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The rheological properties of membrane biofouling layers developing in Membrane Bioreactors (MBR) have not been measured directly so far, although they are essential for understanding biofouling and for determining conditions to mitigate it. The development of a novel method is reported herein, which permits accurate rheological measurements on membrane biofouling layers, using specimens withdrawn from an operating laboratory-scale MBR. A specially designed test-section (with a pair of flat membrane specimens) allows implementation of realistic operating modes, including automatic periodic back-washing. The membrane specimens, with a biofouling layer representative of a well-controlled MBR operating history, are examined in an advanced parallel-plate rheometer, where special care is taken to prevent ex-situ biofouling layer changes. Measurements performed in oscillatory and steady shearing modes provide valuable information on biofouling layer rheological characteristics, confirming that these layers are typical viscoelastic materials with yield stress exhibiting thixotropic, shear-thinning behavior. Rheological properties of the activated sludge liquor are also assessed. The rheological properties of activated sludge and of biofouling layers display qualitative similarities, although the elastic character of the latter is much more pronounced. The new technique is most useful for studying biofouling layers as a function of the main MBR process parameters. Improvements of the technique for such applications are discussed.

Rheological property data (practically and theoretically significant) of typical desalination-membrane fouling layers are reported for the first time in this study, involving two stages. First, desalination of brackish water (with 30 mg/L sodium alginate) was carried out under constant flux; Ca 2+ -ion concentration 1 mM–8 mM was used. Linear temporal trans-membrane pressure increase, associated with constant specific fouling resistance α , indicated uniformity of growing alginate layers. Fouling resistance α increased with calcium concentration. Subsequently, fouled membrane segments were tested in a parallel-plate rheometer, operating in oscillatory and steady shearing modes. Key rheological parameters of fouling layers, including storage ( G ′) and loss ( G ″) moduli, complex and shear viscosities, were assessed in relation to their permeability and other characteristics. Alginate fouling layers possess viscoelastic properties characteristic of rather stiff gels; moreover, they belong in the class of thixotropic materials with yield stress. Layers from feed-water of small Ca +2 -ion concentration exhibit strong elastic character, high viscosities and yield stresses; the elastic character and rheological parameter values are reduced with increasing Ca 2+ -ion concentration. The high Na-ion concentration in the fouling layers appears to significantly influence their structure; however, considering the complicated dynamics of developing layers, the relative significance of the abundant Na-ions compared to Ca 2+ -ions is unclear.

The dispersion of a passive scalar in a turbulent boundary layer has been investigated experimentally in a wind tunnel. Heat was used as a passive scalar based on the fact that the mass and heat diffusivities for gases are of the same order. For that purpose, a planar heat source was mounted on the surface of a flat plate and consequently, the heat released was carried downstream by the plate’s boundary layer. Hot wire anemometry with a specially designed triple-wire probe was employed for the direct measurement of two turbulent heat flux components and a momentum flux component. Measurement of the normal (to the plate) heat flux led to the determination of the eddy diffusivity of heat directly from the experimental data. The experimental data were further analyzed by the quadrant-splitting technique. It was found that primarily, heat was carried by only one basic fluid motion, the “ejections”.

The flow behaviour and flow pattern transitions of two-phase flow of short airlift pumps were investigated in a wide range of submergence ratios and air discharges. This was obtained using conductivity signals from point-conductivity probes along with visual observations. It was found that the transitions between the various flow patterns depend on the submergence ratio and that the two-phase flow structure can change characteristics along the riser tube. A flow regime map is presented which takes into account the operational parameters, namely superficial gas velocity and submergence ratio, of the airlift pump.

Aim To evaluate the effect of root canal taper on irrigant flow inside a prepared root canal during final irrigation with a syringe and two types of needles, using a Computational Fluid Dynamics (CFD) model. Methodology A validated CFD model was used to simulate irrigant flow from either a side-vented or a flat 30G needle positioned inside size 30, .02 taper, 30, .04, 30, .06, ProTaper F3 or size 60, .02 taper root canals, at 3 mm short of working length (WL). Velocity, pressure and shear stress in the root canal were evaluated. Results The side-vented needle could not achieve irrigant replacement to the WL in any of the cases. Significant irrigant replacement was evident further than 2 mm apically to the tip of the flat needle in the size 30, .06 taper, F3 and size 60, .02 taper canal. A wider distribution of wall shear stress was noted as the canal taper increased but the maximum shear stress decreased. The flat needle led to higher mean pressure at the apical foramen. Both needles showed a similar gradual decrease in apical pressure as the taper increased, but the least pressure was calculated in the size 60, .02 taper canal. Conclusions An increase in root canal taper improved irrigant replacement and wall shear stress whilst reducing the risk for irrigant extrusion. Irrigant flow in a minimally tapered root canal with a large apical preparation size also improved irrigant replacement and wall shear stress and reduced the risk for irrigant extrusion, compared to the tapered root canals with a smaller apical preparation size.

