Interrogating the effect of an orifice on the upward two-phase gas–liquid flow behavior

Experiments are reported on an air–water mixture flowing through an orifice in a vertical pipe. Time series of cross-sectionally averaged void fractions have been measured at nine axial positions by using a conductance probe technique. A series of six orifices with different thicknesses and apertures were employed. The Probability Density Function, the Power Spectral Density of the time series of cross sectionally averaged void fractions and the cross-correlation of time series from adjacent probes have been obtained to determine the effect of the orifice on the flow characteristics. The diameter area ratio and the thickness of the orifice have a higher influence on bubbly than on slug and churn flows. The recovery length is about 20, 10 and 7 pipe diameter downstream the orifice for these three flow patterns respectively. Homogenization effect needs a minimum liquid superficial velocity. Its position occurs depends on the value of this velocity and on the orifice fractional open area. Just downstream the orifice, the structure velocity increases for the bubbly and slug flows and decreases for churn flow. For bubble and slug flows, there is persistency of the frequency when passing through the orifice from the upstream to the downstream pipe

Experimental investigation of air–water two-phase flow through vertical 90° bend

The behaviour of two-phase air–water mixture flowing from the horizontal to the vertical through a 90° bend has been investigated experimentally. Cross sectional void fraction at nine positions, three upstream and six downstream of the bend have been measured using a conductance probe technique. The bend, manufactured from transparent acrylic resin has a diameter of 34 mm and a curvature (R/D) equal to 5. The superficial velocity of the air was varied between 0.3 and 4 m/s and that for the water between 0.21 and 0.91 m/s. The characteristics signatures of Probability Density Function (PDF), the Power Spectral Density (PSD) of the time series of cross sectionally average void fraction and visual observations have been used to characterise the flow behaviour. For the experimental conditions, plug, slug and stratified wavy flow pattern occurred in the horizontal pipe while slug and churn flow patterns were present in the vertical pipe. The void fraction increased with the gas superficial velocity. The correlation of Nicklin et al. predicted the structure velocity for the slug flow in both horizontal and vertical pipes reasonably accurately. With regards to the frequency of the periodic structures present, some conditions showed little change from upstream to downstream the bend whilst others showed an increasing in the structure frequency from horizontal to vertical pipe. The slug length increased by passing through the vertical bend

The control and maintenance of desired flow patterns in bends of different orientations

Multiphase flows are common in industrial settings and bends in pipe lines cannot be avoided due to space limitations. Gas-liquid two phase flows could form material discontinuities that could have adverse effect on productivity and the pipe network due to sudden variations resulting due to the rapid momentum flux variations at fittings such as bends. Research into gas-liquid flow and bends can be motivated by the effect of the bend on the flow downstream of it which could alter the flow pattern occurring and the performance of downstream equipment. Alternatively, the interest might come from what occurs in the bend itself, there could be dryout of the film on the walls and consequent damage to the heat transfer equipment. Here we present measurements made with a number of accurate and fast responding sensors on three cases, two on the effect of the bend and one considering effects in the bend. The results show that the flow transformations occur in two phase flows depending on the orientation of the bend and the change could be captured using fast sweeping measurement techniques. We present the evidence of effectiveness of several types of measurement techniques that could fit into various combinations of phases. The results, point to how to achieve certain flow patterns. Also recommendations are provided regarding the position of any sensor installed to determine flow pattern

Extraction des essences du thymus numedius kabylliica

84 p. ; ill. ; 30 cmL’Etude paramétrique a permis d’évaluer, d’une part, les effets individuels sur le rendement en huile essentielle et la vitesse d’extraction des paramètres opératoires choisis. Et de définir le domaine expérimental du plan d’expériences d’autre part. L’étude par plan factoriel 23 et 22 a permis d’estimer les effets individuels et d’interactions des paramètres opératoires sur le rendement en huile essentielle. Ce dernier a été affecté par la porosité du lit, de l’interaction du débit de vapeur avec la porosité du lit aussi par l’interaction des trois paramètres pour l’entraînement à la vapeur d’eau, et affecté par l’effet simple du débit ainsi que l’interaction des deux paramètres pour l’hydrodistillation. Un modèle mathématique décrivant la variation du rendement en fonction de ces paramètres a été proposé. En outre, la condition de Fisher a été vérifiée, par conséquent le modèle établi pour la détermination du rendement est valable. De même, la méthode du simplex a été utilisée pour rechercher les conditions opératoires optimales du modèle établi, celle-ci a donné une valeur de rendement proche à celle obtenue par le plan d’expérience 2k. L’étude de la cinétique d’extraction a montré que les deux procédés évoluent selon l’ordre 1, ainsi que l’existence de deux étapes pour le processus d’entraînement à la vapeur d’eau et une seule étape pour le processus d’hydrodistillation. L’étude de l’influence des paramètres opératoires sur la constante de vitesse a montré que celle-ci est influencée par les variations de ces paramètres. L’activité insecticide, second aspect visé par cette étude, a porté sur l’évaluation de la toxicité par le mode contact de l’huile essentielle totale de thym ainsi que sa fraction recueillie après 2,5 min d’extraction par entraînement à la vapeur d’eau. Les résultats obtenus ont monté que les deux huiles présentent des effets insecticides sur Rhizopertha dominica. En effet, les pourcentages de mortalités croient avec la dose des huiles essentielles testées. Par ailleurs, les DL90 étaient de 4,34 (%V) pour l’huile de la fraction F1 et de 85,19 (%V) pour l’huile totale, la fraction F1 s’est montrée plus toxique que l’huile totale. L’examen de la composition chimique révèle 74,3% de thymol, ce qui laisse supposer que ce constituant pourrait être le principe actif de cette fraction. Des tests plus approfondis sont à envisager pour confirmer ou infirmer cette hypothèse. A travers ce travail, nous avons essayé de lever le voile sur certains aspects liés aux procédés d’extraction et à l’activité insecticide de l’huile essentielle de Thymus numidicus kabylica. Néanmoins, l’étude des procédés et leur application à la récupération des extraits des végétaux est un vaste domaine, notamment pour les secteurs de l’agriculture, pharmaceutique et agro-alimentaires, ouvrant ainsi de larges perspectives de recherche dont l’un des objectifs est la valorisation économique de la flore d’Algéri

Experimental study of the characteristics of an upward two-phase slug flow in a vertical pipe

Characteristics of the slug flow, mean void fraction, liquid slug and Taylor bubble lengths; and structure frequency were all extracted from the void fraction time series. Average void fractions at nine axial positions have been measured on a 6 m long (and 34 mm diameter) pipe test section by using conductance probes.For the flow conditions used, bubbly (with spherical cap bubble), slug/plug and churn/semi-annular flow patterns were observed. These observations were also confirmed by using statistical numbers.Time series analysis of the mean void fraction and its corresponding PDFs show that the effect of the mixer on the flow becomes, practically, negligible from a distance of 95 pipe diameter.It was found that, generally, the structure velocity can be well predicted from other available correlations in the literature.The theoretical model of Brauner and Ullmann was used to estimate the liquid in slug void fraction. It was inferred that this model is able to predict well the liquid slug void fraction; thus, it can be considered as one of the useful methods for predicting such parameter and to ascertain slug flow regime.The total pressure gradient was found to decrease with increasing gas superficial velocity