Gas-liquid two phase flow through a vertical 90deg elbow bend

Pressure drop data are reported for two phase air-water flow through a vertical to horizontal 90° elbow bend set in 0.026 m i.d. pipe. The pressure drop in the vertical inlet tangent showed some significant differences to that found for straight vertical pipe. This was caused by the elbow bend partially choking the inflow resulting in a build-up of pressure and liquid in the vertical inlet riser and differences in the structure of the flow regimes when compared to the straight vertical pipe. The horizontal outlet tangent by contrast gave data in general agreement with literature even to exhibiting a drag reduction region at low liquid rates and gas velocities between 1 and 2 m s -1. The elbow bend pressure drop was best correlated in terms of le/d determined using the actual pressure loss in the inlet vertical riser. The data showed a general increase with fluid rates that tapered off at high fluid rates and exhibited a negative pressure region at low rates. The latter was attributed to the flow being smoothly accommodated by the bend when it passed from slug flow in the riser to smooth stratified flow in the outlet tangent. A general correlation was presented for the elbow bend pressure drop in terms of total Reynolds numbers. A modified Lockhart-Martinelli model gave prediction of the data.

Design criteria for a barrier-based gas-liquid flow distributor for parallel microchannels

This paper presents criteria for the design of a flow distributor for even distribution of gas and liquid flows over parallel microchannels. The design criteria are illustrated for the case of a nitrogen-water Taylor flow (1

Numbered-up gas-liquid micro/milli channels reactor with modular flow distributor

Gas-liquid processing in microreactors remains mostly restricted to the laboratory scale due to the complexity and expenditure needed for an adequate numbering-up with a uniform flow distribution. Here, the numbering-up is presented for multi-phase (gas-liquid) flow in microreactor suitable for a production capacity of kg/h. Based on the barrier channels concept, the barrier-based micro/milli reactor (BMMR) is designed and fabricated to deliver flow non-uniformity of less than 10%. The BMMR consists of eight parallel channels all operated in the Taylor flow regime and with a liquid flow rate up to 150. mL/min. The quality of the flow distribution is reported by studying two aspects. The first aspect is the influence of different viscosities, surface tensions and flow rates. The second aspect is the influence of modularity by testing three different reaction channels type: (1) square channels fabricated in a stainless steel plate, (2) square channels fabricated in a glass plate, and (3) circular channels (capillaries) made of stainless steel. Additionally, the BMMR is compared to that of a single channel regard the slug and bubble lengths and bubble generation frequency. The results pave the ground for bringing multi-phase flow in microreactor one step closer for large scale production via numbering-up. © 2012 Elsevier B.V.

Microelectrode Voltammetry of Dioxygen Reduction in a Phosphonium Cation-Based Room-Temperature Ionic Liquid: Quantitative Studies

Microelectrode voltammetry is used to study the electrochemical reduction of dioxygen, O-2, in the room-temperature ionic liquid trihexyl(tetradecyl)phosphonium trifluorotris(pentafluoroethyl)phosphate [P6,6,6,14][FAP]. The nature of the unusual voltammetric waves is quantitatively modeled via digital simulation with the aim of clarifying apparent inconsistencies in the literature. The reduction is shown to proceed via a two-electron reaction and involve the likely capture of a proton from the solvent system. The oxidative voltammetric signals seen at fast scan rates are interpreted as resulting from the reoxidation of HO2 center dot. In the presence of large amounts of dissolved carbon dioxide the reductive currents decrease by a factor of ca. two, consistent with the trapping of the superoxide radical, O-2(center dot), intermediate in the two-electron reduction process.

Hydrogenation/hydrogenolysis of disulfides using sulfided Ni/Mo catalysts

The mechanism of the hydrogenation/hydrogenolysis of dinitrodiphenyldisulfides using sulfided NiMo/ gamma Al2O3 catalysts has been examined in detail. Although two routes are possible, the major pathway involves an initial S-S bond cleavage followed by reduction of the nitro group. Importantly, the disulfide hydrogenolysis occurs in the absence of the catalyst with the role of the catalyst thought to be to activate the hydrogen and trap the cleaved intermediate as well as facilitate the reduction of the nitro group. Monitoring the mass balance throughout the reaction demonstrates the difficulty in measuring intrinsic kinetics for gas-liquid-solid reactions. Although the mass balance is restored at the end of the reaction, up to 45% of the substrate/products is found to be adsorbed on the catalyst during the reaction. (c) 2008 Elsevier B.V. All rights reserved.

