Tube Exit Research Articles

A numerical investigation in buoyancy effects on micro jet diffusion flame

The buoyancy effect on micro hydrogen jet flames in still air was numerially studied. The results show that when the jet velocity is relatively large (V≥0.2 m/s), the flame height, width and temperature decrease, whereas the peak OH mass fraction increases significantly under normal gravity (g=9.8 m/s2). For a very low jet velocity (e.g., V= 0.1 m/s), both the peak OH mass fraction and flame temperature under g=9.8 m/s2 are lower than the counterparts under g=0 m/s2. Analysis reveals that when V≥0.2 m/s, fuel/air mixing will be promoted and combustion will be intensified due to radial flow caused by the buoyancy effect. However, the flame temperature will be slightly decreased owing to the large amount of entrainment of cold air into the reaction zone. For V=0.1 m/s, since the heat release rate is very low, the entrainment of cold air and fuel leakage from the rim of tube exit lead to a significant drop of flame temperature. Meanwhile, the heat loss rate from fuel to inner tube wall is larger under g=9.8 m/s2 compared to that under g=0 m/s2. Therefore, the buoyancy effect is overall negative at very low jet velocities.

Formation and dynamics of compressible vortex rings generated by a shock tube

Particle image velocimetry experiments were carried out to investigate the formation and dynamics of compressible vortex rings (CVRs) generated by a shock tube apparatus. Five shock Mach numbers ($$M_\mathrm{s}$$) including $$M_\mathrm{s}=\,1.28$$, 1.39, 1.48, 1.56, and 1.59 are designed to generate the three typical CVRs including shock-free CVRs, CVRs with embedded shock, and CVRs with embedded shock and counter-rotating vortex rings (CRVRs). Experimental results show that after the incident shock leaves the tube exit, CVRs roll up, grow in size, and then pinch off at a certain timescale. By referring to the idea of vortex formation time, CVRs are found to pinch off at the dimensionless formation number within the narrow range of $$F^*=3.5\pm 0.5$$ for the range of $$M_\mathrm{s}=\,1.28$$–1.59. When $$M_\mathrm{s}\ge 1.48$$, the embedded shock appears inside the CVRs and axially stretches the vortex core, therefore significantly affecting the dynamics of CVRs. The maximum axial velocity along the centerline, the non-dimensional mean core radius, and the propagation velocity of CVRs all increase with $$M_\mathrm{s}$$ when $$M_\mathrm{s}\le 1.48$$; however, they no longer increase when $$M_\mathrm{s}>1.48$$ owing to the effects of embedded shock. In addition, the propagation velocity estimated by the formula given by Moore (Proc R Soc Lond A 397:87–97, 1985) shows the better agreement with that obtained by experimental measurement for shock-free CVRs than CVRs with embedded shock and CVRs with CRVRs.

An asymptotic-numerical comparative study for axisymmetric free surface liquid jet near and far from exit at high Reynolds number

Purpose The purpose of this study is to examine theoretically the axisymmetric flow of a steady free-surface jet emerging from a tube for high inertia flow and moderate surface tension effect. Design/methodology/approach The method of matched asymptotic expansion is used to explore the rich dynamics near the exit where a stress singularity occurs. A boundary layer approach is also proposed to capture the flow further downstream where the free surface layer has grown significantly. Findings The jet is found to always contract near the tube exit. In contrast to existing numerical studies, the author explores the strength of upstream influence and the flow in the wall layer, resulting from jet contraction. This influence becomes particularly evident from the nonlinear pressure dependence on the upstream distance, as well as the pressure undershoot and overshoot at the exit for weak and strong gravity levels, respectively. The approach is validated against existing experimental and numerical data for the jet profile and centerline velocity where good agreement is obtained. Far from the exit, the author shows how the solution in the diffusive region can be matched to the inviscid far solution, providing the desired appropriate initial condition for the inviscid far flow solution. The location, at which the velocity becomes uniform across the jet, depends strongly on the gravity level and exhibits a non-monotonic behavior with respect to gravity and applied pressure gradient. The author finds that under weak gravity, surface tension has little influence on the final jet radius. The work is a crucial supplement to the existing numerical literature. Originality/value Given the presence of the stress singularity at the exit, the work constitutes a superior alternative to a computational approach where the singularity is typically and inaccurately smoothed over. In contrast, in the present study, the singularity is entirely circumvented. Moreover, the flow details are better elucidated, and the various scales involved in different regions are better identified.

