Coaxial Channels Research Articles

Direct simulation Monte Carlo-driven optimization of vacuum intakes for air-breathing electric thrusters in very low earth orbits

The performance of an atmosphere-breathing electric propulsion (ABEP) intake has been investigated with a focus on the direct simulation Monte Carlo (DSMC) method. A numerical dataset was derived from extensive DSMC analysis of rarefied flow across various intake configurations. The intake geometry, based on a concept from the literature, comprises a cylindrical body with four annular coaxial channels and a conical convergent diffuser. By maintaining the aspect ratio of the coaxial channels, the DSMC simulations were performed by changing three key parameters: inlet area, convergent diffuser angle, and operating discharge voltage, at altitudes ranging from 140 to 200 km. The analysis of the ABEP system revealed that altitude has the most significant influence on the discharge power, while the effects of the diffuser angle and inlet area are comparatively smaller. Analysis at fixed altitudes reveals a strong influence of altitude on discharge power, while the diffuser angle and the inlet area play a minor role. The results also show that the sensitivity of the discharge power to the diffuser angle increases as the altitude approaches the highest level of 200 km. Furthermore, an evolutionary-based optimization methodology was applied, taking into account the requirements of a drag-to-thrust ratio of less than 1 and a discharge power of less than 12 kW. Optimization analysis in the full altitude range revealed that the optimal diffuser angle falls within the narrow range of 15°–20°, corresponding to an optimal operating altitude range of 170–178 km.

Concentric Capillary Microfluidic Devices Designed for Robust Production of Multiple-Emulsion Droplets.

Multiple emulsions are used as templates for producing functional microcapsules due to their unique core-shell geometry. Employing glass capillary devices with coaxial channels has proven effective in creating uniform multiple-emulsion droplets. However, the use of partially miscible fluids, crucial for microcapsule production, often results in clogging and disrupts the stability of these devices. Here, we introduce innovative capillary microfluidic devices with concentric capillary channels, specifically designed to optimize the production of multiple-emulsion droplets while mitigating issues of precipitation and clogging. The key aspect of these devices is their configuration of two or three concentrically aligned capillaries, which form separate, coaxial microchannels for fluid injection. This unique alignment, achieved through rotational adjustments that leverage the natural off-center positioning of tapered capillaries, facilitates the simultaneous coaxial injection of various fluids into a droplet-forming junction, significantly reducing fluid contact before emulsification. The devices, featuring double and triple concentric capillary channels, consistently produce highly uniform double-, triple-, and quadruple-emulsion droplets with precisely controlled diameters and layer thicknesses. The minimal contact between fluids prior to emulsification in these devices broadens the usable range of fluid combinations, heralding new possibilities in microcapsule development for pharmaceutical and cosmetic applications.

The variation law and mechanism of titanium alloy MIG welding process under the synergistic effect of coaxial dual channel gas path

The variation law and mechanism of titanium alloy MIG welding process under the synergistic effect of coaxial dual channel gas path

Coaxial color channel focus evaluation to estimate standoff height in directed energy deposition additive manufacturing

Coaxial color channel focus evaluation to estimate standoff height in directed energy deposition additive manufacturing

Preparation of pH-sensitive alginate-based hydrogel by microfluidic technology for intestinal targeting drug delivery

Hydrogel microspheres stand out in drug delivery due to their small particle size, biocompatibility and good internal stability. In this paper, pH-sensitive hydrogels are prepared by microfluidic technology for targeted drug delivery in the small intestine. A coaxial dual-channel microfluidic chip is constructed. By analyzing the effects of flow rates and three fracture stages (Rayleigh-Plateau instability crushing stage, pressure difference crushing stage and shear force crushing stage) on the size of hydrogel microspheres, the optimal control stage of the microsphere size is determined (shear force crushing stage). Based on this, the accurate control model of the hydrogel microsphere size is proposed. In addition, based on the coaxial dual channel microfluidic chip, a monolayer hydrogel microcapsule loaded with Indometacin is prepared. The core-shell hydrogel microcapsules loaded with Indometacin are prepared by an improved coaxial three channel microfluidic chip. The swelling rates of both microcapsules in simulated intestinal fluid are significantly higher than those in simulated gastric fluid. The results of in vitro simulated release experiments show that the two hydrogel microcapsules basically do not release in simulated gastric juice. In simulated intestinal fluid, single-layer hydrogel microcapsules show rapid release, while core-shell hydrogel microcapsules showed slow release. In conclusion, the alginate-based hydrogel microcapsules have good stability and pH sensitivity, and are suitable for targeted drug delivery in the small intestine.

