Small Diameter Ratio Research Articles

Numerical investigation of CH4/H2/air micro-mixing combustion flow in a micro gas turbine combustor with different head-end structures

In order to investigate the premixed combustion characteristics of CH4/H2/air in a micro-mixing combustor, the effects of different micro-mixing head-ends (HE1, HE2, HE3) and hydrogen mixing ratios on the temperature distribution, heat transfer process, emission characteristic, flames shape are analyzed. The results show that compared with swirl head-end combustion, the micro-mixing combustion performance is better. Among the three head-ends, HE3 has the best combustion characteristics and stable flames. The temperature distribution in the high-temperature zone is uniform, and low-temperature zone is concentrated near the jet, which can suppress the flashback. The velocity and temperature gradient near the central axis of jet streams show a strong synergistic effect. The flames are plume shaped and flames stability is mainly influenced by the H2 combustion process. Increasing the jet diameter, decreasing the jet spacing and increasing the hydrogen mixing ratio all contribute to the flames stability, but these three methods can stabilize the flames by affecting fluid Reynolds number, interaction between small flames and combustion rate, respectively. Moreover, small jet diameter and high hydrogen mixing ratio can reduce OTDF, which contributes to improve outlet temperature uniformity.

Research on the separation chamber diameter ratio of the multi-stage hydrocyclone to inhibit particle misplacement

The particle radial settling distance is determined by the separation chamber diameter ratio of multistage hydrocyclones, affecting particle circulation flow and particle misplacement. The effect of the separation chamber diameter ratio on the flow field and separation performance is explored using numerical simulations and physical experiments. The findings indicate that a larger separation chamber diameter ratio increases the particle circulation flow ratio and coarse particle circulation flow proportion, intensifying the particle enrichment ratio. However, smaller separation chamber diameter ratios result in higher turbulence intensity and higher enrichment ratio of coarse particles in the primary separation chamber. Both oversize and undersize separation chamber diameter ratios exacerbate misplaced coarse particles. Physical test results indicate that misplaced fine particles and coarse particles diminish and eventually increase with increasing the separation chamber diameter ratio. The + 150 μm particle content in the overflow reaches the minimum value of 0.32 % in the separation chamber diameter ratio of 0.5. In comparison, the –23 μm particle content in the underflow reaches the minimum value of 3.7 % in the separation chamber diameter ratio of 0.6, and the classification efficiency of −74 μm reaches the maximum of 61.85 %. Consequently, both large and small separation chamber diameter ratios will aggravate particle misplacement and deteriorate classification performance by augmenting the coarse particle circulation flow.

Multi-factor optimization of thermo-economic performance of coaxial borehole heat exchanger geothermal system based on Levelized Cost of Energy analysis

The deep coaxial borehole heat exchangers (BHEs) are commonly employed for geothermal heating purpose. In this investigation, using the established thermo-economic model and fast algorithm for heat extraction prediction, the response surface approach was adopted for investigating the thermo-economic performance and optimizing the design parameters of the coaxial BHE system. The results show that the heat exchange rate is enhanced from 235 kW to 1,061 kW when the depth varies between 2,000 m and 4,000 m. A change in flow rate from 20 m3/h to 80 m3/h yields a 30% augmentation in heat exchange rate. However, increasing the depth will cause extra drilling costs. Extremely large or small flow rates and pipe diameter ratios result in additional equipment and operating costs. The system's levelized cost of energy (LCOE) is contingent upon the interaction among the depth, flow rate, and diameter ratio. The optimal design parameters to meet the minimum LCOE are 3912.8 m depth, 34.32 m3/h flow rate and 0.64 pipe diameter ratio. The optimized LCOE is $ 7.84/GJ with an improvement of 22.02–63.02%, demonstrating a competitive thermo-economic performance to traditional energy sources. This research will contribute to the parameter design of BHE and effective utilization of geothermal energy.

