Open-ended Tube Research Articles

Thermal performance of pipe-type energy piles with open-ended heat exchange tubes

This paper examines the thermal performance of pipe-type energy piles with open-ended heat exchange tubes (abbreviation as: open-tube energy pile). This study compares the thermal performance of U-tube energy piles with open-tube energy piles through model testing. The analysis focused on heat exchange efficiency, temperature changes at inlet and outlet points, and the piles’ and surrounding soil’s temperature response characteristics. An analytical model using Laplace transform was developed for the open-tube energy pile, with simulations conducted to analyze it at full scale. Results indicate that, under the same cases, the open-tube energy pile exhibits higher heat exchange efficiency than the U-tube energy pile. Additionally, the pile and surrounding soil show more pronounced temperature responses during testing with the open-tube configuration. Compared to existing models, the heat transfer model proposed in this paper is more suitable for analyzing the heat transfer of open-tube energy pile. Moreover, changes in the thermophysical properties of the pipe pile and soil will have different effects on the heat transfer between the pile and the soil.

A Study on the interaction of shock tube-generated blast waves with a circular object at different pressure ratios

The interaction of high peak overpressure blast waves with a circular object placed at two different axial locations from the shock tube exit is studied through numerical simulation using an in-house developed multi-component Navier–Stokes solver. The driver and driven sections of the shock tube were 0.8 m and 6 m, respectively. Helium is used in the driver section, while atmospheric air is used in the driven section and outside the shock tube. The evolution of blast waves inside an open-ended shock tube and its interaction with a rectangular object is reported in Murugan et al.. (2022). Here, the blast wave interacting with a circular object is examined for diaphragm pressure ratios of 13 and 57 by placing the objects at 250 mm and 500 mm from the shock tube exit. The flow field is evaluated through numerical Schlieren, vorticity, density, pressure plots, and the enstrophy plot, which shows the vortical structures that originated in the flow field. The blast load acting on the circular object is calculated for two diaphragm pressure ratios and axial locations. This study helps understand the reflection and diffraction of blast waves and associated flow fields around circular objects used in blast wave attenuation.

On the Absorption of γ-Radiation by Absorbers with a Thickness Equal to a Multiple of the Mean Free Path and Analogies with Standing Waves in a Sound Resonance Tube

This article addresses the phenomenon of the decreased absorption of γ-radiation when the thickness of the absorber equals a multiple of the mean free path, as observed in relevant laboratory experiments with various absorbing materials. This phenomenon can be compared with the periodic peaks in intensity in an open-ended sound tube that appear at multiples of half wavelength. This could suggest that there is analogy between the two physical systems that are the γ-ray absorber and the sound wave resonance tube. More similarities between the two systems are also presented.

Parametric instability in propagating flames and the impact of hydrogen enrichment on the onset of secondary instability

A self-excited acoustic instability of laminar premixed flames propagating in an open-ended tube with a length of 700 mm and a radius of 10 mm was simulated by solving the reacting unsteady compressible Navier–Stokes equations, to understand the way of massive acoustic generation and its onset behaviors. Four fuel–air mixtures with an equivalence ratio of 1.2 were considered, namely, methane–air and methane–hydrogen–air mixtures, to identify the role of hydrogen in rich methane–air mixture. Parametric instability, which generated huge acoustic disturbance and violent flame pulsations, was observed only for a particular methane–hydrogen–air mixture with RH = 0.2, consistent with previously reported experimental observations. For the investigation of the reinforcement mechanism of acoustic instability under parametric instability, the flame surface area modulation was examined. It was found that violent subharmonic flame front pulsations could strongly modulate the flame surface area in the fundamental mode, resulting in a fluctuating heat release rate and increased thermoacoustic coupling. When hydrogen addition was small, attaining a higher level of primary instability, which is the precursor of the parametric instability, was more dominant than increasing the threshold level for the onset of the parametric instability. With larger hydrogen addition, the increase in the threshold level was more dominant than attaining a higher level of the primary instability. In particular, as the flame propagation time decreased, the level of the primary instability was saturated in larger hydrogen addition. This study elucidates the mechanism for the acoustic generation of propagating flames under the parametric instability, and the effects of hydrogen enrichment within rich methane–air mixtures.

