Rectangular Cross-sectional Shape Research Articles

3D investigation of the channel cross-section configuration effect on the power delivered by PEMFCs with straight channels

In the present study, a three-dimensional (CFD) model is performed to investigate the effects of the channel cross-section shape on power density, pressure drop and local transport phenomena of the single straight channel PEMFC. 30 forms of channel cross-section including 5 well-known and 25 new innovative channel cross-section configurations have been investigated using ANSYS-FLUENT. The carried out experimental and numerical validations to verify the present model accuracy have shown a good agreement. The channel cross-section shapes have a significant influence on the power density at medium and higher current density. The best performance is reported by the channel cross-section configuration that has a trapezoidal bottom shape and an inverted trapezoidal top form. Whereas, the worst performance is obtained by the channel cross-section configuration that has an inverted half elliptical bottom shape and an inverted trapezoidal top form. A bad choice of the channel cross-section configuration can lead to a power density loss of 4.65%. The largest pressure drop is obtained from the triangular channel cross-section form whereas; the smallest pressure drop is reported by the rectangular channel cross-section shape.

A lattice Boltzmann model for the open channel flows described by the Saint-Venant equations.

A new lattice Boltzmann method to simulate open channel flows with complex geometry described by a conservative form of Saint-Venant equations is developed. The Saint-Venant equations include an original treatment of the momentum equation source term. Concrete hydrostatic pressure thrust expressions are provided for rectangular, trapezoidal and irregular cross-section shapes. A D1Q3 lattice arrangement is adopted. External forces, such as bed friction and the static term, are discretized with a centred scheme. Bounce back and imposed boundary conditions are considered. To verify the proposed model, four cases are carried out: tidal flow over a regular bed in a rectangular cross-section, steady flow in a channel with horizontal and vertical contractions, steady flow over a bump in a trapezoidal channel and steady flow in a non-prismatic channel with friction. Results indicate that the proposed scheme is simple and can provide accurate predictions for open channel flows.

Multimodal radiation impedance of a waveguide with arbitrary cross-sectional shape terminated in an infinite baffle.

Simulations of waveguide acoustics require a description of the boundary condition at the open end. For problems involving higher order transverse modes, it is often described by a multimodal radiation impedance matrix. Expressions for the computation of this matrix for an infinite flange condition are available only for circular and rectangular cross-sectional shapes. Thus, a general expression valid for arbitrary cross-sectional shapes is of interest. Such an expression is proposed, validated against known cases, and applied to an arbitrary cross-section shape. The solution is shown to be computationally efficient.

Analiza protočnosti kanala različitih oblika poprečnih presjeka i obloženosti

U ovome radu prikazane su hidrauličke analize protočnosti pod utjecajem različitih oblika poprečnih presjeka i vrste obloženosti kanala. Prilikom analize različitih oblika poprečnih presjeka izrađen je hidraulički proračun za jednoliko stacionarno tečenje za trokutni, pravokutni, trapezni i polukružni oblik poprečnog presjeka kanala. Prvom provedenom hidrauličkom analizom uspostavilo se da je, u pogledu protočnosti kanala, najpovoljniji polukružni oblik poprečnog presjeka kanala. U drugoj hidrauličkoj analizi promatrane su različite vrste obloženosti stijenki kanala te se u tu svrhu također proveo hidraulički proračun za jednoliko stacionarno tečenje u kojem su promatrane različite obloge kanala, odnosno koeficijenta hrapavosti na protočnost. Provedena analiza pokazala je kako veći koeficijenti hrapavosti daju manju protočnost u kanalu i obrnuto. Samim time, prilikom dimenzioniranja kanala, odnosno hidrauličkog proračuna, potrebno je uzeti u obzir odgovarajući poprečni presjek kanala te vrstu obloženosti kanala kako bi dimenzionirani kanal bio najpovoljniji u pogledu što manjih hidrauličkih gubitaka i što veće propusne moći.

Performance Comparison of Circular and Square RC Columns under Monotonic Loading Conditions

Current flexural and shear design methods for reinforced concrete members are mainly based upon the rectangular cross-sectional shape. A simplified new approach for designing circular cross sectional Reinforced Concrete (RC) members might be to convert them to equivalent area, square shapes. An experimental study was performed on reinforced concrete circular cross sections and equivalent area, rectangular cross sectional members. The RC members were tested under non linear monotonic loading conditions, under both flexural and shear controlled conditions. Furthermore, the 3D FEM package COM3D was used to simulate the nonlinear performance of circular and its equivalent area, square members. Experimental and analytical results show that the circular RC members and its equivalent square have similar nonlinear performance (load-deflection behavior) in both flexural and shear controlled failure conditions. A good agreement was found in nonlinear performance of main design criteria; initial stiffness, flexural capacity, and shear capacity of both types. Based upon these results, the proposed approach can be considered satisfactory.