Application of the Wave Channels Method to Analyze the Switching Overvoltages in Energizing a High-voltage Cable Line

A study of cable line failures shows that a large number of faults occur in the connecting and terminal couplings of 110--500 kV power lines. Overvoltages caused by operational switching in the substation switchgear circuits contribute to the total number of failures. The switching overvoltage amplitude and frequency depend on the parameters of the source, switched circuits, and switching moment. The aim of the study is to identify the network and switched circuit parameters affecting the maximum overvoltage excited by energizing a 400 kV cable line and to determine the degree of their influence. The following factors are considered: switching phase, cable line length, source inductance, and line residual charge. The analysis was carried out by the wave channels method. To achieve this goal, an analysis model was developed in the EMTP-RV software environment, which made it possible to calculate the electromagnetic transients excited by cable line switching. The model has been verified with respect to the surge propagation velocity along a coaxial wave channel. Overvoltage calculations have shown that the switching phase and the line charge availability in the pre-switching operation mode have the most significant effect on the overvoltage value. The obtained study results apply to high-voltage electrical networks containing cable lines. The study results made it possible to quantify the degree to which the considered factors influence the overvoltages excited by switching 400 kV cable lines and to assess possible exceeding of the values permitted by the relevant standards, which will make it possible to have a preventive influence on the number of failures.

Sequential release of vascular endothelial growth factor-A and bone morphogenetic protein-2 from osteogenic scaffolds assembled by PLGA microcapsules: A preliminary study in vitro

Bone regeneration is a complex process sequentially regulated by multiple cytokines at different stages. Vascular endothelial growth factor-A (VEGF-A) and bone morphogenetic protein-2 (BMP-2) are the two most important factors involved in this process, and the combination of the two can achieve better bone regeneration by coupling angiogenesis and osteogenesis. In this study, poly(lactic-co-glycolic acid) (PLGA) microspheres with core-shell structure (microcapsules) encapsulating VEGF-A or BMP-2 were prepared by coaxial channel injection and continuous fluid technology. The sequential release of two cytokines by microcapsules with different PLGA molecular weight and shell thickness and its performance in vitro were explored. It was demonstrated that the molecular weight of PLGA significantly affected the degradation and release kinetics of microcapsules, while the thickness of the shell can regulate the release in a finer level. VEGF-A encapsulated microcapsules with low molecular weight can induce vascular endothelial cells to form lumens structures in vitro at an early stage. And BMP-2 encapsulated microcapsules could promote osteogenic differentiation, but the effect could be delayed when the microcapsules were prepared with PLGA of 150 kDa. In conclusion, the core-shell PLGA microcapsules in this study can sequentially release VEGF-A and BMP-2 at different stages to simulate natural bone repair.

Effects of equivalence ratios on the normal and inverse diffusion flame of acid gas combustion in the pure oxygen atmosphere