Broadband sound focusing with tunable focus based on reconfigurable acoustic coding metagrating

In this paper, we propose a reconfigurable acoustic coding metagrating composed of rotatable open-ended round tubes for realizing broadband sound focusing with tunable focus. Integrating reconfigurable idea into coding metagrating, we can implement the conversion of the logical units 0 and 1 simply by mechanically adjusting the rotational angle of the open-ended round tubes. The theoretical analysis, the numerical simulations, and experimental results demonstrate that the proposed coding metagrating can precisely manipulate the focus by alternating the coding arrangements. The proposed metagrating has the advantages of broadband property, precise focusing, and tunable focus. Our work provides promising applications in acoustic imaging, medical ultrasound treatment, and nondestructive testing.

Earth pressure distribution on laterally loaded offshore monopiles

Unlike conventional pile foundations, a monopile is a large diameter open-ended steel tube driven into the seabed. Accurate quantification of the earth pressure distribution along a monopile due to lateral loads plays a pivotal role in the design of offshore wind turbines and remains a problem of great interest. This paper presents an attempt to address the problem by means of three-dimensional (3D) finite element modeling, with focus on the effect of pile slenderness on earth pressure distribution and the associated soil deformation mechanisms. The study shows that as pile diameter increases, the deformation mode of the pile will change from flexural to rotational deflection while the deformation pattern of the surrounding soil varies from being the wedge-type to a combination of the wedge-type and the rotation-type. The magnitude of either normal contact stress or shear stress at a pile section decreases with increasing pile diameter, but the distribution pattern of the normalized contact stress (either normal or shear stress) is nearly the same. The implications of these findings for engineering practice are two-fold: (a) Use of the p-y relationship established from field tests on piles of reduced scales in the design of large-diameter piles may still result in a potential risk of overestimating the lateral bearing capacity if the test pile diameter is not large; and (b) a unified factor independent of pile diameter can be introduced to average the contact stress across the pile section in the development of simplified methods.

Effect of driver gas composition on production of scaled Friedlander waveforms in an open-ended shock tube model

With the evolution of modern warfare and the increased use of improvised explosive devices (IEDs), there has been an increase in blast-induced traumatic brain injuries (bTBI) among military personnel and civilians. The increased prevalence of bTBI necessitates bTBI models that result in a properly scaled injury for the model organism being used. The primary laboratory model for bTBI is the shock tube, wherein a compressed gas ruptures a thin membrane, generating a shockwave. To generate a shock wave that is properly scaled from human to rodent subjects many pre-clinical models strive for a short duration and high peak overpressure while fitting a Friedlander waveform, the ideal representation of a blast wave. A large variety of factors have been experimentally characterized in attempts to create an ideal waveform, however we found current research on the gas composition being used to drive shock wave formation to be lacking. To better understand the effect the driver gas has on the waveform being produced, we utilized a previously established murine shock tube bTBI model in conjunction with several distinct driver gasses. In agreement with previous findings, helium produced a shock wave most closely fitting the Friedlander waveform in contrast to the plateau-like waveforms produced by some other gases. The peak static pressure at the exit of the shock tube and total pressure 5 cm from the exit have a strong negative correlation with the density of the gas being used: helium the least dense gas used produces the highest peak overpressure. Density of the driver gas also exerts a strong positive effect on the duration of the shock wave, with helium producing the shortest duration wave. Due to its ability to produce a Friedlander waveform and produce a waveform following proper injury scaling guidelines, helium is an ideal gas for use in shock tube models for bTBI.