Two-phase flow regime identification through local temperature mapping

Two-phase flows underpin some of our most ubiquitous technologies, ranging from micro-scale liquid-liquid cooling of electronics to macro-scale liquid-vapour boiling and condensation in thermal power plants. Establishing the morphology of a two-phase flow, under a prescribed set of conditions, is considered particularly important in the design stage. As the pressure loss and heat transfer characteristics of a two-phase flow are intimately linked to the fluidic arrangement, knowledge of the prevailing flow topology enhances understanding, and can lead to the development of flow-specific correlations and/or models. This paper presents a novel experimental measurement technique for identifying the predominant two-phase flow regime in a circular tube. Specifically, the investigation presented in this paper focuses on condensing flows of steam, at typical Rankine cycle cooling conditions. However, it is proposed that the experimental arrangement and methodology can be applied to any two-phase flow scenario. The approach presented herein employs a temperature measurement platform - composed from localised instrumentation - to measure the temperature drop, associated with the presence of a liquid phase, at any point in the tube. Through analysis and interpretation of local temperature difference measurements around the inside tube circumference, and along the tube length, the predominant flow regime can be identified. In this study, measurements were taken from a 25 mm internal diameter round tube, with steam flow rates in the range of 0.42–0.94 g·s-1. The flow regime was seen to transition from an annular-type profile nearest the tube inlet to a stratified-wavy topology towards the tube exit in all instances.

Shock tube exit flow fields through thin membranes

The flow field characteristics that form for a shock wave propagating through a membrane-like termination at the exit of a shock tube are studied. The strength of the shock wave reflected back into the tube, as well as the strength of the shock wave transmitted, is examined. Six different materials are used, ranging from copper and aluminium foils to a variety of elastic and plastic sheets, in a few cases with different initial pressure differentials. High-speed shearing interferometry imaging is done of the external flow. Three principal characteristics are present in the transmitted flow: a diffracted shock wave, an expansion wave and a re-compression shock wave. It is found that the prominence of these features varies depending on the material type. For the later flow development and material rupture, there are a number of principal characteristics: small vortices, secondary shock waves, a vortex ring, oblique waves and a Mach disc.

Effect of Fuel Nozzle Geometry on Swirling Partially Premixed Methane Flames

Abstract This paper presents an experimental study of the effect of fuel nozzle geometry on swirling partially premixed methane flames, where the focus is put on the ensuing flowfield and its role on coherent structures' suppression. The burner consists of a central interchangeable fuel nozzle surrounded by a swirling co-airflow where both discharge into a short mixing tube. The nozzle geometry is classified into two groups, namely, single- and multi-orifice nozzles. The swirling motion of the co-airflow is produced using a radial-type swirl generator with a swirl number of 1.15. The flowfield characteristics and coherent structures are documented using particle image velocimetry (PIV). Flame front dynamics are captured using Mie scattering technique. Quantitative laser sheet (QLS) is used to qualitatively shed light on the mixing characteristics downstream of the mixing tube exit, and laser Doppler velocimetry (LDV) is used to extract the coherent structures' peak frequency from the power spectra. The results revealed that the fuel nozzle geometry significantly affects the mean flowfield, mean, and root-mean-square (RMS) of the flame front location, flame front asymmetry, and coherent structures' amplitude. Higher spread rate and faster decay caused by single-orifice nozzles inside the mixing tube result in divergent flames with higher degree of flame front asymmetry downstream of the mixing tube exit. On the other hand, multi-orifice nozzles mitigate coherent structures, enhance mixing, and hence, promote the most appropriate conditions for coherent structures' suppression.