The experimental studies on the effect of equivalence ratios to the acid gas (H2S and CO2) combustion in the pure oxygen atmosphere was presented in a coaxial jet double channel burner. Three equivalence ratios (Φ = 0.8, 1.0 and 1.5) are examined to analyze the distribution of the flame temperature and gas composition in the normal and inverse diffusion flame along central axial (R = 0.0) and axial line at 3 mm (R = 0.75) in radial direction. The results revealed that acid gas combustion mainly occurred chemical decomposition of H2S and oxidation of H2S and H2 at R = 0.0, while mainly occurred H2S and H2 oxidation at R = 0.75 in the normal diffusion flame. Reducing Φ increased the flame temperature and it is higher at R = 0 than that at R = 0.75 because of heat loss. It also increased the volume fraction of CO, H2 and COS in the flame combustion area, while decreased downstream reactor because of occurring oxidation. CO was formed by the reaction of CO2 and H, and H2 primarily derived from chemical decomposition of H2S. COS was generated by the reaction of CO2 with SH, H2S and S as well as the reaction of CO with SO and SH at R = 0.0, while was mainly formed by the reaction of CO with SO and SH at R = 0.75. H2S mainly occurred the oxidation in the inverse diffusion flame. The temperature at R = 0.0 was still higher than that at R = 0.75, and it was higher than that in the normal diffusion flame in the combustion area. Increasing Φ promoted the formation of CO, H2 and COS, and each gas under Φ of 1.5 was higher significantly. The Φ had no significant effect on the distribution of SO2 compared to the normal diffusion flame, but changed the distribution of CO, H2 and COS. It can be inferred that the content of CO, H2 and COS will be more higher under Claus condition in the inverse diffusion flame.

Effect of carbon dioxide on oxy-fuel combustion of hydrogen sulfide: An experimental and kinetic modeling

CO2 is an important component in the acid gas and it is necessary to study the effect of CO2 presence on the oxy-fuel combustion of H2S with particular focus on the formation of carbonyl sulfide (COS). The oxy-fuel combustion of acid gas was conducted in a coaxial jet double channel burner. The distribution of flame temperature and products under stoichiometric condition along axial (R = 0.0) and radial at about 3.0 mm (R = 0.75) were analyzed, respectively. The Chemkin-Pro software was used to analyze the rate of production (ROP) for gas products and the reaction pathway of acid gas combustion. Both experimental and simulation results showed that acid gas combustion experienced the H2S chemical decomposition, H2S oxidation and accompanied by H2 oxidation. The CO2 presence reduced the peak flame temperature and triggered the formation of COS in the flame area. COS formation at R = 0.0 was mainly through the reaction of CO2 and CO with sulfur species, whereas at R = 0.75 it was through the reaction of CO with sulfur species. The ROP results indicated that H2 was mainly from H2O decomposition in the H2S oxidation stage, and COS was formed by the reaction of CO2 with H2S. ROP and other detailed analysis further revealed the role of H, OH and SH radicals in each stage of H2S conversion. This study revealed the COS formation mechanisms with CO2 presence in the oxy-fuel combustion of H2S and could offer important insights for pollutant control.

Simulation of strain waves evolution in the walls of coaxial annular and circular channels filled with viscous fluid and made from incompressible material with fractional physical nonlinearity

Simulation of strain waves evolution in the walls of coaxial annular and circular channels filled with viscous fluid and made from incompressible material with fractional physical nonlinearity

Расчет конструктивных параметров мультицилиндрового теплового генератора на основе течения Куэтта–Тэйлора

Direct conversion of wind energy into heat is a relevant direction for the development of alternative heat power engineering. The paper considers an efficient wind heat generator that consists of two rotors nested in each other's annular gaps and forming a system of cylindrical coaxial annular channels filled with a viscous working fluid. Depending on the properties of the working fluid, the velocity of the rotors, the number of annular channels and their geometry, there are combinations of parameters for the optimal design of the heat generator. The proposed method for selecting the design parameters of coaxial rotors makes it possible to directly select the optimal design of rotors for a given power of the heat generator and the properties of a viscous working fluid. The design of the multi-cylinder system of the heat generator, which uses the annular Couette–Taylor flow, is presented in the form of an equivalent single annular gap, which made it possible to generalize the results of investigations carried out with different working fluids under various conditions, in the form of a single dependence of the dimensionless power of the heat generator on the number Reynolds. The obtained dependence is well approximated by a linear function in the experimentally studied range of Reynolds numbers. An algorithm for calculating the geometric design parameters of a multi-cylinder annular system is proposed. As an example, calculations of the structural dimensions of nine variants of heat generators for three power values are given: 10 kW, 20 kW and 50 kW.

