Large Diameter Tubes Research Articles

Microstructure characteristics in weld zone of the novel thick 08Cr9W3Co3VNbCuBN heat-resistant steel welded joint by fusion welding

ABSTRACTOne of the primary candidate materials used in 650°C ultra-supercritical (USC) thermal power plant units is a novel thick grade of heat-resistant steel, 08Cr9W3Co3VNbCuBN (G115), for which China has complete intellectual property rights. In this study, G115 steel with a 115 mm thick wall was successfully welded using gas tungsten arc welding (GTAW) + shielded metal arc welding (SWAM), which was a significant step toward achieving its application in large-diameter boiler tubes. The influence of the welding process on the microstructure and mechanical properties of the G115 welded joint after post-weld heat treatment (PWHT) at 770°C for 11 h was investigated. The findings demonstrate that the weld zone (WZ) after PWHT was composed of martensite and ferrite, and M23C6 was the precipitate. The average hardness of WZ was 273.1 HV, and the average impact toughness was above 39J, which was sufficient for actual production applications. It offered the necessary theoretical foundation for the practical development of thick-walled G115 heat-resistant alloy steel during welding.

Bond-Slip Performances of Ultra-High Performance Concrete Steel Tube Columns Made of a Large-Diameter Steel Tube with Internally Welded Steel Bars.

Large-diameter concrete-filled steel tube (CFST) members are being increasingly utilised owing to their ability to carry larger loads and resist bending. Upon incorporating ultra-high-performance concrete (UHPC) into steel tubes, the resulting composite structures are lighter in weight and much stronger than conventional CFSTs. The interfacial bond between the steel tube and UHPC is crucial for the two materials to effectively work together. This study aimed to investigate the bond-slip performance of large-diameter UHPC steel tube columns and the effect of internally welded steel bars in steel tubes on the interfacial bond-slip performance between the steel tubes and UHPC. Five large-diameter UHPC-filled steel tube columns (UHPC-FSTCs) were fabricated. The interiors of the steel tubes were welded to steel rings, spiral bars, and other structures and filled with UHPC. The effects of different construction measures on the interfacial bond-slip performance of UHPC-FSTCs were analysed through push-out tests, and a method for calculating the ultimate shear bearing capacities of the interfaces between steel tubes containing welded steel bars and UHPC was proposed. The force damage to UHPC-FSTCs was simulated by establishing a finite element model using ABAQUS. The results indicate that the use of welded steel bars in steel tubes can considerably improve the bond strength and energy dissipation capacity of the UHPC-FSTC interface. R2 exhibited the most effective constructional measures, resulting in a significant increase in ultimate shear bearing capacity by a factor of approximately 50 and energy dissipation capacity by a factor of approximately 30 compared to R0 without any constructional measures. The load-slip curve and ultimate bond strength obtained from finite element analysis and the interface ultimate shear bearing capacities of the UHPC-FSTCs obtained using the calculation method agreed well with the test results. Our results provide a reference for future research on the mechanical properties of UHPC-FSTCs and their engineering applications.

Characterisations of self-excited nonlinear oscillations at varied system parameters in a Rijke tube with a premixed laminar flame

Thermoacoustic instability has been one of the major concerns in various industrial combustion systems, such as Rich burn, Quick mix, Lean burn engine and aerospace engines. The complex interactions between heat release and pressure fluctuations could generate thermoacoustic oscillations with high amplitudes and frequencies in a combustion chamber, which causes many combustion problems even severe structural damage. The studies about the effects of various system parameters on thermoacoustic instability would be important due to their crucial roles in characterising the system oscillations. In this study, the effects of different system parameters in a Rijke tube, including equivalence ratio, methane flowrate, burner position and tube inner diameter, have been investigated. The time-domain analysis methods, including both phase space analysis constructed from the time-delayed method and recurrence analysis, have been conducted to explore the system characteristics under different system parameters. Furthermore, the Recurrence Quantitative Analysis (RQA) and Wayland translation error have been processed to quantify the system nonlinearity. The study has shown the effects of system parameters on system frequency response, deterministic nature and nonlinear dynamics. The system oscillation tends to be more complex and unstable when the burner is moved to lower positions or in a large diameter tube. The phase space and recurrence analysis are found to be efficient for characterising the system nonlinearity with useful insights of self-excited thermoacoustic oscillations.