Thermoeconomic analysis on a molten salt parabolic trough‐based concentrated solar organic Rankine cycle system

Solar thermal electricity generating technology is an alternative solution to energy crises and environmental problems, which has caused wide concern in recent decades. In this paper, a molten salt parabolic trough-based concentrated organic Rankine cycle system is proposed and investigated. A quadribasic nitrate salt with low melting temperature is employed as a heat transfer and storage medium. A stable heat transfer and economic model is established with Matlab. The radial and axial temperature distributions in the collector tube are obtained, and the impact of condensation and evaporation temperatures on the heat transfer area is analyzed. Results show that the temperature along the axial direction linearly increases, and the temperature at the collector tube exit decreases with the increase of molten salt mass flow rate. The maximum temperature difference along the radial direction of the collector tube happens in the annular gap. Heat transfer and thermodymanic analysis indicates that condensation temperature has a more evident effect on heat transfer area than that of evaporation temperature. An increase in condensation temperature leads to a decrease in the evaporator area, the condenser area increases, and the total area decreases. Economic analysis indicates the collector cost plays a predominant role in total capital costs, and decreasing molten salt mass flow rate can considerably reduce collector cost. Levelized energy cost sensitivity analysis indicated that operation time per year has a more evident effect than that of the four factors. Heat transfer and economic analysis on the system helps in the selection of operation parameters.

An experimental verification on existence of air-drag force influencing yarn tension during rotor spinning

PurposeMost researchers have neglected the effect air-drag force on yarn tension during rotor spinning. This paper aims to study the effect of rotor air-vacuum pressure in conjunction with opening roller speed and yarn linear density on the yarn tension generated during the rotor spinning, which has established their significant influences on both the mean and the peak tension.This is the first of one-of-a-kind experimental study being reported to demonstrate the influence of air-drag force on yarn tension during the rotor spinning under dynamic condition.Design/methodology/approachThe dynamic measurements on yarn tension at the exit of the doffing tube were carried out by using an electronic capacitive yarn tension meter during rotor spinning. The derived experimental data were fitted into equations to construct the response equations and to work out the coefficients of multiple correlation between the data and the predicted equation for both the mean and the peak tension. Various surface plots were constructed by using those response surface equations, so as to study the effect of variables on yarn tension generated during the rotor spinning.FindingsThe study has established that the rotor vacuum is responsible in causing a change in yarn tension, it increases with the decrease in air-vacuum inside the rotor. The involvement of the opening roller speed in altering yarn tension during rotor spinning has been proved. As the opening roller speed changes, so does the air stream surrounding the opening roller speed with consequent alteration of the centrifugal force generated due to the rotation of the rotor. The centrifugal force and, hence, the yarn tension generated in the rotor will be simultaneously affected by both the rotor relative vacuum and the opening roller speed.Research limitations/implicationsThis is a structured experimental study to verify the influence of air-drag force generated during rotor spinning on yarn tension. Very limited theoretical work has been carried out in this direction as reported in the introductory part of the paper. The result of the present study will encourage future researchers to revisit the theory on generation of air-drag force during rotor spinning and work out a new formula.Practical implicationsNext only to the conventional ring spinning system, the rotor spinning holds the second place in the share of global yarn production. Because of its advantage of lower cost of production and amenability to automation, the rotor spinning has gained acceptance in spun yarn production, particularly for spinning coarse and medium counts of yarns. Currently, it has acquired about 25 per cent share in the world’s spun yarn production. As many of the rotor machine variables significantly affect fibre configurations and, subsequently, the yarn properties by influencing the airflow characteristics inside the rotor unit, the study of yarn tension during rotor spinning and its analysis assumes a significance.Social implicationsRotor spinning is a relatively new and faster method of conversion of discrete fibres into continuous staple yarn and, subsequently, various textiles and garments. Its yarn is distinct and a bit different compared to the conventional ring yarn. It has got wide acceptance in the market and fashion. As such, the spinning sector that converts fibres into yarns is an important industry world over, providing employment to many. Besides, being the basic operation in the fibre value chain, it supports many downstream activities, including human clothing and fashion. Thus, the research on rotor spinning, particularly the yarn engineering to produce better products will be helpful to strengthen and grow the textile value chain.Originality/valueThis is an original research study. The magnitude and the direction of the air drag on the yarn during rotor spinning is very difficult to assess. Thus, most researchers for the sake of simplicity in analysis have neglected its effect on yarn dynamics, but a few of them have taken note of it in their theoretical propositions. However, no experimental result has been reported so far in the literature, supporting the influence of such air-drag force on yarn tension in the rotor spinning. In fact, none of the above studies have considered the induced effect of centrifugal force caused because of the rotation of the opening roller on the airstream that flows from the transfer channel inlet into the rotor because of its partial vacuum, causing consequential effects on air-drag force and tension in the yarn inside the rotating rotor. This is the first of one-of-a-kind experimental study being reported to demonstrate the influence of air-drag force on yarn tension during the rotor spinning under dynamic condition.