Numerical Investigation the Effects of Cone Diameters on the Flow Pattern and Separation Efficiency in a Cyclone Separator

In this work, the impact of cone diameters on the flow field and separation efficiency in a cyclone separator is examined numerically employing Reynolds Stress Model for eight various geometries of cyclone separators. The motion of solid particle in the flow field is modelled utilizing the Eulerian-Lagrangian method. Three-dimensional simulation of the air flow with solid particles in the cyclone is carried out by a commercial computational fluid dynamics software, ANSYS Fluent 18.2. The outcomes depict that by augmenting the small cone diameter, the maximum tangential velocity, static pressure, and collection efficiency decrease, however, cut-off diameter rises. Moreover, the axial velocity has steady trend throughout the cyclone. In addition, according to the obtained results, increasing the large cone diameter causes an increase in the tangential velocity and static pressure and improves the collection efficiency. While, the higher large cone diameter, the lower cut-off diameter. Growing the cyclone’s cone small diameter leads to a decrease in the collection efficiency. At a constant particle diameter, four microns, as the cone small diameter ratio augments by 150%, collection efficiency declines by about 10.42%. Augmentation the cyclone’s cone small diameter causes an increase in the cutoff diameter. By increasing the cone small diameter by about 150%, the cut-off diameter value increases by about 75%. Furthermore, the collection efficiency rises by growing the cyclone’s cone large diameter. At a constant particle diameter, four microns, as the cone large diameter augments by 50%, the collection efficiency increases by about 18.75%. Also, in all considered cone large diameter, the collection efficiency increases as the particle diameter rises. The cut-off diameter decreases by growing the cyclone’s cone large diameter. By augmenting the cone large diameter by about 50%, the cut-off diameter value declines by about 57.69%.

Numerical study of the impact and aggregation characteristics of alumina droplets on a wall in the solid rocket motor

The impact and aggregation of multiple alumina droplets on the inner wall of the solid rocket motor may generate a larger rebound aggregated droplet or adhere to the wall to form a liquid film. The rebound and adhesion characteristics of the aggregated droplet are of great significance for slag deposition and two-phase flow prediction in the motor. In this paper, the VOF (Volume of fluid) method is used to study the impact and aggregation process of multiple alumina droplets on the wall. Detailed numerical verifications are carried out, including the impact and aggregation of moving droplets, the aggregation and rebound of stationary droplets and the impact process of a single alumina droplet on the wall. It is found that the aggregated droplet will rotate when two droplets aggregate under small droplet diameter ratio, which is caused by the asymmetry aggregation process. The oscillation process intensifies when three droplets impact and aggregate on the wall, as a result, the aggregated droplet is easier to adhere to the wall. The viscous dissipation in the aggregation of droplets is huge, and the total viscous dissipation energy accounts for about 50% of the total energy when the aggregated droplets rebound. The influence of droplet diameter on the V⁎ (rebound recovery coefficient) of the aggregated droplet and the rebound/adhesion results are dominated by the viscosity effect. While the influence of the parameters involving the initial spatial arrangement of droplets is dominated by the oscillation process, which will reduce the effective rebound kinetic energy, making a lower V⁎ and the aggregated droplet easier to adhere.

Morphology and biometry of two Chinese diploid parthenogenetic Artemia populations with a special emphasis on the gonopods and frontal knobs of rare males

Morphological and biometric characters of rare males and females of two diploid parthenogenetic populations from Gahai Lake (GH) and Chengkou Saltern (CK-par) (China) were surveyed. The characters were compared with those of six bisexual species. The gonopod of rare males consists of a basal portion and a distal portion. The distal portion of the gonopod ends in a fine digitiform apex and is ornamented with numerous spines (distal gonopod spines). The number and height of spines on the posterior surface (posterior spines) are conspicuously larger than spines on the exo-lateral surface (exo-lateral spines). The morphology of distal gonopod spines of rare males is most closely related to Artemia urmiana, but posterior spines are apparently taller in the rare males than in A. urmiana. Frontal knobs of rare males are sub-spherical in lateral view, and sub-elliptic in frontal view. The large diameter against small diameter ratio of the frontal knob of GH is significantly larger than that of CK-par. The number of frontal knob spines in rare males is close to that of Artemia salina, Artemia franciscana and Artemia persimilis, but significantly smaller than that of Artemia sinica, Artemia tibetiana and A. urmiana. The number of solitary spines of GH is significantly smaller than that of CK-par. Discriminant analyses using 13 parameters in females and 24 parameters in males show that GH and CK-par are close to each other but divergent from bisexual species. The analytical result based on male genital parameters is likely to be more coincident with the molecular phylogeny than that based on the non-sex-related parameters.