Annealing effect on the thermoelectric properties of multiwall carbon nanotubes

In this article, it is demonstrated that transport properties and thus thermoelectric performance of multiwall carbon nanotubes (MWCNTs) can be enhanced significantly by annealing. Two different samples of MWCNTs with small and large diameters were investigated. The as-prepared MWCNT samples were treated at different conditions of annealing. The pristine and annealed MWCNTs were investigated using x-ray diffraction, Raman spectroscopy and scanning electron microscope in order to investigate the microstructure, defect content and morphology before and after the annealing process. The electrical conductivity, Seebeck coefficient and thermal conductivity were measured over the temperature range of (300–450 K) and were found to correlate with the tube diameter and the annealing conditions. The electrical conductivity and Seebeck coefficient measurements show that the conduction mechanism in MWCNTs is thermal activation as the samples have degenerate semiconductor-like behavior. Upon annealing, the Seebeck coefficient increases, followed by a reduction in the thermal conductivity. The thermoelectric power factor was enhanced by annealing to realize the highest value of 1.06 μW m −1 K −2 at 475 K for the sample with the larger diameter. The thermoelectric figure of merit ZT was calculated to determine the performance of the materials. ZT of the sample of the larger tube's diameter was enhanced by about 247% at 450 K. • Pristine and annealed MWCNTs were investigated using x-ray diffraction, Raman spectroscopy and scanning electron microscope. • Thermoelectric performance of multiwall carbon nanotubes (MWNTs) is significantly enhanced by annealing. • The thermoelectric figure of merit ZT was enhanced by about 247% at 450 K.

Current status of the thermohydraulic behavior of supercritical refrigerants: A review

Supercritical heat transfer has already been applied for decades, as it has several benefits such as improved thermal efficiency of the thermodynamic cycle. Accurate knowledge about supercritical heat transfer and pressure drop of the different working fluids is required to design the heat exchangers and other components used in these systems. In literature, supercritical heat transfer of water and CO 2 has already been widely investigated, the research involving refrigerants (for their application in low-temperature heat conversion systems) is however rather scarce. This paper gives an overview of the existing research on supercritical heat transfer. An overview of the applications, general characteristics and the main findings for water and other fluids are summarized. Due to the sharp variations in thermophysical properties, heat transfer and pressure drop cannot be accurately predicted on a single-phase based approach only. An in-detail review of the current research and status of knowledge about supercritical heat transfer of refrigerants is presented. The effect of the different investigated refrigerants and operating parameters on heat transfer and pressure drop, both for heating and cooling applications, is discussed. The remaining gaps in literature are highlighted, which include studies involving larger diameter tubes, horizontal flow, cooling heat transfer and pressure drop estimations and creation of a wider database for a more general correlation development and measurements on newer refrigerants (with low Global Warming Potentials) as these will become increasingly important in the near future. In addition, advances in numerical research should focus on development of suitable turbulence models. Overall, further improving the basic understanding of the fluid structure and occurrence of deteriorated heat transfer, as well as forming reliable models for the thermophysical properties are key in future efforts. • Extensive review on thermohydraulic behavior of refrigerants. • Remaining gaps highlighted, including horizontal flow, cooling and large diameters. • Accurate fluid-to-fluid scaling laws needed to transfer knowledge from different fluids. • Improvement in numerical turbulence models and measurements required. • Need for a large refrigerant database, covering heat transfer deterioration.

