Double-layered Tube Research Articles

Energy Absorption Characteristics and Parameter Optimization of Anti-Climb Energy-Absorbing Devices for Subway Vehicles under Impact Loads

To further enhance the crashworthiness of subway vehicle anti-climb energy-absorbing devices, this paper proposes a novel collapsible structure, which is embedded with honeycomb aluminum blocks and consists of an inner and outer double-layer square tube. An impact finite element model of the subway vehicle’s anti-climb energy-absorbing device was established using LS-DYNA (v.17.2). The effects of the connecting diaphragm thickness, the inner and outer tube thicknesses of the thin-walled tubes, and the yield strength of the honeycomb aluminum on the energy absorption and impact force of the anti-climb energy-absorbing device were investigated. The results indicate that changes in the inner and outer tube thicknesses of the thin-walled tubes significantly affect the energy absorption and impact force of the anti-climb energy-absorbing device. However, changes in the connecting diaphragm thickness only increase the maximum energy absorption by up to 7.5% but have a significant impact on the maximum peak force. It was also found that the difference in energy absorption due to changes in the yield strength of the honeycomb aluminum is only 3.6%, suggesting that the yield strength of the honeycomb aluminum and the connecting diaphragm thickness have a limited influence on the crashworthiness design of the anti-climb energy-absorbing device. Furthermore, a multi-objective surrogate model characterizing the specific energy absorption and maximum peak force was established for the aforementioned four influential parameters using the response surface method. The model was then optimized using a genetic algorithm, resulting in optimal parameters that increased the energy absorption and specific energy absorption by 27.3% and 13.8%, respectively, compared to the original values, leading to a significant improvement in crashworthiness. The findings provide valuable references for and insights into the crashworthiness design and optimization of subway vehicles’ anti-climb energy-absorbing devices.

Design and optimization analysis of a new double-layer tube type heat exchanger for lead-bismuth reactors

Double-layer heat tubes have been designed to effectively reduce the occurrence of heat pipe rupture accidents. However, inter-tube thermal contact resistance can decrease heat transfer efficiency, thus hampering the heat dissipation in the primary loop system of lead-bismuth reactors. Therefore, optimizing the design of double-layer heat tubes is necessary. This work focuses on the double-layer heat exchanger of a lead-bismuth reactor and utilizes gallium-based graphene nanofluids as a thermal interface material to fill the gap between the heat tubes. Furthermore, the impact of the length, wall thickness, outer diameter, and spacing of heat tubes on the heat transfer performance of the double-layer heat exchanger with and without the nanofluids has been analyzed. The study aims to optimize the JF factor and cost-effectiveness ratio (CER). Genetic algorithms are employed to optimize and evaluate the heat transfer performance of the main heat exchanger based on the four aforementioned parameters. Consequently, a new design scheme is obtained for the double-layer heat exchanger, which increases the optimized overall heat transfer coefficient of the main heat exchanger by 5.79%, pressure drop in the primary loop by 2.32%, JF factor by 5%, and CER by 24.62%. These results demonstrate that the gallium-based graphene nanofluids can effectively enhance the heat transfer performance of the double-layer heat exchanger while reducing the likelihood of steam generator tube rupture accidents.

A comparative analysis of the performance of backfill heat exchangers in deep mine geological environments

