Double Tube Research Articles

Crushing performances and crashworthiness optimization of polygonal double tubes under multiple angle loadings

Crushing performances and crashworthiness optimization of polygonal double tubes under multiple angle loadings

Thermal performance enhancement in a double tube heat exchanger using combination of bubble injection and helical coiled wire insert

In this experimental study, a novel approach combining a helical coiled wire (HCW) turbulator and bubble injection (BI) method has been employed to synergistically improve the heat transfer efficiency of double tube heat exchanger. The thermal-frictional characteristics were evaluated by investigating different parameters, including the bubble injection flow rate ranging from 2 to 5 l/min and HCW pitch ranging from 2.5 to 10 mm. For all cases, the thermal enhancement factor (TEF) is employed to determine the optimal configurations. The experimental findings indicate that the introduction of bubble injection, the implementation of the HCW turbulator, and the simultaneous utilization of both methods result in an enhancement of heat transfer by 66 %, 78 %, and 156 % respectively. However, it should be noted that the usage of these methods also leads to an increase in pressure drop. Also, the findings indicate that the integration of two methods yields favorable outcomes in terms of thermal performance when compared to their individual functions. In the optimal scenario, the TEF has the potential to reach a maximum value of 1.28. Furthermore, in order to obtain a more precise comprehension of the relationship between TEF and the parameters under investigation, an empirical equation have been derived and presented.

Compression behavior of the concrete-filled double skin steel tube columns under hydrostatic pressure: Experimental and modeling study

This paper conducted an experimental study focusing on the axial compressive behavior of circular concrete-encased concrete-filled steel tubular (CFDST) columns composed of a circular inner steel tube under active confinement. The investigation aimed to explore the impact of concrete compressive strength grades and diameter-to-thickness ratio of steel tubes in the presence of hydrostatic pressure. The effects of varying outer diameter-to-thickness ratios (44, 45.6, 85.84, and 86) and concrete compressive strength grades (10 and 20 MPa) on the performance of CFDST columns were investigated in this paper. Additionally, the study considered the impact of two inner steel tube diameter-to-thickness ratios (20.5 and 39). The experimental results demonstrated that external pressure can significantly enhance both the load-carrying capacity and ductility of the specimens. The ultimate strength of the columns was improved by a minimum of 34% and a maximum of 92%. Finally, empirical formulas for predicting the axial compression capacity of CFDST under active confinement using gene expression programming were presented. The accuracy of the proposed model was then assessed by the artificial neural network, and the results indicate that both models perform well when compared to the empirical equations that take into account the hydrostatic pressure of wet concrete.

Numerical Evaluation of Heat Transfer and Conversion Efficiency by Tube Design and Flow Configuration for a Compact Steam-Methane Reformer

In the chemical industry, hydrogen (H2) production through steam-methane reforming is a well-established process. With the growing demand for H-fueled vehicles and charging stations, there is a need for compact reformers with efficient heat transfer capabilities. In this study, computational fluid dynamics simulations were performed to evaluate the methane (CH4) conversion and heat transfer efficiency of various reformer designs. These designs include single, double, and triple tubes, each with parallel- and counter-flow configurations between the reformate feed and heat source. The findings revealed substantial disparities in methane conversion between the tube designs and flow configurations. Notably, the triple-tube design outperforms single and double tubes, exhibiting higher methane conversion and improved heat transfer efficiency. This superior performance is attributed to the larger wall area facing the heat source and additional heat recovery from the reformate flowing in the inner annulus. This led to the highest temperature at the catalyst exit among the cases, increasing methane conversion, and the lowest reformate temperature at the reformer tube exit, which is also beneficial for the subsequent water–gas shift reaction process. Installing external fins on the reformer tube provided a more effective enhancement of heat transfer than using internal fins in the catalyst section. Regardless of the tube design employed, the counter-flow configuration consistently enhanced the heat transfer efficiency, resulting in 4.6–11.9% higher methane conversion than the parallel-flow configuration. Consequently, the triple-tube design with the counter-flow configuration achieved the highest methane conversion, offering flexibility in the reformer design, including the potential for lower heat input and a reduced catalyst volume.