Aim To evaluate the effect of apical preparation size on irrigant flow inside a root canal during final irrigation with a syringe and two different needles types, using a Computational Fluid Dynamics (CFD) model. Methodology A validated CFD model was used to simulate the irrigant flow from either a side-vented or a flat 30G needle positioned inside root canals having sizes of 25, 35, 45 and 55, all with a .06 taper, at 3 mm short of working length (WL). Velocity, pressure and shear stress in the root canal were evaluated. Results Different preparation sizes resulted in minor differences in the flow pattern in the apical root canal. Major differences were observed between the two needle types. The side-vented needle could not achieve irrigant replacement to the WL even in a size 55, .06 taper root canal. Significant irrigant replacement was evident almost to the WL in size 35, 45 and 55, .06 taper root canals with the flat needle. The maximum shear stress decreased as the preparation size increased. The flat needle developed higher mean pressure at the apical foramen. Both needles led to a similar gradual decrease in apical pressure as the preparation size increased. Conclusions Apical preparation size affected irrigant replacement, the shear stress on the canal wall and the pressure at the apical foramen. Root canal enlargement to sizes larger than 25 appeared to improve the performance of syringe irrigation. Adequate space between the needle and the canal wall should be ensured to allow for an effective reverse flow of the irrigant towards the canal orifice

The pressure behaviour in riser tubes of a short airlift pump was investigated for various submergence ratios, air discharges and riser tube lengths. Two high-frequency response pressure transducers were placed at various positions along the riser tube. The analysis of the recorded pressure signals gave the mean local pressure at specified vertical positions for various submergence ratios, air discharges and riser tube lengths. The experimental data show a non-linear pressure behaviour near the exit of the air ejector due to the increased friction losses in this region. The pressure behaviour for increasing air discharge at a position along the riser tube is related to the corresponding two-phase flow pattern in the riser tube. The pressure distributions along the riser tube for various submergence ratios were compared with the predictions of the Stenning–Martin model.

This paper reports the preparation of lignite−water slurries (LWS) and critical characteristics affecting their rheology. The slurries were prepared using wet grinding in a ball mill, having particle size distributions up to 300 μm and concentrations up to 50 wt % in solids. Surfactants and polyelectrolytes were used as additives in the slurryfication process to achieve acceptable rheological behavior and stability. Rheological measurements were performed using parallel disks geometry, and the typical shear rates were on the order from 10−2 to 103 s−1. The effect of the particle size distribution was investigated, and the apparent viscosity of the slurries, for the same solids volume fraction, was found to be lower for broad multimodal distributions. In addition, oscillatory rheological measurements were carried out to investigate the microstructure of the slurries, and it was observed that, for dense LWS (ϕ > 0.40), the viscoelastic behavior was controlled by the elastic contribution than the viscous one...

Boutsioukis C, Verhaagen B, Versluis M, Kastrinakis E, van der Sluis LWM. Irrigant flow in the root canal: experimental validation of an unsteady Computational Fluid Dynamics model using high-speed imaging. International Endodontic Journal 43, 393‐403, 2010. Aim To compare the results of a Computational Fluid Dynamics (CFD) simulation of the irrigant flow within a prepared root canal, during final irrigation with a syringe and a needle, with experimental high-speed visualizations and theoretical calculations of an identical geometry and to evaluate the effect of off-centre positioning of the needle inside the root canal. Methodology A CFD model was created to simulate irrigant flow from a side-vented needle inside a prepared root canal. Calculations were carried out for four different positions of the needle inside a prepared root canal. An identical root canal model was made from poly-dimethyl-siloxane (PDMS). Highspeed imaging of the flow seeded with particles and Particle Image Velocimetry (PIV) were combined to obtain the velocity field inside the root canal experimentally. Computational, theoretical and experimental results were compared to assess the validity of the computational model. Results Comparison between CFD computations and experiments revealed good agreement in the velocity magnitude and vortex location and size. Small lateral displacements of the needle inside the canal had a limited effect on the flow field. Conclusions High-speed imaging experiments together with PIV of the flow inside a simulated root canal showed a good agreement with the CFD model, even though the flow was unsteady. Therefore, the CFD model is able to predict reliably the flow in similar domains.

In the present study synovial fluid (SF) obtained from the stifle joint of healthy adult dogs and of dogs after cranial cruciate ligament rupture was analyzed regarding its rheological characteristics according to the condition of the joint. The viscoelastic and shear flow properties were measured at 25 and 38 °C. The results showed that the healthy SF exhibits practically temperature independent viscosity curve and satisfactory viscoelastic characteristics, i.e. G′ > G′′, over frequencies of 0.05–5 Hz, and characteristic relaxation time λ of the order of magnitude of 100 s. Creep measurements demonstrate that the zero shear viscosity was in the range of 10–100 Pa s. In shear flow viscosity measurements, by increasing $$ \dot{\gamma } $$ from 10−4 s−1 up to 103 s−1, non-Newtonian shear thinning behavior was observed and the viscosity values were decreased from 103 to 0.1 Pa s. On the contrary, in pathological conditions of cranial cruciate ligament rupture (CCLR), the measured viscosity was found drastically reduced, i.e. between 100 and 10 mPa s. The CCLR synovial fluid, similar to healthy SF, exhibits insignificant temperature dependence. The present study showed also that about one week after a surgery for CCLR repair the SF exhibits non-Newtonian behavior of dilute polymers. After two weeks from the operation, however, the rheological behavior converges to the one of healthy SF.