Desulfurisation of oils using ionic liquids: selection of cationic and anionic components to enhance extraction efficiency

Extraction of dibenzothiophene from dodecane using ionic liquids as the extracting phase has been investigated for a range of ionic liquids with varying cation classes (imidazolium, pyridinium, and pyrrolidinium) and a range of anion types using liquid-liquid partition studies and QSPR (quantitative structure-activity relationship) analysis. The partition ratio of dibenzothiophene to the ionic liquids showed a clear variation with cation class (dimethylpyridinium > methylpyridinium > pyridinium approximate to imidazolium approximate to pyrrolidinium), with much less significant variation with anion type. Polyaromatic quinolinium-based ionic liquids showed even greater extraction potential, but were compromised by higher melting points. For example, 1-butyl-6-methylquinolinium bis{(trifluoromethyl)sulfonyl} amide (mp 47 degrees C) extracted 90% of the available dibenzothiophene from dodecane at 60 degrees C.

Two-phase flow regimes in microchannels

Capillary hydrodynamics has three considerable distinctions from macrosystems: first, there is an increase in the ratio of the surface area of the phases to the volume that they occupy; second, a flow is characterized by small Reynolds numbers at which viscous forces predominate over inertial forces; and third, the microroughness and wettability of the wall of the channel exert a considerable influence on the flow pattern. In view of these differences, the correlations used for tubes with a larger diameter cannot be used to calculate the boundaries of the transitions between different flow regimes in microchannels. In the present review, an analysis of published data on a gas-liquid two-phase flow in capillaries of various shapes is given, which makes it possible to systematize the collected body of information. The specific features of the geometry of a mixer and an inlet section, the hydraulic diameter of a capillary, and the surface tension of a liquid exert the strongest influence on the position of the boundaries of two-phase flow regimes. Under conditions of the constant geometry of the mixer, the best agreement in the position of the boundaries of the transitions between different hydrodynamic regimes in capillaries is observed during the construction of maps of the regimes with the use of the Weber numbers for a gas and a liquid as coordinate axes.

Pressure drop of gas–liquid Taylor flow in round micro-capillaries for low to intermediate Reynolds numbers

In this paper, a model is presented that describes the pressure drop of gas-liquid Taylor flow in round capillaries with a channel diameter typically less than 1 mm. The analysis of Bretherton (J Fluid Mech 10:166-188, 1961) for the pressure drop over a single gas bubble for vanishing liquid film thickness is extended to include a non-negligible liquid film thickness using the analysis of Aussillous and Qu,r, (Phys Fluids 12(10):2367-2371, 2000). This result is combined with the Hagen-Poiseuille equation for liquid flow using a mass balance-based Taylor flow model previously developed by the authors (Warnier et al. in Chem Eng J 135S:S153-S158, 2007). The model presented in this paper includes the effect of the liquid slug length on the pressure drop similar to the model of Kreutzer et al. (AIChE J 51(9):2428-2440, 2005). Additionally, the gas bubble velocity is taken into account, thereby increasing the accuracy of the pressure drop predictions compared to those of the model of Kreutzer et al. Experimental data were obtained for nitrogen-water Taylor flow in a round glass channel with an inner diameter of 250 mu m. The capillary number Ca (gl) varied between 2.3 x 10(-3) and 8.8 x 10(-3) and the Reynolds number Re (gl) varied between 41 and 159. The presented model describes the experimental results with an accuracy of +/- 4% of the measured values.

