening reaction are present in the alumina gel following gelation, but can be removed via solvent exchange. Alumina aerogels with surface areas as high as 790 m 2 /g and bulk densities as low as 0.05 g/mL were prepared. Preliminary characterization of these aerogels, utilizing a catalytic test bed and a simulated emissions gas blend, demonstrates that they have moderate ability for removal of hydrocarbons, carbon monoxide and nitrogen oxide.

No abstract

No abstract

This paper describes the methods and initial results of an investigation aimed at answering questions of engineering significance pertaining to slug flow. The authors use two approaches to study slug flow. First, the analytical solution of Gaskell et al and Gurcan [5,6] is examined in detail, with special attention being paid to its predictions pertaining to the special case of slug flow. The numerical behavior of this solution and the measures needed to enhance its convergence are also commented upon. Second, micro-PIV data of water/oil slug flow in a micro-channel is reported and examined in light of the predictions of the Gaskell model. Quantitative results showing the details of the re-circulating internal flow fields in the slugs are presented. Results for wall shear stress distributions and evolution of the velocity profiles from the centerline to the rear interface are also presented. Significant increases in the wall shear stress (compared to a fully developed Poiseuille flow) are observed in the regions near the fluid interfaces.