Search Results (54)

This study investigates the impact of circumferential angle (φ) and interaction angle (θ) between hydrogen jets and diesel sprays in a co-axial hydrogen–diesel injector on combustion and emissions in a hydrogen–diesel dual-fuel engine using 3D CFD simulations. The results demonstrate that a co-axial dual-layer nozzle design significantly enhances combustion performance by leveraging hydrogen jet kinetic energy to accelerate fuel–air mixing. Specifically, a co-axial alignment (φ = 0°) between hydrogen and diesel sprays achieves optimal combustion characteristics, including the highest in-cylinder pressure (20.92 MPa), the earliest ignition timing (−0.3° CA ATDC), and the maximum indicated power of the high-pressure cycle (47.26 kW). However, this configuration also results in elevated emissions, with 29.6% higher NOx and 34.5% higher soot levels compared to a φ = 15° arrangement. To balance efficiency and emissions, an interaction angle of θ = 7.5° proves most effective, further improving combustion efficiency and increasing indicated power to 47.69 kW while reducing residual fuel mass. For applications prioritizing power output, the φ = 0° and θ = 7.5° configuration is recommended, whereas a φ = 15° alignment with a moderate θ (5–7.5°) offers a viable compromise, maintaining over 90% of peak power while substantially lowering NOx and soot emissions. Full article

Deep learning-based surrogate models have received wide attention for efficient and cost-effective predictions of fluid flows and combustion, while their hyperparameter settings often lack generalizable guidelines. This study examines two different types of surrogate models, convolutional autoencoder (CAE)-based reduced order models (ROMs) and fully connected autoencoder (FCAE)-based ROMs, for emulating hydrogen-enriched combustion from a triple-coaxial nozzle jet. The performances of these ROMs are discussed in detail, with an emphasis on key hyperparameters, including the number of network layers in the encoder (l), latent vector dimensionality (dim), and convolutional stride (s). The results indicate that a larger l is essential for capturing features in strongly nonlinear flowfields, whereas a smaller l is more effective for less nonlinear distributions, as additional layers may cause overfitting. Specifically, when employing CAE-based ROMs to predict the spatial distribution for H₂ ($X_{H_2}$) with weak nonlinearity, the reconstruction absolute average relative deviation (AARD) from the two-layer model was marginally higher than that of three- and four-layer models, whereas the prediction AARD was approximately 5% lower. A smaller dim yields better performance in weakly nonlinear flowfields but may increase local errors in some cases due to excessive feature compression. A CAE-based ROM with a dim = 10 achieved a notably lower AARD of 4.01% for $X_{H_2}$ prediction. A smaller s may enhance the spatial resolution yet raise computational costs. Under identical hyperparameters, the CAE-based ROM outperformed the FCAE-based ROM in both cost-effectiveness and accuracy, achieving a 35 times faster training speed and lower absolute average relative deviation in prediction. These findings provide important guidelines for hyperparameter selection in training autoencoder (AE)-based ROMs for hydrogen-enriched combustion and other similar engineering design problems. Full article

This research introduces the first design concept for a ducted coaxial-rotor amphibious spherical robot (BYQ-A1), utilizing the principle of variable mass control. It investigates whether the BYQ-A1’s variable-mass slider has a certain regularity in its impact on the aerodynamic properties of the BYQ-A1. Utilizing the Blade Element Momentum Theory (BEM) and Wall Jet Theory, an aerodynamic calculation model for the BYQ-A1 is established. An orthogonal experimental method is used to conduct tests on the impact of the variable-mass slider on the aerodynamic properties of the ducted coaxial-rotor system and validate the effectiveness of the aerodynamic calculation model. The results show that the slider generates an internal ground effect and ceiling effect within the BYQ-A1 that enhance the lift of the upper and lower rotors when the robot is equipped with it. The increased total lift compensates for the additional aerodynamic drag caused by the presence of the slider. This novel finding provides guidance for the subsequent optimization design and control method research of the BYQ-A1 and also offers valuable references for configuration schemes that incorporate necessary devices between coaxial dual rotors. Full article