Non-Isothermal Flow of a Non-Newtonian Fluid with the Free Surface in a Coaxial Channel

Non-Isothermal Flow of a Non-Newtonian Fluid with the Free Surface in a Coaxial Channel

Study on the monitoring method of cavity growth in underground coal gasification under laboratory conditions

The growth state of the combustion cavity during underground coal gasification (UCG) affects the gasification process's efficiency, stability, and accurate monitoring and control. In this study, a simulation experiment of UCG was performed, and a horizontal coaxial gasification channel was drilled based on the constructed artificial coal seam. Oxygen and air are used as gasification agents to provide a sufficient temperature field to sustain the gasification process. Moreover, the derivation of the gasification zone during UCG was developed using stratified temperature monitoring and acoustic emission damage monitoring. After the experiment, the artificial coal seam was cut to obtain the profile shape of the combustion cavity, which was compared with the temperature and acoustic emission monitoring results. The results show that the temperature distribution results in the coal seam and the calibration results of the acoustic emission source during horizontal coaxial UCG are consistent with the two-dimensional and three-dimensional combustion cavities reconstructed by the profile. Thus, the effectiveness of stratified temperature monitoring and acoustic emission monitoring to infer the gasification combustion cavity is proven.

Comparative study of unilateral biportal endoscopy and coaxial large channel endoscopy for lumbar spinal stenosis

Objective: To compare the efficacy of unilateral biportal endoscopy (UBE) and coaxial large channel endoscopy for lumbar spinal stenosis. Methods: A total of 176 patients with lumbar spinal stenosis treated in Tianjin Hospital from March 2015 to October 2021 were included in this study. Of the patients, 110 cases were treated with UBE, including 52 males and 58 females, with a mean age of (75.1±10.4) years; while 66 cases were treated with coaxial large channel endoscopy, including 31 males and 35 females, with an average age of (77.2±13.1) years. The visual analogue scale (VAS) score of pain and Oswestry disability index (ODI) were compared before and after surgery between the two groups, with the improvement rate calculated. The operation time, intraoperative blood loss, perioperative conditions and complications were compared. The operation efficacy was evaluated according to MacNab scale and was compared between the two groups. Results: There was no significant differences in age, gender, disease course, VAS of pain, ODI and index levels between the two groups before operation (all P>0.05). The operation time and postoperative drainage in UBE group and coaxial large channel endoscopy group were comparable [(60.1±12.4)min, (62.5±13.2)min and (103.8±20.7)ml, (98.5±22.1)ml, respectively, both P>0.05]. After the operation, the VAS score of low back pain, VAS score of leg pain and ODI of the two groups were all lower than those before operation, and decreased continuously during follow-up; and under the repeated measures analysis of variance, significant differences were found between different time points (all P<0.05), no significant difference was found between the two groups (all P>0.05), nor interaction between groups and time points was detected (all P>0.05). The patients were followed-up for (18.0±4.2) months (6 to 30 months). There was no significant difference in VAS and ODI improvement rates and excellent rate of efficacy between the two groups at the last follow-up (all P>0.05). Conclusions: Both UBE and coaxial large channel endoscopy can provide excellent results for lumbar spinal stenosis. UBE has sufficient decompression and is convenient to explore and remove the herniated disc.

Analysis of curative effect of percutaneous coaxial large channel endoscopic lumbar interbody fusion in the treatment of degenerative lumbar spinal stenosis.

