Narrow Duct Research Articles

Influence of heat-loss on compressibility-driven flames propagating from the closed end of a long narrow duct

This study focuses on the dynamics of compressibility-driven flames that emerge in narrow tubes, closed at their ignition end, when conductive heat losses through the walls are appreciable. A narrow gap approximation is used to reduce the governing equations to an effectively one-dimensional problem. In long channels this problem admits traveling-wave solutions which we have investigated numerically for finite values of the Zel’dovich number, and asymptotically in the limit of large Zel’dovich numbers. In particular, we describe the flame structure and the dependence of the propagation speed on the physico-chemical parameters, including the heat loss and compressibility parameters, and examine the transition from compressibility-driven to isobaric flames when systematically reducing the representative Mach number.

Nasolacrimal stent with shape memory as an advanced alternative to silicone products

Epiphora is the overflow of tears typically caused by obstruction or occlusion of the nasolacrimal duct. More attention is required to address this global health issue owing to the increase in air pollution. Implantation of a silicone stent is the preferred treatment for epiphora; however, introducing a silicone stent into a narrow duct with complex geometry is challenging as it requires guidance by a sharp metal needle. Additionally, silicone can cause adverse reactions such as biofilm formation and tear flow resistance due to its extreme hydrophobicity. To overcome these problems, in this study we developed a new type of biocompatible shape memory polymer (SMP) stent with elasticity capacity for self-expansion. First, SMPs in the form of x%poly(ε-caprolactone)-co–y%poly(glycidyl methacrylate) (x%PCL–y%PGMA) were synthesized via ring opening polymerization by varying the molar ratio of PCL (x%) and PGMA (y%). Second, the shape memory and mechanical properties were tuned by controlling the crosslinking degree and concentration of x%PCL–y%PGMA solution to produce a test type of SMP stent. Lastly, this 94%PCL–06%PGMA stent exhibited more standout critical functions in a series of in vitro and in vivo experiments such as a cell growth-supporting level of biocompatibility with nasal epithelial cells without significant inflammatory responses, better resistance to biofilm formation, and more efficient capacity to drain tear than the silicone control. Overall, 94%PCL–06%PGMA can be suggested as a superior alternative to the currently used materials for nasolacrimal stents. Statement of significanceSilicone intubation (stenting) has been widely used to treat nasolacrimal duct obstruction, however, it can cause adverse clinical effects such as bacterial infection; presents procedural challenges because of the curved nasolacrimal duct structure; and shows poor drainage efficiency stemming from the highly hydrophobic nature of silicone. In this work, we describe an innovative shape memory polymer (SMP) as a superior alternative to conventional silicone-based materials for nasolacrimal duct intubation. We demonstrate the clear advantages of the SMP over conventional silicone, including a much higher drainage capacity and superior resistance to bacterial infection.

Influence of streamwise vortical structures on heat transfer in the far cylinder wake in a slot channel flow

We report on Large-eddy simulations (LES) of a flow around a cylinder in a narrow duct channel (slot) at the Reynolds number 3750 based on the bulk velocity and the diameter of the cylinder. Secondary streamwise vortical structures in the far wake are investigated appearing near the mixing layer at the midplane and near the duct channel surface. We investigate the correlation between the heat flux and friction velocity fluctuations and evaluate the propagation speed of these disturbances, which appears to be different.

Transition to turbulence in confined flow over a cylinder with low aspect ratio

We report on Large-eddy simulations (LES) of a flow around a cylinder in a narrow duct channel at the Reynolds number of 2 000, 3 000 based on the bulk velocity and diameter of the cylinder. We investigate a mechanism of the transition occurring from steady laminar flow at Re = 2 000 to turbulent flow at Re = 3 000 with attached recirculation zone and thin sinusoidal far wake.