Central line training models: limitations and modifications

Training in simulated environments allows clinicians to practise procedures and make mistakes without risk to patients. It is important training models offer sufficient fidelity, allowing the trainee to face the same difficulties and hazards that they would in clinical practice. This is particularly true of technical skills training using part-task trainers. Current designs of central-venous cannulation simulators may not fully meet this need. Not all training models allow for the guidewire in the Seldinger technique to be over-inserted. This means guidewire loss cannot be demonstrated in many simulators, which undermines recognition of this important complication, one of the preventable and significant hazards of the procedure [1]. Our simulation centre uses Blue Phantom’s Gen II Central Line Ultrasound Training Model. This simulator replicates the upper torso and neck, with a right internal jugular vein and carotid artery that can be cannulated. The simulated vessels terminate in clear tubes that run outside of the manikin’s torso and contain a reservoir of fluid. Full insertion of the line is blocked due to the diameter of the reservoir tubing being too small to accommodate the J-tip of the guidewire. In order to permit over-insertion of the guidewire, the tubing connected to the internal jugular vein has to be replaced with one of a larger diameter, sufficient to allow passage of the guidewire’s J-tip. We developed a 3D printed adaptor which allows smooth passage of the wire into the larger-diameter tubing. The connection between the tube and adaptor is then made water-tight with silicone sealant. The modifications were designed using SolidWorks, Dassault Systèmes, and printed using VeroWhitePlus™ on a Object500 Connex1™ by Stratasys. Since the reservoir tubing can now accommodate guidewire retention, a further modification was required to allow for retrieval of the wire at the end of the simulation. We have achieved this by including access to the tubing secured by a screw cap. With the modifications made ( Modified central line insertion model with over-inserted guidewire. The trainee cannot now rely on the manikin preventing them from making this potentially serious mistake, so training now more accurately replicates the real-life experience. This allows for a richer training experience and a more valuable post-simulation learning conversation. 1- Cheung ME, Mellert LT, Firstenberg MS. Bedside Procedure: Retained Central Venous Catheter. In: Firstenberg MS & Stawicki SP, editors. Vignettes in Patient Safety – Volume 2. London: IntechOpen; 2017.

Pulsation incitation and performance investigations for 3D Fin-and-Tube heat pipe heat exchanger by inserting dividing boards for various working fluids

In our previous study, we have shown that a heat pipe heat exchanger system modified from a commercial air-to-air heat exchanger operates without pulsations for working fluids of dielectric HFE-7000 or R134a, or under low heat loads for water, due to the large internal tube diameter of 5.6 mm. To incite pulsation and enhance the thermal performance, a straight dividing copper board is inserted into the straight section of each of the tube to form two semicircular compartments with an effective hydraulic diameter of 3.4 mm. The heat transfer characteristics and thermal performance against the hot air inlet temperature for the novel boarded model and the non-boarded model are experimentally explored with three working fluids (water, HFE-7000 and R134a) under six filling ratios (35%, 38.5%, 50%, 55%, 65%, 71.5%). Because water already works in a PHP mode in the non-boarded model under high heat loads, the thermal performance in the boarded model improved mildly by 2.7%–10.6%. Whereas, for HFE-7000 and R134a, the heat transfer mode is successfully incited from thermosyphon in the non-boarded model into PHP in the boarded model. The most significant thermal performance improvement was observed for HFE-7000 by 8.3%–24.5%. The improvement can be attributed to the switch of heat transfer mode, the generated corners for condensate accumulation, and the additional heat conduction via the copper board.

A new neurosurgical adjustable pressure suction apparatus with a mechanically controlled air inlet: the study of precise regulation and atraumatic suction.

BackgroundAn essential surgical tool in neurosurgery is the suction tube. The skillful and accurate use of a suction tube facilitates the neurosurgical operation.ObjectiveThis study is to verify the practicality of an adjustable pressure suction tube (APS tube) and to explore the ideal APS tube diameter and tip negative pressure for different intracranial structures.MethodsAPS tubes were used to aspirate brain tissues and carotid arteries of rats. Laser speckle contrast imaging (LSCI) was used to record the blood flow velocity (BFV). We measured APS tube diameter, air inlet size, tip negative pressure and central negative pressure and calculated the correlation between them. In our department, intraoperative real-time parameters including APS tube diameter, length, air inlet size, and central negative pressure were recorded, and the tube tip negative pressure suitable for different intracranial structures and parts was calculated.ResultsAll experiments were carried out using APS tubes. Experiments on rats objectively reflected a severe structural damage to the brain and blood vessels by the suction tube, which might even result in an irreversible reduction in blood flow., Rat carotid arteries and brain tissue suffered severe damage when the tip negative pressure exceeded 33.4 ± 1.8 and 29.2 ± 2.0 kPa, respectively. BFV failed to return to the preoperative level 3 min after the operation (p < 0.05), and this decrease was more pronounced when the suction tube diameter was large (p < 0.05). The tip negative pressure was positively and negatively correlated with central negative pressure and the air inlet size, and was independent of APS tube diameter. A total of 50 operations including 39 tumor resection operations and 11 moyamoya disease bypass operations were recorded. Large-diameter APS tubes (3.5 mm) with an closed air inlet were frequently used to maintain a greater tip negative pressure before the incision of dura mater. When important structures such as motor cortex and brainstem were involved, 1.5- or 2.0-mm-diameter APS tubes were mostly used, and an air inlet was opened up to 0.7–2.1 mm to maintain a safe tip negative pressure (7.4–27.9 kPa).ConclusionAPS tubes with a mechanical knob provide stable and precise adjustment of the tip negative pressure, avoiding excessive negative pressure that causes serious damage to the intracranial structure. And, this allows the surgeon to hold the suction tube more freely and operate at any angle with an appropriate fulcrum near the incision to achieve efficient atraumatic suction and enhance surgical safety.