Hydrodynamics and mixer-induced bubble formation in micro bubble columns with single and multiple-channels

A hydrodynamic characterization of an industrially used gas-liquid contacting microchannel. device is discussed, viz. the micro bubble column of IMM. Furthermore, similar characterization of a gas-liquid flow microchip of TU/e, with two tailored mixer designs, is used to solve fundamental issues on hydrodynamics, and therefore, to achieve further design and operating optimization of that chip and the IMM device. Flow pattern maps are presented in a dimensionless fashion for further predictions on new fluidic systems for optimum single-channel multiphase operation. Bubble formation was investigated in the two types of mixers and pinch-off and hydrodynamic decay mechanisms are observed. The impact of these mechanisms on bubble size, bubble size distributions, and on the corresponding flow patterns, i.e., the type of mixer design, can be decisive for the flow pattern map and thus, may be used to alter flow pattern maps. The bubble sizes and their distribution were improved for the tailored designs, i.e., smaller and more regular bubbles were generated. Finally, the impact of multi-channel distribution for gas and liquid flow is demonstrated. Intermediate flow patterns such as slug-annular flow, also found for single-phase operation, and the simultaneous coexistence of flow regimes are presented, with the latter providing evidence of flow maldistribution.

Magma Evolution in the Primitive, Intra-oceanic Tonga Arc: Petrogenesis of Basaltic Andesites at Tofua Volcano

Tofua volcano is situated midway along the Tonga oceanic arc and has undergone two phases of ignimbrite-forming activity. The eruptive products are almost entirely basaltic andesites (52 center dot 5-57 wt % SiO2) with the exception of a volumetrically minor pre-caldera dacite. The suite displays a strong tholeiitic trend with K2O <1 wt %. Phenocryst assemblages typically comprise plagioclase + clinopyroxene +/- orthopyroxene with microlites of Ti-magnetite. Olivine (Fo(83-88)) is rare and believed to be dominantly antecrystic. An increase in the extent and frequency of reverse zoning in phenocrysts, sieve-textured plagioclase and the occurrence of antecrystic phases in post-caldera lavas record a shift to dynamic conditions, allowing the interaction of magma batches that were previously distinct. Pyroxene thermobarometry suggests crystallization at 950-1200 degrees C and 0 center dot 8-1 center dot 8 kbar. Volatile measurements of glassy melt inclusions indicate a maximum H2O content of 4 center dot 16 wt % H2O, and CO2-H2O saturation curves indicate that crystallization occurred at two levels, at depths of 4-5 center dot 5 km and 1 center dot 5-2 center dot 5 km. Major and trace element models suggest that the compositions of the majority of the samples represent a differentiation trend whereby the dacite was produced by 65% fractional crystallization of the most primitive basaltic andesite. Trace element models suggest that the sub-arc mantle source is the residuum of depleted Indian mid-ocean ridge basalt mantle (IDMM-1% melt), whereas radiogenic isotope data imply addition of 0 center dot 2% average Tongan sediment melt and a fluid component derived from the subducted altered Pacific oceanic crust. A horizontal array on the U-Th equiline diagram and Ra excesses of up to 500% suggest fluid addition to the mantle wedge within the last few thousand years. Time-integrated (Ra-226/Th-230) vs Sr/Th and Ba/Th fractionation models imply differentiation timescales of up to 4500 years for the dacitic magma compositions at Tofua.

A microbiological study of Papillon-Lefévre syndrome in two patients

AIM: To analyse the microflora of subgingival plaque from patients with Papillon-Lefévre syndrome (PLS), which is a very rare disease characterised by palmar-plantar hyperkeratosis with precocious periodontal destruction.

METHODS: Bacterial isolates were identified using a combination of commercial identification kits, traditional laboratory tests, and gas liquid chromatography. Some isolates were also subjected to partial 16S rDNA sequencing. Plaque samples were also assayed for the presence of Porphyromonas gingivalis, Prevotella intermedia, and Actinobacillus actinomycetemcomitans in a quantitative enzyme linked immunosorbent assay (ELISA) using monoclonal antibodies.

RESULTS: The culture results showed that most isolates were capnophilic and facultatively anaerobic species-mainly Capnocytophaga spp and Streptococcus spp. The latter included S. constellatus, S. oralis, and S. sanguis. Other facultative bacteria belonged to the genera gemella, kingella, leuconostoc, and stomatococcus. The aerobic bacteria isolated were species of neisseria and bacillus. Anaerobic species included Prevotella intermedia, P. melaninogenica, and P. nigrescens, as well as Peptostreptococcus spp. ELISA detected P gingivalis in one patient in all sites sampled, whereas A. actinomycetemcomitans was detected in only one site from the other patient. Prevotella intermedia was present in low numbers.

