Entrance Of Duct Research Articles

Developing Flow and Heat Transfer in Strongly Curved Ducts of Rectangular Cross Section

A numerical study of heat transfer in 90 deg, constant cross section curved duct, steady, laminar, flow is presented. The work is aimed primarily at characterizing the effects on heat transfer of duct geometry and entrance conditions of velocity and temperature by considering, especially, the role of secondary motions during the developing period of the flow. Calculations are based on fully elliptic forms of the transport equations governing the flow. They are of engineering value and are limited in accuracy only by the degree of computational mesh refinement. A comparison with calculations based on parabolic equations shows how the latter can lead to erroneous results for strongly curved flows. Buoyant effects are excluded from the present study so that, strictly, the results apply to heat transfer flows in the absence of gravitational forces such as arise in spacecraft.

Visualization of the Longitudinal Fold of the Duodenum by Computed Tomography

The longitudinal fold of the duodenum can be visualized by computed tomography (CT). Visualization of the fold helps localize the hepatopancreatic duct entrance into the duodenum. Many pathological processes of the head of the pancreas such as pancreatitis or malignancy can produce swelling involving the longitudinal fold, which can be visualized by CT.

Extensional stresses during polymer flow in ducts

During the flow of high molecular weight, narrow-, and broad-distribution polybutadienes and polyisoprenes rheo-optical measurements were conducted of extensional stresses acting along the flow axis in the preentrance and entrance regions of the duct and of their subsequent relaxation in the duct. The extensional stresses increase in the preentrance region, reach their maximum values at a distance of two or three tenths of the duct width from its edges, and then relax. The position of the maximum extensional stress is independent of polymer characteristics, shear stresses in the duct, and shape of the entrance and dimensions of the rectangular duct. The dependence of the maximum extensional stress on the shear stress of the duct wall can be assumed to be linear for small values. The length of the stress relaxation zone depends on the shear stress at the duct wall and the molecular mass distribution. It is independent of the molecular masses in narrow-distribution polymers. For the polymers investigated, a generalized dependence was obtained for the reduced duct length over which the extensional stresses relax to zero from the reduced deformation rate. This dependence takes into account the characteristic polymer relaxation times and the value of the molecular mass of the chain between the fluctuation entanglement. A considerable decrease in the duct's length-to-width ratio leads to an increase in the maximum values of the extensional stresses. A decreases in the duct entrance angle causes a reduction in the rate of increase of extensional stresses, the maximum values, and the acceleration of the relaxation processes in the duct. A decrease in the ratio of the width of the preentrance region to the duct width leads to a reduction in the maximum in extensional stresses. It is shown that one of the causes for the instability of the polymer flow in the ducts can be the rupture of polymers due to their extension in the preentrance and entrance regions. Calculations were done that describe satisfactorily the relationship between the values of the maximum extensional stresses and the shear rate and stresses on the duct wall.

Gravitational deposition of aerosol particles from a developing flow in a horizontal circular tube

Aerosol particle deposition due to gravitational settling in a horizontal circular duct is examined for steady laminar flow, which develops from a uniform velocity profile at the entrance to a parabolic velocity profile downstream. Numerical calculation methods, based on the analysis of the limiting trajectories of the particles, are used to determine the deposition efficiency as a function of the duct entrance length. The results show that the deposition for the limiting cases of very large or small settling approach the solutions for deposition in a slug or a Poiseuille flow, respectively. In addition, particle inertial effects were included and for relatively large inertia, the deposition rate was significantly affected.

Heterogeneous fluorine atom recombination/reaction on several materials of construction

Heterogeneous F-atom recombination/reaction probabilities on several construction materials were computed from measurements of F-atom flow rates at the entrance and exit of a catalytic duct in a low-pressure reactor. Atom loss probabilities at 300 K and pF^ 13N-m ~ (~1.3 -10~atm) are 6.4 -10~ 5 for A12O3, 1.6-10' for quartz and pyrex glass, 2.8-10 for type-304 stainless steel, 4.2-10 for molybdenum, 7.2-10 for nickel, 1.8-10 ~ for aluminum, and > 10 ~ for copper, brass, and zinc. The values for steel and aluminum vary little with temperature up to 470 and 560 K, respectively. Application of these materials in gas dynamic hydrogen fluoride laser nozzles is discussed briefly.

