Leaky Tube Research Articles

An Analytical Study of Creeping Flow of a Second‐Order Fluid through a Small Diameter Leaky Tube with Linearly Diminishing Absorption

This study is focused on investigating the effects of linear absorption parameter on creeping flow of a second‐order fluid through a narrow leaky tube. These flows are experienced in several biological and industrial procedures, for instance, in proximal convoluted tubule of a human kidney, in hemodialysis devices, in filtration processes of food industry, journal bearing, and slide bearing. Inertial effects are neglected due to creeping motion assumption and low Reynolds number. Langlois recursive approach method is used to linearize the governing compatibility equation and to obtain an approximate analytical solution by reverse solution method. Analytical expressions for various physically important quantities like velocity profile, bulk flow, mean pressure drop in longitudinal direction, wall shear stress, leakage flux, fractional absorption, and stream function are obtained in dimensionless form. The obtained solution shows great similarity with the already available work in the literature. Variation in flow variables with linear absorption parameter is analysed in detail. The special case of uniform absorption in creeping motion of second‐order fluid is presented in a separate section. It is noticed that velocity field, in case of uniform absorption, is independent of non‐Newtonian parameters. Therefore, it is asserted that any two dimensional axisymmetric Newtonian velocity fields is also a solution for second‐order fluids with identical boundary conditions.

Sistem Monitoring Kebocoran Gas SF6 Pada Sistem GIS menggunakan Modul LoRa Berbasis IoT

The research introduces a Gas Insulating Substation (GIS) Monitoring System for SF6 gas leakage, aiming to mitigate the risk of significant gas leaks. The GIS, comprising three phases (R, S, T), utilizes SF6 gas with protective alarms and leakage indicators on each phase. However, the current practice of sequentially checking leak points among phases poses challenges, such as potential damage to the SF6 gas refill valve, leading to larger leaks. In response, a Monitoring System using LoRa-based IoT modules was developed. The research methodology involved checking electrical flow through voltage sensors and pressure sensors on the nonferrous tubes of the three phases to identify leakage points. The results indicated that the implemented SF6 Gas Leakage Monitoring System using LoRa-based IoT Modules effectively assists High Voltage Substation operators in reducing valve damage caused by mishandling SF6 gas leaks. Operators can monitor leaky tubes through a web interface and receive Telegram notifications, expediting response times. Additionally, the system proves cost-effective, requiring only around 1 million rupiahs compared to the conventional cable installation costing approximately 5 million rupiahs, without necessitating modifications to the existing Substation system.

Wall reabsorption effects on heat and mass transfer of viscous fluid in a narrow leaky tube

The steady heat and mass transfer problem of flow of an incompressible Newtonian fluid is investigated in this study. The axisymmetric flow of a non-isothermal and highly viscous fluid is considered through a narrow leaky tube of uniform cross-section with linear reabsorption across the wall. The Navier–Stokes equations are solved for axially symmetric and slow flow in the tube. The effects of linear reabsorption parameter on the dimensionless radial and axial velocities, temperature, concentration, shear stress, leakage flux, fractional reabsorption, pressure drop across the tube as well as the Nusselt and Sherwood numbers have been investigated analytically. For 50% fractional reabsorption, inlet radial velocity is half of the reabsorption velocity along the tube. It has been shown that increase in the strength of linear reabsorption parameter considerably reduces the radial velocity, while, axial velocity shows opposite behaviour. At the exit region (z=0.9), reverse flow phenomenon is observed for higher values of reabsorption parameter. The pressure, flow rate and wall shear stress decreases after entrance region (z=0.1) of the tube. Nusselt number and Sherwood number show opposite behaviour inside the tube. At z=0.1 the magnitude of Nusselt number is maximum, while the Sherwood number is minimum at the exit region with higher value of reabsorption parameter.

Разработка методики прогнозирования глушения теплообменных трубок парогенератора атомных электростанций с водо-водяным энергетическим реактором

The main feature of an NPP steam generator (SG) is that in addition to steam generation, it shall reliably and constantly cool the NPP reactor’s core. The SG shall also comply with a stringent requirement of ensuring tightness of the primary and secondary circuits with respect to each other; i.e., its design shall exclude the possibility of damage to the heat-transfer and other elements loss of tightness of which entails ingress of radioactive primary coolant into the NPP steam--water circuit with the subsequent possibility of radioactive products releasing into the environment. Thus, ensuring reliable operation and design life of SG heat-transfer tubes (HTTs) is among top-priority objectives for different types of NPPs used both in the domestic nuclear power industry and abroad. Thin-walled SG HTTs constitute an important part of the primary circuit boundary, and in order to perform the function of an efficient barrier, HTTs shall not have through defects or defects generating the need to blank off them. The article describes methods used to predict blanking off heat-transfer tubes and the residual technical life of the SG tube bundle used at an NPP equipped with a water-cooled water-moderated power-generating reactor (VVER) and presents the results from calculating the permissible average value of chloride ion concentration during the operation. To assess the SG operation time to failure, a computer program has been written in the MathCad environment, using which the above-mentioned assessment can be performed within an acceptable timeframe and with sufficient accuracy. A conclusion has been drawn about the need to adopt more stringent requirements for the chloride ion concentration in the SG blowdown water to avoid the need of blanking off leaky tubes damaged as a result of stress corrosion cracking.