Aim To study using computer simulation the effect of irrigant flow rate on the flow pattern within a prepared root canal, during final irrigation with a syringe and needle. Methodology Geometrical characteristics of a side-vented endodontic needle and clinically realistic flow rate values were obtained from previous and preliminary studies. A Computational Fluid Dynamics (CFD) model was created using FLUENT 6.2 software. Calculations were carried out for five selected flow rates (0.02–0.79 mL sec−1) and velocity and turbulence quantities along the domain were evaluated. Results Irrigant replacement was limited to 1–1.5 mm apical to the needle tip for all flow rates tested. Low-Reynolds number turbulent flow was detected near the needle outlet. Irrigant flow rate affected significantly the flow pattern within the root canal. Conclusions Irrigation needles should be placed to within 1 mm from working length to ensure fluid exchange. Turbulent flow of irrigant leads to more efficient irrigant replacement. CFD represents a powerful tool for the study of irrigation.

Aspects of dense lignite–water slurries (LWS) rheology were investigated using controlled stress and controlled strain rheometers with parallel disks and Couette geometries. During the preparation of the slurries, the achieved solids volume fractions were up to 0.425 and the particle size distributions were polydispersed with sizes up to 300 μm. In the ascending parts of consecutive flow loops, a slope transition of the flow curve was observed and studied in relation to the solids volume fraction. The obtained results with the different geometries and rheometers were qualitatively the same. By following the model proposed by Cheng (Rheol Acta 42:372–382, 2003) for thixotropic fluids, and taking into account the yield stress appearance, a suitable correlation for LWS is proposed, which is consistent with the experimental flow curves.

An investigation of the rheological properties of dense lignite-water suspensions is reported here in order to evaluate the parameters that affect the rheology of these suspensions. Different types of particle size distributions were achieved via wet grinding with particle sizes down to 1 µm. Polyelectrolytes and surfactants were used to improve the stability and rheology of suspensions. The achieved solid volume fraction, φ, with acceptable rheological behavior was 0.45, while the ratio of φ/φ m was close to 0.85; φ m is the maximum solid volume fraction. Various types of flow tests were performed on lignite-water suspensions with various preshear times and stress levels. Typical shear rates varied in the range between 10–2 to 102 s–1. The low shear behavior was found to be quite different from the high shear behavior for the most concentrated suspensions, with a plateau value at low shear rates indicating the appearance of a yield stress. These plateau values, however, depend on shear history, which is responsible for the development of different structures in the sample. The viscosity curves corresponding to the ascending and descending parts of the flow curve were found to be different; these flow curve parts can be described either by well established models or by modified ones. The non-Newtonian time dependent behavior of the lignite-water suspensions is attributed to the high value of the ratio φ/φ m , the polydispersity of the particle size distribution, and the non-spherical shape of the lignite particles.

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An experimental study of heat transport in the interaction region between the wake of a cylinder and a turbulent boundary layer is presented in this work. The cylinder was placed parallel to a flat plate and normal to the flow. Its position was selected above the boundary layer edge, so that the lower part of the wake was interacting with the boundary layer. Heat was supplied to the boundary layer flow by means of a line heat source. Presence of surface roughness on the cylinder resulted in the deviation of the velocity power spectrum scaling region from the −5/3 power law which is characteristic of three-dimensional turbulence. Point measurements of the instantaneous values of two velocity components and temperature have been taken using hot-wire anemometry. Two turbulent scalar flux components and a Reynolds shear stress component have been obtained directly from the experimental data. Results were assessed in conjunction with the periodic coherent structures in the wake (a von Karman vortex street) using a phase-averaging technique that provided a clear picture of the heat transport procedures involved.

The root canal system of a tooth is a complex geometrical entity, consisting not only of the main root canal, but also of accessory and lateral canals. Bacteria can reside up to hundreds of micrometers inside those channels and may be difficult to reach for the antimicrobial agents with which root canals are irrigated during a root canal treatment. A combined numerical and experimental study was performed to assess the penetration rate of a root canal irrigant into the lateral canals and tubules, considering both diffusion and convection. The numerical model was validated experimentally using a fluorescent dye. Convection was studied separately using a Computational Fluid Dynamics model, validated with Particle Imaging Velocimetry experiments. Both diffusion and convection were found to be slow on the timescale of an irrigation procedure. The contribution of convection was limited to two canal diameters from the canal entrance, making diffusion the main irrigant transport mechanism. More than 10 min of fresh irrigant delivery was required to obtain an 86 % concentration of the irrigant at the far end of a tubule, in the ideal case of a straight tubule without reaction taking place. Diffusion was even slower when the concentration at the lateral canal entrance was not kept constant, as in the case of a single delivery, which suggests that frequent irrigant replenishment and/or irrigant activation during a root canal treatment are beneficial. Alternative methods should be considered to improve irrigant penetration into lateral canals and tubules.

