Adjacent Orifices Research Articles

Spatial characteristics study of hydrodynamics and bubble dynamics in baffled stirred tank based on CLSVOF method

The limited understanding of intricate mesoscale bubble structures in stirred tank reactors under forced convection poses significant challenges to the design and optimization of related agitation systems. In this study, the coupled level set with volume of fluid (CLSVOF) method is employed to investigate bubble dynamics and macroscopic hydrodynamics in a gas–liquid stirred tank after model validation. The results demonstrate that: i) based on the dynamics of bubble clusters within the system, the stirred tank can be categorized into four distinct regions: the dispersal region, accumulation region, rising wall-region, and reflex region; ii) in the dispersal region, the rear of impeller blade generates large-scale vortex. Two merging modes are identified during the bubble rupture process: the merging of bubbles at adjacent orifices and the merging of discrete bubbles with the back of impeller blade due to negative pressure. Two bubble breakup modes are observed: bubble breakup at the back of the impeller blade due to stretching and the breakup of bubbles growing at orifices due to disturbance caused by the impeller blade; iii) the inertial forces predominantly control most bubbles in the system. A predictive correlation for bubble velocity is proposed; iv) elevating the stirring speed increases bubble number in the accumulation region. Moreover, enlarging gas flow rate and fluid viscosity leads to a discernible augmentation of overall bubble size; v) at the macroscopic scale, the radial, axial, and tangential velocities of the system exhibit an increase with enlarging stirring speed, while showing no significant change with the increase in gas flow rate. Additionally, as fluid viscosity and density increase, the flow undergoes a transition from turbulent flow to laminar flow.

Extraction and characteristic analysis of the nonlinear acoustic impedance of circular orifices

For investigating the nonlinear acoustic behavior of circular orifices under high amplitude sound excitation, an approach based on the three-dimensional time-domain computational fluid dynamics simulation is proposed to extract the nonlinear acoustic impedance of circular orifices. By solving laminar flow equations, the propagation of the acoustic signal in the vicinity of orifice is simulated, and the effect of the interaction among adjacent orifices is considered by using the lateral periodic boundary condition. The effects of diameter, thickness, and porosity on acoustic impedance under different amplitude sound excitations are studied. By using nonlinear regression analysis of the dimensionless parameters composed of particle velocity amplitude, frequency, and geometric parameters, fitting formulas of nonlinear acoustic impedance of circular orifices are presented. As an application of engineering computation, transmission loss of perforated silencers under low and high amplitude sound excitations is predicted by using the present acoustic impedance fitting formulas and via the finite element computation. By comparing the predicted and measured results, the accuracy and practicability of fitting formulas of nonlinear acoustic impedance of circular orifices are validated.

Effects of Jet-to-Jet Spacing of Air-Jet Vortex Generators in Shock-Induced Flow-Separation Control

Experiments were carried out to assess the influence of spanwise spacing between adjacent orifices of an air-jet vortex-generator (AJVG) array on their separation-control effectiveness. The array was applied to a 24° compression-ramp-induced shock-wave / turbulent boundary-layer interaction at M_{infty } = 2.52 and Re_{theta } = 8225. Three spanwise oriented AJVG arrays of small, intermediate, and large jet spacings were studied. Their influence on the mean-flow organisation and turbulence quantities was assessed using flow visualisations and planar particle image velocimetry across multiple measurement planes. The streamwise vortices induced by the AJVGs incited different control effects depending on the degree of interaction between adjacent vortices. The array with intermediate spacing achieved the most favourable effects with reductions in separation length and area of about 25% and 52%, respectively. This reduction was brought about by the formation of stable, interacting streamwise-elongated coherent vortices downstream of jet injection and the associated entrainment of high-momentum fluid. The smallest jet spacing incites vortex interactions to adverse strength, breaking up the coherent structures and even increasing separation. The AJVGs with the largest spacing display characteristics similar to single jets in crossflow, with only a local modification of the separation region. Turbulent quantities are amplified both by the jets and the separation-inducing shock; AJVG control reduces the amplification across the shock-wave/boundary-layer interaction and the intermediate jet spacing is most effective also here.