With the increase of mineral mining depth, the technologies of constructing heat exchanger in stopes to exploit geothermal resources from deep mines have received great attention. The heat extraction capacities of heat exchangers are closely related to the geological environments of deep mines, especially backfill mines. Therefore, a three-dimensional unsteady heat transfer and seepage coupling model of backfill heat exchangers (BFHEs) is created and verified in this work using COMSOL simulation software. Then, the influences of geological environments, involving groundwater seepage, initial temperature and thermal conductivity of surrounding rock etc., on the ability of five BFHEs with the equal buried tube length to extract heat in different configurations are investigated by this model. The findings indicate that groundwater flow can significantly improve the performance of BFHEs. Double-layer tube BFHEs have the best overall performance in the studied seepage velocity range. Only when there is no or little seepage is the performance of single-layer tube BFHEs equivalent to that of double-layer tube BFHEs. The heat extraction capacity of BFHEs is greatly improved under seepage conditions with the increase in the initial temperature of surrounding rock, although the impact is low in the absence of groundwater seepage. The benefit of backfill body's thermal conductivity on BFHEs' ability to transport heat is significantly greater than that of surrounding rock, but the effect becomes smaller as the value increases. Further increasing the thermal conductivity of the backfill body will not considerably increase the heat extraction capability of BFHEs after it reaches 2.5 (W·m−1·K−1). Therefore, if the cost is too high, continued enhancement is not recommended. The findings offer theoretical recommendations for optimizing BFHEs’ setup to better adapt to deep mine geological environments and increase geothermal extraction capability.

Research on the performance of double-layer tube phase change units based on thermal storage tanks

Research on the performance of double-layer tube phase change units based on thermal storage tanks

Hydroforming of double-layer Y-shaped tube controlled by a novel backward punch shape

PurposeA new backward punch shape was designed and used in the hydroforming process of double-layer Y-shaped tubes to achieve uniform wall thickness. This study focuses on the implementation and effectiveness of this novel punch shape.Design/methodology/approachA numerical simulation and experimental validation of the hydroforming process of double-layer Y-shaped tubes under various backward punch, replenishment ratios (left and right feed ratios) and internal pressure loading paths was performed using finite elements. During the hydroforming process, an analysis was made on the distribution of stress, strain and wall thickness in both the inner and outer layers of the Y-shaped conduit.FindingsThe novel backward punch parallel to the main tube has been found to improve the distribution of wall thickness in Y-shaped tubes. By controlling the feeding ratio and modifying the loading path of the internal pressure, it is possible to obtain the optimal forming part of the double-layer Y-shaped tube. The comparison between the simulation and experimental results of the double-layer Y-shaped tube formed under the optimal path indicates that the error is within 5% and the distribution of wall thickness is consistent.Originality/valueA novel backward punch technique is employed to control the hydroforming process in a Y-shaped tube. A study on hydroforming of double-layer Y-shaped tubes with asymmetric features and challenging forming conditions is being suggested.

Identification of Anisotropic Coefficients in the Non-Principal Axis Directions of Tubular Materials Using Hole Bulging Test.

We propose an experimental method to identify anisotropic coefficients in non-principal axis directions of thin-walled tubes. The method involves extracting specimens from the parent tubes and machining a hole in the axial center. The specimens are then inserted into a tube without a hole. The inner diameter of the specimen is theoretically equal to the outer diameter of the inner tube. The double-layer tube undergoes free bulging under internal pressure in our self-developed experimental equipment, with the hole on the specimen expanding simultaneously. The stress states around the hole are uniaxial, and the hole deformation can reflect the anisotropic plastic flow characteristics of the tube. Furthermore, based on the information obtained from the proposed experimental method, a hybrid numerical-experimental method was used to identify the anisotropic coefficients of tubes. Through FE simulations, the relationships between the thickness, stress, and strain states around the hole, the hole shape, and anisotropic coefficients of non-principal axis directions are revealed, and the factors that affect the hole deformation are analyzed. Finally, the hole bulging experiments and FE simulations of AA6061-O extruded tube were conducted, and modeled with Hill48 and calibrated by uniaxial tensile and hoop tensile tests. Its in-plane anisotropy coefficients in any direction are given for the first time which first increase and then decrease from 0° to 90°, reaching a maximum of 1.13 in 60° and a minimum of 0.69 in 0°. This work can provide the key experimental data for establishing an accurate anisotropic plastic constitutive model of thin-walled tubes.