Investigation on solar drying system with double pass solar air heater coupled with paraffin wax based latent heat storage: Experimental and numerical study

Since solar energy uses the sun's free energy and is environmentally friendly, it is generally accepted for various applications like drying products. However, the drawback of this system is the inconsistent and unpredictable nature of solar radiation. The best solution for the above said problem is using thermal energy storage. In this study forced convection indirect solar drying system that has a double pass solar air heater (DPSAH), shell and tube type latent heat storage (LHS) with paraffin wax as phase change material (PCM), blower and drying chamber is developed and tested. Numerical study is conducted on the DPSAH to determine the effect of mass flow rate on its performance and appropriate flow rate is selected for the drying experiment. It was found that outlet temperatures of the DPSAH is higher at lower mass flow rates and lower at higher mass flow rates and mass flow rate of 0.01 kg/s gives the required outlet temperature. Whereas numerical simulation is done on the LHS to predict the charging and discharging behavior of the PCM and found that the storage can reach a fully charged state within 133 min, which can be achieved around the peak hours during the experiment. The performance of the components of the dryer and the overall performance of the dryer is investigated with experiment. From the experimental result, a maximum temperature of 69 °C is obtained at the outlet of the DPSAH and the energy and exergy efficiencies are 25 % and 1.5 %, respectively. The LHS reduces the fluctuations in the outlet temperature of the SAH and extends the drying process for extra 3 h a day. The drying experiment is conducted by drying 5 kg fish and took 21 h to reduce the moisture content of the fish from an initial value of 75 %–12.5 %. The efficiency of the drying chamber was 35 % and the overall efficiency of the dryer was 9.4 %.

CFD Analysis for a Twisted Elliptical Double Tube Heat Exchangers Integrated with a Twisted Tape

CFD Analysis for a Twisted Elliptical Double Tube Heat Exchangers Integrated with a Twisted Tape

Advances in triple tube heat exchangers regarding heat transfer characteristics of single and two-phase flows in comparison to double tube heat exchangers part 1

Abstract Triple concentric-tube heat exchangers are used widely in refrigeration, drying, energy storage, chemical systems, and the food industry. To handle excessive temperature differences, the heat transfer area, as an option, the heat exchanger’s length, is necessary to be increased. Triple tubes have a significant advantage in this regard in comparison to double ones. The target of this review is to discuss the most recent publications, including the single-phase flows in these heat exchangers, focusing on the heat transfer and hydrodynamic characteristics, and to classify them with various contemporary aspects. The operating conditions, enhanced surfaces, and sizes, as well as the geometrical parameters, are categorized as being part of experimental, numerical, and analytical research. The studies indicate that the heat transfer characteristics of triple concentric-tube heat exchangers are better than those of double tube heat exchangers. In single-phase studies, the convective and overall heat transfer coefficients, Nusselt number, heat transfer rate, and effectiveness are greater in triple heat exchangers than in double heat exchangers, and the heat exchanger length required to achieve the same heat transfer performance is shorter in triple heat exchangers than in double heat exchangers. Heat transfer surface area increases by adding a concentric third tube. Advanced surfaces enhance heat transfer compared to smooth surfaces and flow turbulence in comparison to smooth surfaces. Heat transfer from triple-one enhanced surfaces is not well-analyzed. Design and use of triple ones as a double one’s alternative should advance shortly.

Advances in triple tube heat exchangers regarding heat transfer characteristics of single and two-phase flows in comparison to double tube heat exchangers part 2

Abstract Triple concentric-tube heat exchangers are often used in a variety of industries, including HVAC, food and beverage manufacturing, and chemical processing. They may also be utilized in applications requiring thermal homogeneity, such as food and pharmaceutical production. They are appropriate for a number of applications since they may be constructed to withstand a range of temperatures and pressures. The purpose of this study is to examine the most current papers, covering single- and two-phase flows having pure and nanofluids with a particular emphasis on the heat transfer and hydrodynamic properties. The use of advanced surfaces improves heat transfer with respect to smooth surfaces, and the use of nanofluids has a positive influence on heat transfer characteristics with the increase in nanoparticle volume concentration since nanoparticles rise thermal conductivity, heat transfer area, and Brownian motion. The practical calculation methodologies, proposed correlations for calculating the Nusselt number and friction factor in triple ones are shown. There are insufficient studies to comment on pressure drop features, and correlations for Nusselt numbers and friction factors that are only known for single-phase flows. The research indicates that the heat transfer characteristics of triple concentric-tube heat exchangers surpass those of double tube heat exchangers. Important progress is supposed to occur for the design and utilization of triple ones as a substitute for double ones soon. Finally, there are a limited number of experimental two-phase flow studies in triple ones. It is essential to work on this topic to meet the important lack in open sources.