The behavior of two adjacent vortex rings produced by synthetic jets

Synthetic jets are expected as an effective method of active boundary layer control. A synthetic jet device generates jets by vibrating the diaphragm of a speaker or a piezoelectric actuator by using a method of suction and blowing. The actuators are low power, zero-net-mass-flux and compact devices. Mixing enhancement is one of the key technologies in boundary layer control and it is necessary to control the behavior of vortex rings to promote mixing the crossflow and the boundary layer. The purpose of this study is to investigate the effect of vortex ring interaction due to differences in orifice distance (S=1.5D, 1.7D, 2.0D) on the behavior of vortex rings. In this experiment, the smoke flow visualization was used to describe the interaction process by changing the distance between adjacent orifices. It was confirmed that the height where two vortex rings collapse that in the case of S=2.0D was lower that in the case of S=1.5D.

Modified Dual Hepatic Vein Anastomosis in Pediatric Living-Donor Liver Transplantation Using Left Lateral Segment Grafts With Two Wide Orifices.

Background: The anatomic variation of hepatic vein in the left lateral segment (LLS) increases the risk of outflow complication in pediatric living liver transplantation (LDLT). Here, we share a modified method for dual hepatic vein reconstruction in pediatric LDLT using LLS with two wide orifices.Methods: From Sep 2018 to Dec 2019, 434 pediatric LDLTs using LLS were performed in our center. Hepatic veins of grafts were classified into three types with emphasis on the number, size, and location of orifices at the cut surface: a single opening (type I, n = 341, 78.57%); two adjacent orifices (type II, n = 66, 15.21%); two wide orifices with orifices distances <20 mm (type IIIa, n = 15, 3.46%); and two wide orifices with orifices distances >20 mm (type IIIb, n = 12, 2.76%). Rv was defined as the ratio of diameter of V2 and V3 (refer to hepatic vein drained segments II and III). We developed a modified dual hepatic vein anastomosis to reconstruct outflow for type IIIb grafts with Rv ≤1. Briefly, the hepatic vein of segment II was anastomosed to the common stump of middle hepatic vein (MHV) and left hepatic vein (LHV), followed by unification of V3 and the longitudinal incision orifice in inferior venous cave (IVC).Results: During median follow-up of 15.6 months (7.5–22.9 months), no hepatic vein complications occurred.Conclusion: This novel modified dual hepatic vein anastomosis could serve as a feasible surgical option for type IIIb LLS grafts with Rv ≤1 in pediatric LDLT.

Characteristics of array of distributed synthetic jets and effect on turbulent boundary layer

An array of distributed round synthetic jets was used to control a fully developed turbulent boundary layer. The study focused on the related skin friction drag reduction and mechanisms involved. The control effects were analyzed by measuring the streamwise velocities using a hot-wire anemometer downstream of the array. A reduction in the skin friction was observed both in the regions downstream of the orifices and in the regions between two adjacent orifices. A statistical analysis with the variable-interval time-averaging (VITA) technique demonstrated a weakened bursting intensity with synthetic jet in the near-wall region. The streamwise vortices were lifted by the upwash effect caused by synthetic jet and induced less low-speed streaks. The control mechanism acted in a way to suppress the dynamic interaction between the streamwise vortices and low-speed streaks and to attenuate the turbulence production in the near-wall region. The forcing frequency was found to be a more relevant parameter when synthetic jet was applied in turbulent boundary layer flow control. A higher forcing frequency induced a higher reduction in the skin friction. The power spectral density and autocorrelation of the fluctuating velocities showed that the synthetic jets gradually decayed in the streamwise direction, having an effect as far as 34.5 times the displacement thickness that was on the trailing edge of the distributed synthetic jets array.