Compressible Flow Ejectors: Part I—Development of a Finite-Difference Flow Model

A general method of calculating two-dimensional (plane and axisymmetric) mixing of a compressible jet in variable-area ducts has been developed. The method incorporates finite-difference approximations to the conservation equations, and is applicable to a wide range of Mach number, mass flow ratio, and initial conditions. The model was based on mixing length approximations deduced from boundary-layer and free-jet mixing for the upstream portion of the flow, and on a new mixing length distribution for the downstream zone which is entirely occupied by shear flow. The method has been tested and found satisfactory with existing data on boundary layer, constant-diameter duct entrance flow, constant-pressure jet mixing, and jet mixing in variable-area ducts. Part II of the paper describes tests of the method with new data from an experimental ejector study.

The dependence of lipid absorption in vivo on solubilized concentration

1. 1. The aim of the experiments was to test in vivo whether absorption of lipid varied with the concentration solubilized in the lumen. Such a dependence has been demonstrated for everted sacs in vitro. 2. 2. Two types of perfusates were prepared in which the total concentration of absorbable labelled lipid and of conjugated bile acid was the same. In one type, most of the lipid was in micellar solution; in the other type, the solubilized concentration was lowered by adding an unabsorbable oil, glyceryl triether, into which micellar lipid was partitioned. 3. 3. Absorption was tested in rats prepared in two ways: (A) unanaesthetized with common bile duct and thoracic lymph duct cannulated in which lipid was continuously perfused by duodenal cannula; (B) anaesthetized with the small intestine cannulated proximally below the entrance of the common bile duct and distally in the lower third of the ileum. In Preparation B, the whole perfusate was injected at zero time and an even exposure to the entire mucosa ensured by to and fro displacement. 4. 4. In Preparation A absorption of [ 14C]oleic acid and glyceryl[ 3H]monooleyl ether into the lymph was the same for both lipids and both perfusates. Lipid was almost completely absorbed before the perfusate reached the distal half of the small intestine. 5. 5. In Preparation B disappearance of lipid from the lumen and uptake by the mucosa was less for the perfusate in which the concentration solubilized was lower. Oleic acid was absorbed more rapidly than monoether, relative to the concentrations solubilized. These findings agreed with results for everted sacs in vitro. 6. 6. It is suggested that in Preparation A decreased absorption per unit area can be compensated by utilization of more of the total absorptive area. In Preparation B and in everted sacs, no such compensation is possible and variation in absorption rate with solubilized concentration can be readily demonstrated.

Insemination and sperm storage in the alfalfa weevil, Hypera postica (gyllenhal) (Coleoptera : Curculionidae)

Observations on the microanatomy of the aedeagus, bursa copulatrix, spermatheca, spermathecal duct, and spermathecal gland and on the activity of the sperm within the female alfalfa weevil, Hypera postica (Gyllenhal), were used as a basis for interpreting the mode of insemination and sperm storage. The aedeagus is inserted deeply into the bursa copulatrix during copulation. The endophallus protrudes from the aedeagus and attaches to the bursa copulatrix by sclerotized spines. Semen is deposited from the phallotreme into the bursa copulatrix near the entrance of the spermathecal duct. Muscle contractions by the bursa copulatrix and the spermathecal duct facilitate sperm in reaching the spermatheca. A nutritive secretion from the spermathecal gland permits sperm to maintain constant activity within the spermatheca. Stored sperm or a factor associated with sperm stimulates alfalfa weevil oviposition and causes other biological changes in the female.