Single-polarization single-mode broadband ultra-low loss hollow-core anti-resonant fiber with nested double C-type cladding tubes

A novel five-tube nested double C-type single-polarization hollow-core anti-resonant fiber (HC-ARF) is proposed for single-polarization single-mode, ultra-low loss, and broadband characteristics. Different tube thicknesses are introduced along the orthogonal direction to couple the x-polarized fundamental mode (FM) to the silica modes (SMs). At the same time, the y-polarized FM is tightly bound in the core, achieving a high polarization extinction ratio (PER). In order to achieve large bandwidth, a layer of high-refractive-index silicon material is coated on the inner surface of the cladding tube. To the best of our knowledge, the proposed single-polarization HC-ARF has the highest PER at 1.55μm with a remarkable value of 162486 so far, while the y-polarized FM loss is only 1.4 × 10-3 dB/km. However, the single-polarization bandwidth remains limited. By optimizing the structural parameters on single-polarization bandwidth, the HC-ARF at 1.55μm for single-polarization single-mode transmission is obtained with a high-order mode extinction ratio (HOMER) and PER of 2891, 9531, respectively. In addition, a remarkably high single-polarization bandwidth of up to 150 nm is achieved with ultra-low confinement loss (CL) as low as 2.8 × 10-3 dB/km. Furthermore, the proposed fiber exhibits good bending characteristics, with a bending loss of 6.7 dB/km at the bending radius of 5 cm in the x-direction.

One-step method to control the temperature of S and Mo source and its effect on the size and morphology of MoS2

Molybdenum disulfide (MoS2) is a typical two-dimensional material, which is widely used in many fields because of its excellent electrical and optical properties. In recent years, the high-quality growth of MoS2 has attracted more and more attention from researchers. Many studies have reported a two-step method for the production of MoS2 by pre-deposition of molybdenum (Mo) source and then vulcanization, which is cumbersome and time-consuming, and the preparation temperature is mostly above 800 °C, increasing energy consumption and experimental risk. In this paper, S source and Mo source can be distinguished by double temperature zone tube furnace to prepare MoS2 material in one-step method. The temperatures of S and Mo sources were designed separately, and the effect of each temperature on the quality of MoS2 was investigated. And the monolayer MoS2 with high crystalline quality was obtained at a S source temperature of 165 °C and a Mo source temperature of 680 °C. We produce MoS2 in one-step method at low temperature, which provides a reference for the synthesis of high-quality monolayer MoS2.

Transition acceleration of electrons and reconnection of magnetic fields driven by two-beam relativistic laser pulses traversing a NCD plasma slab target

The self-generation and reconnection of magnetic fields and accompanying electron acceleration were studied when two ultrafast intense laser beams propagate synchronously through a thin plasma slab target with homogeneous near-critical density (NCD). The results show that the magnetic reconnection occurs behind the target and the electrons undergo three important accelerating stages, ponderomotive force acceleration in the plasma channels, transition (or transboundary) acceleration from the plasma medium to the vacuum, and acceleration by the reconnecting fields. In the reconnection process the hot electrons are compelled to be reverse-accelerated (generating refluxes) and consequently the double annular magnetic tube fields in channels are collapsed into one large-scale annular magnetic tube structure, in which a significant pinching effect is revealed. Meanwhile, two peculiar enclosed “field-free” zones were shown, which is suggested to be a combined effect of magnetic annihilation (MA) and longitudinal quasi-static electric field generated by separation of positive and negative charges.

Tunable double-layer dual-band metamaterial with negative mass density

Due to the huge structure and low efficiency of acoustic metamaterial (AM) with local resonance, a tunable dual-band AM with nested double layer hollow tube (NDLHT) is presented here, which is achieved by adjusting the inner or outer layer tube’s lengths or diameters to modulate the frequency band with the negative mass density. In addition, an accurate resonant frequency formula for OE-CE (Open End-Close End) NDLHT was derived based on the principle of standing wave resonance. The theoretical calculated resonant frequencies exhibit in good agreement with the simulated frequencies. Thus, the structural unit can then be actively constructed in the desired response frequency range using the geometric parameters that were obtained from this theoretical formula. This type of the nested AM with negative mass density has the advantages of high space utilization, active design, programmed modelling, customized production, 3D quantitative printing and is easily combined with other structure units with negative modulus to prepare AM with double negative in the desired frequency band.