Root canal isthmi and interorifice distance in human permanent teeth of an Indian subpopulation using cone-beam computed tomography: A retrospective cross-sectional study.

Objective:The aim of the study was to evaluate the prevalence of root canal isthmus (RCI) and measure the interorifice distance (IOD) between the root canals. Additionally to correlate IOD with the RCI in human permanent teeth using conebeam computed tomography (CBCT) in an Indian sub-population (Chennai).Materials and Methods:A total of 5881 teeth from 280 CBCT full mouth scans were analyzed. The presence or absence of complete and incomplete RCI of each tooth was identified using the map-reading strategy. IOD was calculated by measuring the distance between the center of each root canal orifice to that of the center of the adjacent orifice at the level of the cementoenamel junction using the axial and sagittal sections. Chi-square analysis and correlation statistics using Spearman's rank-order test was done (P < 0.05).Results:High prevalence of RCI was found in maxillary first premolars, mesial root of mandibular molars, and mesiobuccal root of maxillary first molars, while its prevalence was low in maxillary canines and mandibular premolars and absent in maxillary incisors. RCI was predominantly seen in the cervical and middle third of the root canal in all the teeth evaluated. A weak negative correlation was established between the IOD and RCI for maxillary premolars, whereas a weak positive correlation was seen in maxillary first molars and mandibular second molars.Conclusion:The prevalence of RCI was high in the posterior teeth in comparison to the anterior teeth in the present study. There was no strong correlation between IOD and RCI in all the teeth evaluated.

Bubble coalescence efficiency near multi-orifice plate

Bubble coalescence reduces specific area and weakens the work performance of bubble column. The bubble coalescence near gas sparger which is caused mainly by bubble growing is different from the ones occurring in major liquid. Bubble coalescence efficiency near gas sparger is influenced by many factors including sparger configuration, gas flow rate, bubble deformation, solution composition, etc. This work has conducted a set of visual experiments to study the coalescence characteristics near multi-orifice plate. The experiment parameters cover a wide range of conditions including large scope of gas flow rate, different kinds of solution and orifice configurations. The experimental results suggest that coalescence time is applicable to reflect the influence of the pitch of orifices and gas flow rate on bubble coalescence efficiency. As the number of orifices increases, bubble coalescence efficiency is reduced by the disturbance from the bubbles at adjacent orifices. A hindering coefficient is used to consider the hindering effect of additives on bubble coalescence efficiency. Finally a new calculation expression is established to predict bubble coalescence efficiency near multi-orifice plate whose fundamental form is based on the logistic curve of binary response. The calculated values that refer to this calculation expression are well consistent with the experimental results.

The effect of multi-orifice plate configuration on bubble detachment volume

Abstract The multi-orifice plate gas sparger, mainly composed of a multi-orifice plate and a gas chamber, is one of the most common sparger facilities. The aeration performance of multi-orifice plate has a close relation with the multi-orifice plate configuration. In addition, the weeping phenomenon has a considerable influence on the gas chamber condition which affects the bubble detachment volume directly. This paper conducts a set of visual experiments to study the influence of multi-orifice configuration and gas chamber condition on the aeration performance of gas sparger. For multi-orifice plate, an improved theoretical model is proposed which considers the wave effect of the previous bubbles generated from adjacent orifices and the variance of the number of active bubbling orifice. A parameter is proposed to evaluate the aeration performance in order to overcome the difficulty caused by the randomness of bubble formation process. The experimental results suggest that the gas chamber filled with water is in favor of large bubble formation. The influence of the pitch of orifice on aeration performance can only be observed in high-restricted case. According to the theoretical model and experimental results, the influences of gas flow rate and the number of open orifices on the aeration performance are analyzed and a design criterion for the number of open orifice is proposed.