Aim(i) To evaluate the effect of needle type and insertion depth, root canal size and irrigant flow rate on the entrapment of air bubbles in the apical part of a root canal (apical vapor lock) during syringe irrigation using experiments and a Computational Fluid Dynamics (CFD) model, (ii) to investigate whether the irrigant contact angle affects bubble entrapment, (iii) to examine if an established vapor lock can be removed by syringe irrigation.MethodologyBubble entrapment during irrigation of straight artificial root canals of size 35 or 50 was evaluated by real-time visualizations. The irrigant was delivered by a closed-ended or an open-ended needle positioned at 1 or 3mm short of working length (WL) and at a flow rate of 0.033-0.260mLs(-1). Results were analysed by nonparametric tests at 0.05 significance. Selected cases were also simulated by a two-phase CFD model.ResultsA vapor lock was observed in 48% of the cases investigated experimentally. Increasing the apical size, using an open-ended needle, positioning the needle closer to WL and delivering the irrigant at higher flow rate resulted in significantly smaller vapor lock. An increased contact angle resulted in the entrapment of a larger bubble when a low flow rate was used. Both brief insertion of the needle to WL whilst irrigating at a flow rate of 0.083mLs(-1) and delivering the irrigant at 0.260mLs(-1) without changing the needle position were capable of removing an established vapor lock.ConclusionsApical vapor lock may occur under certain conditions, but appears to be easily prevented or removed by syringe irrigation.

The turbulent kinetic energy aspects related to production and transport in the wake of a cylinder interacting with a boundary layer have been investigated experimentally. Using a simple but efe cient technique, the velocity power spectral characteristics in the intermediate wake were modie ed to comply with the requirements for quasitwo-dimensional behavior, i.e., to display a scaling region deviating from the i 5 power law, which is typical of homogeneous, three-dimensional turbulence. The cylinder was placed parallel to the plate and normal to the e ow, with its wake developing just outside of the boundary layer but with its lower part in contact and interacting with it. The streamwise and normal-to-the-plate velocity components have been recorded simultaneously in the intermediate wake using hot-wire anemometry. In addition to the calculation of kinetic energy production, thirdorder correlations of the two velocity e uctuation components, denoting streamwise and lateral transport of the corresponding kinetic energy terms, have also been evaluated. There is signie cant reduction of kinetic energy production in the lower half wake, in contact with the boundary layer, as compared to the upper half on the freestream side. This is associated with a considerable buildup of kinetic energy production within the boundarylayer e ow. The transport mechanisms in the present e ow have been investigated and are discussed to provide a basis for formulation and ree nement of numerical models and methodologies.

The process of laminar to turbulent transition induced by a von Karman vortex street wake, was studied for the case of a flat plate boundary layer. The boundary layer developed under zero pressure gradient conditions. The vortex street was generated by a cylinder positioned in the free stream. An X-type hot-wire probe located in the boundary layer, measured the streamwise and normal to the wall velocity components. The measurements covered two areas; the region of transition onset and development and the region where the wake and the boundary layer merged producing a turbulent flow. The evolution of Reynolds stresses and rms-values of velocity fluctuations along the transition region are presented and discussed. From the profiles of the Reynolds stress and the mean velocity profile, a `negative' energy production region along the transition region, was identified. A quadrant splitting analysis was applied to the instantaneous Reynolds stress signals. The contributions of the elementary coherent structures to the total Reynolds stress were evaluated, for several x-positions of the near wall region. Distinct regions in the streamwise and normal to the wall directions were identified during the transition.

The process of a strong wake-induced laminar/turbulent transition on a flat-plate boundary layer was investigated from the point of view of the occurring coherent structures. The wake was generated by a horizontal cylinder positioned in the freestream and upstream of the flat plate's leading edge. An X-type hot-wire probe measured the stream wise and normal-to-the-wall velocity components, whereas a gradient hot-wire probe, located in the cylinder's wake and at the same stream wise position as the X-type hot-wire probe, detected the passage of the von Karman vortices. From the simultaneously acquired velocity and gradient signals, the intermittency factor distribution and cross-correlation functions, combined with a quadrant-splitting analysis, were computed. Furthermore, an ensemble-average technique was applied to the signals. The analysis of the signals revealed that during the transition a secondary vortical structure occurs near the wall. Turbulent kinetic energy transfer to and from the wall during the transition was evaluated