Electrocoalescence of water droplets in sunflower oil using a novel electrode geometry

Electrocoalescence is an energy-efficient and environmentally-friendly process for breaking water-in-oil emulsions. It has been used extensively in the oil and petroleum industries. However, the current technology requires long residence times, giving rise to bulky vessels for industrial scale operations and making it less attractive for offshore application. It is also highly desirable to develop compact devices for down-the-well use. In this study, the performance of a novel electrode geometry, a ladder-shaped set of electrodes through which the emulsion flows, is assessed for enhancing the electrocoalescence, hence providing the potential for a compact design. The electrodes are formed into a V shape, with the apex pointing towards the direction of flow. This configuration enables nesting a series of electrodes in a compact form. Furthermore, the water-in-oil emulsion flows through the electrodes rather than passing by them, thus maximizing the effect of the electric field for coalescence. The system under study uses dispersed water droplets in sunflower oil, flowing in a narrow rectangular duct through the electrodes, providing essentially a two-dimensional flowing stream. The performance of this design is investigated for different electrical parameters (i.e. electric field intensity, frequency and waveform), fluid physical properties (i.e. conductivity and water content) and residence time. Of the three types of electric field waveform (i.e. half-sinusoidal, square and sawtooth), sawtooth performs best at high conductivities. Experiments reveal the existence of optimal values of electric field intensity, electric field frequency, salt concentration and water concentration, where the coalescence efficiency is maximum for the current design. Numerical simulation of the electrocoalescence process is conducted to assess the influence of various geometric and process parameters on the coalescence mechanisms of the V-shape electrodes. The outcome of this work is potentially useful for optimizing the design of compact and efficient oil–water separators.

Nasolacrimal Stent with Shape Memory as an Advanced Alternative to Silicone Products

Epiphora is the overflow of tears typically caused by obstruction or occlusion of the nasolacrimal duct. Implantation of a silicone stent is the preferred treatment for epiphora; however, introducing a silicone stent into a narrow duct with complex geometry is challenging as it requires guidance by a sharp metal wire. Additionally, silicone can cause adverse reactions such as biofilm formation and tear flow resistance due to its extreme hydrophobicity. To overcome these problems, in this study we developed a new type of biocompatible shape memory polymer (SMP) stent with elasticity capacity for self-expansion. We demonstrate both in vitro and in vivo that the SMP stent is more efficient in terms of tear drainage capacity and exhibits greater resistance to biofilm formation than a silicone control, suggesting that it is a superior alternative to currently used materials for nasolacrimal stents.

Acoustic performance of a resonating perforated liner with incident axial and circumferential acoustic modes

Perforated liners are a common form of passive damping device used in engineering applications to damp acoustic pressure fluctuations. The liner has many orifices arranged over the surface with a rear cavity, where the liner can be designed to resonate akin to an array of Helmholtz resonators in parallel. However, whilst a Helmholtz resonator is insensitive to the incident mode, the large surface area and rear cavity of a perforated liner can generate internal mode shapes that affect the acoustic performance. This paper presents a quasi-one-dimensional analytical model capable of capturing the variation in acoustic performance as the internal cavity segmentation is altered with incident higher-order acoustic modes in a narrow annular duct. Thus, the model can allow the generation of circumferential mode shapes. The model shows, when the liner is highly segmented circumferentially, the liner behaviour is akin to that with an incident axial wave. The segmentation causes the internal cavity pressure to fluctuate uniformly at a similar frequency to a Helmholtz resonator with the same effective cavity dimensions. When the cavity length is significant relative to the wavelength, circumferential mode shapes are generated within the cavity and the frequency of resonance increases based on the circumferential frequency component. The model is then compared to an example experimental data set obtained from a facility designed to allow circumferential modes to cut-on simultaneously with an axial mode. A description of the facility and the multi-microphone decomposition method applied to decompose simultaneous modes of unknown orders and relative magnitudes is presented. The model has good agreement with the experimental results for a small cavity segmentation, although there is deviation observed at high frequencies when the cavity length becomes significant relative to the circumferential wavelength.

Interfacial Structures in Bubbly-to-Slug Transition Flows in a Duct

As a critical closure equation to the two-fluid model and an important tool to characterize the two-phase-flow interfacial transport, the interfacial area transport equation (IATE) was formulated by taking various physical mechanisms causing interfacial area change into account. To fulfill the dynamic prediction advantage of IATE and further replace the flow regime–based constitutive relations, the IATE model should be validated by transition data to ensure model reliability and robustness. Air-water experiments are performed in bubbly-to-slug transition flows in a 200 × 10-mm narrow rectangular duct. Four-sensor conductivity probes are used to measure the local void fraction, interfacial area concentration (IAC), and bubble velocity at three axial locations. The void fraction distribution changes significantly with the flow developing. Flow conditions with a similar area-averaged void fraction but different superficial mixture velocities are compared, and it is found that the superficial mixture velocity significantly affects the IAC. In addition, the two-group IATE model for narrow rectangular channel is evaluated using the collected data. The average relative error for the total IAC prediction is 11.4%, but the group II IAC is overestimated for most flow conditions.

