Air/fuel mixing in jet flames

The paper examines eight diverse regimes in which fuels can mix and react with air. These comprise: (i) Lifted subsonic; and (ii) supersonic jet flames, with (iii) and without (iv) cross flows; (v) Rim-attached flames; (vi) Early Downwash flames; (vii) Downwash-attached jet flames; and (viii) Fire Whirls.Correlations of characteristics within these regimes are principally in terms of a dimensionless Flow Number, U*, Cross Flow Reynolds number, Re_c, and, for Fire Whirls, a dimensionless Critical Velocity, CV. Boundaries of seven of the eight regimes are identified, through plots of U*, against Re_c, and of the eighth through a plot of CV against U*. The circumstances of transitions between regimes are identified. The study involves a variety of CH₄ cross flow flame measurements, in a wind tunnel. Cross flows can initially create a small lee-side flame downwash, due to the depression in pressure. With increasing fuel flow this might extend 1.3 m downwards from the horizontal tip of the vertical burner. Jet flames can attach to the downwash, which can become significant above Re_c ≈ 2000. More extensive downwash might further delay blow-off. Regime boundaries are constructed on the U*/Re_c diagram covering lifted flames, early downwash, and downwash-attached flames. The most powerful flames tend to be lifted, choked, flames, with cross flow, and fire whirls. Combustion becomes less efficient at high Re_c and low U*, although CH₄ was efficiently reacted.Experimental values of the ratio of fuel to air velocity, u/u_c, of CH₄ flames ranged between about 10 and 30 for lifted flames, and between 0.3 and 3.6, at blow-off, for rim-attached flames. The latter comprise an important category, often intermediate between lifted flames and downwash-attached flames.     

Catalytic Enantioselective Amination of Alcohols by the Use of Borrowing Hydrogen Methodology: Cooperative Catalysis by Iridium and a Chiral Phosphoric Acid

The catalytic asymmetric reduction of ketimines has been explored extensively for the synthesis of chiral amines, with reductants ranging from Hantzsch esters, silanes, and formic acid to H₂ gas. Alternatively, the amination of alcohols by the use of borrowing hydrogen methodology has proven a highly atom economical and green method for the production of amines without an external reductant, as the alcohol substrate serves as the H₂ donor. A catalytic enantioselective variant of this process for the synthesis of chiral amines, however, was not known. We have examined various transition‐metal complexes supported by chiral ligands known for asymmetric hydrogenation reactions, in combination with chiral Brønsted acids, which proved essential for the formation of the imine intermediate and the transfer‐hydrogenation step. Our studies led to an asymmetric amination of alcohols to provide access to a wide range of chiral amines with good to excellent enantioselectivity.     

3D Printed High‐Throughput Hydrothermal Reactionware for Discovery,Optimization, and Scale‐Up

3D printing techniques allow the laboratory‐scale design and production of reactionware tailored to specific experimental requirements. To increase the range and versatility of reactionware devices, sealed, monolithic reactors suitable for use in hydrothermal synthesis have been digitally designed and realized. The fabrication process allows the introduction of reaction mixtures directly into the reactors during the production, and also enables the manufacture of devices of varying scales and geometries unavailable in traditional equipment. The utility of these devices is shown by the use of 3D printed, high‐throughput array reactors to discover two new coordination polymers, optimize the synthesis of one of these, and scale‐up its synthesis using larger reactors produced on the same 3D printer. Reactors were also used to produce phase‐pure samples of coordination polymers MIL‐96 and HKUST‐1, in yields comparable to synthesis in traditional apparatus.     

Dispersion of cellulose nanocrystals in polar organic solvents

In an attempt to prepare stable dispersions of cellulose nanocrystals in dipolar aprotic solvents, dilute aqueous suspensions of cellulose nanocrystals were prepared by sulfuric acid hydrolysis of cotton. The aqueous suspensions were freeze-dried, and then sonicated in the solvent of interest. Dispersions of 1 and 3% w/v concentration were prepared in polar organic solvents DMSO and DMF. The dispersions showed flow birefringence. The redispersion was incomplete, and there was some evidence for aggregation in the suspensions. A small amount of water appeared to be critical to suspension stability. Birefringent cellulose films were prepared from the dispersions by drying under vacuum and at ambient conditions.     

Crystal Shape Characterisation of Dry Samples using Microscopic and Dynamic Image Analysis

A standard method to determine particle shape and size is by image analysis. This paper addresses microscopic image analysis (semi‐automated) investigations of two different organic crystalline chemicals generated by batch cooling crystallisation. The results generated from microscopic image analysis were compared with data obtained by dynamic image analysis (automated) because very few contributions are available in the open literature. The chemical systems were polymorphic L‐glutamic acid which crystallises into α (prismatic) or β (needle) form and the non‐polymorphic mono sodium glutamate which crystallises into needles. The images from these techniques were processed to generate information on crystal shape and size. It has been observed that shape effects can distort the size obtained in size characterization studies. In this study, comparisons were made of processing time, number of crystals and accuracy between microscopic and dynamic image analysis. For representative microscopic image analysis, 5000 crystals were analysed in an average of eight hours while several hundred thousand crystals were processed using dynamic image analysis within 15 minutes. Using the parameters D₁₀, D₅₀, D₉₀, span and aspect ratio for statistical comparison, it was found that the results obtained for D₅₀ by the two techniques were comparable and in accordance with other measurements (laser diffraction spectroscopy and ultrasonic attenuation spectroscopy) even though these non‐spherical particles had different orientations during measurement by the two methods. However, substantial differences in span of the distribution and aspect ratio were returned by the two techniques.