A conditional averaging technique has been used for the analysis of experimental data obtained from heat flux measurements in the region of interaction of a cylinder wake with a boundary layer. The circular cylinder was placed normal to the flow and parallel to a flat plate, just outside of the boundary layer. The surface of the cylinder was intentionally rough, following our observation that in this way the velocity power spectrum in the intermediate wake could be forced to acquire some quasi two-dimensional turbulence characteristics, namely to display a scaling region deviation from the −5/3 power law which is characteristic of homogeneous, three-dimensional turbulence. The streamwise and the normal (to the plate) velocity components, as well as the temperature at the same position, have been recorded simultaneously, using hot wire anemometry. Time variations of the relevant Reynolds shear stress and heat fluxes were evaluated directly from the experimental data. These results were then conditionally averaged according to the quadrant splitting analysis technique. It was found that in the boundary layer region, a particular fluid motion (‘ejections’, in the quadrant splitting analysis terminology) dominate the flow. That motion is the main carrier of hot fluid from the boundary layer to the wake.

An airlift pump operating at submergence ratios between 0.2 and 0.6 and using water as the pumping liquid, has been investigated. Circular pipes of constant short length of 1 m and inner diameters of 3 and 5 cm were used as riser tubes. The water flow rate measurements for various air flow rates allowed the study of the pumping efficiency as a function of the air flow rate, submergence ratio and certain geometrical parameters (riser tube diameter and injector design). The efficiency curves start from a zero efficiency at a minimum air flow rate, then increase rapidly with the air flow rate up to an efficiency maximum. For higher air flow rates, the efficiency decreases exponentially. Diagrams showing the influence of the riser tube diameter and injector design, are presented. Additionally, based on the experimental data, two equations are presented, which allow the prediction of the maximum efficiency and the corresponding water and air flow rates inside the experimental range. On a etudie une pompe ascendante fonctionnant a des taux de submergence de 0,2 a 0,6 et utilisant de l'eau comme liquide de pompage. Des tubes circulaires courts d'une longueur constante de 1 m et de diametres interieurs de 3 et 5 cm ont servi de colonnes montantes. Les mesures de debit de l'eau pour divers debits d'air ont permis l'etude de l'efficacite de pompage en fonction du debit d'air, du taux de submergence et de certains parametres (diametre des colonnes montantes et conception de l'injecteur). Les courbes d'efficacite commencent a une efficacite nulle pour un debit d'air minimum, puis augmentent rapidement avec le debit d'air jusqu'a un maximum de l'efficacite. Pour des debits d'air plus eleves, l'efficacite diminue exponentiellement. Des diagrammes montrant l'influence du diametre de la colonne montante et de la conception de l'injecteur sont presentes. De plus, les donnees experimentales permettent l'etablissement de deux equations, qui predisent l'efficacite maximum et les debits d'eau et d'air correspondants a l'interieur de la gamme experimentale.

A conductivity probe having one electrode with a small surface (the sensing electrode) can be used for the measurement of the instantaneous local concentration during liquid mixing in an electrolytic solution. The presence of solid particles in the mixing field causes fluctuations of the electrolyte concentration signal, contaminating in this way the concentration measurement. The influences of the volume fraction and size of the solid particles on the electrolyte-concentration signal are investigated. The data indicate how to estimate the effect of the presence of particles in the specification of the electrolyte concentration. Furthermore, a method which allows the measurement of the mean electrolyte concentration at high solids volume fractions in electrolytic liquid/solid suspensions is proposed.

The mixing process in the near wake of a circular cylinder was studied by measuring instantaneous values of the local concentration. A conductivity probe (space resolution 6.5×10 -5 cm 3 ) was used for the measurement of the instantaneous concentration in a system composed of two liquid streams (water and NaCl in water solution) originally separated by a splitter plate. The flow in the test section was confined by the side walls of the channel. The purpose of the work was to study wake scalar transport at high Schmidt numbers. In the present case the Schmidt number was around 700. Data were acquired at cylinder Reynolds numbers in the range of 200–650. A global picture of the mixing process was obtained independently from a visual study; the experiment involved photographing the process of a diffusion controlled chemical reaction (a pH indicator, phenolphthalein, in one stream and NaOH-solution in the other). Various statistical quantities of the concentration signals, characteristic for the mixing process were computed. An interpretation of the data is presented from the point of view of instantaneously occurring flow structures in the wake of the cylinder.

This work describes a calibration technique for hot-wire anemometry which is accurate, fast, easy to implement, and covers extended temperature and velocity ranges. The novel feature of the technique is the collection of large quantities of data during a calibration experiment, by recording and analysis of the dynamic response of hot-wires to gradual heating. This approach differs from static methods, where the response of hot-wires to only one, constant value of temperature and velocity is obtained per calibration experiment.