RT-nestRPA is a new technology for the rapid and sensitive detection of nucleic acid detection of pathogens used for a variety of medical application scenarios

BackgroundThe effective detection of pathogens is of great importance for the diagnosis and treatment of infectious diseases. We have proposed the novel RT-nestRPA technique for SARS-CoV-2 detection, which is a rapid RNA detection technique with ultra-high sensitivity. ResultsThe RT-nestRPA technology has a sensitivity of 0.5 copies/uL of synthetic RNA targeting the ORF7a/7b/8 gene or 1 copy/uL synthetic RNA targeting the N gene of SARS-CoV-2. The entire detection process of RT-nestRPA only takes only 20 min, which is significantly shorter than RT-qPCR (nearly 100 min). Additionally, RT-nestRPA is capable of detecting dual genes of SARS-CoV-2 and human RPP30 simultaneously in one reaction tube. The excellent specificity of RT-nestRPA was verified by analyzing twenty-two SARS-CoV-2 unrelated pathogens. Furthermore, RT-nestRPA had great performance in detecting samples treated with cell lysis buffer without RNA extraction. The innovative double-layer reaction tube for RT-nestRPA can prevent aerosol contamination and simplify the reaction operation. Moreover, the ROC analysis revealed that RT-nestRPA had high diagnostic value (AUC = 0.98), while the AUC of RT-qPCR was 0.75. SignificanceOur current findings suggested that RT-nestRPA could serve as a novel technology for nucleic acid detection of pathogens with rapid and ultrahigh sensitive features used in various medical application scenarios.

Limit and shakedown analysis of double-layer tube considering different material properties

This paper is devoted to the maximum bearing capacity of double-layer tubes subjected to monotonic and cyclic loading, within the framework of static limit and shakedown analysis. The double-layer tube comprises inner and outer layers made of different materials, both obeying the von Mises criterion. The effects of different geometric dimensions (thickness and volume fraction) and material properties (elastic modulus, Poisson’s ratio, and yield stress) on the effective mechanical behavior are studied analytically and numerically. The results indicate that the bearing capacity of the double-layer tube under monotonic load reaches its maximum value when both inner and outer layers reach their elastic or plastic limits simultaneously. The computation of plastic and shakedown limits are presented, divided into different cases by considering the volume fraction of the inner and outer layers. The double-layer structure under cyclic loads may fail due to fatigue and excessive deformation mechanisms of the inner or outer layers at the first cycle. Only when both layers fail due to fatigue simultaneously, the shakedown limit of the structure reaches its maximum value. Compared to a single-layer tube, the long-term strength of the double-layer tube can be significantly improved by applying appropriate geometric dimensions and materials in fabrication.

Performance modeling of quartz tube for gravity-driven solid particle solar receiver

The interest in high-temperature solar receivers is increasing due to more and more applications in industrial fields. The solid particle is a promising heat transfer fluid for high-temperature receivers owing to the advantages of direct absorption, low cost, and high allowable temperature (∼1300 °C). The re-radiation losses of solid particles inevitably increase with the higher operating temperature. The quartz tube with a spectral selective transmissivity may be used for reducing re-radiation losses. This paper proposed a mathematical model to describe the heat transfer behaviors of the gravity-driven solid particle solar receiver with a quartz tube covered. The wavelength-dependent radiative properties of the quartz tube and particles were approximated by a gray band method. On-sun tests based on a linear-focused solar furnace were conducted, and test results verified the proposed model. Analysis results show that a reduction in β from 3676m−1 to 1000m−1 can boost the volume absorption effect and increase the solar-to-thermal efficiency from 0.54 to 0.64. A double-layered quartz tube design provides the best thermal performance by increasing the greenhouse effect of the quartz tube from −0.02∼0.08 to 0.41. The analysis results could be used for the optimal design and operation of the gravity-driven solid particle solar receiver.