Study on Discharge Coefficients of Drain Orifices in Closed Cavities

The numerical method was used to simulate the discharge flow, and discharge coefficients were obtained. The main factors affecting the discharge coefficient of orifices were analyzed by dimensional analysis, and the empirical formulas for calculating discharge coefficient were fitted. The results show that when the water head height is less than 200mm, the discharge coefficient decreases with the increase of head height. When the water head height is more than 200mm, the discharge coefficient is stable around 0.61. The discharge coefficient with different thickness diameter ratio shows two different forms: the orifices with small thickness diameter ratio show thin orifice flow characteristics, and the discharge coefficient is about 0.6; the orifices with large thickness diameter ratio show thick orifice flow characteristics, and the discharge coefficient is about 0.8.

Influence of Micro-Blowing Technique Hole Parameters on Drag Reduction of Civil Aircraft Engine Nacelle: A Computational Study

The numerical parametric analysis conducted to analyze the impact of micro-blowing technique (MBT) hole-parameters are quite few at the present stage. The main aim of this research paper is to analyze the effect of micro blowing flow rate and its different hole-parameters on the skin friction drag reduction of an aircraft engine nacelle operating at cruise conditions. The primary tasks are focused to understand the behavior of the flow characteristics at the vicinity of the micro-porous holes by means of different types of MBT configurations. The interaction between main-stream flow and the micro-channel flow is numerically solved by using the Reynolds average Navier-Stokes equation and the k-omega SST is used to model the turbulent flow at the vicinity of the wall region. The hole-pattern is kept aligned in a single-row channel and the shape of the hole cross-section is kept straight to obtain an overall simplicity of the simulation model. The influences of the micro blowing technique are quite clearly seen from the simulation results, as there is a significant reduction in the velocity gradient between the solid engine nacelle surface and all the MBT configurations. The porous engine nacelle surface with zero blowing velocity is capable to reduce the skin friction drag by 7.045 % than of its solid surface, implying that the presence of the micro-porous holes possesses low effective surface roughness, and it is an effective method to manipulate the turbulent boundary layer. The optimum skin friction drag reduction is observed when the geometrical characteristics of the holes possess small diameter and high aspect ratio.

A fast approximate method for simulating thermal pile heat exchangers

Ground source heat pump systems, operating in conjunction with vertical ground heat exchangers, will play a key role in decarbonising heating and cooling of buildings. Design of traditional borehole heat exchangers relies on tools which implement routine analytical relationships between heat transferred and the temperature change in the ground and circulating thermal fluid. However, for novel piled foundations used as ground heat exchangers, there are few such analytical solutions available that are practical for routine implementation. This paper examines the use of a radial approximation to simulate the dynamic thermal behaviour of pile heat-exchangers. Originally developed for small diameter and high aspect ratio borehole heat exchangers, the approach is more challenging for piles since unsteady heat transfer within the pile material is more significant over typical timescales. Nonetheless, we demonstrate that for pile diameters between 300 mm and 1200 mm, generally the error is <1 °C with centrally placed heat transfer pipes or four or more pipes placed near the edge with circumferential spacing less than 550 mm. The radial model is therefore practical for most pile configurations. The strong performance of the model is demonstrated for a year of hypothetical heating and cooling cycles, and also against a field-scale thermal response test.

Droplet rebound and dripping during impact on small superhydrophobic spheres

While droplet impact processes on hydrophilic and hydrophobic spheres have been widely investigated experimentally and numerically, the impact behaviors of water droplets on small superhydrophobic spheres are studied numerically and theoretically in this research. The numerical model adopts the volume of fluid method (VOF) and is verified by comparing the simulation results with the experimental observations in the literature. The effects of Weber number and sphere-to-droplet diameter ratio on the droplet impact dynamics are discussed. The final outcomes of the impact droplets are classified into rebound and dripping types with the latter appearing at a larger Weber number or a smaller diameter ratio. As the Weber number and diameter ratio increase, droplet deformation during impact is reinforced with the maximum width factor of the rebound droplet becoming greater. The maximum width factor of the dripping droplet is nearly independent of the Weber number but is enlarged by the increasing diameter ratio. Moreover, a larger diameter ratio reduces the contact time of the rebound droplet but raises that of the dripping one. A theoretical model based on energy conservation is established to predict the boundary between the droplet rebound and dripping outcomes and is in good agreement with the simulation results. The diameter ratio limit for droplet dripping at a zero Weber number is also obtained. Our results and analyses provide insight into the interaction mechanism between the impact droplet and small spheres or particles.