Les phenomenes de formation et de coalescence des bulles au-dessus d'orifices submerges dont le diametre est compris entre 1 et 7 mm ont ete etudies visuellement dans une colonne d'eau stagnante. Les orifices sont alimentes en air a debit constant et la hauteur du champ d'etude est de 14 cm a partir de la sortie de l'orifice. Le nombre de Reynolds de l'air base sur le diametre de l'orifice s'echelonne entre 50 et 40000. L'etude porte surtout sur une description unifiee des phenomenes de bullage, depuis la formation d'une bulle unique jusqu'a la formation de jets, ainsi que sur les transitions entre les diverses regions de bullage. On a conclu que pour les orifices utilises comme dispositifs d'injection et le systeme air/eau etudies, le nombre de Reynolds constitue la variable de controle pour les phenomenes de bullage au-dessus des tuyeres et pour la transition entre les diverses regions de bullage.

To evaluate (i) the effect of irrigant flow rate, needle type, needle insertion depth and apical constriction diameter and (ii) the effect of ultrasonic, sonic and manual dynamic agitation on irrigant extrusion using a recently introduced method.Thirty-two human teeth with a straight root canal were prepared to size 35, 0.06 taper and assigned to group A or B. The apical constriction diameter was 0.15-0.25 mm. Specimens were mounted on a plastic vial filled with distilled water to simulate a periapical lesion. A point-conductivity probe was used to determine the volume of irrigant extruded into the vial. Within group A, NaOCl was delivered at 0.14 or 0.26 mL s(-1) by an open-ended or a closed-ended needle at 1 or 3 mm short of working length (WL). In group B, NaOCl was agitated at high or low power either by an ultrasonically or sonically oscillating instrument inserted at 1 or 3 mm short of WL or by manual push-pull strokes of a gutta-percha cone. Results were analysed by repeated-measures anovas, at 0.05 significance.An increase in the flow rate resulted in increased extrusion (P0.001). The open-ended needle extruded significantly more irrigant than the closed-ended (P0.001). Extrusion decreased as needles moved away from WL (P0.001). The effect of apical constriction diameter was not significant (P0.454). Manual dynamic agitation extruded significantly more irrigant than sonic and ultrasonic agitation (P0.001).Irrigant flow rate, needle type and insertion depth and agitation technique had a significant effect on extrusion.

In this work, an experimental study of a jet issuing in cross flow is reported. Support is offered to a theory on the origin of Karman-like vortices, in the wake of jets issuing in boundary layers. Further, a coherent structure with strong contribution to the energetics of the flow field is identified here. This structure has not been reported earlier, according to the present authors' knowledge, and it is shown to be related to engulfment of external fluid at the bottom of the jet, and to interesting stochastic and spectral characteristics of the flow field. Three-dimensional plots of the coherent quantities, based on experimental data, reveal a double-helical morphology of the coherent structure. The same morphology has recently been proposed for the far field of jets issuing in stagnant fluid (i.e., without cross flow). The results of this study are expected to support theoretical and numerical work on jets issuing in cross flow.

A study has been made of the process of laminar to turbulent transition induced by a von Karman vortex street wake, in the boundary layer on a flat plate. The boundary layer developed under zero pressure gradient conditions while the vortex street was generated by a cylinder positioned in the free stream. Hot-wire measurements over a range of Strouhal frequencies and free stream velocities were used for the identification of the transition onset. From the analysis of the experimental data, two different transition mechanisms known in the literature as ‘strong’ wake and ‘weak’ wake induced transition, could be identified. It was established that, the onset of the strong von Karman wake induced transition process was a function of the free stream velocity, the position of the cylinder with respect to the plate, the cylinder diameter, the drag coefficient and the minimum velocity in the developing wake at the streamwise position of the onset of the boundary layer transition. The end of the strong wake induced transition, was defined at the streamwise distance, where the wake of the cylinder met the wall. A correlation for the prediction of the onset of the transition was developed

This work reports on experimental data and generalized correlations, which display the modification of a scalar field by the presence of obstacles. The data were obtained by means of a triple hot-wire probe in a wind tunnel. The global picture of the flow was visualized and recorded by a high-speed video system. The flow studied was a buoyant jet in a cross wind. This flow simulates an accidental ammonia release from a pressurized containment. The obstacle is found to enhance scalar turbulent dispersion and mixing. The simulated ammonia plume exhibits similar dynamic behavior with and without the obstacle, obtaining a self-similar state at distances downwind predicted by dimensional arguments. The scalar probability density functions display deviations from Gaussian distribution, depending upon their distance from the jet center. The data support a gradient transport hypothesis modeling. Recirculation patterns contributing to the entrainment processes were identified in the near wake of the obstacle.

