Velocity profile characterization in sub-millimeter diameter tubes using molecular tagging velocimetry

Fluid flow through microtubes is of interest to many industries and there exists a need for detailed measurements of the velocity field. Velocity profile data are critical for momentum, mass, and heat transport analysis, and thus the design of devices utilizing microgeometries. This paper outlines a measurement technique that has led to time-resolved measurements of velocity profiles in microtubes (less than 1,000 μm). The research program was experimental in nature and consisted of an extension of molecular tagging velocimetry to the microscale. Average velocity and rms profile data in the fully developed region, in addition to mass flow rate and pressure drop data, are presented for numerous Reynolds numbers ranging from 600 to 5,000 in a tube of diameter 705 μm. Received: 20 December 1999 / Accepted: 20 March 2001     

Sorption of inorganic nanoparticles in woven cellulose fabrics

Titanium dioxide was deposited from aqueous suspension onto cellulosic surfaces.Titania was sourced from Degussa (P25TM,70:30 anatase:rutile).Dry uptake of particles was shown to be rapid and dominant with one-third of the deposition occurring in less than 30 s and over one-half in the first minute.Isotherms were recorded to compare the rate of titanium deposition on dry and pre-wetted cotton.In the dry case uptake reached a maximum in 30 min whereas in the pre-wetted case the uptake was seen to continue beyond 180 min.A broad trend of higher deposition occurring at lower pH was seen,corresponding to the region where surface charges were opposite and thus attractive.Dry pickup was less significant at high pH.The response to varying ionic strength was complex and was attributed to the combined effect of charge screening,particle aggregation and consequent particle entrapment or occlusion.Titania deposition into the interstices of woven cotton sheets resulted in the formation of inorganic,nanoparticulate skeletons which could be isolated by controlled combustion of the cellulose and thus cotton was suggested to have potential for the templated synthesis of high surface area semiconductor materials.     

Safety concerns in ultrahigh pressure capillary liquid chromatography using air-driven pumps

Ultrahigh pressure liquid chromatography (UHPLC) is an emerging technique which utilizes pressures higher than 10,000 p.s.i. to overcome the flow resistance imposed when using very small particles as packing materials in fused-silica capillary columns (1 p.s.i.=6894.76 Pa). This technique has demonstrated exceptionally high separation speeds and chromatographic efficiencies. However, safety is a concern when extremely high pressures are used. In this study, the safety aspects of capillary column rupture during operation were identified and carefully evaluated. First, liquid jets may be formed as a result of blow-out of the on-column frits or from rupture of the capillary at or near the column inlet. Second, incorrect installation of the capillary at the injector, failure of the ferrule used in the capillary connection, or rupture of the capillary can produce high speed projectiles of silica particles or column fragments. Experiments were carried out in the laboratory to produce liquid (water) jets and capillary projectiles using a UHPLC system, and the power density, an important parameter describing water jets in industrial practice, was calculated. Experimental results were in accordance with theoretical calculations. Both indicated that water jets and capillary projectiles under ultrahigh pressures might lead to skin penetration under limited conditions. The use of a plexiglass shroud to cover an initial length of the installed capillary column can eliminate any safety-related concerns about liquid jets or capillary projectiles.     

Syntheses and reactions of some fluorinated dienes,cyclobutenes and furans

There are many reports¹ of the pyrolysis of fluorinated organic compounds, including the defluorination of cyclic fluorocarbons over iron to give aromatic compounds. Extending this technique we have investigated the flow pyrolysis of some readily accessible unsaturated fluorocarbons, such as I, II, and III, and found these to be synthetically

useful routes to fluorinated dienes, cyclobutenes, and furans. Pyrolyses were carried out using a nitrogen flow over platinum, iron or caesium fluoride heated at 430–700°. The various products can all be rationalized in terms of intermediate allylic radicals, and the solid substrate influences which allylic radicals are formed.We are also investigating the chemistry of those now accessible compounds, such as IV, V, and VI, and some of the preliminary results are described.

For example the fluoride ion induced dimerisation of IV gave two major products VII and VIII via a particular interesting mechanism.