Torsional Properties of Bundles with Randomly Packed Carbon Nanotubes.

Carbon nanotube (CNT) bundles/fibers possess promising applications in broad fields, such as artificial muscles and flexible electronics, due to their excellent mechanical properties. The as-prepared CNT bundles contain complex structural features (e.g., different alignments and components), which makes it challenging to predict their mechanical performance. Through in silico studies, this work assessed the torsional performance of CNT bundles with randomly packed CNTs. It is found that CNT bundles with varying constituent CNTs in terms of chirality and diameter exhibit remarkably different torsional properties. Specifically, CNT bundles consisting of CNTs with a relatively large diameter ratio possess lower gravimetric energy density and elastic limit than their counterpart with a small diameter ratio. More importantly, CNT bundles with the same constituent CNTs but different packing morphologies can yield strong variation in their torsional properties, e.g., up to 30%, 16% and 19% difference in terms of gravimetric energy density, elastic limit and elastic constants, respectively. In addition, the separate fracture of the inner and outer walls of double-walled CNTs is found to suppress the gravimetric energy density and elastic limit of their corresponding bundles. These findings partially explain why the experimentally measured mechanical properties of CNT bundles vary from each other, which could benefit the design and fabrication of high-performance CNT bundles.

Thermally drawn rechargeable battery fiber enables pervasive power

The increasing demand for mobile computing, communications, and robotics presents a growing need for suitable portable power solutions in non-flat customized electronic devices. Fibers as fundamental building blocks of fabrics and 3D-printed objects provide unique opportunities for developing pervasive multidimensional power systems. The characteristic small diameter (<10−3 m) and high aspect ratios (>106) of fibers and expansion of fibers into 2D and 3D power systems necessitate ultra-long lengths to meet the energy specifications of portable electronic systems. Here, we present a Li-ion battery fiber, fabricated for the first time using a thermal drawing method which occurs with simultaneous flows of multiple complex electroactive gels, particles, and polymers within protective flexible cladding. This top-down approach allows for the production of fully-functional and arbitrarily long lithium-ion fiber batteries. The continuous 140 m fiber battery demonstrates a discharge capacity of ∼123 mAh and discharge energy of ∼217 mWh. The scalability and material tunability of these fibers position them for use in varied non-planar electronic systems, including a 1D-flexible electronic fiber, a 2D-large-scale machine woven electronic fabric (∼1.6 m2), and a 3D-printed structural electronic system. The fiber battery satisfies the requirements of portable electronics systems as it is machine washable, flexible, usable underwater, and fire/rupture-safe. We have demonstrated the powering of a submarine drone, LiFi fabric, and flying drone communication through different rechargeable fiber battery schemes, which paves the way for the emergence of the pervasive battery-powered electronics.

Extent and characteristic of relationships in canal dimension and canal body ratio between cervical and lumbar spine

A known prevalence of concurrent cervical and lumbar spinal stenosis was shown to be 5–25%, but there is a lack of evidence regarding direct relationships in canal dimension and canal-body ratio between cervical and lumbar spine. Total 247 patients (mean age: 61 years, male: 135) with cervical and lumbar computed tomography scans were retrospectively reviewed. Midsagittal vertebral body and canal diameters in reconstructed images were measured at all cervical and lumbar vertebrae, and canal-body ratios were calculated. The canal diameter and ratio were also compared according to the gender and age, and correlation analysis was performed for each value. There were significant correlations between cervical (C3–C7) and lumbar (L1–L5) canal dimension (p < 0.001). C5 canal diameter was most significantly correlated with L4 canal diameter (r = 0.435, p < 0.001). Cervical canal-body ratios (C3–C7) were also correlated with those of lumbar spine (L1–L5) (p < 0.001). The canal-body ratio of C3 was most highly correlated with L3 (r = 0.477, p < 0.001). Meanwhile, mean canal-body ratios of C3 and L3 were significantly smaller in male patients than female (p = 0.038 and p < 0.001) and patient’s age was inversely correlated with C5 canal diameter (r = − 0.223, p < 0.001) and C3 canal-body ratio (r = − 0.224, p < 0.001). Spinal canal dimension and canal-body ratio have moderate degrees of correlations between cervical and lumbar spine and the elderly male patients show the tendency of small canal diameter and canal-body ratio. This relationship of cervical and lumbar spine can be an important evidence to explain to the patients.