A new serpulid species (Polychaeta) from the late Eocene lower part of the Lincoln Creek Formation in western Washington State (USA)

ABSTRACT A new species of serpulid tube worm, Metavermilia (Vepreculina) gollieti sp. nov., is based on tubes found in the late Eocene lower part of the Lincoln Creek Formation exposed along the Middle Fork of the Satsop River, Mason County, Washington State. Metavermilia (V.) gollieti differs from other species of the subgenus Metavermilia (Vepreculina) by its relatively large tube diameter, possession of 5 to 7 sharp longitudinal lines of granula, with a tube cross-section tunnel-shaped posteriorly and pentagonal at the aperture. Metavermilia (V.) gollieti extends the known geochronological range of the predominately Cretaceous subgenus Metavermilia (Vepreculina) from the Barremian to the late Eocene, only the second Cenozoic occurrence because there is the possiblity that ‘Serpula’ granosa from the Miocene (‘Tortonian’) may belong to Vepreculina. At the least, the new Eocene species fills a long gap in the geologic record of Vepreculina midway between Maastrichtian and Miocene as well as being the first record of the subgenus in North America.

Comparison of the efficacies of 1.0 and 1.5 mm silicone tubes for the treatment of nasolacrimal duct obstruction

This retrospective observational study analyzed the postoperative outcomes of bicanalicular intubation using different diameters of tube stents for treating postsaccal nasolacrimal duct obstruction. A total of 130 patients diagnosed with postsaccal obstruction who underwent endoscopic-assisted silicone tube intubation were included in the study. Patients intubated with a 1.5-mm large-diameter tube were designated as the LD group, and those with a 1.0-mm normal-diameter tube were designated as the ND group. The patency rates of the two groups at 1 year after tube removal were compared using the Kaplan–Meier curve and restricted mean survival time (RMST) method with τ = 365 days. Results demonstrated that the recurrence rate after tube removal was significantly lower in the LD group as compared with the ND group (p = 0.001). The patency rates at 1 year after removal in the LD and ND group were 85.7% (95% confidence interval [CI]: 75.4, 91.9) and 73.9% (95% CI: 61.7, 82.8), respectively. When comparing the patency rates by the RMST method at τ = 365 days, the RMST difference, RMST ratio, and RMTL ratio were higher in the LD group at p = 0.045, 0.052, and 0.046, respectively.

END CONNECTIONS OF TUBULAR MEMBERS BY CIRCULAR PLATE AND CENTRAL FLANGE

The connection of tubular members, used as bridge hangers or in 3-D coverings, has been widely researched, both for resistance and for fatigue. Such members are also often used in scaffoldings or as lighter bracings. The connection of the tube to a single bolted or welded plate consists of a circular end plate, covering the tube’s cross section on which a perpendicular rectangular plate is welded. No analytical approximation is available to calculate stresses in such a circular plate. Hence, FE-models have to be used for each application. As this is time consuming, a systematic survey of normal and shear stress has been conducted, for 6 unity connection forces of the gusset plate. The latter are normal force, shear in 2 directions, torsion and bending moments in 2 directions. The 3 types of stresses are kept separate, to allow for linear superposition, simulating any kind of real situation. The tube diameter and plate thickness have been varied to allow regression and obtain closed formulas. It appears that larger tube diameters have the capacity to distribute force, albeit the stress should be larger due to the increase of diameter. The former effect seems to overrun the latter and stress conditions are lower for wider tubes, which is rather surprising and may prove to be useful in practice. This is also confirmed by the displacement patterns, which show larger effective width of the higher diameter circular plate.