Gas-assisted coaxial electrospinning (GACES) is a simple and general method for the mass preparation of coaxial nanofiber membranes, which has great industrial potential. However, in the manufacturing process, due to the bending instability of the jet in the electric field and the pulling effect of the gas flow field, the deposition uniformity of the fiber is still a big problem. Through finite element simulation analysis of the flow field in the manufacturing process and the construction of the jet mechanics model after adding the flow field, the influence mechanism of coaxial auxiliary flow on the fiber deposition area and its uniformity was successfully revealed in this research. Finally, the deposition area and thickness uniformity of coaxial fibers are increased by 3 times (the deposition area: 19.63 cm² → 78.50 cm²) and 2.34 times (the standard variance: 3 μm² → 10 μm²) by gas-assisted coaxial electrospinning. At the same time, the coaxial auxiliary gas flow also reduces the coaxial fiber diameter by 36.9% (the average fiber diameter: 241 nm ± 5 nm → 152 nm ± 23 nm) and the distribution range by 66% (the standard variance: 1.5 × 10² nm² → 51 nm²). This research provides a reliable idea and experimental basis for homogeneous preparation of coaxial nanofiber membranes. Full article

The continuous synthesis of nanoparticles (NPs) has been actively studied due to its great potential to produce NPs with reproducible and controllable physicochemical properties. Here, we achieved the high throughput production of nanostructured lipid carriers (NLCs) using a coaxial turbulent jet mixer with an added heating system. This device, designed for the crossflow of precursor solution and non-solvent, combined with the heating system, efficiently dissolves solid lipids and surfactants. We reported the flow regime according to the Reynolds number (Re). Also, we confirmed the size controllability of NLCs as dependent on both Re and lipid concentration. The optimized synthesis yields NLCs around 80 nm, ideal for targeted drug delivery by enhanced permeability and retention (EPR) effect. The coaxial turbulent jet mixer enables effective mixing, producing uniform size distribution of NLCs. The NLCs prepared using the coaxial turbulent jet mixer were smaller, more uniform, and had higher drug loading compared to the NLCs synthesized by a bulk nanoprecipitation method, showcasing its potential for advancing nanomedicine. Full article

In this study, a transient viscosity adjustment method using a coaxial nozzle was explored to fabricate nanofibers from non-spinnable m-poly(hydroxyamide) (m-PHA). Unlike conventional electrospinning methods that often require additives to induce fiber formation, this approach relies on a sheath-core configuration, introducing tetrahydrofuran (THF) to the sheath to temporarily adjust solution viscosity. The diffusion of THF into the core m-PHA solution resulted in momentary solidification at the interface, promoting nanofiber formation without compromising polymer solubility. SEM and rheological analyses confirmed that optimized sheath-to-core flow ratios yielded nanofibers with significantly reduced particle formation. Notably, increasing the THF flow rate facilitated a faster solidification rate, enhancing jet elongation and resulting in uniform nanofibers with diameters of approximately 180–190 nm. Although complete nanofibers without beads were not achieved in this study, this coaxial electrospinning approach presents a possible pathway for fabricating nanofibers from polymers with limited spinnability, potentially expanding the application scope of electro-spun materials in high-performance fields. Full article

The gas–liquid Venturi injector has been widely applied in industrial production due to its advantages of high entrainment and low energy consumption. In this study, Computational Fluid Dynamics (CFD) was employed to investigate the effect of the gas–liquid interface structure within the mixing section on entrainment behavior by varying the geometry of the mixing section during gas–liquid coaxial flow. The simulation results indicate that along the jet direction, the gas–liquid interface generally transitions from a smooth cylindrical shape to a lobed structure in the mixing section. Surface waves mainly appear in the lobed region. Furthermore, lobed and surface wave structures reduce pressure loss and enhance entrainment. Additionally, the study found that longer mixing sections enhance entrainment under low flow resistance. This study provides valuable insights for achieving high jet entrainment and offers supplementary research on gas–liquid interface structures in jets constrained by solid boundaries. Full article

(1) Background: Spinal cord injuries and diseases necessitate sophisticated tools for accurate diagnosis and treatment planning. However, the lack of reliable phantoms mimicking the complex structure of the spinal cord hinders the development and validation of advanced imaging techniques. This study aims to address this critical unmet need by exploring the application of electrospinning to create polymeric fibers resembling the human spinal cord; (2) Methods: Direct jet coaxial electrospinning (DJ-co-ES) is a specialized electrospinning process characterized by the presence of solely the straight segment of a fluid jet. The research firstly investigates the effects of various solution properties and process parameters on the formation and characteristics of core/shell fibers with polycaprolactone (PCL) as the shell and polyethylene oxide (PEO) as the core. Furthermore, the study explores the potential of these DJ-co-ES fibers as phantoms by measuring various diffusion MRI parameters; (3) Results: Scanning electron microscopy (SEM) revealed the successful production of hollow PCL microfibers (2–12 μm diameter) with smooth, cylindrical morphology and high orientation. The DJ-co-ES process demonstrated optimal stability when utilizing 10 w/v% PCL in DCM/DMF for the shell and 4 w/v% PEO in deionized water for the core. Additionally, the high miscibility between core and shell solvents in other core and shell solutions cases facilitated the production of fibers with smaller diameters. The findings demonstrate that the measured values fall within the range observed in both healthy and diseased spinal cord tissues; (4) Conclusions: This research paves the way for utilizing DJ-co-ES technology to develop reliable phantoms for spinal cord applications, ultimately fostering advancements in diagnosis, treatment, and research related to spinal cord conditions. Full article