ObjectiveTo investigate the clinical efficacy and technical points of Percutaneous Coaxial Large-channel Endoscopic Lumbar Interbody Fusion (PCLE-LIF) in the treatment of degenerative lumbar spinal stenosis.MethodsThe clinical data of patients with single-segment degenerative lumbar spinal stenosis who underwent PCLE-LIF surgery from January 2019 to June 2021 were retrospectively analyzed. Surgery-related data included symptom duration, operation time, hospital stay, and complication rate. Functional score data included low back pain and lower extremity pain VAS score, ODI score, and MacNab criteria were used to evaluate clinical effects. The Brantigan criteria were used to evaluate the interbody fusion.ResultsThere were 62 patients in this group, including 35 males and 27 females. The surgical sites were all lower lumbar spine, including 35 cases of lumbar L4/5 and 27 cases of L5/S1. The length of hospital stay was 7.7 ± 1.4 days. All patients were followed up regularly for 1 year. The interbody fusion rate was 93.5% at 1 year after operation. There were 2 cases of numbness, 2 cases of nerve edema and pain, 1 case of cage displacement, and 1 case of pedicle screw loosening. The complication rate was 9.6%. The VAS scores of low back pain 1 day before surgery, 3 days, 3 months and 1 year after surgery were 4.48 ± 1.06, 0.84 ± 0.81, 0.40 ± 0.56, 0.39 ± 0.69, and the VAS of lower extremity pain at each time point of appeal were 5.58 ± 0.98, 0.91 ± 0.58, 0.31 ± 0.46, 0.19 ± 0.40. The ODI scores at 1 day before surgery, 3 months and 1 year after surgery were 60.01 ± 6.21, 15.58 ± 2.84, 8.82 ± 2.15. The ODI scores and VAS scores of low back pain and lower extremity pain at each follow-up time point after operation were significantly lower than those before operation (p < 0.05). The 1-year follow-up after operation was evaluated by the modified MacNab standard, and the results were excellent in 36 cases, good in 23 cases, fair in 3 cases, and poor in 0 cases, with an excellent and good rate of 95.2%.ConclusionPercutaneous coaxial large-channel endoscopic lumbar interbody fusion in the treatment of degenerative lumbar spinal stenosis has good short-term efficacy and high safety, and is worthy of popularization.

Microfluidic encapsulation of soluble reagents with large-scale concentration gradients in a sequence of droplets for comparative analysis

Concentration gradient is important for comparative analysis in the fields of biomedicine and chemistry, especially with the in-depth research of material synthesis, enzyme kinetic analysis and cell biology. In this work, we reported a simple coaxial injection microfluidic device for encapsulation of soluble reagents with large-scale concentration gradients in a sequence of nanoliter-scale water-in-oil(W/O) droplets for comparative analysis. The concentration gradients can be adjusted straightforwardly by changing the flow rates of phases in two coaxial channels. The concentration gradients of the components can reach the order of 105. As proofs of this concept, acid-base reaction, L-Ascorbic acid redox reaction and synthesis of metal organic frameworks(MOFs) are conducted using this concentration gradient generator. Nanoliter-grade reagents preparation, reactions and analyses with higher concentration gradients and less sample consumption can be achieved without stopping experiments and changing solutions by using this simple microfluidics concentration gradient generator.

A 3D multi-modal intelligent intervention system using electromagnetic navigation for real-time positioning and ultrasound images: a prospective randomized controlled trial.

BackgroundAnesthesia, nerve block, therapeutic injections, and biopsies all require an acupuncture intervention. However, traditional two-dimensional (2D) ultrasound-guided needle puncture is often challenging and therefore requires the use of three-dimensional (3D) ultrasound images to accurately identify and evaluate the patient’s anatomical structure.MethodsIn this study, a 3D multi-modal intelligent intervention system using electromagnetic navigation for real-time positioning and ultrasound images was described. A total of 190 cases requiring puncture were randomly divided into control (conventional 2D ultrasound instrument) and experimental (novel 3D ultrasound imedis9000) groups. The advantages and disadvantages of the two puncture methods were prospectively analyzed in the 190 cases, and the feasibility of electromagnetic navigation real-time positioning was compared to ultrasound imaging.ResultsThis study included 190 cases from two centers that required puncture treatment and were randomly assigned to the control (conventional 2D ultrasound instrument; n=95) or the experimental (novel 3D ultrasound imedis9000; n=95) groups. Percutaneous vascular puncture, percutaneous biopsy, percutaneous bile duct puncture, thoracic paravertebral nerve block, and sciatic nerve block operations were performed separately. The results indicated that the puncture time and number of trials in the experimental group were significantly lower than those in the control group. No significant difference was identified in the basic vital signs between the two groups before and after surgery. The success rate of the novel 3D ultrasound imedis9000 was 100%, and the success rate of the conventional 2D ultrasound instrument was 95.7%. Furthermore, the results also showed that the novel 3D ultrasound imedis9000 and the matching coaxial positioning channel puncture needle had low pain, good toughness and strength, and great convenience.ConclusionsThe new 3D multi-modal intelligent intervention system using electromagnetic navigation real-time positioning and ultrasound images has significant advantages compared with conventional 2D ultrasound in terms of puncture time, number of trials, operation difficulty, and convenience, and is worthy of further promotion and use in clinics.Trial RegistrationBeijing Municipal Drug Administration, 20190015.