The evolution of secondary flow phenomena and their effect on primary shock conditions in shock tubes: Experimentation and numerical model.

Compressed gas-driven shock tubes are widely used for laboratory simulation of primary blasts by accurately replicating pressure profiles measured in live-fire explosions. These investigations require sound characterization of the primary blast wave, including the temporal and spatial evolution of the static and dynamic components of the blast wave. The goal of this work is to characterize the propagation of shock waves in and around the exit of a shock tube via analysis of the primary shock flow, including shock wave propagation and decay of the shock front, and secondary flow phenomena. To this end, a nine-inch shock tube and a cylindrical sensing apparatus were used to determine incident and total pressures outside of the shock tube, highlighting the presence of additional flow phenomena. Blast overpressure, impulse, shock wave arrival times, positive phase duration, and shock wave planarity were examined using a finite element model of the system. The shock wave remained planar inside of the shock tube and lost its planarity upon exiting. The peak overpressure and pressure impulse decayed rapidly upon exit from the shock tube, reducing by 92–95%. The primary flow phenomenon, or the planar shock front, is observed within the shock tube, while two distinct flow phenomena are a result of the shock wave exiting the confines of the shock tube. A vortex ring is formed as the shock wave exited the shock tube into the still, ambient air, which induces a large increase in the total pressure impulse. Additionally, a rarefaction wave was formed following shock front expansion, which traveled upstream into the shock tube, reducing the total and incident pressure impulses for approximately half of the simulated region.

The effect of convergent-divergent tube on the cooling capacity of vortex tube: An experimental and numerical study

In this investigation, experimental and computational fluid dynamics (CFD) technique is used to study a newly designed Ranque-Hilsch vortex tube (RHVT), such as a convergent-divergent one. The FLUENT code is used to solve the governing equations with three dimensional compressible and turbulent models using the standard k-ε turbulence model. In this study, based on obtained results by the CFD study, the investigation point of the minimum temperature of cold reversed flow is analyzed, and results show that the minimum cold temperature is not located exactly in the cold exit of the vortex tube. Finally, in order to attain more temperature separation in the vortex tube system, some suggestions and results are presented. Moreover, a comparison of a convergent-divergent vortex tube with the simple one and their influence on the maximum cooling point are some other results presented in this manuscript. There is an acceptable agreement between CFD and experimental results in the present paper. The obtained results show that reducing the throat diameter from 8 to 2.5 enhances the amount of cooling capacity in the vortex tube.

ПОВЫШЕНИЕ ПРОДУКТИВНОСТИ ОЗИМОЙ ПШЕНИЦЫ НА БИОЛОГИЧЕСКОЙ ОСНОВЕ

The purpose of the research is to determine the impact of new environmentally friendly preparations on the formation of the crop and resistance of winter wheat to the most common fungal diseases. To achieve the goal of the research a field experiment was carried out on the basis of the scientific and educational production center "Integration" in the Orel district of the Orel region in 2016-2018. The options in the field experiment were arranged systematically in one tier. Repeatability in the experiments was 3-fold. Winter wheat was sown in the first decade of September. The background of mineral nutrition was N30P30K30. In spring double fertilizing with ammonium nitrate was carried out at 125 kg / ha. The experience options were: 1 – Control, without treatment; 2 – Trichodermin, seed treatment + treatment of crops in the tillering phase + in the tube exit phase; 3 – Trichodermin + Ultramag Combi grain, seed treatment + treatment of crops in the tillering phase + in the tube exit phase. The high efficiency of trichodermin and Ultramag Combi grain preparations on the winter wheat Moskovskaya 39 on dark gray forest soil was revealed. When treating seeds with a mixture of these preparations, the germination energy increased by 7%, and the laboratory germination rate increased by 9% compared to the control variant (without treatments). The high biological effectiveness treatment of seeds and double treatment of crops with a mixture of Trichoderma Ultramega Kombi grain against the causative agents of mushroom diseases was revealed. The development of Septoria decreased by 35.1% and brown rust-by 42.4% relative to the control option. The treatment of seeds and plants of winter wheat with Trichodermin alone provided an increase in yield by 19%, and a mixture of Trichodermin and Ultramagus Combined grain – by 23%.