Three-dimensionally printed vascularized tissue, which is suitable for treating human cardiovascular diseases, should possess excellent biocompatibility, mechanical performance, and the structure of complex vascular networks. In this paper, we propose a method for fabricating vascularized tissue based on coaxial 3D bioprinting technology combined with the mold method. Sodium alginate (SA) solution was chosen as the bioink material, while the cross-linking agent was a calcium chloride (CaCl₂) solution. To obtain the optimal parameters for the fabrication of vascular scaffolds, we first formulated theoretical models of a coaxial jet and a vascular network. Subsequently, we conducted a simulation analysis to obtain preliminary process parameters. Based on the aforementioned research, experiments of vascular scaffold fabrication based on the coaxial jet model and experiments of vascular network fabrication were carried out. Finally, we optimized various parameters, such as the flow rate of internal and external solutions, bioink concentration, and cross-linking agent concentration. The performance tests showed that the fabricated vascular scaffolds had levels of satisfactory degradability, water absorption, and mechanical properties that meet the requirements for practical applications. Cellular experiments with stained samples demonstrated satisfactory proliferation of human umbilical vein endothelial cells (HUVECs) within the vascular scaffold over a seven-day period, observed under a fluorescent inverted microscope. The cells showed good biocompatibility with the vascular scaffold. The above results indicate that the fabricated vascular structure initially meet the requirements of vascular scaffolds. Full article

The spray and combustion characteristics of a gas-centered swirl coaxial (GCSC) injector used in oxidizer-rich staged combustion cycle engines were analyzed. The study focused on varying the recess ratio, presence of gas swirl, and swirl direction to improve injector performance. The impact of the recess ratio was assessed by increasing it for gas jet-type injectors with varying momentum ratios. Gas-swirl effects were studied by comparing injectors with and without swirl against a baseline of a low recess ratio gas injection. In atmospheric pressure-spray experiments, injector performance was assessed using backlight photography, cross-sectional imaging with a structured laser illumination planar imaging technique (SLIPI), and droplet analysis using ParticleMaster. Increasing the recess ratio led to reduced spray angle and droplet size, and trends of gas swirl-type injectors were similar to those of high recess ratio gas jet-type injectors. Combustion tests involved fabricating combustion chamber heads equipped with identical injectors, varying only the injector type. Oxidizer-rich combustion gas, produced by a pre-burner, and kerosene served as propellants. Combustion characteristics, including characteristic velocity, combustion efficiency, and heat flux, were evaluated. Elevated recess ratios correlated with increased characteristic velocity and reduced differences in the momentum–flux ratios of injectors. However, increasing the recess ratio yielded diminishing returns on combustion efficiency enhancement beyond a certain threshold. Gas swirling did not augment characteristic velocity but notably influenced heat flux distribution. The trends observed in spray tests were related to combustion characteristics regarding heat flux and combustion efficiency. Additionally, it was possible to estimate changes in the location and shape of the flame according to the characteristics of the injector. Full article

Media exposed to atmospheric pressure plasma (APP) produce reactive oxygen and nitrogen species (RONS), with hydrogen peroxide (H₂O₂), nitrite (NO₂⁻), and nitrate (NO₃⁻) being among the most detected species due to their relatively long lifetime. In this study, a standardized microwave-excited (ME) APP jet (APPJ) source was employed to produce gaseous RONS to treat liquid samples. The source was a commercially available plasma jet, which generated argon plasma utilizing a coaxial transmission line resonator at the operating frequency of 2.45 GHz. An ultraviolet-visible spectrophotometer was used to measure the concentrations of H₂O₂ and NO₃⁻ in plasma-activated media (PAM). Three different types of media (deionized water, Hank’s balanced salt solution, and cell culture solution Dulbecco’s modified eagles medium [DMEM]) were utilized as liquid samples. Among these media, the plasma-treated DMEM was observed to have the highest levels of H₂O₂ and NO₃⁻. Subsequently, the feasibility of using argon ME-APPJ-activated DMEM (PAM) as an adjuvant to enhance the therapeutic effects of cisplatin on human bladder cancer cells (T-24) was investigated. Various cancer cell lines, including T-24 cells, treated with PAM were observed in vitro for changes in cell viability using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. A viability reduction was detected in the various cancer cells after incubation in PAM. Furthermore, the study’s results revealed that PAM was effective against cisplatin-resistant T-24 cells in vitro. In addition, a possible connection between HER expression and cell viability was sketched. Full article