Excision of a part of the bile duct as an iatrogenic injury typical for laparoscopic cholecystectomy - characteristics, treatment and long-term results, based on own material.

IntroductionCholecystectomy is associated with the risk of bile duct injury (BDI). The nature of the injury in laparoscopic cholecystectomy (LC) cases seems to be more serious.AimWe present an analysis of long-term results of the treatment of patients who underwent operations at our department due to iatrogenic excision of a part of the bile duct (EPBD).Material and methodsOut of all 120 patients treated for BDI in our department we selected a group of 40 with EPBD. In all cases the corrective operation was hepaticojejunostomy. The median follow-up time was 157 (56–249) months. We evaluated risk factors for EPBD during LC compared to open cholecystectomy (OC).ResultsAmong bile duct injuries referred to our centre, EPBD occurred more frequently during LC (46.7%) compared to OC (11%), p < 0.001. Injuries located in the hepatic hilum occurred more often in the case of LC (68.6%) than OC (20%), p = 0.056. We did not find a difference in the frequency of EPBD between LC and OC groups depending on the presence of acute or chronic cholecystitis. The narrow common hepatic duct was reported more frequently in the LC (68.6%) vs. OC (20%) group, p = 0.056. Satisfactory long-term reconstructive treatment results were observed in 36 (90%) of 40 patients.ConclusionsExcision of a part of the bile duct occurs more often during LC than OC. It is often located in the hepatic hilum. Presence of a narrow common hepatic duct is a risk factor for EPBD during LC. Large diameter hepaticojejunostomy is a reconstructive procedure that promises good long-term results.

Ventilation of molds for die casting

This paper describes the factors that affect gas content in castings during pressure molding. The possibility of removing air and gases from the cavity of the mold through the ventilation channels in the process of filling it with liquid metal is considered. It is shown that the previously used assumption about the outflow of gases from the mold as through a hole in a thin wall is not correct. The calculations, taking into account the friction factor in narrow ventilation ducts, showed that the required crosssectional area of the ventilation ducts increases 4–6 times with a depth of 0,12 mm. If the obtained value of the cross-sectional area of the ventilation ducts is not possible to realize, at a given depth, it is proposed to use an accompanying vacuum to solve the problem.

Evolution of premixed stoichiometric hydrogen/air flame in a closed duct

Experiments were performed in a narrow duct to scrutinize the evolution of premixed stoichiometric hydrogen/air flame propagation at varied initial pressures. Besides the formation of the classic tulip flame, new stages of flame deformation have been observed using high speed Schlieren photography, e.g. elongated tulip flame and T-shape flame. With decreasing initial pressure, the flame propagation tends to be milder, but the classic tulip shape is of robust appearance at all conditions. The measured characteristic times of flame deformation were compared with the predictions of Bychkov's model. The pressure wave generated upon the flame-wall contact at very early stage does not trigger the classic tulip inversion, but will collide with the flame front modifying the tulip structure after reflection on the end wall. Thereafter, three different types of pressure dynamics are initiated depending on the initial pressure, P0≥0.7atm,0.5≤P0<0.7atm, or P0<0.5atm. The Rayleigh–Taylor instability primarily accounts for the flame deformation, whose amplitude growth rate, ω is periodic and determined mainly by the flame acceleration, g according to the linear theory. The measured pressure dynamics by sensor is a combined manifestation originating from the flame dynamics, flame-induced flow and pressure waves excited during combustion.