Numerical simulation of gas-bubble formation through two submerged orifices

In this work, two-dimensional numerical simulations are carried out to analyse the dynamics of gas-bubble formation at two adjacent orifices submerged in an immiscible Newtonian liquid under the condition of constant gas flow rate using finite-volume-based commercial CFD solver Ansys Fluent. Two conditions for the ambient liquid are considered: firstly the liquid is in quiet condition and secondly, it is also co-flowing with the gas stream. The full cycle from the bubble formation to its detachment and the corresponding dynamics are simulated using the volume of fluid (VOF) method, which is one of the efficient front capturing techniques of Eulerian family. The study includes: (i) time sequence profile of bubble formation to clearly represent the bubble growth, neck formation and bubble break-up at a given Weber number (We), Reynolds number (Re), Bond number (Bo) and liquid to gas mean velocity ratio (Vr); (ii) bubble growth history for different Vr and at constant Re, We and Bo; (iii) effect of orifice spacing on bubbling synchronicity and frequency at given Vr, We, Re and Bo and (iv) synchronous bubbling regime, bubble size and formation time determination, bubble coalescence phenomenon and technique for its inhibition.

Testing the μ(I) granular rheology against experimental silo data

Industrial storage of granular material using silos is common, however, improved understanding of silo flow is needed. Various continuum models attempt to describe the velocity of dense granular flow in silos. Kinematic, and recently, stochastic models, based upon the diffusion of some quantity, perform well when there is a single orifice, and when the yield criterion is satisfied. However, if system stresses are insufficient to satisfy the yield criterion, or if there is a second orifice, these models fail to capture the entire flow behaviour. Advances in granular rheology have allowed a pressure dependent friction law to be defined which can capture the behaviour of granular silo flow including un-yielded zones, flow-rate independence of fill height, the Beverloo flow-rate, and various other phenomena. We performed silo discharge experiments in a flat bottomed planar silo with a single and two adjacent orifices, for two grain types. The velocity was measured using Particle Image Velocimetry. Results were compared to a mathematical model based on the μ (I) rheology which was shown to qualitatively capture the observed phenomena including plug-like zones where the yield criterion is not satisfied. These preliminary results strongly encourage future investigations into the effect of friction parameters and numerical boundary conditions.

Effects of multi-orifice configurations of the quench plate on mixing characteristics of the quench zone in an RQL-TVC model

CO2 concentration measurements and Particle Image Velocimetry (PIV) measurements were performed to investigate the effect of multi-orifice plate geometry on mixing characteristics of a rich-burn quick-quench lean-burn trapped vortex combustor (RQL-TVC). The mixing characteristics in the quench zone were discussed in terms of the mixing degree and the mixing uniformity. And the penetration and the residence time of discrete jet flows conducted by multi-orifice plates were analyzed. The diameter (D) and the quantity (n) of orifices in the multi-orifice plate which composed two rows of orifices was varied, but the blockage ratio (BR) remains constant as approximately 81.5%. The distance of the orifice rows (h) equals D corresponding to the orifice in each plate respectively. The location of the first row is not changed, consequently the position of the second row and the orifice relative position ratio of S/D (S presents the spacing between adjacent orifice mid-points) were varied with D. Through measuring the CO2 concentration, the mixing degree and the mixing uniformity in the quench zone are determined. The penetration and residence time of discrete jet flow conducted by multi-orifice quench plates were quantified by PIV measurements. Results show that the quench plate with the smaller number and the larger diameter of orifices has the most momentum and mass corresponding to the longer penetration and residence time, so that this multi-orifice quench plate has the highest unmixedness rate. On the contrary, that with the shortest penetration is not benefit for occurring the full mixing in the quench zone. Therefore, there is an optimization of multi-orifice configuration existing for the design of multi-orifice quench plates which affect the mixing characteristics of the quench zone in RQL-TVC. The mixing progress in the quench zone depends greatly on discrete jet flows, of which the penetration depth falls into the range from 28mm to 48mm. The multi-orifice plate, designated as M6D8.0 with 6 orifices and 8.0mm-diameter, offers the intermediate length of penetration depth (approximately 35mm). The residence time of discrete jet flows derived from PIV results is between 0.6ms and 1.2ms. Most of that is less than 1ms and meets the requirement of the critical time scale of complete quick-mixing.