A System-Level Performance Evaluation for a 5G System under a Leaky Coaxial Cable MIMO Channel for High-Speed Trains in the Railway Tunnel

As one of the typical application scenarios in the fifth generation (5G) mobile communication system, the situation of high-speed mobile communication is receiving increasing attention. The railway tunnel is a typical environment for high-speed mobile communications. Railway tunnels for high-speed trains are generally installed with leaky coaxial cables (LCXs), which can radiate and receive electromagnetic waves through slots; thus, providing communication. To evaluate the system-level performance of the LCX channel in a tunnel, we propose a modified geometrically based single-bounce multiple-input-multiple-output (GBSB-MIMO) channel model considering the effect of Doppler spread. The time-domain statistics of the channel model are studied from numerical simulations. Based on the proposed channel model, we also simulate and analyze the effects of different factors on the 5G system-level performance, including the interval of cable slots and the quantity and location of LCX.

A particle-based method using the mesh-constrained discrete point approach for two-dimensional Stokes flows

Meshless methods inherently do not require mesh topologies and are practically used for solving continuum equations. However, these methods generally tend to have a higher computational load than conventional mesh-based methods because calculation stencils for spatial discretization become large. In this study, a novel approach for the use of compact stencils in meshless methods is proposed, called the mesh-constrained discrete point (MCD) approach. The MCD approach introduces a Cartesian mesh system to the background of a domain. And the approach rigorously constrains the distribution of discrete points (DPs) in each mesh by solving a dynamic problem with nonlinear constraints. This can avoid the heterogeneity of the DP distribution at the mesh-size level and impose compact stencils with a fixed degree of freedom for derivative evaluations. A fundamental formulation for arrangements of DPs and an application to unsteady Stokes flows are presented in this paper. Numerical tests were performed for the distribution of DPs and flow problems in co-axial and eccentric circular channels. The proposed MCD approach achieved a reasonable distribution of DPs independently of the spatial resolution with a few iterations in pre-processing. Additionally, solutions using the obtained DP distributions in Stokes flow problems were in good agreement with theoretical and reference solutions. The results also confirmed that the numerical accuracies of velocity and pressure achieved the expected convergence order, even when compact stencils were used.

Coaxial cable-like dual conductive channel strategy in polypyrrole coated perovskite lanthanum manganite for high-performance asymmetric supercapacitors

Perovskite transition metal oxides are promising materials for supercapacitor electrodes due to their high theoretical capacities. However, these materials still suffer from poor conductivity, low specific capacitance, and moderate cycle stability, restraining their practical applications. In this study, LaMnO3@CC-PPy materials were prepared by two-step electrodeposition based on the inspiring design of coaxial cables. To this end, electrochemically active LaMnO3 was first grown on carbon cloth (CC) with good flexibility and conductivity and then followed by further coating with polypyrrole (PPy) layer. The best PPy load was identified by adjusting the deposition time. The resulting LaMnO3@CC-PPy electrodes showed excellent specific capacitance reaching 862F g−1 at 1 A g−1 with retention rate of 75% at high current density of 10 A g−1, indicative of excellent rate performance. The cycle stability of the electrodes also improved after 3000 cycles at 10 A g−1 with a retention rate reaching 66%. To assemble asymmetric supercapacitor (ASC) devices, NiCo2O4@CC cathodes were prepared by electrodeposition. Ultra-high energy density of about 73 Wh kg−1 and good cycle stability were recorded with the devices. The high performance of the as-obtained materials was attributed to the existence of internal and external double electric channels, as well as the abundant internal space. These features ensured good conductivity, rapid charge transfer, and fast ion diffusion, thereby significantly improving the overall material cycle stability. In sum, these findings look promising for future preparation of high-performance perovskite supercapacitors.