Usefulness of vein graft for arterial anastomosis with diameter mismatch in head and neck reconstruction

Considerable progress has resulted in microvascular free flaps becoming a cornerstone in the management of head and neck cancer. An important determinant of the success of free flap reconstruction is the proper choice of vessels, but the literature shows that donor-recipient diameter mismatch in arterial anastomosis is common, and can increase the rates of thrombosis and flap loss.1 The invagination technique and the oblique cut method are commonly used in the management of arteries with a large:small diameter ratio of 1.5:1 or less.

Electrical Characteristics of a Carbon Nanotube-Functionalized Probe for Kelvin Probe Force Microscopy

Carbon nanotubes (CNTs) have been demonstrated as a functional probe for scanning probe microscopy because of their good mechanical properties, small diameter, and high aspect ratio. However, their...

First evidence of convergent lifestyle signal in reptile skull roof microanatomy

BackgroundThe study of convergently acquired adaptations allows fundamental insight into life’s evolutionary history. Within lepidosaur reptiles—i.e. lizards, tuatara, and snakes—a fully fossorial (‘burrowing’) lifestyle has independently evolved in most major clades. However, despite their consistent use of the skull as a digging tool, cranial modifications common to all these lineages are yet to be found. In particular, bone microanatomy, although highly diagnostic for lifestyle, remains unexplored in the lepidosaur cranium. This constitutes a key gap in our understanding of their complexly interwoven ecology, morphology, and evolution. In order to bridge this gap, we reconstructed the acquisition of a fossorial lifestyle in 2813 lepidosaurs and assessed the skull roof compactness from microCT cross-sections in a representative subset (n = 99). We tested this and five macroscopic morphological traits for their convergent evolution.ResultsWe found that fossoriality evolved independently in 54 lepidosaur lineages. Furthermore, a highly compact skull roof, small skull diameter, elongate cranium, and low length ratio of frontal and parietal were repeatedly acquired in concert with a fossorial lifestyle.ConclusionsWe report a novel case of convergence that concerns lepidosaur diversity as a whole. Our findings further indicate an early evolution of fossorial modifications in the amphisbaenian ‘worm-lizards’ and support a fossorial origin for snakes. Nonetheless, our results suggest distinct evolutionary pathways between fossorial lizards and snakes through different contingencies. We thus provide novel insights into the evolutionary mechanisms and constraints underlying amniote diversity and a powerful tool for the reconstruction of extinct reptile ecology.

Study on taper reduction of high aspect ratio micro-shafts fabricated by twin-mirroring-wire tangential feed electrical discharge grinding (TMTF-WEDG)

• New method, named TMTF-WEDG, was proposed for manufacturing micro-shaft. • The main reasons for the taper of micro-shaft are the deformation of the micro-shaft and the wear of wire electrodes. • According to the experimental results, the parameters were selected to control the discharge energy to minimize the taper. • The feed strategy was improved to avoid the effect of wire electrode wear on taper. • High-precision micro-shaft with small diameter and large aspect ratio was successfully prepared. Efficiently fabricating large-aspect-ratio micro-shaft with small diameter and high accuracy is a significant technology in micro-manufacturing. In this paper, based on the newly proposed method, named twin-mirroring-wire tangential feed electrical discharge grinding (TMTF-WEDG), we developed the micro-shaft fabrication system to improve the efficiency by twin-mirroring-wire and accuracy by tangential feed. Besides, the narrow slit formed by twin-mirroring-wire constrains the diameter of micro-shaft, which allows improving the repeatability of micro-shaft diameter by controlling the tangential feed distance and narrow slit width. But during the TMTF-WEDG, we found that the micro-shafts with small diameter and large-aspect-ratio tend to have processing taper. The reasons for the tapered micro-shaft are the wire electrode wear due to non-running during finishing and the deformation of micro-shaft with low stiffness due to the small diameter and large aspect ratio. The heat generated by the discharge causes the deformation and its conduction inside the micro-shaft. Discharge energy needs to be controlled during the finishing of TMTF-WEDG, which was achieved by controlling processing parameters. By studying the effects of parameters on the processing taper, optimized parameters minimized the taper of the micro-shaft. The feed strategy was improved so that the micro-shaft always discharges with new wire electrodes. In this way, we successfully fabricated a tungsten micro-shaft with a diameter of 8.5 μm and a length of 400 μm, and the diameter variation is less than 2 μm. The aspect ratio of another micro-shaft with a diameter of 39.38 μm is larger than 50, with the diameter variation within ± 2 μm. By using such micro-shaft, we performed micro-holes processing by micro-EDM on a 304 stainless steel sheet, and the accuracy of 49 micro holes was controlled within 1 μm.