Drainage of infected kidneys with ureteral stents: does size matter?

The purpose of our study was to evaluate the ability of ureteral stents with different diameters to drain pus that accumulates in an obstructed kidney using an in vitro model. We developed an in vitro model of an obstructed kidney filled with pus. The model included a silicon kidney unit based on computed tomography (CT) data, a 3D printed ureteral stone based on a real extracted ureteral stone, a latex ureter model, a bladder vessel, and a fluid with qualities resembling pus. Identical printed stones were inserted into four ureter models containing stents with varying diameters (4.8F, 6F, 7F, 8F), each of which was connected to the kidney unit and the bladder vessel. The kidney unit was filled with artificial pus to pressures of 30 cmH2O to simulate an infected and obstructed kidney. The obstruction was relieved with stents in place, while artificial urine was pumped into the kidney; pressure in the kidney and remaining pus were measured continuously. The rate of pressure drop and the final pressure measured in the kidney were unaffected by the diameter of the stent. For all stent diameters, the pressure reached non-obstructed levels within 30s, final pressure was reached within 90-120s, and minimal amounts of pus remained in the kidney after 120min. In vitro experiments demonstrate that all stent diameters drain pus-filled, obstructed kidneys with the same efficacy. The common perception that larger diameter tubes are more effective under such circumstances should be re-examined.

Results of using transfistula videoscopic necrosequestrectomy to treat purulent-necrotic parapancreatitis

Aim. To improve the efficacy of minimally invasive surgical treatment for infected pancreatic necrosis.Materials and methods. The study analyzed the data of 142 patients with moderate to severe infected pancreatic necrosis treated from 2012 to 2017. In 2012–2014, an incision and drainage procedure involving multiple drainage replacements and debridements was used in 84 (59.2%) patients comprising Group 1. Since 2015, 58 (40.8%) patients comprising Group 2 have been treated using large-diameter (30–32 Fr) tube drainage followed by debridement and transfistula videoscopic necrosequestrectomy.Results. The best results were obtained by draining pathological cavities using large-diameter double-lumen drainage, as well as by actively removing sequestra using the developed technique of transfistula videoscopic necrosequestrectomy. In Group 2, the incidence of local complications amounted to 6.8% as compared to 22.6% in Group 1. Group 2 exhibited significantly lower case mortality rate (12.3% and 19.4%; t = 2.1; p ≤ 0.05), while patients in Group 1 required longer hospitalization: 96 ± 7.4 days as compared to 71 ± 3.2 days in Group 2 (t = 2.9 p ≤ 0.05).Conclusion. Minimally invasive procedures involving transfistula videoscopic necrosequestrectomy improve treatment outcomes, as well as reducing case mortality rate in the setting of purulent-necrotic parapancreatitis.

END CONNECTIONS OF TUBULAR MEMBERS BY CIRCULAR PLATE AND CENTRAL FLANGE

The connection of tubular members, used as bridge hangers or in 3-D coverings, has been widely researched, both for resistance and for fatigue. Such members are also often used in scaffoldings or as lighter bracings. The connection of the tube to a single bolted or welded plate consists of a circular end plate, covering the tube’s cross section on which a perpendicular rectangular plate is welded. No analytical approximation is available to calculate stresses in such a circular plate. Hence, FE-models have to be used for each application. As this is time consuming, a systematic survey of normal and shear stress has been conducted, for 6 unity connection forces of the gusset plate. The latter are normal force, shear in 2 directions, torsion and bending moments in 2 directions. The 3 types of stresses are kept separate, to allow for linear superposition, simulating any kind of real situation. The tube diameter and plate thickness have been varied to allow regression and obtain closed formulas. It appears that larger tube diameters have the capacity to distribute force, albeit the stress should be larger due to the increase of diameter. The former effect seems to overrun the latter and stress conditions are lower for wider tubes, which is rather surprising and may prove to be useful in practice. This is also confirmed by the displacement patterns, which show larger effective width of the higher diameter circular plate.