Cavitation bubble dynamics in a funnel-shaped tube

Control of cavitation in confining geometries is vital to the safety of hydraulic conduits and structures. Here, we investigate cavitation bubble dynamics in one typical type of open-ended tube with varying cross sections, i.e., a funnel-shaped tube, defined as a funnel-shaped section connected to a cylindrical section. In our experiments, single cavitation bubbles are generated by spark along the symmetric axis of the funnel-shaped tube at different positions, including in the funnel-shaped section (regime 1), near the throat (regime 2), and in the cylindrical section (regime 3). With high-speed photography, we observe that at the end of collapse, bubbles produce weak jets in regime 1, jets in a shape of an inverted cone in regime 2, and jets in a cylindrical shape with a rounded end in regime 3. With the help of OpenFOAM simulation, we better understand the surrounding flow fields during the bubble evolution. By capturing the main features of the flow fields, we derive dynamics equations for bubbles in each regime. Scaling laws are proposed for the bubble jet velocity, which depends on the position of bubble generation, the inner diameter of the cylindrical section of the tube, and the maximum distance where the bubble's upper surface can reach before the collapse. Our findings may be inspiring for understanding cavitation bubble dynamics in tubular conduits with complex geometries, e.g., cavitation in pipelines and draft tubes in hydrodynamic systems, and ultrasonic diagnosis in blood vessels.

Thermoacoustic analysis of premixed methane–hydrogen flames in open-ended tubes

Methane–air mixtures (ϕ =1.2) enriched with hydrogen at different concentrations (RH 0, RH 0.1, RH 0.2, RH 0.3 and RH 0.4) were ignited in an open-ended horizontal tube at 20 °C and atmospheric pressure of 1.013 bar. Flame propagation was filmed with a high-speed camera and the pressure captured to study the thermoacoustic interaction of flames at different hydrogen concentration. Two-thirds along the tube, the flames encountered an acoustic field and were subjected to longitudinal oscillations. Depending on the hydrogen content, significant differences were observed in the behaviour of the flames. For lower hydrogen concentrations (RH 0.1 – 0.3), the flame speed initially decreased as it entered the field, and was then subjected to violent oscillations, resulting in a high acceleration and speed. The accelerations were attributed by the formation of Rayleigh–Taylor instabilities, which existed in the form of spikes of unburned mixture into the burned gasses that coupled with the pressure oscillations. This satisfied the Rayleigh criteria that the acoustically driven instabilities require the heat release and pressure waves to be in phase. When the hydrogen content was increased, as the flame passed through the acoustic field, the flame speed decreased, and no Rayleigh–Taylor instabilities were observed, attributed to the higher flame speeds at RH 0.4. The main concern with high hydrogen addition to the existing natural gas infrastructure (for transportation or direct use by consumers) is mainly related with safety. The absence of violent oscillations in RH 0.4 flames shows that they do not increase monotonically with hydrogen addition, and may potentially be investigated further to be applied in existing natural gas infrastructures.

Investigation on esterified pectin as natural hydrate inhibitor on methane hydrate formation

Flow assurance treatment with chemical have become more common as new natural polymers are being develop and are viable for inhibiting hydrate formation in production systems due to its eco-friendly and economical properties. Using high-pressure micro-differential scanning calorimetry (HP-µDSC), the influence of kinetic inhibition on methane gas hydrate formation from synthetic polymer; polycaprolactam (PVCap) and organic polymers (low- and high-methoxylated pectin) was investigated. HP-µDSC was combined with the use of open-ended capillary tubes to counter the stochasticity of hydrate formation which often results in an inconclusive data set without numerous repetitions. By adding the capillary tubes within the cell, more data points on the performance of the inhibitors. Generally, the addition of these inhibitors increased the delay in formation of hydrates compared to the control sample which contained deionized water at 25˚C subcooling and 10 MPa pressure. However, the two types of organic inhibitors, which are distinguished primarily by the functional group ratios (carboxyl and ester), performed in contrast to one another. The results suggest that the presence of higher carboxyl functional groups is affecting the overall polarity (i.e., low-methoxylated pectin) significantly improved the hydrate inhibition at optimum concentration where both high-methoxylated pectin and PVCap; a commercial inhibitor, performed relatively weaker. In comparison with PVCap, high-methoxylated pectin showed comparable trend and slightly better performances at most concentrations; however, the peak structures indicate discernible difference in the formation mechanism. The use of low-methoxylated pectin at optimum concentration may offer inhibition performance up to three times to that of PVCap at high subcooling.