Axisymmetric free jet of Re → 0 from a round tube

An axisymmetric free jet of Reynolds number Re → 0 from a round tube is investigated in a theoretical way in order to elucidate pressure and velocity fields in the downstream of the tube exit. The Stokes approximation is performed to the Navier–Stokes equations expressed by the spherical coordinate system. The whole flow field is divided into two regions, a closed region consisting of both the tube exit and the hemisphere with the tube radius, i.e. inner region, and a region outside of the hemisphere, i.e. outer region. The pressure and velocity components in the inner region are expanded by a series of unknown functions of the angle θ, multiplied by powers of the radial distance r, whilst those in the outer region by a series of unknown functions of θ, multiplied by inverse powers of r, both of which satisfy the respective boundary conditions at the tube exit and infinity. The inner-region and outer-region pressures are patched together well at an arbitrary point over the hemisphere common to both regions, and the velocity components are done at the same point likewise. The parabolic velocity distribution at the exit is derived from the velocity in the inner region. The jet-ejection pressure and the pressure gradient coefficient are related by one parameter σ and the role of the parameter in the patching is clarified. Stream lines show a typical flow characteristic of the free jet flow for Re → 0 in the outer region.

Study of continuous wave 33 keV H- beam transport through the low energy beam transport section.

The transport of a continuous wave 33 keV negative ion beam through the low energy beam transport section, designed for beam injection into the tandem accelerator, was studied. The continuous wave H- beam, produced by the Penning surface-plasma source with hollow cathodes and cesium addition, was separated and focused by the 90° bending magnet and then transported through the 0.8 m long transport tube, equipped with beam electrical and optical diagnostics. The beam current was measured by a water-cooled Faraday cup at the transport tube exit. Beam sizes and profiles were measured by CCD cameras looking into the beam from the back and sides. The additions of hydrogen, argon, and xenon to the transport tube and to the bending magnet chamber in the pressure range of 10-6 to 10-4 Torr were tested. The influence of gas addition on the beam space charge compensation and beam transport was studied. A mechanism for the H- beam focusing due to space charge overcompensation and beam compression by the positive charge, produced with positive ion accumulation in the beam, is discussed.

Design of X-ray units for inspection applications (review)

A review of the structural elements (individual components, printed circuit boards, etc.) of X-ray systems intended for inspection of electronic products is presented. The basic principles of constructing such systems and typical composition of the equipment capable of providing the minimum necessary functionality are considered. Among the main technical characteristics an emphasis is made on the resolution power, which depends on the pixel size and thickness of the scintillator layer of the X-ray detector, as well as on the size of the effective focal spot of the X-ray tube. Comparative analysis of the advantages and shortcomings of clastic (open type) and sealed (closed type) X-ray tubes – one of the main nodes of such systems-is carried out. A structural diagram of a clastic X-ray tube is presented along with and the characteristics of domestic and foreign developments. The main disadvantages of the systems based on clastic tubes are considered. Large dimensions, large weight, relative complexity of the construction, presence of the vacuum-tight collapsible connections, the necessity of using a pumping system providing high vacuum, the necessity of high-voltage training of the tube assemblies after their replacement, and high cost are noted separately. The design of sealed off BS microfocus X-ray tube and radiation sources on their base which can be used in the development of domestic X-ray systems are briefly described. The diameter and length of the metal-glass cylinder tube are 75 and 315 mm, and the diameter and length of the copper anode tube 10 and 100 mm, respectively. A tungsten target is deposited on a beryllium substrate (X-ray tube exit window) with a thickness of 0.2 mm. The minimum focal length during x-ray photography is 0.5 mm. A comparative analysis of the characteristics of a clastic (collapsible) X-ray tube with continuous pumping and an X-ray tube sealed from an exhaust cart revealed the possibility of successful use of sealed tubes in modern X-ray systems used for inspection applications.