The operation of an airlift pump, working under low submergence ratios (between 0.17 and 0.31), has been visually studied. The two-phase flow structures occurring in the riser channel and around the injector section were recorded by a high speed video system. A quasi-periodic burst-like behaviour characterised the flow pattern in the riser tube, which appeared to dominate the operation of the airlift pump under the conditions of low submergence ratios. An interesting aspect of the airlift pump operation, under these conditions, is that the two phases show a large interface area; this is due to the high dispersion degree of the two-phase mixture in the riser duct. Data and pictures from video recordings regarding the sequence, time and length scales of the occurring flow patterns are reported. Nous avons etudie visuellement le fonctionnement d'une pompe de fluidisation, pour de faibles taux de submersion (entre 0,17 et 0,31). Les structures d'ecoulement diphasique apparaissant dans la conduite de la colonne montante et autour de la zone de l'injecteur ont ete enregistrees a l'aide d'un systeme video a grande vitesse. Un comportement de type explosion quasi periodique caracterise le profil d'ecoulement dans le tube de la colonne montante; ce phenomene semble dominer le fonctionnement de la pompe dans des conditions de faibles taux de submersion. Un aspect interessant du fonctionnement de la pompe de fluidisation, dans ces conditions, est que les deux phases montrent une importante surface interfaciale; cela est dǔ au degre eleve de dispersion du melange diphasique dans la conduite de la colonne. Nous presentons des donnees et des photographies des enregistrements video sur les echelles de sequence, de temps et de longueur pour les profils d'ecoulement obtenus.

The mixing process of high Schmidt number (700-35000) aqueous solutions was investigated in an oscillating grid mixing vessel. The influence of the following variables on the mixing time was studied: Schmidt number, initial solution concentration, volume ratio of the liquids to be mixed and oscillating grid frequency. The measurements were compared with Corrsin's isotropic turbulent mixing theory. The data were correlated in the form of dimensionless groups, involving the aforementioned variables. On a etudie le procede de melange de solutions aqueuses ayant un nombre de Schmidt eleve (700-35000) dans une cuve de melange a grille oscillatoire. On a analyse l'influence des variables suivantes sur le temps de melange: le nombre de Schmidt, la concentration initiale de la solution, le rapport volumique des liquides a melanger et la frequence d'osillation de la grille. Les mesures ont ete comparees a la theorie du melange turbulent isotropique de Corrsin. Les donnees ont ete correlees sous la forme de groupes adimensionnels, faisant intervenir les variables susmentionnees.

Introduction: The aim of this study was to evaluate the effect of needle-insertion depth on the irrigant flow inside a prepared root canal during final irrigation with a syringe and two different needle types using a Computational Fluid Dynamics (CFD) model. Methods: A validated CFD model was used to simulate irrigant flow from either a side-vented or an open-ended flat 30-G needle positioned inside a prepared root canal (45.06) at 1, 2, 3, 4, or 5 mm short of the working length (WL). Velocity, pressure, and shear stress in the root canal were evaluated. Results: The flow pattern in the apical part of the root canal was similar among different needle positions. Major differences were observed between the two needle types. The side-vented needle achieved irrigant replacement to the WL only at the 1-mm position, whereas the open-ended flat needle was able to achieve complete replacement even when positioned at 2 mm short of the WL. The maximum shear stress decreased as needles moved away from the WL. The flat needle led to higher mean pressure at the apical foramen. Both needles showed a similar gradual decrease in apical pressure as the distance from the WL increased. Conclusions: Needle-insertion depth was found to affect the extent of irrigant replacement, the shear stress on the canal wall, and the pressure at the apical foramen for both needle types. (J Endod 2010;36:1664-1668)

IntroductionThe aim of this study was to evaluate the effect of needle tip design on the irrigant flow inside a prepared root canal during final irrigation with a syringe using a validated Computational Fluid Dynamics (CFD) model.MethodsA CFD model was created to simulate the irrigant flow inside a prepared root canal. Six different types of 30-G needles, three open-ended needles and three close-ended needles, were tested. Using this CFD model, the irrigant flow in the apical root canal was calculated and visualized. As a result, the streaming velocity, the apical pressure, and the shear stress on the root canal wall were evaluated.ResultsThe open-ended needles created a jet toward the apex and maximum irrigant replacement. Within this group, the notched needle appeared less efficient in terms of irrigant replacement than the other two types. Within the close-ended group, the side-vented and double side-vented needle created a series of vortices and a less efficient irrigant replacement; the side-vented needle was slightly more efficient. The multi-vented needle created almost no flow apically to its tip, and wall shear stress was concentrated on a limited area, but the apical pressure was significantly lower than the other types.ConclusionsThe flow pattern of the open-ended needles was different from the close-ended needles, resulting in more irrigant replacement in front of the open-ended needles but also higher apical pressure.

Conductivity probes, as they are proposed by Gibson and Schwarz, are suitable for local concentration measurements in electrolyte turbulent flows. The dependence of the drifting behaviour in NaCl-s...

To model bounded turbulent shear flows, one would like to have an accurate mechanistic picture of the coherent motions in the wall region; unfortunately, this picture is still far from completely clear. The present effort is to combine several techniques we have developed in the past in an attempt to further clarify the correct mechanism.