Methane hydrogen laminar burning velocity blending laws in horizontal open-ended flame tube rig

Different fuel properties and chemical kinetics of two different fuels would make it challenging to predict the combustion parameters of a binary fuel. Understanding the effect of blending methane and hydrogen gas is the main focus of this paper. Utilizing a horizontal tube combustion rig, methane-hydrogen fuel blends were created using blending laws from past literature, over a range of equivalence ratios from 0.6 – 1.2 were studied, while keeping one combustion parameter constant, the theoretical laminar burning velocity. The selected theoretical laminar burning velocity for all the mixtures tested were kept constant at 0.6 ms−1. Different factors affected the flame propagation across the tube, including acoustic pressure oscillations, heat loss from the rig, and obvious difference in hydrogen percentage in the fuel blends. The average experimental laminar burning velocity of all the flames was 0.368 ms−1, compared to the expected value of 0.6 ms−1. In an attempt to keep the theoretical laminar burning velocity constant for different mixtures, it was discovered that this did not promise the same flame propagation behaviour for the tested mixtures. Further experimentation and analysis are required in order to better understand the underlying interaction of the fuel blends.

Aerodynamic fragmentation of water, ethanol and polyethylene glycol droplets investigated by high-speed in-line digital holography

Digital holography is a remarkable interferometric technique for determining the size, shape, distribution, and spatial location of particles. Therefore, when combined with high-speed imaging technology, it represents a relevant technique for the study of the aerodynamic fragmentation phenomenon wherein the aerodynamic strengths counterbalance the cohesion forces of the drops causing thus their decomposition. We discuss in this paper the droplets fragmentation of water, ethanol and polyethylene glycol 300 solutions interacting with a shock wave and flow generated by an open-ended shock tube. In this context, a shock tube device was set up, and both the released flow as well as the shock wave generated were characterized by ultrafast imaging shadowgraphy and high speed pressure measurement. Millimeter diameter average drops are fragmented and imaged by high-speed digital in-line holography at a rate of 24800 fps, and then the image retrieved numerically. The Weber numbers are determined for each liquid and the observed fragmentation patterns are consistent with the description of the ‘chaotic regime’ reported in the literature by Pilch and Erdman (1987) [1].

Different perspectives on predicting the thermoacoustic energy conversion response in a Rijke tube

In this work, six different perspectives on characterizing the thermoacoustic field in an open-ended Rijke tube are considered and discussed. These begin with a three-pronged approach consisting of theoretical, experimental, and numerical investigations of the Rijke tube's time-dependent field. It is followed by a discussion of effective techniques that rely on either Green's function or differential equation models. Finally, a perturbation expansion is introduced that leverages a naturally occurring small parameter in the open tube configuration. This approach is shown to produce accurate predictions of pressure modal shapes and frequencies for an arbitrary specified temperature distribution. It also leads to a set of linear partial differential equations that can be solved in conjunction with a Green's function expression for the thermoacoustic pressure, velocity, and heat oscillations. In this study, the underlying framework is presented and evaluated for the pressure disturbance only. Another fundamental result includes a similarity parameter, coined the Rijke number, which plays an essential role in driving thermoacoustic oscillations, namely, by relating heat-flux fluctuations to the acoustic velocity and pressure. In this context, we find that the peak value of the energy-flux vector modulus, which stands for the modular product of acoustic velocity and pressure, does indeed occur at the heat source location and increases with the heat power input.