Numerical simulation of flow boiling in an orthogonally rotating duct

Numerical predictions of flow boiling in a square tube rotating in vertical direction at a uniform rotating speed are presented. There-dimensional physical model and numerical model were established for simplified problem. Realizable k−e (RKE) turbulent model was employed to study vapor–liquid two-phase turbulent flow. Heat and mass transfer between vapor and liquid were solved based on volume of fluid multiphase flow model combined with user-defined function. The transient results show that wall superheat at onset of nucleate boiling (ONB) condition in rotating tube is obviously higher than that in stable tube. Based on Jens–Lottes formula of Bowring model, empirical formulas for wall superheat at ONB condition were modified with consideration of Rossby number. As the rotation speed increased, location of ONB shifts to the tube exit. Flow pattern in tube is determined by coupling effect of heating and rotation. Stability of flow pattern is gradually weakened during the increase in rotation speed. The numerical results are in fair agreement with two sets of experimental data for same physical model and working conditions.

2743 Tumor Seeding at Gastrostomy Site Secondary to Percutaneous Endoscopic Gastrostomy Placement in Esophageal Squamous Cell Carcinoma

INTRODUCTION: Insertion of a percutaneous endoscopic gastrostomy (PEG) tube in many patients with oropharyngeal and esophageal cancer is standard of care to ensure enteral feeding. The most commonly applied pull-through insertion technique involves direct contact with the tumor. We present a case of direct invasion of tumor through stomach wall attributed to PEG tube placement via pull technique. CASE DESCRIPTION/METHODS: A 72-year-old female with squamous cell carcinoma of esophagus undergoing chemotherapy and radiation, s/p PEG tube placement, was hospitalized for femur replacement after a fracture of her right femur secondary to a minor fall. GI service was consulted for severe irritation visualised around the PEG site. Patient reported that her dysphagia symptoms had much improved owing to ongoing treatment, so she had not used her PEG in a few weeks. Physical exam revealed tenderness to deep palpation in left upper quadrant. External bolster of the PEG tube was noted at 7cm with purulent drainage, sloughed skin and erythema at the insertion site. She was started on broad spectrum antibiotics and CT scan was obtained to evaluate for deep infection which reported a superficial ulcerating wound with an 8.1 × 4.1 cm soft, tissue lesion along the track of the PEG tube concerning for seeding along the surgical tract. It extended from the skin to the greater curvature of stomach with loss of fat plane concerning for direct invasion. Biopsies from the gastrostomy site and right femur revealed squamous cell carcinoma. Direct seeding through the stomach wall at the time of PEG tube placement was the working diagnosis. Decision of not removing the PEG tube was made given extensive tumor at site and concern for non-healing fistula formation. DISCUSSION: Cancer metastatic to a PEG tube exit site is a dreaded complication with carcinoma of the upper aerodigestive tract. Rare reports in medical literature regarding increased risk of developing seeding from the "pull-through" technique of PEG tube placement. Use of laparoscopic, open, or the "push" technique of PEG tube placement in patients with head and neck cancer may prevent direct implantation of malignant cells into an enteral access site. Management involves multi-disciplinary approach with treatment options including radiation, resection of site and chemotherapy. However, our case further emphasizes the importance of avoiding techniques that may put patients at risk for a, albeit rare, disease and life altering complication.

Acoustic Coupling between Resonator Tubes in Quartz-Enhanced Photoacoustic Spectrophones Employing a Large Prong Spacing Tuning Fork.