Critical regimes of shear in linear polymers

AbstractThe state of the problem of elastic turbulence is critically discussed. It is shown that the development of elastic turbulence is associated with the transition of polymer systems to the high elastic state.Model experiments with a narrow‐MWD polybutadiene have been carried out. The method of vizualization of the flow in a flat slit with the aid of circular‐polarized light has been used. The results of polarization‐optical investigation are compared with the results of capillary viscometry and dynamic measurements at small amplitudes. It is shown, in accordance with theoretical predictions, that when a polymer passes from the fluid to the high elastic state with an increase in the shear rate, it ceases to behave as a fluid under shear. This is accompanied by various forms of flow perturbation at the duct exit and entrance and inside the duct. Perturbations at the duct entrance and exit are due to stress concentration in these zones. The transition of a polymer to the high elastic state near the walls inside the duct gives rise to the “stick‐slip” process or to continuous slippage along the duct walls, depending on the velocity of polymer movement. This can be clearly traced by the changes in the interference band pattern. Still higher velocities result in an intensive process of continuity break (rupture) in the polymer and in its chaotic movement in the duct as an aggregate of irregularly shaped lumps, which, relaxing, may form a continuous body again. Attention is drawn to the significance of these observations for a quantitative description of the viscosity anomaly of polymer systems and of the relationship between the viscosity anomaly with various flow irregularities and perturbations in such systems.

Determination of the Thermal Constants of the Heat Flow Equations of Electrical Machines

One of the major problems in obtaining accurate predictions of temperature distribution within an electrical machine is the values of the thermal constants used in the solution of the heat flow equations. A line source method is developed for anisotropic materials and is used to determine the thermal conductivity of sheet steel laminations. Results are given for three typical sheet steels showing the effect of varying core clamping pressure. The thermal conductivity of high-voltage insulation is obtained from tests on production machine coils and values are given for typical insulation systems. A model test is described for the evaluation of the heat transfer coefficients from the cooling surfaces of the radial air ducts, based on the assumption of a uniform distribution of air across the duct entrance. The heat transfer coefficients from the other cooled surfaces within the machine are determined from full-scale temperature measurements on production machines. The limitation of this latter method of determination of heat transfer coefficient is evaluated.

A Numerical Treatment of the Attenuation of Neutrons by Air Ducts in Shields

Expressions for the neutron flux at the exit of a cylindrical duct of radius δ and length l (with λ = δ2/l2), have been found by the use of the albedo concept and by the method of single-collision sources in the duct wall, based on monoenergetic integral transport theory. In contrast with other methods of solution, the isotropic area source of radius δ at the duct entrance is not approximated by a point source, and the numerical evaluation of integrals does not impose restrictions on the values of λ. Calculation of the neutron flux at the duct exit is expedited by the use of the tables given, which are a function of the duct geometry and were generated from the numerical evaluation of the integrals that appear in the expressions for the flux.Comparison of the results as predicted by the formulas developed in this paper and those predicted by already existing formulas with the results of a stochastic neutron-transport code indicates that the formulas developed here are always in better agreement with the results of the code. For values of λ < 1, the formulas developed here differ by a maximum of ± 10%, while the existing formulas differ by a maximum of more than 100%.

Entry of common bile and pancreatic ducts into a duodenal diverticulum. Cause of pancreaticobiliary disease.

The entry of the common bile duct and pancreatic duct into a duodenal diverticulum has been demonstrated with increasing frequency in recent years, largely due to advances in radiological technique. Diverticula occur throughout the gastrointestinal tract. In the small intestine they develop in close association with the entry of blood vessels suggesting a gradual protrusion of mucosa through a weak spot so formed. Most duodenal diverticula occur on the inner concave aspect of the duodenum near the ampulla of Vater. It is surprising that the entrance of the common bile duct and pancreatic duct into a diverticulum does not occur more often. Less than 40 cases of the anomaly have been described. In our hospital 18 patients with the abnormality were encountered in a period of eight years leading us to believe that the condition is more common than has been previously realized. Ten were male and eight were female.