Image-Based Analysis of Interactions Between a Steady Jet and an Impulsively Started Jet

Ignition overpressure (IOP) is a principal dynamic load experienced by a launch vehicle during liftoff. The IOP arises due to the sudden ignition of the solid rocket boosters (SRBs) of a launch vehicle. The present work attempts to simulate the ignition of an SRB with an impulsively started supersonic jet generated using a quick-open valve. High-speed schlieren flow visualization is used to document the evolution of an impulsively started jet flowfield that included the characteristic precursor shock wave (that simulates the blast wave causing the IOP) and the following vortex ring. The dynamic interactions between the impulsively started supersonic jet and an established steady supersonic jet from another nozzle () in close proximity are also investigated. Both the precursor shock wave and the vortex ring interact strongly with the established steady-jet column as they proceed downstream from the nozzle exit, thereby introducing new sources of acoustic waves. When a generic jet blast deflector is introduced downstream of the nozzles, the precursor shock wave reflected from it, propagating upstream toward the nozzle exit. The reflected shock wave is recognized as the source of IOP experienced by the launch vehicle. The results show that the quick-open valve presents a unique way to generate impulsively started jets for understanding transients associated with the ignition of the SRB leading to the IOP, without the complexity associated with the use of open-ended shock tubes for carrying out such simulations.

Structural disruption of the blood\u2013brain barrier in repetitive primary blast injury

BackgroundBlast-induced traumatic brain injury (bTBI) is a growing health concern due to the increased use of low-cost improvised explosive devices in modern warfare. Mild blast exposures are common amongst military personnel; however, these women and men typically do not have adequate recovery time from their injuries due to the transient nature of behavioral symptoms. bTBI has been linked to heterogeneous neuropathology, including brain edema, neuronal degeneration and cognitive abnormalities depending on the intensity of blast overpressure and frequency. Recent studies have reported heterogeneity in blood–brain barrier (BBB) permeability following blast injury. There still remains a limited understanding of the pathologic changes in the BBB following primary blast injuries. In this study, our goal was to elucidate the pathologic pattern of BBB damage through structural analysis following single and repetitive blast injury using a clinically relevant rat model of bTBI.MethodsA validated, open-ended shock tube model was used to deliver single or repetitive primary blast waves. The pathology of the BBB was assessed using immunofluorescence and immunohistochemistry assays. All data were analyzed using the one-way ANOVA test.ResultsWe have demonstrated that exposure to repetitive blast injury affects the desmin-positive and CD13-positive subpopulations of pericytes in the BBB. Changes in astrocytes and microglia were also detected.ConclusionThis study provides analysis of the BBB components after repetitive blast injury. These results will be critical as preventative and therapeutic strategies are established for veterans recovering from blast-induced traumatic brain injury.

Fabrication of the Polymersomes with Unique and Even Nonequilibrium Morphologies.

Herein, efficient fabrication of polymersomes that have unique and nonequilibrium morphologies is reported. Starting from preparing big polymeric vesicles sized around 2µm with a flexible but crosslinkable structure, a controllable morphological transformation process from the vesicles via prolate vesicles and the pearl-chain-like structure, which are the two intermediate structures, to vesicle-end-capped tubes is conducted. Significantly, each of the intermediates is a regular polymersome and occupies a distinct phase space in the transformation process and thus can be separately processed and prepared. By crosslinking the structures, respectively, regular polymersomes with unique but stable morphologies are fabricated. Furthermore, the 1D polymersomes contain narrow necks. These narrow necks are sensitive to ultrasound vibration and broken by gentle ultrasound treatment to form regular open-ended tubes and open-ended vesicles, which are nonequilibrium but stable morphologies and difficult to prepare by existing methods.