CFD-DEM coupling simulation of fixed bed reactor with small diameter ratio

Fixed bed reactor as a commonly used catalytic device and adsorption equipment in the chemical industry has attracted widespread attention. This paper presents a simple and feasible method which combines CFD with DEM to simulate the fixed bed reactor with the diameter ratio ranges in 2–8. The variation of the void ratio with different diameter ratios obtained from the model used in this paper was in comparison with the theoretical results derived by de Klerk and Dixon. The maximum error between the simulated results and the theoretical results was less than 10%, indicating that the model used in this study had a high degree of confidence. On this basis, the effects of the diameter ratio on the distribution of velocity and pressure were investigated. The distribution of velocity and pressure at different diameter ratios illustrated that when the diameter ratio was 5, the velocity distribution was uniform, and the pressure drop was relatively insignificant, which was beneficial to the reaction process. The model used in this paper could provide a new and concise method for the design and verification of fixed bed reactor.

Nickel Nanofibers Manufactured via Sol-Gel and Electrospinning Processes for Electrically Conductive Adhesive Applications

The electrospun fibers of poly(vinyl pyrrolidone) (PVP)-nickel acetate (Ni(CH3COO)2·4H2O) composite were successfully prepared by using sol-gel processing and electrospinning technique. Nickel oxide (NiO) nanofibers were obtained afterwards by high temperature calcinations of the precursor fibers, PVP/Ni acetate composite nanofibers, at 700 °C for 10 h. Following with the reduction of NiO nanofibers at 400 °C using hydrogen gas (H2) under inert atmosphere, the metallic nickel (Ni) nanofibers were subsequently produced. In addition, as-prepared Ni nanofibers were chemically coated with silver (Ag) nanoparticles to enhance their electrical property and prevent the surface oxidation. The characteristics of as-prepared fibers, such as surface morphology, fiber diameters, purity, the amount of NiO nanofibers, and metal crystallinity, were determined using a scanning electron microscope (SEM), a Fourier transform infrared spectrometer (FT-IR), a thermogravimetric analyzer (TGA), and a wide-angle x-ray diffractometer (WAXD). The volume resistivity of epoxy nanocomposite filled with Ag-coated short Ni nanofibers was lower than the one containing short Ni nanofibers with no coating due to the synergetic effect of Ag nanoparticles created during the coating process. We also demonstrated that the volume resistivity of epoxy nanocomposite filled with Ni nanofibers could be dramatically decreased by using Ni nanofibers in the non-woven mat form due to their small fiber diameter and high fiber aspect ratio, which yield a high specific surface area, and high interconnecting network.

Performance improvement of centrifugal compressors for fuel cell vehicles using the aerodynamic optimization and data mining methods

Centrifugal compressors are one of the most important auxiliary components in polymer electrolyte membrane fuel cell vehicles, which tend to operate at a narrow area with low specific speed. Here, the optimal design goals of centrifugal compressors are investigated on the basis of a lumped model for fuel cell systems. A three-dimensional multi-objective and multi-point aerodynamic optimization and data mining method for centrifugal compressors named ODM is presented via integrating a multi-island genetic algorithm, Reynolds-Average Navier-Stokes solver technique and self-organization map based data mining technique. Data mining indicates that compressor geometry would move to a small inlet diameter ratio and a narrow region of the outlet width ratio. Based on the optimization results, a centrifugal compressor for 100 kW fuel cell stack is manufactured. The experimental results show that the improvement of isentropic efficiency near low mass flow has been achieved, which indicates that the proposed ODM is effective in the performance improvement of centrifugal compressors for fuel cell vehicles.