Life habits and evolutionary biology of new two-winged long-proboscid scorpionflies from mid-Cretaceous Myanmar amber

Long-proboscid scorpionflies are enigmatic, mid-Mesozoic insects associated with gymnosperm pollination. One major lineage, Aneuretopsychina, consists of four families plus two haustellate clades, Diptera and Siphonaptera. One clade, Pseudopolycentropodidae, from mid-Cretaceous Myanmar amber, contains Parapolycentropus. Here, we newly establish Dualula, assigned to Dualulidae, constituting the fifth lineage. Parapolycentropus and Dualula lineages are small, two-winged, with unique siphonate mouthparts for imbibing pollination drops. A cibarial pump provides siphonal food inflow; in Dualula, the siphon base surrounds a hypopharynx housing a small, valved pump constricted to a narrow salivary duct supplying outgoing enzymes for food fluidization. Indirect evidence links long-proboscid mouthpart structure with contemporaneous tubulate ovulate organs. Direct evidence of gymnospermous Cycadopites pollen is associated with one Parapolycentropus specimen. Parapolycentropus and Dualula exhibit hind-wing reduction that would precede haltere formation, likely caused by Ultrabithorax. Distinctive, male Aneuretopsychina genitalia are evident from specimens in copulo, supplemented by mixed-sex individuals of likely male mating swarms.

Laparoscopic-assisted cyst excision and ductoplasty plus widened portoenterostomy for choledochal cysts with a narrow portal bile duct

BackgroundComplete cyst excision with Roux-en-Y hepaticojejunostomy is the standard procedure for choledochal cysts (CCs). In recent years, neonates have been increasingly diagnosed with CCs prenatally. Earlier treatment has been recommended to avoid complications. For type IVa malformation without extensive intrahepatic bile duct dilatation, laparoscopic hepaticojejunostomy is technically challenging, and anastomotic stricture is a concern. Therefore, we propose laparoscopic synthetical techniques—laparoscopic excision of cyst and ductoplasty plus widened portoenterostomy to avoid stricture in CCs with a narrow hilar duct.MethodsAn anastomosis was created around the transected end of the common bile duct in 12 minipigs (Group A), and another 12 minipigs (Group B) received conventional cholangiojejunostomy. Anastomotic diameter measurements and cholangiography were conducted at different times. Histological findings of inflammation and scarring were compared. The expression levels of TGF-β1 and type I collagen were detected by real-time quantitative PCR. Between January 2012 and January 2016, laparoscopic excision of cyst and ductoplasty plus widened portoenterostomy were performed on 29 children with confirmed CCs with a narrow portal bile duct who were followed up for 12–48 months.ResultsGroup A survived well without obstruction. Slight inflammation and fibrotic tissue were confined to the bile duct periphery. In Group B, five pigs developed stricture. Severe inflammation and diffuse fibrosis affected the whole layer of the anastomosis. Fibrotic biomarkers were significantly higher postoperatively in Group B. Clinically, 29 patients exhibited satisfactory outcomes. No anastomotic stricture has been observed to date.ConclusionsLaparoscopic synthetical techniques may be a superior option to prevent anastomotic stricture in treating CCs with a narrow portal bile duct.

Bubble dynamics in evaporation flow of R-134a in narrow annular ducts due to flow rate oscillation

This article aims to investigate the influence of imposed flow rate oscillation on the bubble behaviors of evaporative flow of R-134a in horizontal narrow annular ducts. Particularly, the effects of amplitudes and periods of the oscillating flow rates along with the vapor quality of the R-134a on the bubble characteristics are examined in details. Moreover, the R-134a flow photos captured at the middle axial location are presented to illustrate the shift between the annular two-phase flow pattern and the bubble nucleation at different operating conditions and time instances. The observations reveal that the imposed mass flow rate oscillation results in the fluctuation of bubble departure diameter and frequency along with the density of active nucleation sites with the same frequencies. The larger amplitudes and longer periods of the mass flow rate oscillation lead to the stronger fluctuations in bubble dynamics. Furthermore, it is found that the bubble nucleation on the heating surface is the dominant mechanism at the low vapor quality of 0.05. However, the annular two-phase flow prevails over a relatively large portion of the periodic cycle at the dryness fraction of 0.5 and over the entire cycle at the dryness fraction of 0.95. Finally, the evaporative heat transfer of R-134a subject to the flow rate oscillation is correlated as a function of the mass flow rate and the vapor quality.

Morphology of the spermatheca of Triatoma lecticularia (Hemiptera: Reduviidae) (Stal, 1859).