Entrance of the Common Bile Duct into a Duodenal Diverticulum—Report of Two Cases

Entrance of the Common Bile Duct into a Duodenal Diverticulum—Report of Two Cases

The fine structure of the spermathecae and their ducts in the mosquito Aedes aegypti

A study of the ultrastructure of the spermathecae and their ducts in Aedes aegypti revealed two principal cell types: (i) epithelial cells which surround the cuticular shell of the spermatheca and the cuticular lining of the spermathecal duct, and (ii) glandular cells which are associated with the spermatheca and with the spermathecal duct. The glandular cells of the spermatheca form a group situated near the entrance of the spermathecal duct, and they discharge their secretion through short cuticle-lined ductules into the lumen of the spermatheca. Isolated glandular cells are also present on the surface of the spermathecal duct, near the spermatheca, and they discharge their secretion through long cuticle-lined ductules into the lumen of the spermathecal duct. One end of each glandular cell is filled with a mass of microvilii, up to 3·8 μ long, closely entwined with one another and converging on the ductule. The cuticular shell of the spermatheca has a lamellar structure. The cuticular lining of the spermathecal duct is not lamellar, but is has nevertheless a complex structure. Material with the appearance of resilin can be seen in electron micrographs of the cuticle of the spermathecal duct, and the presence of resilin is confirmed by the properties of the cuticle including its fluorescence under u.v. illumination and birefringence when strained, its elasticity, and the ease with which it is hydrolysed by protease. The spermatozoon of Aedes aegypti has a narrow head region followed directly by a very elongate tail region. The tail region contains an axial filament complex consisting of one central and nine outer fibrils, and also contains two rod-shaped mitochondria with dense, granular contents.

A Systematic Approach to the Duct Streaming Problem and Some Results to Unscattered Flux Calculations

A systematic plan for calculating the flux distribution at the center and near the exit of a straight cylindrical duct is proposed. An infinite plane source on one side of the shield harrier is assumed to have either an isotropic or a cos n ϑ angular distribution. To obtain the flux distribution on the other side of the shield barrier, calculation is performed to separately obtain a. the flux coming from the disk source at the entrance of the duct b. the flux coming from the annular source surrounding the entrance of the duct. Moreover, (1) unscattered flux, (2) single scattering flux, (3) multiple scattering flux are considered separately. These fluxes are compared with that for the case of infinite slab shield without duct. The ratio of the unscattered flux oduct at the center of the duct exit to the unscattered flux oslab at a point behind the slab, and that of the unscattered flux oannular from the annular source to the unscattered flux odisk from the disk source are obtained for plane isotropic and p...

THE INTRINSIC CONTRACTILE ACTIVITY OF THE DUODENUM. EXTRINSIC INFLUENCES.

Much evidence has accumulated indicating that the rhythmic contractile activity of the duodenum and small intestine is primarily intrinsic in nature. It has also been suggested that this intrinsic muscular activity is under the supplementary influence of a pace maker, probably located in the duodenum near the entrance of the common bile duct. Milton et al 1,2 demonstrated the presence of a slow, rhythmic, electrical wave which starts in the first part of the duodenum and passes aborally as a coordinated stimulus to the muscular wall of the distal small bowel. Brass et al confirmed this observation and, by means of radially placed electrodes, showed that the electrical impulses travel down the intestine in a sheathlike manner. 3 Later, they added additional data which indicate that the electrical activity is conducted by the smooth muscle fibers themselves, and that the pylorus serves as a type of insulating barrier across which

ROENTGEN FEATURES OF CONGENITAL CYSTIC DILATATION OF THE COMMON BILE DUCT: A REPORT OF TWO CASES.

Differences in the pattern and. course of the biliary ducts, their size and shape, and the site of entrance of the common bile duct into the duodenum are so frequently encountered and so numerous that they are usually considered normal variations. The major anomalies of the biliary system are duplication of the gallbladder and the so-called choledochal cyst. In this paper 2 patients are presented with choledochal cysts which were demonstrated preoperatively by oral cholecystography with iopanoic acid.2 Choledochal cyst was first described by Vater in 1723. In a comprehensive review Alonso-Lej (1) collected 405 cases of which only 3 were preoperatively diagnosed by means of oral cholecystography (4, 6, 8). Most cases were discovered before the fourth decade ; the average age was twenty-five years. The condition occurs approximately four times more commonly in females than in males. We prefer the designation “cystic dilatation of the common bile duct” which is a more descriptive term than the commonly used ...