Analytical solution for laminar flow through leaky tube

The laminar flow through a leaky tube is investigated, and the momentum and conservation of energy equations are solved analytically. By using the Hagen-Poiseuille velocity profile and defining unknown functions for the axial and radial velocity components, the pressure and mass transfer equations are obtained, and their profiles are plotted according to different parameters. The results indicate that the axial velocity, the radial velocity, the mass transfer parameter, and the pressure in the tube decrease as the fluid moves along the tube.

The role of instrumental vaginal delivery in low resource settings

This commentary discusses instrumental vaginal delivery (IVD) and the issues experienced with that practice in low resource settings. It states that IVD is a key element of essential obstetric care and the improvement of maternal and neonatal outcomes will require the scaling up of IVD use with the provision of equipment and trained operators to areas where they are currently unavailable.

Coronal Leaky Tube Waves and Oscillations Observed with Trace

Leaky tube waves are examined in the context of kink oscillations in coronal loops, observed in recent years using TRACE. It is pointed out that the standard (non-leaky) principal kink mode has a leaky bifurcated counterpart with decay time τl≈4π−4(L/R)2P, where R and L are the loop radius and length, and P is the oscillation period. This is somewhat too long to explain the observed decays, except for very short or thick loops, but may be implicated in the initial excitation. Higher harmonics decay much more rapidly. The external solution takes the form of a wave running nearly parallel to the tube, but with a small outward component. In addition, a number of other leaky modes are described which decay on timescales of seconds, τl=Rae/a2, where a and ae are the loop and external Alfven speeds respectively, and which can be identified as being almost radially propagating fast magnetoacoustic waves. These are outside the currently observable range, but are likely to be important energetically.

A natural gas feed preheater fire

This paper examines an incident in an ammonia plant which began when a leakage in the radiant section tube of a natural gas preheater ignited a small fire. The small fire ultimately developed into a major blaze which caused the leaky tube to burst resulting in the plant shutdown. A subsequent investigation revealed inadequate equipment safety procedures. These faulty measures included the bypassing of an instrument interlock system provided for the gas feed preheater. The bypass caused operational problems because two plants were operating from a single natural gas supply header. In the aftermath of the incident, the instrument interlock system of equipment was modified to handle an emergency shutdown in the affected plant safely and, in the process, avoid hampering other ammonia plants.

The transpiration stream in the leaf apoplast: water and solutes

Flow of the transpiration stream in the lumen apoplast of the xylem appears hydrodynamically orthodox in being approximately described by the Hagen-Poiseuille Law, and by Murray’s Law for branching pipes. Flow may be followed in the major (supply) veins by labelling the stream with dye solutions. Progress of the dye in the stream into the minor (distribution) veins is obscured by surrounding tissues. Observations of the spread of fluorescent tracers from these veins in living leaves gave results that have been seriously misinterpreted to present a false view of the cell wall apoplast. Microscopy of the stabilized water-soluble fluorescent tracers moving out of the minor veins has revealed that: (i) the dye is separated from the water by filtration through cell membranes, and the water moves through the symplast; and (ii) the dye diffuses in the cell wall apoplast at rates 1/100 to 1/10 000 the rate of diffusion in water. As a consequence of (i), high concentrations of dye build up at sites called sumps. In grasses these sumps may be in the intercellular spaces outside the xylem. In dicotyledons these sumps are within the small tracheary elements. In fact, flow in the lumen apoplast is flow through leaky tubes, and is inadequately described by the Hagen-Poiseuille Law. Leaky tubes have a critical radius, below which (for a given pressure gradient) flow cannot occur. As a consequence of this, a wedge of xylem made up of vessels of different radii acts as a unit to concentrate dye tracers in a sump at its apex. Sumps may also be formed by evaporation of the water in the stream, especially at leaf margins. Investigations with the cryo-analytical scanning electron microscope of the natural ions of the transpiration stream reveal high concentrations of K, Cl, P and Ca in the stream in all the sizes of vessel and vein of sunflower leaves. These high concentrations appear to be produced, not by the mechanisms responsible for the formation of sumps of dyes, but by some other processes, probably occurring in the stem. The absence of sump formation by ions at the places where dyes form sumps is probably due to the more rapid penetration of the ions through the cell membranes. Reasons for the discrepancy between these measurements of salt concentrations in the stream and those obtained from sap expressed from leaves by pressure vessels are discussed. Implications of these facts for the design and interpretation of experiments with leaves are presented.