Free Suspended Thin-Walled Nickel Electroplated Tubes for Microfluidic Density and Mass Flow Sensors

In this paper, a novel fabrication method is proposed for microfluidic tubes with a large diameter, circular cross-section, and thin wall. These properties make the tubes especially suitable for density sensors and Coriolis mass flow sensors, because of the resulting low tube mass, low-pressure drop, and low pressure-dependence of the tube shape. A demonstrator sensor was fabricated and the first measurement results of fluid density and mass flow are presented. The low-cost fabrication method is based on electroplating technology and results in tubes with a near-perfect circular cross-section. Diameters ranging from 120 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> to 1 mm and wall thicknesses from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8~\mu \text{m}$ </tex-math></inline-formula> to 60 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> have been achieved. For the demonstrator sensor presented in this paper a freely suspended tube was realized with a total length of 37 mm, a diameter of 600 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> , and a wall thickness of 20 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> . Density measurements were performed using various gases, liquids, and liquid mixtures at 21°C to 23°C lab temperature. The accuracy of the measured densities of gases such as nitrogen, argon, and helium is 5%. For liquids including DI water, isopropyl alcohol (IPA), and their various mixtures an accuracy of 0.5% was obtained. Preliminary mass flow rate measurements were performed with water and isopropyl alcohol up to 30 g/h with less than 30 mbar pressure drop thanks to the large tube diameter. [2021-0179]

Condensation Flow and Heat Transfer Characteristics of R410A in Micro-Fin Tubes and Three-Dimensional Surface Enhanced Tubes

Condensation heat transfer characteristics (using R410A as the working fluid) were studied experimentally to evaluate the heat transfer performance in copper and stainless-steel heat transfer tubes (smooth and enhanced). Experiments were carried out for a mass flux that varied from 250 to 450 kg m−2 s−1, at a saturation temperature of 318 K. Single-phase heat balance verification found that the heat loss is less than 6%, and the deviation between single-phase experimental results and various prediction correlations is less than 15%. Additionally, tube side condensation flow patterns were observed and recorded. Experimental results found that the enhancement ratio of the condensation heat transfer coefficient (enhanced tube/smooth tube) of the three-dimensional surface (1EHT) tube is in the range of 1.15~1.90, while the ratio of the micro-fin (HX) tube is in the range of 1.18~1.80. Heat transfer performance is affected by material conductivity, with the thermal conductivity of the smooth tube slightly affecting the heat transfer performance; larger heat transfer enhancements are produced in the enhanced tubes. At a low mass flow rates and vapor qualities, the flow pattern is a stratified wavy flow, while at higher mass flow rates and vapor qualities, the flow pattern is an annular flow (with the area in the enhanced tube being larger than the area of a smooth tube). Flow patterns in the smooth tube are consistent with the predicted values shown in previously reported flow pattern maps. A flow pattern diagram for condensation heat transfer in enhanced tubes is presented as part of this study. The condensation heat transfer coefficient increases with an increase in mass flow. When the mass flow rate increases, the turbulence of the liquid flow increases and the liquid film becomes thinner; thermal resistance is reduced and the heat transfer coefficient increases. Heat transfer values at lower mass velocities increase slightly with increasing mass flux values; however, at higher mass flux rates the heat transfer increase is larger than that at low mass flux values. Finally, tubes produced from high thermal conductivity materials produce larger heat transfer performance gains than the gains found in smooth tubes; small diameter tubes produce larger gains than larger diameter tubes.

Multi-step hydroforming process and wall thickness optimization of 5A02 aluminum alloy five-way tube with different branch diameters

The different branch diameters of five-way tube affect the design of loading internal pressure in the hydroforming process, where the large-diameter branch is broken more easily than the small-diameter one due to the same ultimate stress of tube material in one-step forming method. Therefore, the first four-way and then five-way of multi-step forming (FFTF) method and the first three-way and then five-way of multi-step forming (FTTF) method were proposed to fabricate the 5A02 aluminum alloy five-way tube with two kinds of branch diameters to avoid the burst of large-diameter branch tube. The finite element simulation of five-way tube hydroforming process shows that the height of small-diameter branch tube is lower and serious wrinkles appear at the large-diameter branch tube in the one-step forming and FFTF method. By optimizing the length of punch, a five-way tube with a big branch height and uniform wall thickness was obtained with the FTTF method. The approach of lengthening the punch in the experiment increased the height of formed branch and reduced the wall thickness reduction rate of five-way tube in FTTF method. Overall, the findings mentioned above cannot only offer guide in creating five-way tube with excellent quality, but also be taken as reference to the hydroforming studies on multi-way tube in the future.