Suppression of Rijke tube oscillations by delay coupling

This study experimentally analyzes the cessation of self-sustained periodic oscillations of gas columns in delay-coupled Rijke tube oscillators. The Rijke tube oscillator comprised an open-ended resonance tube with a Bunsen burner inserted into it. Delay coupling was introduced using acoustic waves propagating through a gas-filled tube with both ends connected to the resonance tubes. Two coupling methods, single- and double-tube coupling, were tested for comparison. A significant reduction in the acoustic amplitude was observed with relatively narrow tubes in double-tube coupling when the tube lengths were equal to half the wavelength and one wavelength of the acoustic waves of the uncoupled oscillator. The experimental results were analyzed using the theoretical model of the delay-coupled Rijke tube oscillators, whose coupling strength varied with the delay time. The present results would be useful in establishing a simple method for suppressing unwanted acoustic oscillations observed in various combustors.

Partial spectral flow and the Aharonov\u2013Bohm effect in graphene

We study the Aharonov–Bohm effect in an open-ended tube made of a graphene sheet whose dimensions are much larger than the interatomic distance in graphene. An external magnetic field vanishes on and in the vicinity of the graphene sheet and its flux through the tube is adiabatically switched on. It is shown that, in the process, the energy levels of the tight-binding Hamiltonian of pi -electrons unavoidably cross the Fermi level, which results in the creation of electron–hole pairs. The number of pairs is proven to be equal to the number of magnetic flux quanta of the external field. The proof is based on the new notion of partial spectral flow, which generalizes the ordinary spectral flow already having well-known applications (such as the Kopnin forces in superconductors and superfluids) in condensed matter physics.

Full-scale observations of dynamic and static axial responses of offshore piles driven in chalk and tills

This paper describes and interprets tests on piles driven through glacial tills and chalk at a Baltic Sea windfarm, covering an advance trial campaign and later production piling. The trials involved six instrumented 1·37 m dia. steel open-ended tubes driven in water depths up to 42 m. Three piles were tested statically, with dynamic re-strike tests on paired piles, at 12–15 week ages. Instrumented dynamic driving and re-strike monitoring followed on up to 3·7 m dia. production piles. During driving, the shaft resistances developed at fixed depths below the seabed fell markedly during driving, with particularly sharp reductions occurring in the chalk. Shaft resistances increased markedly after driving and good agreement was seen between long-term capacities interpreted from parallel static and dynamic tests. Analyses employing the sites’ geotechnical profiles show long-term shaft resistances in the chalk that far exceed those indicated by current design recommendations, while newly proposed procedures offer good predictions. The shaft capacities mobilised in the low-plasticity tills also grew significantly over time, within the broad ranges reported for sandy soils. The value of offshore field testing in improving project outcomes and design rules is demonstrated; the approach described may be applied to other difficult seabed conditions.

Inertagrams for a Variety of Semi-Occluded Vocal Tracts.

Objective This investigation addressed the desirable source-airway interaction obtained with vocalization through a semi-occlusion at the mouth. The semi-occlusion was a flow-resistant tube of varying length and diameter. Method The methodology was strictly computational. Airway shapes resembling those obtained from magnetic resonance or computed tomography imaging were stylized. Supraglottal and subglottal acoustic impedances were calculated, from which inertagrams were plotted over a frequency range of 0-4000 Hz. The inertagrams predict which harmonics are likely to be strengthened. Results The combination of epilaryngeal airway narrowing and lengthening, a pharyngeal expansion, and an oral narrowing behind the tube produce the best overall inertagram for pitch glide exercises. This configuration supports harmonics of the source evenly over a range of 300-4000 Hz. Conclusions For clinical applications, theory predicts that the length of a tube or straw does not matter if the inner diameter is on the order of 3 mm or less. For wider open-ended tubes, greater length can compensate for the wider diameter for the beneficial inertance effect, but the desired steady pressure in the airways for vocal fold posturing cannot be maintained.