Double-Layer Nanofibrous Sponge Tube via Electrospun Fiber and Yarn for Promoting Urethral Regeneration

Double-Layer Nanofibrous Sponge Tube via Electrospun Fiber and Yarn for Promoting Urethral Regeneration

Gap Measurement of Double-Layer Metal Tube Based on Analytical Solution of Eddy Current Array Under Transmit-Receive Mode

Gap Measurement of Double-Layer Metal Tube Based on Analytical Solution of Eddy Current Array Under Transmit-Receive Mode

New explanation on formation mechanism of anodic TiO2 nanotubes

Anodic TiO2 nanotubes (ATO) have attracted considerable scientific interests due to their various applications and mysterious growth mechanism. In particular, it has puzzled scientists for decades why ATO displays the distinct nanotubular morphology. For comparison, anodic Al2O3 (AAO), another important anodic oxide, features nanochannels. Different theories have been proposed, but the tube-formation mechanism is not clearly understood. Here, the top surface and cross-section morphologies of ATO obtained under different experimental conditions are investigated, and a new evolution mechanism of ATO is proposed. The formation, flow, and decomposition of a highly defective metastable sublayer in-between the neighboring pores plays an essential role in the formation of the characteristic morphology features, such as the “cap” layer at the ATO top surface, intertubular gaps, double-layered tube walls, nano-scaled ridges connecting the tube outer walls. The “cap” layer is due to the absence of the metastable substance at the ATO film top surface. The double-wall structure results from the different reaction environment and products at the upper and lower parts of the barrier layer. The intertubular gaps and ridges between neighboring tubes arise from decomposition and volume shrinkage of the metastable sublayer at the tube outer walls. This study offers insights to the growth kinetics of the ATO and other anodic oxides.

Prediction and control of bending quality of double-layered gap tube

Thin-walled double-layered gap tube (DLGT) has a promising potential to be widely used in making aerospace pipeline systems and the complicated structures in many industrial clusters. However, it presents a challenge to achieve precisely forming of the needed tube structure. During the rotary draw bending (RDB) of DLGT, the diversities of materials and geometries to be made lead to the difficulties in accurate prediction and efficient control of the forming quality. For an accurate prediction, the anisotropic characterization of the thin-walled tube was realized by designing a novel ring hoop specimen and the viscoplastic self-consistent model simulation. Three yield criteria were employed, and it is found that Yld2000-2D criterion has the best prediction accuracy. For efficient control, the rigid constraints of forming dies and flexible constraints of filling medium were employed. For rigid constraints, it is proven that the traction force provided by the inner clamp die is decisive in preventing the wrinkling and slip of tube and the fully constrained die structure has the best controllability of forming quality. For flexible constraints, the solid structure of filling medium provides more uniform constraints to tubes and is the most ideal structure. When a special channel structure is required, the outer channel structure plays a more significant role in the deformation of the inner tube, resulting in a better controllability of forming quality than the inner channel structure.

Research on hydroforming through combination of internal and external pressures for manufacturing the structure of double-layer tube with gap

Research on hydroforming through combination of internal and external pressures for manufacturing the structure of double-layer tube with gap

Braided-textile reinforced thin-walled conical tubular structures: Designing, manufacturing and testing

Carbon fiber reinforced composite (CFRC) tubes and polyurethane foams have been widely applied as lightweight energy absorbing elements. The purpose of this paper is to design and make braided-textile reinforced conical tubular structures and investigate the tapering effects on the textile structure and energy absorption (EA) characteristics. Single-layer CFRC conical tubes, double-layer CFRC conical tubes and foam-filled CFRC conical tubes were manufactured and their axial compression behaviors were tested and compared. The crushing modes and EA evaluation indexes were revealed and discussed. Compared with straight circular tubes, conical tubes have more progressive folding and much better crushing force efficiency (CFE). Compared with single-layer conical tube, the crushing mode of double-layer conical tube changes from diamond folding to concertina folding and the EA is increased by 4.5 to 6.9 times. The specific energy absorption (SEA) of tube D40/50 reaches 25.983 J/g, increased by 142.2% compared with that of the single-layer conical tube. Foam filling is beneficial to the total EA and improves the CFE to 100%, but multi-layer will reduce the foam filling effect.

Filler parameters affected wrinkling behavior of aluminum alloy double-layered gap tube in rotary draw bending process

Filler parameters affected wrinkling behavior of aluminum alloy double-layered gap tube in rotary draw bending process

A One-pot-synthesized Double-layered Anticoagulant Hydrogel Tube.