Parametric Study of Synthetic-Jet-Based Control for Performance Enhancement of a Vertical Tail

Application of aerodynamic flow control to the vertical tail of an aircraft could enable significant decrease in its size, with corresponding reductions in drag, weight, and fuel costs. Wind-tunnel experiments at a Reynolds number of 350,000 were conducted on a sweptback tapered vertical tail capable of sideslip rotation. The model used in the present work was approximately th scale with a NACA 0012 airfoil section. It was instrumented with an array of finite-span synthetic jet actuators distributed along the span, just upstream of the rudder hingeline. When the synthetic jets were activated, the side force coefficient was increased by a maximum of 0.17 (34%) over the baseline vertical tail. A primary objective of this work was to explore the effect of the orientation, location, and geometry of the synthetic jet orifices on control effectiveness. The parameters under investigation were orifice aspect ratio, spacing between adjacent orifice edges, the chordwise jet location, spanwise location, skew angle, and spanwise actuator density. This set of experiments suggested that the actuators’ spanwise spacing can be too dense (that is, maintaining constant individual jet strength and reducing the spanwise density of active actuators such that the total area-based momentum decreased, did not have a detrimental effect on side force enhancement for some conditions). The relative importance of other parameters that are typically used to quantify synthetic jet strength was also analyzed; the area-based momentum coefficient was determined to be a much more dominant factor than the blowing ratio and chord-based momentum coefficient.

Endoscopic biliary stenting and pancreatitis.

Endoscopic biliary stenting across the duodenal papilla can obstruct the adjacent pancreatic orifice and disturb the flow of pancreatic juice, which may result in pancreatitis. However, the relationship of endoscopic biliary stenting to post-procedure pancreatitis has not been thoroughly examined. Therefore, we have reviewed the published literature on this issue. Although biliary stenting, especially with large-bore and self-expandable metallic stents (SEMSs), has been considered a possible additional risk factor for pancreatitis following biliary stenting, most studies have not provided convincing supporting evidence; this failure may be due to inadequate study design or insufficient numbers of subjects. It also remains unclear whether endoscopic sphincterotomy (EST) performed prior to biliary stenting decreases the incidence of post-stenting pancreatitis; some recent studies have claimed that EST is not necessary before biliary stenting, even with placement of SEMSs. Well-designed studies with a large number of subjects will be needed to clarify these issues.

Eggs containing larvae of Enterobius vermicularis in vaginal smear

Enterobius vermicularis also known commonly as pinworm is the most common intestinal parasite. It is a nematode that inhabits the human terminal ileum, colon and appendix. The fertilized female migrates to the perianal area where eggs are deposited but occasionally introduces itself into adjacent orifices, most commonly the female genitourinary tract. Thus the eggs can be seen in the vaginal smear as a result of contamination. We report a case wherein the patient presented with signs and symptoms of vulvovaginitis. In her vaginal smear there were eggs of Enterobius vermicularis which showed a coiled larva within it. In the background there were plenty of acute inflammatory cells. This patient responded favorably to antihelminthics. We report this case to highlight the morphology of the parasite and also to emphasize that such findings should not be neglected. Timely reporting and appropriate treatment of such cases will prevent further complications of this parasite including endometritis, salphingitis and peritonitis.