Study of He + 0.2% O2 plasma jet impinging on liquid surface from He(23S1) metastable atoms density measurements

This work presents spatial variations of the helium He(23S1) metastable atom absolute densities in a plasma jet at atmospheric pressure in He + 0.2% O2 gas mixture impinging on a liquid target. The plasma jet is ignited with 6 kV pulses of 2.5 μs duration and 8 ns rise and fall times at 20 kHz repetition rate. Streamers are created in both rising and falling fronts of the high voltage (HV). From Abel inversion of the line averaged absorbance of 1083 nm helium line, measured by laser absorption spectroscopy, the radial profiles of He(23S1) density along the plasma jet are deduced in two sources with different residence time of the gas within the discharge volume, having three different outlet tube diameters and with two gas flow rates. The metastable densities up to ∼3 × 1013 cm−3 have been measured. The radial profile remained always axially centered for the 1.5 mm outlet tube and with 0.5 slm for the larger diameter tubes. But in this later tubes and with 2 slm gas flow rate, the profile changed from a ring shape at the tube exit to axially centered when increasing the distance from the tube edge. In the rising front of the HV, the ring profile of He(23S1) density in the tube exit is attributed to the shape of the electric field, produced by the applied HV to the electrode wrapped around the dielectric tube. In the falling front of the HV, the electric field results from electrons deposited on the inner surface of the dielectric tube and positive ions accumulated on the surface of liquid during the 2.5 μs duration of the HV pulse. The influence of oxygen by-products formed in the plasma volume (O, O2(Δ), O3, positive and negative oxygen ions) on the dynamic of the plasma jet are analyzed.

Experimental Flow Boiling Study of R245a at High Reduced Pressures in a Large Diameter Horizontal Tube

Evaporators used in organic Rankine cycles (ORC) are designed using existing flow boiling correlations that are mainly based on HVAC&amp;R data. However, the ORC evaporators employed in the industry typically have larger diameters and operational conditions at higher reduced pressures compared to the HVAC&amp;R applications. The present study presents the results of flow boiling heat transfer experiments in operational conditions that are representative for an industrial waste heat recovery low-temperature ORC’s evaporator tube, by being performed at high reduced pressures and in a large-diameter horizontal tube with R245fa as working fluid. The measurements are performed within a range of mass flux, saturation temperature and heat flux at 83–283 kg/m2s, 85–120 °C (8.9–19.2 bar) and 17–29 kW/m2, respectively. Test section is a round and plain horizontal carbon steel tube with 21 mm I.D., 2.5 m length. 513 local two-phase heat transfer coefficients are recorded. The experimental results are compared with each other to reveal heat transfer coefficient trends with respect to varying experimental conditions. Four distinctive heat transfer zones are observed, namely, the nucleate boiling dominant (NBD) zone, weakening nucleate boiling dominance (WNBD) zone, flow boiling zone (FBZ) and the dry-out zone (DOZ). Heat transfer coefficient vs vapor quality trends partly resembled CO2 flow boiling results reported in the literature. Two flow boiling correlations moderately predicted the data.

Influence of pressure die's boosting on forming quality in bending process of thin-walled tube

For large-diameter and thin-walled metal tubes, it is necessary to master the influence law of pressure die's boosting on forming quality during the cold-bending process. By introducing equivalent additional compressive stress in theoretical analysis, the wall thinning, springback and axial elongation analytical models under pressure die's boosting are established respectively, considering the effects of geometric and material intrinsic parameters. The influence law of boosting on forming quality is obtained. Finite element (FE) models are established to simulate the processes of tube bending and springback. The accuracy of FE numerical simulation results is verified by being compared with experimental results. By using FE simulation combined with physical experiments, underlying effects of the pressure die's boosting on bending quality are explored. The results show that the pressure die's boosting can effectively reduce the wall thickness reduction and the axial elongation of the bent tube, but the springback angle will increase significantly. The boosting force increases, the effect on forming quality will increase. The actual moving speed of the pressure die should be set to be slightly greater than the theoretical value to produce an effective boosting effect. These achievements are helpful to the design and optimization of the tube bending process.