CONCLUSIONS: Patients with PLS have a very complex subgingival flora including recognised periodontal pathogens. However, no particular periodontopathogen is invariably associated with PLS.

A note on the prediction of liquid hold-up with the stratified roll wave regime for gas/liquidco-current flow in horizontal pipes.

This note presents a simple model for prediction of liquid hold-up in two-phase horizontal pipe flow for the stratified roll wave (St+RW) flow regime. Liquid hold-up data for horizontal two-phase pipe flow [1, 2, 3, 4, 5 and 6] exhibit a steady increase with liquid velocity and a more dramatic fall with increasing gas rate as shown by Hand et al. [7 and 8] for example. In addition the liquid hold-up is reported to show an additional variation with pipe diameter. Generally, if the initial liquid rate for the no-gas flow condition gives a liquid height below the pipe centre line, the flow patterns pass successively through the stratified (St), stratified ripple (St+R), stratified roll wave, film plus droplet (F+D) and finally the annular (A+D, A+RW, A+BTS) regimes as the gas rate is increased. Hand et al. [7 and 8] have given a detailed description of this progression in flow regime development and definitions of the patterns involved. Despite the fact that there are over one hundred models which have been developed to predict liquid hold-up, none have been shown to be universally useful, while only a handful have proven to be applicable to specific flow regimes [9, 10, 11 and 12]. One of the most intractable regimes to predict has been the stratified roll wave pattern where the liquid hold-up shows the most dramatic change with gas flow rate. It has been suggested that the momentum balance-type models, which give both hold-up and pressure drop prediction, can predict universally for all flow regimes but particularly in the case of the difficult stratified roll wave pattern. Donnelly [1] recently demonstrated that the momentum balance models experienced some difficulties in the prediction of this regime. Without going into lengthy details, these models differ in the assumed friction factor or shear stress on the surfaces within the pipe particularly at the liquid–gas interface. The Baker–Jardine model [13] when tested against the 0.0454 m i.d. data of Nguyen [2] exhibited a wide scatter for both liquid hold-up and pressure drop as shown in Fig. 1. The Andritsos–Hanratty model [14] gave better prediction of pressure drop but a wide scatter for liquid hold-up estimation (cf. Fig. 2) when tested against the 0.0935 m i.d. data of Hand [5]. The Spedding–Hand model [15], shown in Fig. 3 against the data of Hand [5], gave improved performance but was still unsatisfactory with the prediction of hold-up for stratified-type flows. The MARS model of Grolman [6] gave better prediction of hold-up (cf. Fig. 4) but deterioration in the estimation of pressure drop when tested against the data of Nguyen [2]. Thus no method is available that will accurately predict liquid hold-up across the whole range of flow patterns but particularly for the stratified plus roll wavy regime. The position is particularly unfortunate since the stratified-type regimes are perhaps the most predominant pattern found in multiphase lines.

Dramatic liquid-phase dehydrogenation rate enhancements using gas-phase hydrogen acceptors

The dehydrogenation of 1,2,3,4-tetrahydrocarbazole (THCZ) to form carbazole (CZ) over supported palladium catalysts was examined in the presence of hydrogen acceptors. As expected, liquid hydrogen acceptors increased the rate of reaction but, importantly, gaseous hydrogen acceptors also have been used. Ethene, propene, and but-1-ene showed up to a fivefold increase in the rate of dehydrogenation. Moreover, compared with the analogous liquid systems, the gaseous alternatives are a potentially more economic method of enhancing the activity and provide a simpler workup. The mechanism for the increase in rate was examined by density functional theory calculations, which showed that the propene hydrogenation competes effectively with the back-hydrogenation of the intermediates formed during the THCZ dehydrogenation, resulting in a shift in the equilibrium toward to the formation of CZ. (C) 2007 Elsevier Inc. All rights reserved.

Evaluation of Pt and Re oxidation state in a pressurized reactor: difference in reduction between gas and liquid phase

Determination of metal oxidation state under relevant working conditions is crucial to understand catalytic behaviour. The reduction behaviour of Pt and Re was evaluated simultaneously as a function of support and solvent in a pressurized reactor (autoclave). The bimetallic catalysts are used in selective hydrogenation of carboxylic acids and amides. Gas phase reduction reduced the metals more efficiently, in particular Pt.