Extracorporeal membrane oxygenation(ECMO) has emerged as a viable treatment in severe cases of acute respiratory distress syndrome, acute respiratory failure, and adult respiratory distress syndrome. However, thromboembolic events stemming from the use of ECMO devices results in significant morbidity and mortality rates; the inner surface of the ECMO tubing comes into contact with the blood and can readily initiate coagulation. In addition, the tubing needs to be continually replaced due to thromboses on the inner tube wall, which not only increases the risk of infection but also the economic burden. Despite considerable effort, a surface modification strategy that effectively addresses these challenges has not yet been realized. In this study, we developed an integrated hollow core-shell-shell hydrogel tube of gelatin/alginate/acrylamide-bacterial nanocellulose(GAA) that meets the anticoagulant requirements for the inner tubing layer as well as the highly elastic soft material needed for the outer layer. Using static blood from healthy volunteers, we confirmed that the platelets or coagulation is not stimulated by the GAA tubing. Importantly, experiments with dynamic blood also demonstrated that the inner layer of the tubing does not elicit blood clotting. The one-pot-synthesized process may provide guidance for the design of anticoagulation tubes used clinically.Electronic Supplementary MaterialSupplementary material is available in the online version of this article at 10.1007/s40242-021-1267-3.

Crashworthiness study of double-layer sinusoidal tubes under axial loading

Thin-walled tubes are widely used as energy absorption devices because of their excellent crashworthiness. In this paper, a novel tubular configuration with a double-layer sinusoidal corrugated section, namely, a double-layer sinusoidal tube (D-LSCT), is proposed to improve the energy absorption capacities. Quasi-static compression experiments and finite element simulations were used to analyse the axial crushing behaviour and energy absorption performance of the D-LSCTs. The results revealed that the geometric parameters had a significant effect on the crashworthiness of the D-LSCTs and that the D-LSCTs had four deformation modes: ordered progression extensional mode (OPEM), ordered progression inextensional mode (OPIM), inextensional mode (IM) and mushroom mode (MM). OPEM and OPIM were more ideal modes, while the IM and MM were unideal modes. To further improve the deformation stability, D-LSCTs were transformed into a three-layer structure by superimposing a regular polygon tube. Experiments and simulations showed that the improved structural design can indeed stabilise deformation and improve the crashworthiness performance.

Dynamic model for controlled uniform processing under microwave heating by using a heat exchanger

The development of microwave heating technology promotes the improvement of industry quality and efficiency, but the drawbacks of microwave heating, such as uneven heating, prevent its wide application in industry. In this paper, a double-layer ring tube is proposed for improving the heating uniformity and achieving the target temperature. The gap between the inner and outer tubes is evenly divided into four regions, and the cooling liquid flows through the gap to control the temperature of the heating target placed in the inner tube. Maxwell's equation, heat conduction equation, Navier-Stokes equation and the mass conservation equation are coupled to simulate the heating process, and the experimental data and simulation data are compared to verify the correctness of the model. Meanwhile, the heating uniformity of structure with or without heating exchanger is compared, and the effect of different fluid velocities, different sizes of the reactor and different dielectric constant of heating target on the heating performance is discussed.

Manufacturing of a corrugated double-layered tube for the high-performance compact heat exchanger

Compact heat exchangers are expected to be one of the solutions for advanced heat exchanger having light weight, minimum volume, and high performance to improve the uses of energy sources and contribute to sustainability. Conventional double-pipe heat exchangers allow poor heat transfer performance owing to the concentrically arranged simple cylindrical structure. Therefore, passive enhancement technique employing circumferentially corrugated double tubes has been characterized and manufactured in this study as one of the most realistic alternatives to enhance heat transfer performance. To fabricate double-layered tube with circumferentially corrugated pattern, the customized hydroforming process using corrugate forming bars was developed and experimentally implemented on the basis of the simulated bulge height, internal pressure, and contracted stroke at various forming bar diameters. The circumferential cross-sectional profiles were observed to estimate the soundness of the hydroformed corrugated tube, and the results provide a useful solution for manufacturing high-performance compact heat exchangers with enhanced reliability and applicability.