The xylem wedge as a functional unit – speculations on the consequences of flow in leaky tubes

summaryXylem, as a mixture of elements of large and small diameter, presents a paradox when viewed as a conductor of sap flow, since the quantity carried is determined by only the largest diameter elements. The paradox may be s resolved, and an important function for the smallest elements revealed, by consideration of flow in leaky tubes. It is shown how the balance between axial flow and leakage becomes critical at a certain diameter, called the critical diameter (D0). Below D0, no axial flow can occur. When a stack of connected tracheary elements of different diameters is assembled into a xylem wedge, as in the major veins of dicotyledon leaves, this wedge will act as a functional unit. Elements with D > D0 have axial flow, but those where DD0 have only radial flow. The mixture of elements then acts to concentrate solutes of the sap in the smallest elements at the apex of the wedge, left behind as the water leaves. The balance between radial and axial flow is also self‐adjusting to changes in the longitudinal gradient of pressure. Consideration is given to the functions of these graded stacks in the metaxylem of leaves, of stem vascular bundles, within secondary wood, and in roots. It is shown how some xylem fibres may be expected to mediate exchanges of water and solutes, and may act as regulators of these exchanges in space and time. Some experimental demonstrations are presented of the predictions of this hypothesis.

Reproducible leaky tube diffusion of Cd in InP at 500 °C

We report for the first time the successful application of the leaky tube method to diffuse elemental Cd into InP at 500 °C. Specular surfaces are consistently realized while additional phosphorus in the ambient is not required. Free-carrier concentration profiles and junction depths were experimentally determined for times ranging from 20 min to 21/2 h. A reproducible surface concentration of ionized acceptors is ∼1×1018 cm−3 (T=300 K). A concentration dependent diffusion coefficient ranging from approximately 1×10−14 to 1×10−10 cm2/s is calculated for the conditions under investigation. Secondary ion mass spectroscopy analysis shows the atomic Cd concentration to be very similar to that of the ionized acceptors, with the atomic surface concentration approximately two times greater than the surface hole concentration.

Sputtered dielectric films for GaAs diffusion masks

We have explored the use of sputtered dielectrics, rather than the more conventional thermal or plasma enhanced chemical vapor deposition films, as masks for localized zinc diffusion into GaAs. The masks employed in this study were films of Si02, Si3N4, and A12O3, and part of the routine characterization included measurement of the mechanical stress within the films. Zinc diffusion was carried out for 60 min at 600° C in a “leaky tube” diffusion furnace. In short, it was found that (1) the alumina films did not work as diffusion masks, (2) the build-in stress within the SiO2 and Si3N4 films was dependent upon the thickness of the film (increasing with thickness for SiO2, and diminishing with thickness for Si3N4), and (3) the lateral diffusion of the zinc underneath the mask increased with the stress content of the film, regardless of the mask composition.

Diffusion of zinc into Ga1−xAlxAs

A study of the diffusion of zinc into Ga1−xAlxAs with a ‘‘leaky tube’’ diffusion furnace has been carried out. The Ga1−xAlxAs epitaxial layers were grown with liquid phase epitaxy, and the aluminum concentration was varied from 0 to 44% in 4% increments; diffusions were performed in the temperature range 550–650 °C. It was found that the junction depth versus aluminum concentration was not a simple, monotonically increasing curve; rather, dramatic decreases in the apparent diffusion coefficient at xAl≊0.05 and xAl≊0.20 suggest that point defects, possibly including the DX center, are playing a significant role.

Anomalous Diffusion of Tin in GaAs

We have used a “leaky tube” diffusion system to carry out tin diffusion in p‐type substrates in an attempt to produce n‐p junctions with a low temperature processing technique. Solid was used as the source for the tin, and the diffusions were carried out in the temperature range 650°–750°C for times varying from 2 to 24h. Both secondary ion mass spectrometry (SIMS) and Rutherford backscattering spectrometry (RBS) showed that tin had been introduced into the substrates in concentrations as high as and to depths as large as 2 μm. However, electrochemical carrier concentration profiling revealed that the diffused region remained p‐type with net carrier concentration barely altered by the diffusion process. The reason for this anomalous behavior is not understood, but pairing or some other compensation may be taking place.

Pulse-wave propagation in an artery with leakage into small side branches.

Linear pulse propagation theory is applied to a network of elastic tubes. The network is specialized to one having a main branch with many low-admittance side branches. Continuum approximations and an asymptotic analysis of side-branch network input admittance reduce the original network to a tapered leaky tube. The outflow law is equivalent to distributed Windkessels. The conductance and time constant of the Windkessels are related to the geometry of the side-branch networks. Viscous effects are included in the theory. Asymptotic methods are used to determine the dispersion relation and waveform amplitude in the frequency domain. Periodic pressure and flow waveforms are computed using Fourier synthesis.

Reproducible “Leaky Tube” Diffusion of Zinc into GaAs with Submicron Junction Depths

not Available.

Use of a sputtered SiO2 coating for surface protection during ‘leaky tube’ diffusion of Zn into GaAs

Thin SiO2 layers, deposited by low-power room-temperature sputtering, have been employed as surface protection coatings during Zn diffusion into GaAs. These layers prevent surface erosion of the GaAs, but allow the Zn diffusion to proceed with negligible attenuation. The use of arsenic over-pressure during diffusion can thus be avoided.

XLIV. Steady flow of a viscous fluid through a leaky tube

XLIV. Steady flow of a viscous fluid through a leaky tube