Numerical investigation and design of concrete-filled double square steel tube columns under axial compression

This paper introduces a novel cross-sectional design for concrete-filled steel tubular (CFST) columns termed “concrete-filled double square steel tube” (CFDSST). The CFDSST columns incorporate an inner square steel tube positioned diagonally at 45° relative to the outer square steel tube, which serves as a stiffener for the outer tube. A three-dimensional finite element simulation model is presented to accurately predict the behavior of axially loaded CFDSST short columns. This model considers the influence of concrete confinement by the steel tubes. Experimental data are employed to validate the accuracy of the finite element model. The validated model is then utilized to assess the performance of the proposed columns, considering various geometric and material properties. The results highlight the substantial enhancement in structural performance achieved by the innovative CFDSST column configuration compared to conventional square CFST columns. The integration of the inner CFST components enhances both buckling resistance and the confinement mechanism of the column. This contributes to the increased load-bearing capacity, ductility, and residual strength of the columns. Notably, the steel tube thickness, the yield strength, and the concrete compressive strength greatly affect the performance of the column. Lastly, a simplified design model is formulated to predict the compressive capacity of the CFDSST stub columns, providing accurate outcomes validated by numerical analysis.

Enhancing heat transfer performance in a double tube heat exchanger: Experimental study with twisted and helical tapes

Efficient energy exchange is vital for designing compact and effective heat exchangers. This study investigates various twist ratios for tape inserts and exterior helical tape in a counterflow setup using water as the working fluid. Reynolds numbers are varied on both sides of the heat exchanger. The analysis reveals that incorporating twisted tape inserts inside the pipe, along with helical tape on the exterior, significantly enhances thermal characteristics. Compared to a plain pipe heat exchanger, Nusselt numbers increase by 219 %–315 % for the pipe with twisted tape inserts and helical tape. Friction factors are also higher, ranging from 4.4 to 8.7 times for pipe inserts with twist ratios of 6.77, 4.51, and 3.38. An empirical relationship between Nusselt number and friction factor is derived from experimental data, demonstrating remarkable agreement with predicted values. A maximum thermal performance factor (TPF) of 3.06 is achieved, emphasizing the critical role of twist ratios in optimizing heat transfer efficiency while minimizing energy consumption. These findings provide valuable insights for designing energy-efficient heat exchangers with enhanced heat transfer rates.

Analyzing the Performance of Double Spiral Tube Ground Heat Exchangers in a Zero-Energy Building Using Measurement Data

A ground-source heat pump (GSHP) system is a renewable energy technology that effectively reduces greenhouse gas emissions and consequently mitigates the progression of global warming. The thermal efficiency of ground heat exchangers (GHEs) is a critical component in the GSHP system that must be accurately estimated for its long-term operationality. Therefore, in this study, the thermal performance of double-spiral GHEs incorporated within the thermal piles of a zero-energy building in Sapporo, Japan, was investigated using the actual measured data obtained from the site and a novel metric, namely, the coefficient of heat extraction/injection, for a more precise evaluation. Moreover, this study assessed the coefficient of performance (COP) of the GSHP units during various periods of cooling or heating. The temperature of the circulating fluid remained within an ideal operational range over an operational period of 2 years, and the COP calculations indicated a high operational efficiency. The results derived in this study substantially exceeded those of traditional U-tube GHEs, indicating the enhanced efficiency and superior performance of large-diameter thermal piles with augmented thermal capacity. Our findings suggest that GSHP systems with double-spiral-tube GHEs have superior efficiency than conventional GHEs.

Anticandidosis activity of aqueous and ethanolic extracts of Harungana madagascariensis, Zanthoxylum leprieurii and Xylopia aethiopica

Some ailments have been cured either by the use of plant parts or by mixing different plant parts (recipes). It is with this in mind that this study originated, focusing on the valorization of plants from the African pharmacopoeia. Thus, the activity of single extracts and aqueous and hydroalcoholic mixtures of the bark and leaves of Harungana madagascariensis, the bark of Zanthoxylum leprieurii and the fruit of Xylopia aethiopica was evaluated on the in vitro growth of Candida strains (Candida albicans 18650 and Candida albicans 18792 and Candida glabrata). Antifungal tests were carried out by plating 1,000 cells of each fungal germ on Sabouraud agar medium using the double dilution slant tube method. Deth70% extract inhibited the growth of Candida albicans 18650 and Candida albicans 18792 at an FMC value of 25 mg/mL, and Candida glabrata at an FMC value of 50 mg/mL. Phytochemical screening revealed the presence of chemical compounds such as polyphenols, flavonoids, saponosides, gallic and catechic tannins and the absence of sterols.