The efficient fabrication of titanium components using laser direct metal deposition (DMD) is gaining significant importance in the aerospace and medical sectors. The DMD process must be appropriately designed to address the issue of oxidation, as titanium exhibits a high affinity for oxygen. The carrier gas flow and shield gas flow, which have been considered secondary factors so far, are shown to exert a substantial influence on the gas dynamics of the DMD process. By varying these parameters, it is possible to identify the influence of the gas volume flows on the oxidation behavior exhibited during the DMD process. To quantify the oxygen uptake in titanium structures during buildup, hot carrier gas extraction is employed. Experiments are conducted using both a three-jet and a coaxial nozzle to assess the influence of nozzle geometry. Additionally, the experiments are conducted within a shielding gas chamber to demonstrate the benefits of such a chamber in mitigating oxidation. Finally, the study reveals that by appropriately combining the parameters of carrier gas volume flow, shield gas volume, and travel speed, it is possible to fabricate titanium components, which fulfill the requirements regarding oxygen content of aerospace and medical applications even without the utilization of a shielding gas chamber. Full article

A novel compound multi-jet impingement system for enhanced cooling of a flat surface by augmenting its area with cylindrical protrusions (CPs) equipped with coaxial guide vanes (CGVs) and reducing deflection of jets by crossflow has been developed for high-heat removal applications. The cooling performance of coaxial circular jets impinging on the top faces of CPs placed in hexagonal configuration on a flat plate is evaluated by three-dimensional (3D) computational fluid dynamics (CFD) simulations. Jets impinging on the top faces of the protrusions are directed to their lateral faces and then to the base plate by the CGVs around the protrusions, resulting in up to 62.8% improvement in heat transfer rate with a minor increase in pressure drop. Effects of protrusion height and diameter on the pressure drop and cooling performance are studied for jet Reynolds ($Re$ number range of 5000–20,000. Due to both shortened jet impingement lengths as the height of protrusions is increased and directing the expended fluid away from the impinging jets by CGVs, adverse effects of jet–crossflow interactions on cooling performance and fluid pumping power are significantly reduced. Performance evaluation criterion ($PEC$) of the novel compound multi-jet impingement cooling system (CMJICS) can be as high as 1.52. Full article

To increase the printing stability of low-viscosity solutions, an auxiliary method was proposed using a coaxial electrohydrodynamic jet. A high-viscosity solution was employed as the outer layer in the printing process, and it could be removed (dissolved away) after printing the structures. A combination of mechanical and electrical forces was proposed to enhance the consistency, durability, and alignment of the printed versatile structures. The instability of the jet trajectory (which arose from the repulsion between the jet and the base with a residual charge, in addition to the winding effect of the solution) was also reduced using the drag force along the direction of movement. Moreover, the jet velocity, the surface charge, and the influence of various working voltages on the jet speed were simulated. An array of IDT-BT nanostructures measuring about 100 nm was prepared on silicon dioxide (using an inner needle with a diameter of 130 µm) by equating the moving speed (350 mm/s) of the substrate to the speed of the jet. Moreover, the moving speed (350 mm/s) of the substrate was compared exclusively to the speed of the jet. The method proposed throughout this study can provide a reference for enhancing the stability of low-viscosity solutions on substrates for high-efficiency fabrication devices (NEMS/MEMS). Full article

Additive manufacturing processes are among the most innovative manufacturing processes of this century. Powder-based direct metal deposition (DMD) is one of these processes. In the DMD process, local shielding takes place via the powder nozzle. The process is therefore critical for oxidation, especially for materials with an affinity for oxidation such as titanium, aluminum and their alloys. In order to study the oxidation behavior in more detail, the present gas dynamics must be further understood. Wirth and Wegener have made a first approach with their gas flow simulation. In this study, a measurement method for spatial oxygen concentration determination is presented. It can be shown that the spatial oxygen concentration follows the nozzle geometry. Furthermore, the coaxial nozzle is superior to the three-jet nozzle with respect to a low oxygen concentration from a carrier gas to shielding gas volume flow ratio of equal to or greater than 0.4. Finally, it can be shown that the use of a shielding gas chamber eliminates the optimization of the gas flow settings. Full article