Triatoma lecticularia (Hemiptera: Reduviidae) (Stal, 1859) is a potential vector of Chagas's disease and the comprehension of its reproductive biology is an important tool to control this insect. In the reproductive tract of female insects, the spermatheca plays a crucial role storing male spermatozoa after mating. Whithin insects the spermatheca shows a wide morphological diversity and the analysis of this characteristic can contribute to understand the reproductive biology of the species. This study describes the histology and histochemistry of the spermatheca of T. lecticularia. Females have a pair of elongated spermathecal reservoirs without associated accessory gland. The reservoir opens into the common oviduct via a narrow muscular duct. The reservoir epithelium has single layer of columnar secretory cells. The control of the release of spermatozoa from the spermatheca occurs via the muscular duct. The anatomical features of the spermatheca of T. lecticularia resemble those described of other Reduviidae. However, the histological and histochemical features of spermatheca observed in T. lecticularia were important to explain the maintenance of the viability of the spermatozoa stored.

Peripancreatic bacterial contamination can trigger the development of pancreatic fistula after pancreaticoduodenectomy

Introduction: Bacterial contamination in the ascitic fluid after pancreaticoduodenectomy (PD) may be an initiating event that leads to clinically relevant postoperative pancreatic fistula (CR-POPF). The aim of this study was to analyze the relationship between CR-POPF after PD and bacteria isolated from the drain fluid and also to investigate the bacterial species in the contaminated ascitic fluid and evaluate useful antibiotics for CR-POPF. Method: A prospectively collected database comprising 267 consecutive patients who underwent PD between May 2012 and December 2018 was analyzed. Amylase and microbial culture were routinely obtained from the peripancreatic drain fluid on postoperative day (POD) 1, 3, and 6. CR-POPF was defined as grade B/C by the international definition. Result: CR-POPF occurred in 81 (30.3%) patients. A significant association with CR-POPF was found for male (P=0.008), Non-pancreatic disease (P<0.001), body mass index (BMI) >25 kg/m2 (P=0.006), preoperative obstructive jaundice (P=0.016), preoperative biliary drainage (P=0.044), narrow pancreatic duct <3 mm (P=0.008), soft pancreas (P<0.001) and bacterial contamination in the drain fluid on POD1 (P<0.001). Multivariate analysis showed that male (Odds ratio [OR]=2.11; P=0.022), BMI (OR=2.24; P=0.027), soft pancreas (OR=3.94; P=0.001), and bacterial contamination in the drain fluid on POD1 (OR=4.70; P<0.001) were independent risk factors of CR-POPF. Bacterial contamination in the drain fluid on POD1, 3, and 6 were seen in 34 (12.7%), 66 (24.7%), and 126 (47.2%) of all patients. The most commonly isolated bacteria on POD1 were Enterococcus sp. (8.6%), Pseudomonas aeruginosa (1.5%), and Enterobacter sp. (1.5%) which were sensitive to piperacillin, imipenem, meropenem, and levofloxacin. In contrast, on POD6, Staphylococcus sp. (19.9%) and Candida sp. (14.2%) were commonly isolated. Conclusion: Early bacterial contamination of the ascitic fluid can be responsible for CR-POPF. To perform the early administration of more sensitive antibiotics for the patients with high risk of postoperative infection is important.

Pancreaticojejunostomy with seromuscular jejunal flap formation to prevent pancreatic fistula

Background: Pancreatic fistula following pancreaticoduodenectomy is a serious complication associated with high morbidity rates.We present a modification for duct-to-mucosa, end-to-side pancreaticojejunostomy with a seromuscular jejunal flap,in order to increase the safety of the anastomosis. Methods: The technique we describe is an end-to side, duct-to-mucosa,two layer pancreaticojejunostomy with a seromuscular jejunal flap and insertion of a silicon stent. We performed this modified anastomosis in sixty-three patients who underwent a pancreaticoduodenectomy procedure from July 2009 to November 2016. The procedure was classic pancreaticoduodenectomy except six cases with pyloric preservation. Results: There were 63 patients with periampullary tumor that underwent pancreaticoduodenectomy with the modified pancreaticojejunostomy technique. Thirty-six (57%) of them were males and 27 (43%) females, with a mean age of 67.4 years (range 32-82). The mean operative time was 308.2+37 min and the mean time needed to perform the anastomosis was 24.6 min (range 21-26 min). Five patients (8%) developed pancreatic fistula; four grade A and one grade C who needed reoperation due to bleeding. The overall morbidity was 22%. There was no anastomosis- related mortality. Conclusion: This modified pancreaticojejunostomy appears to be a safe and reliable technique without adversely affecting operative time. The seromuscular jejunal flap intends to promote healing process especially in cases of soft pancreas and narrow pancreatic duct.