Discontinuous yielding behavior, strengthening effect and deformation mechanism of double wall copper-brazed steel tube under various continuous sectional cooling

Unlike traditional cooling, continuous sectional cooling (CSC) consists of various cooling modes, which is of decisive significance to the microstructure and performance of double wall copper-brazed steel tube (DWBT). In this work, three CSC (CSC-A/B/C) processes are chosen to reveal strengthening and deformation mechanisms of DWBT. The results show that there are significant differences in discontinuous yield behavior, natural aging phenomenon, and tensile properties of the DWBT among three CSC processes due to diverse grain size and precipitates, but a similar texture is obtained due to Kurdjumov-Sachs relationship. For discontinuous yielding, the propagation velocity of Lüders band is a key factor to determine the yield point elongation (YPE), which reduces with decreasing grain sizes due to the interaction between dislocation and grain boundary. Thus, the CSC-C (1120 °C→4s940 °C…360 °C→16s110 °C) with small grains has a longer YPE. Meanwhile, the precipitation strengthening dominates the highest strength and lowest elongation of the CSC-A (1120 °C…100 °C) due to abundant MC carbides. Compared with CSC-B (1120 °C…170 °C), the yield strength of CSC-C is higher while ultimate tensile strength is lower, which is attributed to different contributions of precipitation and grain boundary strengthening to both. The MC carbide causes the natural aging of DWBT. Moreover, the geometrically necessary dislocations (GNDs) and low angle grain boundaries (LAGBs) raise linearly with strain. The GNDs prefer to be distributed in small grains, and uniform grain can weaken the difference of GNDs distribution in different grain sizes. The LAGBs including dense dislocation walls or microbands are formed by the grain subdivision mechanism.

Anesthetic management of a case of pulmonary alveolar proteinosis for whole lung lavage

Abstract Pulmonary Alveolar Proteinosis (PAP) is a rare disease of the lungs characterized by deposition of lipo-proteinaceous material in the alveoli. This leads to reduced lung compliance and V/Q mismatch, causing respiratory failure. Patients with PAP may be posted for Whole Lung Lavage (WLL) under anesthesia, which is a challenging case for anesthetists. Preexisting respiratory failure is complicated by requirement of single lung ventilation with the help of double lumen tube during the procedure. Intraoperative ventilation is difficult and is managed with blood gas and airway pressure monitoring. Some degree of hypoxemia and hypercapnia may have to be tolerated. Large volumes of fluid are instilled into the lung which may cause hypothermia, hypervolemia, and electrolyte disturbances. These patients frequently require elective ventilation and intensive care admission in the postoperative period. We report the case of a young woman with PAP, posted for unilateral WLL under anesthesia. We wish to highlight the possible challenges posed by this case and how to conduct a safe anesthesia for this patient.

ANN-Based Axial Strength Prediction of Short Columns with Double and Bar-Reinforced Concrete-Filled Steel Tubes Subjected to Concentric and Eccentric Loading

ANN-Based Axial Strength Prediction of Short Columns with Double and Bar-Reinforced Concrete-Filled Steel Tubes Subjected to Concentric and Eccentric Loading

Axial compression behaviour of concrete filled double skin steel tube columns anchored with orbicular rings: Experimental and numerical approach

Double-skin tube column sections have been used extensively in recent years. These sections are composed of two adjacent, coaxially spaced steel casings, and the space in the middle of them is occupied with concrete. These CFDST columns behave similarly to CFST sections but are more rigid and have a lesser self-weight. The behavior of a novel type of CFDST column, the orbicular anchored CFDST column, was assessed under axial compression in the current research. It comprises an inside and an outside steel tube with orbicular rings near the ends of the columns. The orbicular rings were positioned at various spots such as [Formula: see text] and [Formula: see text] and a wide range of tests were accomplished to evaluate the functionality of orbicular anchored CFDST columns in respect of maximum load-bearing capability, load-strain behavior, and load-deformation behavior. A FE model was developed and its accuracy was authenticated by comparing its findings with experimental results. Furthermore, a parametric investigation was carried out employing the authenticated FE model to examine the functioning of the proposed CFDST to variations in orbicular position, cross-sectional dimensions of rings, yield strength of orbicular ring, etc. The outcomes of the study indicated that orbicular anchored CFDST columns had 15% higher ultimate load capacity than unstiffened counterparts. The orbicular anchorage improved the ductile response and increased the axial stiffness of the CFDST column. Further, it was concluded that orbicular rings enhanced the constraining effect of external steel casing on sandwiched concrete and improved the composite action of CFDST specimens. The design formula to ascertain the load-bearing ability of columns was also developed and can be employed amid preliminary designs of proposed column sections.