A theoretical model describing the acoustic coupling between two resonator tubes in spectrophones exploiting custom-made quartz tuning forks (QTFs) is proposed. The model is based on an open-end correction to predict the optimal tube length. A calculation of the sound field distribution from one tube exit allowed for the estimation of the optimal radius as a function of the QTF prong spacing and the sound wavelength. The theoretical predictions have been confirmed using experimental studies employing a custom QTF with a fundamental flexural mode resonance frequency of 15.8 kHz and a quality factor of 15,000 at atmospheric pressure. The spacing between the two prongs was 1.5 mm. Spectrophones mounting this QTF were implemented for the quartz-enhanced photoacoustic detection of water vapor in air in the mid-infrared spectral range.

Characterization of a novel open-ended shock tube facility based on detonation transmission tubing

Abstract This paper proposes and demonstrates a novel shock tube driven by commercially available detonation transmission tubing in a safe, repeatable, and controllable manner for laboratory scale experiments. A circular cross-sectional open-ended shock tube (inner-diameter D = 22 mm ) driven by detonation transmission tubing was used to investigate the working principle of this novel shock tube using a dynamic pressure transducer and time-resolved shadowgraph photography. Specifically, the shock Mach number, repeatability, and flow structure generated from the tube exit were characterized. The experimental result shows that the flow structure including an initial shock wave, a vortex ring, an embedded shock, and an oblique shock pattern is similar to that of the conventional compressed-gas driven shock tubes. Furthermore, the shock tube has good repeatability of less than 2% with a shock Mach number up to 1.58. The versatile and cost-effective nature of the shock tube driven by detonation transmission tubing opens a new horizon for shock wave-assisted interdisciplinary applications.

Spatio-temporal distribution of absolute densities of argon metastable 1s5 state in the diffuse area of an atmospheric pressure nanosecond pulsed argon microplasma jet propagating into ambient air

Atmospheric microplasma jets (MPJs) sustained in rare gases have gained increased attention due to their potential to generate highly reactive species. In this paper, we present space- and time-resolved argon metastable densities, Ar(1s5), measured in an atmospheric pressure MPJ operated in Ar and propagating into ambient air using tunable diode laser absorption spectroscopy (1s5 → 2p9 optical transition). The MPJ was produced using a dielectric barrier discharge energized by short duration (230 ns) high-voltage positive pulses (4.2–6.2 kV) at a repetition frequency of 20 kHz. The spectral absorption line profile was recorded and allowed measurements of the absolute metastable Ar(1s5) density integrated in the line-of-sight of the laser beam under various operating conditions of the MPJ. The results reveal a sensitive dependence of the Ar(1s5) density on spatial coordinates, i.e., distance from the exit of the capillary tube of the discharge and from the axis of the argon jet. The highest Ar(1s5) densities of about 3 × 1013 cm−3 were measured at the axis of the argon jet at longitudinal distances between 4 and 5.5 mm downstream from the nozzle of the tube. The temporal distribution of the Ar(1s5) density, which presents three maxima, is thoroughly discussed in this paper. The spatial distribution of the effective Ar(1s5) lifetime (<250 ns) is also reported, giving some insight into the surrounding environment of the argon metastable atoms. The determined spatiotemporal distributions of the Ar(1s5) density can be useful for the optimization of argon MPJs for different applications like surface or biomedical processes.

Validation of Heat Transfer between Theoretical and Experimental from the Internal Surface of Vertical Tubes with Internal Rings Heated by Electrical Heating Coils

The comparison between experimental and theoretical heat transfer inside heated vertical channels that dissipate heat from the internal surface with and without internal rings is studied. The experimental setup consists of a circular pipe which is heated electrically by providing constant heat flux on the wall. The theoretical and experimental analysis is conducted in several pipes of same diameter but different lengths. The length of the pipe varies from 450 mm to 850 mm. The length to diameter ratios are taken as L/D = 10, 12.22, 15.56, and 18.89. The value of imposed heat flux varies from 250 to 3340 W/m2. The internal ring thickness varies from 4 mm to 8 mm. separation distance between the internal rings varies from 75mm to 300 mm. The theoretical results are compared with experimental data to ascertain numerical accuracy of the method. The effects of L/D ratio, thickness of internal rings and separation distance on the heat transfer performance are studied. The experimental result is compared with theoretical, theoretical results are found by using ANSYS. In this study theoretical result for wall temperature along the height of tube, fluid temperature at exit of tube are compared with experimental data.