Assessment of frequency, transmission, and genitourinary complications of enterobiasis (pinworms)

Pinworms are the most common helminth infection in the USA and Western Europe, with prevalence rates in some communities of as high as 30-50%. Pinworms generally live in the gastrointestinal tract, and helminth infestations have been noted in over one-quarter of acute appendectomies on histologic examination. Although transmission is often attributed to the ingestion of infective eggs by nail biting and inadequate hand washing, inhalation and ingestion of airborne eggs also occur. The female Enterobius vermicularis migrates nightly to the perianal area to deposit her eggs, but some worms find their way into adjacent orifices, most commonly the female genitourinary tract, producing an array of symptoms. More consideration of this entity is justified in patients presenting with genitourinary complaints not responding to normal therapies. In the treatment of pinworms affecting genitourinary organs, treatment with possibly two oral agents, namely mebendazole and ivermectin, and a topical therapy for the eggs may be warranted.

A study of synthetic jets from rectangular and dual-circular orifices

AbstractThe results of an investigation into the effect of both the number of orifices and the geometry of these orifices on the fluid structures exiting from a synthetic jet actuator are presented. The experiments have used smoke and laser visualisation and single hotwire measurement techniques to establish the flow field exiting the various orifices and the fluid velocities in the exit plane of the orifice. The results indicate that the use of two small orifices can perhaps produce two coherent vortex rings with a total circulation greater than that found in the ring produced by a large, single orifice of equivalent area. However, they have also shown that there are three different types of interaction between two adjacent orifices, related to the spacing between them and the level of excitation applied to the diaphragm. In addition, these interactions may affect the overall level of circulation in different ways. Finally the results have shown that a rectangular orifice of a given exit plane area is more likely to produce a turbulent ring than the equivalent circular orifice due to a ‘smoothing’ process which endeavours to create an axisymmetric ring from a non-axisymmetric slug of fluid. This work has shown that when using synthetic jet actuators in flow control applications, care should be taken in selecting the spacing and geometry of the orifices used, as certain set-ups may be more suited to certain applications than others.

Pinworms and postmenopausal bleeding.

The human pinworm Enterobius vermicularis is normally found within the human gastrointestinal tract. Pregnant females migrate out of their host's anus at night to lay their eggs perianally. As a...

Experimental study on autoignition in a scramjet combustor

A UTOIGNITION characteristics of hydrogen fuel in a scramjet combustor were examined using a direct-connect test apparatus with particular reference to the effect of fuel injection patterns. Autoignition behavior fell into four distinct categories, separated by the three bounding curves. One of the boundaries was independent of fuel injection patterns, while the others significantly depended on them. In the case of fuel injection from a single wall or from a single orifice, local flame quenching caused by expansion wave emanating from the step on the opposite wall was observed. Compared with injection from a single orifice, injection from multiple orifices appreciably enhanced autoignition. The reason for this is that fuel jets from adjacent orifices and from the opposite wall tended to attenuate the local flame quenching caused by the expansion waves from the opposite wall. Ignition limit curves derived from the present experiment were compared with an autoignition criteria proposed by Huber et al. They agree well in the case of fuel injection from a single orifice. For the case of injection from multiple orifices, however, the agreement is poor.

DEVELOPMENT OF IMPACTOR SIZE-SELECTIVE DUST SAMPLERS AT THE ELLIOT LAKE LABORATORY

The Elliot Lake Laboratory designs and uses impactor size selectors for respirable and other dust samplers both in the laboratory and in mines. Advantages of the selectors are compact size, reproducibility of size-selection performance based on the high precision of drill manufacture and use, flexibility in design and layout, and manufacturing ease in a machine shop. The major problems in design and performance were secondary deposition of dust and overloading with coarse dust. Secondary deposition modified the calculated size selection and either limited the spacing between adjacent orifices or orifices and other features or required a final calibration. Overloading of the coarse dust deposition zone led to changes in size-selection characteristics as the dust load increased, giving a definite limit to acceptable dust collection quantities. The use of multiple stages increased the coarse dust-holding capability manyfold. All the dust samplers developed at the Elliot Lake Laboratory used two or more successive stages to increase dust-holding capacity.