FINE STRUCTURAL CHANGES IN THE INTESTINAL EPITHELIUM OF THE BULLFROG DURING METAMORPHOSIS

The fine structural changes occurring in the columnar absorbing cells of the intestinal epithelium during metamorphosis of the bullfrog, Rana catesbeiana, have been examined by phase contrast and electron microscopy. Tissue samples taken just posterior to the entrance of the hepatopancreatic duct were fixed in veronal acetate-buffered osmium tetroxide and embedded in methacrylate. Under the action of the metamorphic stimulus (thyroid hormone), specific and characteristic responses were given by differentiated larval cells and undifferentiated basal cells within the same epithelium. The functional larval cells underwent degenerative changes and were retained for a time within the metamorphosing epithelium. Dense bodies appeared and increased in number in association with the loss of normal cell structure. Because of their morphology and time of formation, these bodies have been tentatively identified as lysosomes. Early in metamorphosis the basal cells did not change, but they subsequently proliferated to form a new cell layer beneath the remaining degenerating cells that lined the lumen. After the dying cells were sloughed into the gut, the new epithelium differentiated to form the adult tissue. The columnar epithelial cells of the mature animal differed in their fine structural organization from their larval precursors. Therefore, their adult configuration was molded by the action of the metamorphic stimulus.

STAPHYLOCOCCAL MUSCLE INVASION AND ANURIA.

ducts with dilatation and obstruction of the common bile duct. The second operation was undertaken on February 24, I962, i.e. about two months after the first, under general intubation aniesthesia. The old scar was excised. Adhesions of the colon and great omentum to the gallbladder were dissected. The common bile duct, which was found to be dilated (about 1.5 cm. in diameter), was explored through an incision below the junction of the cystic duct; two dark-greenish (bilestained) daughter cysts were removed from the common bile duct at the entrance of the cystic duct. The common bile duct was probed and dilated using Bakes dilators and a T-tube choledochostomy instituted. Cholecystectomy was also done; the gallbladder was removed with some difficulty due to dense adhesions from previous inflammation and surgery (Fig. i). A post-operative 'T' cholangiogram done on March 9, I962, i.e. 12 days after the second operation, showed a free passage of the dye into the duodenum with no apparent obstruction of the common bile duct. The T-tube was removed on the same day; this was followed by no drainage of bile at all. All wounds healed well and the patient left the hospital on March 12, I962, in a very satisfactory condition.

Taxonomic Significance of Spermathecal Structure in Some Species of Tribollum

RECENT examination of spermathecae in tenebrionid beetles associated with stored products has revealed that there are two distinct types of structure which are termed here the ‘tenebrio’ type and the ‘chamber’ type. Their basic plan and relationship to the rest of the female reproductive system are similar ; but there are certain differences which, in regard to the genus Tribolium, are considered to be of some phylogenetic significance. In both types, a duct of varying width and length, which terminates in the main sperm storage region, arises from the common oviduct. In Tenebrio molitor this duct is short and wide and ends in a group of convoluted, thin-walled tubes bound together by a tough membrane. Arising from their common base is a single, longer structure which may be glandular, having large-celled walls and a restricted lumen. Dissection of fertilized females has shown that the convoluted tubes carry sperm. In the chamber type, found in Gnathocerus, Alphitobius, Alphitophagus and some Tribolium species, there is a similar duct which runs to a strongly chitinized chamber in which motile spermatozoa are easily detected. This is variously shaped and arising either from the end opposite the duct entrance or from the side is a more-or-less elongate glandular region. In Palorus species this basic pattern is modified, associated with a muscular bursa.