Boutsioukis C, Lambrianidis T, Kastrinakis E, Bekiaroglou P. Measurement of pressure and flow rates during irrigation of a root canal ex vivo with three endodontic needles. International Endodontic Journal, 40, 504‐513, 2007. Aim Tomonitorexvivointra-canalirrigationwiththree endodontic needles (25, 27 and 30 gauge) and compare them in terms of irrigant flow rate, intra-barrel pressure, duration of irrigation and volume of irrigant delivered. Methodology A testing system was constructed to allow measurement of selected variables with pressure and displacement transducers during ex vivo intracanal irrigation with a syringe and three different needles (groups A, B, C) into a prepared root canal. Ten specialist endodontists performed the irrigation procedure. Each operator performed ten procedures with each needle. Data recorded by the transducers were analysed using Friedman’s test, Wilcoxon Signed Rank test, Mann‐Whitney U-test and Kendall’s Tb test. The level of significance was set to 95%. Results Significant differences were detected among the three needles for most variables. Duration of delivery and flow rates significantly decreased as the needle diameter increased, whilst pressure increased up to 400‐550 kPa. Gender of the operator had a significant impact on the results. Experience of the operators (years) were negatively correlated to volume of irrigant (all groups), to the duration of delivery (groups A, B) and to the average flow rate (group A). Conclusions Finer diameter needles require increased effort to deliver the irrigant and result in higher intra-barrel pressure. The syringe and needles used tolerated the pressure developed. Irrigant flow rate should be considered as a factor directly influencing flow beyond the needle. Wide variations of flow rate were observed among operators. Syringe irrigation appears difficult to standardize and control.

Work on lignite-water slurries has been carried out in the Laboratory of Chemical Engineering Fundamentals, with the goal of producing premium fuels.

A jet issuing in cross flow is encountered in several engineering applications. The description of the jet structure and the identification of the sources of the jet wake vorticity, however, are still open questions. This work is part of a series of experimental studies on turbulent buoyant jets in cross flow [1,2]; here, a coherent contribution to the turbulent entrainment and mixing of a buoyant air jet issuing in a cross wind is reported. Further, this work offers support to a theory on the generation of the jet wake vorticity.

An experimental investigation of the transport characteristics of momentum and heat in a turbulent wake of a cylinder interacting with a turbulent boundary layer has been carried out (Figure 1). The cylinder was placed just outside the plate’s boundary layer. The von Karman street of vortices produced behind the cylinder interacted with the boundary layer downstream of x/D=10. Heat was supplied to the boundary layer flow by means of the line heat source shown. Simultaneous recording of the instantaneous values of temperature and two velocity components were performed using hot wire anemometry employing a triple-wire probe. Time variations of one Reynolds stress component and two turbulent scalar flux components were obtained directly from the experimental data, by digital post-processing.

Mixing of a turbulent round heated air jet, issuing in an ambient cross flow, was studied in a wind tunnel. Point measurements acquired by a triple-wire sensor were coupled with flow visualization and image analysis. Two turbulent heat transport terms and one component of Reynolds stress tensor were directy measured. The main gross parameters of the flow and certain mixing parameters were found to develop a self similar behavior in the jet far field. The scalar probability density function varied from Gaussian to exponential with long tails, depending on the location within the flow field.

The stochastic dispersion model DIPCOT was validated against data from wind tunnel experiments where heat, used as the tracer, was released in a quasi two-dimensional turbulent flow. Dispersion simulations, based on Langevin equation, were performed using measurements and the model predictions were quantitatively compared to the experimental data. Two approaches of the drift term in Langevin equation were examined, utilising the first three and the first four moments of turbulent velocity, respectively. The overall behaviour of the model is quite satisfactory. The form of the drift term affected the predictions; the introduction of the fourth moment resulted in better estimations of the maximum concentrations. However, the mean performance of the model remained stable, irrespective of the drift term formulation.

The output signal of a Kovasznay type vorticity probe is in first-order approximation proportional to the longitudinal component of the vorticity omegax= partial differentialw/ partial differentialy- partial differentialv/ partial differentialz and does not depend on the two transverse components of the flow velocity v, w. An experimental investigation of the influence of all three fluctuating velocity components on the longitudinal vorticity signal showed that their influence may not be neglected. The error in the probe response caused by the longitudinal component of the flow velocity was easily corrected using the instantaneous longitudinal velocity component and digital measuring techniques. On the other hand, the error caused by the two transverse velocity components could not be corrected. The contamination of the vorticity signal produced by the two transverse velocity components has been calculated by considering first- and second-order terms. The agreement between the calculations and experimental measurements is good. It is concluded that in a turbulent flow field this probe cannot be used without the simultaneous knowledge of the instantaneous transverse velocity components.

A new probe — which measures the streamwise vorticity component, ωx, and all three velocity components, Ū + u, v, w - was used to recognize and analyse coherent structures quantitatively in a fully-developed, turbulent, channel flow. A quadrant analysis was applied to classify events related to the four possible combinations of signs of u and v. To isolate the most energetic events a threshold was introduced in the instantaneous value of the Reynolds shear stress. It was found that the ejections provided the major contribution to ωx 2 regardless of the threshold and distance from the wall. Information on the scales of detected events is also given.