Pancreaticojejunostomy with seromuscular jejunal flap formation to prevent pancreatic fistula

Background: Pancreatic fistula following pancreaticoduodenectomy is a serious complication associated with high morbidity rates.We present a modification for duct-to-mucosa, end-to-side pancreaticojejunostomy with a seromuscular jejunal flap,in order to increase the safety of the anastomosis. Methods: The technique we describe is an end-to side, duct-to-mucosa,two layer pancreaticojejunostomy with a seromuscular jejunal flap and insertion of a silicon stent. We performed this modified anastomosis in sixty-three patients who underwent a pancreaticoduodenectomy procedure from July 2009 to November 2016. The procedure was classic pancreaticoduodenectomy except six cases with pyloric preservation. Results: There were 63 patients with periampullary tumor that underwent pancreaticoduodenectomy with the modified pancreaticojejunostomy technique. Thirty-six (57%) of them were males and 27 (43%) females, with a mean age of 67.4 years (range 32-82). The mean operative time was 308.2+37 min and the mean time needed to perform the anastomosis was 24.6 min (range 21-26 min). Five patients (8%) developed pancreatic fistula; four grade A and one grade C who needed reoperation due to bleeding. The overall morbidity was 22%. There was no anastomosis- related mortality. Conclusion: This modified pancreaticojejunostomy appears to be a safe and reliable technique without adversely affecting operative time. The seromuscular jejunal flap intends to promote healing process especially in cases of soft pancreas and narrow pancreatic duct.

An Evaluation of Correlations for Predicting Pressure Drop of Air-Water Flow in Narrow Rectangular Duct

Aiming at developing a more common method for predicting two-phase flow pressure drop for small channels, experiments on frictional pressure drop of air-water flow in a vertical narrow rectangular duct with a cross-section of 40 mm by 1.6 mm were conducted at atmospheric pressure. The mass flow rates of air and water covered the ranges from 0.03 to 12.5 kg/h and from 19 to 903 kg/h, respectively. It was found that the two-phase flow can be divided into three regions according to the liquid only Reynolds number, by which a modified Chisholm two-phase multiplier was proposed for predicting frictional pressure drop. Some leading correlations for predicting two-phase flow pressure drop were compared with the new correlation against current experimental data, the latter had and a mean deviation of 7.2%, showing a better agreement with the experimental results.

Acoustical Characteristics of the Air Filter in the Engine Intake Air Cleaner

Linear acoustic theory is used for estimating the acoustical performance of the air cleaner box composed of the porous filter and encasing box in the engine intake system. The pleated filter structure is modeled as coupled multiple ducts having permeable micro-perforated walls and rectangular section, in which each duct area is assumed being homogeneous or inhomogeneous. Mathematical models describe the sound propagation within the narrow duct considering the visco-thermal effect at the filter pleats. For the validation, transmission loss (TL) is measured, and a change in TL spectrum is clearly observed by including the filter into the box. It is shown that the predicted TL counting the effect of visco-thermal loss agrees reasonably well with the experimental results. Noticeable effects of the filter on the TL are observed as highly smoothing effect at high frequencies and enhancing the TL magnitudes at troughs and lobes at low frequencies. Comparing homogeneous and inhomogeneous channel modelings, the latter is superior in precisely predicting the trough frequencies of TL curve, but the former is a bit better in predicting its magnitude. Parametric study on material and shape factors reveals that the number of pleats, length of the pleated filter, and distance between neighboring pleats are the key factors in determining the TL. It is concluded that an air filter element that has small number of long pleats with high flow resistance would bear the best acoustical performance among all designs.