Mixture flow of water and methane through shale nanopore by molecular dynamics simulation

The coexistence and flow of water and methane is important during hydraulic fracturing process in shale gas. In this work, the mixture flow of water and methane inside the kaolinite nanopore under shale reservoir conditions is investigated using nonequilibrium molecular dynamics simulations. The kaolinite pore has rectangular cross-sectional shape with inner pore surface area of basal surface and B chain edge surfaces. The B chain edge surface is determined by Periodic Bond Chain theory and the partial charge of edge oxygen atoms are computed by bond valence coordination method. The force field is CLAYFF which is specifically for clay minerals. The external body force field is applied to drive the water gas to flow. The results indicate that clay surface is hydrophilic and methane is hydrophobic due to the affinity difference between water and methane. Methane has more affinity with siloxane oxygen atoms of kaolinite surface than water molecules. The nanoscale confinement makes the water channel in the cuboid pore exhibit quasi-round shape, which is due to the potential overlap from the pore corner atoms. The fluid flow reaches stable in one nanosecond, indicated by the stabilized flux. The flow of methane exhibits Poiseuille flow feature in the round pore. The calculated number flux of methane is about two times as large as water, and the slip velocity of water and methane increase from 0.4 m/s, 1.6 m/s to 9 m/s, 15.2 m/s respectively as external pressure changes from 10 to 400 MPa. The viscosity components of water along different planes show significant anisotropy due to the anisotropic pore surface chemistry and irregular pore shape. In addition, the water gains much larger viscosity (11.4 mPa∙s) when confined in the kaolinite nanopores, significantly higher than its bulk state viscosity of 0.47 mPa∙s at 333 K, while the viscosity of methane changes relatively small compared with its bulk state.

Design versions of HTS three-phase cables with the minimized value of AC losses

Design versions of HTS three-phase cables consisting of 2G HTS tapes have been investigated by the numerical simulation method with the aim of AC losses minimization. Two design versions of cables with the coaxial and extended rectangular cross-section shape are considered – the non-sectioned and sectioned one. In the latter each cable phase consists of sections connected in parallel. The optimal dimensions of sections and order of their alteration are chosen by appropriate calculations. The model used takes into account the current distribution between the sections and its non-uniformity within each single HTS tape as well. The following characteristics are varied: design version, dimension, positioning of extra copper layer in a cable, design of HTS tapes themselves and their mutual position. The dependence of AC losses on the latter two characteristics is considered in details, and the examples of cable designs optimized by the total set of characteristics for the medium class of voltages (10 – 60 kV) are given. At the critical current JC=5.1 кA per phase and current amplitudes lower than 0.85JC, the level of total AC losses does not exceed the natural cryostat heat losses.

Study on Temperature Field of Fire Smoke in Utility Tunnel with Different Cross Sections

Abstract In order to study the influence of different section shapes on the temperature distribution of fire in utility tunnel systems, circular and rectangular cross-sectional shapes of tunnels are established. In this paper, combustion behaviors are represented by setting volumetric heat source, and the temperature data of the measuring points is analyzed. The results showed that the smoke temperature of the circular tunnel was higher than that of the rectangular section at the same location in the longitudinal direction, and the temperature reduced faster in the range of 30 m away from the fire source. On the cross section of the fire, the smoke temperature in the middle of the circular tunnel increased continuously with the vertical height, while the smoke temperature of the rectangular section increased at first and then tends to be stable. Nevertheless, the maximum temperature of smoke in circular and rectangular tunnels appeared at the top of the tunnel. Therefore, it is desirable to place the heat and smoke detectors at the top of the tunnel.

Approximate 3D model of electromagnetic modes in waveguide cross-shaped junctions with dielectric filling

A three-dimensional electrodynamic model of hybrid electromagnetic modes in a waveguide junction of cylindrical and rectangular waveguides with dielectric filling of a cylindrical waveguide is proposed in this study. To solve the vector problem, the mode matching technique (MMT) is applied with the separation of the common waveguide junction region and the representation of the field in this region in the form of superposition of the fields of the partial eigenwaves of waveguides. Classification of eigenmodes is carried out: intrinsic resonances of junction based on transcendental modes and resonances of a waveguide-dielectric type. The investigated structure can be used for measuring the electrical parameters of dielectric samples of both cylindrical and rectangular cross-section shape. Since the spectral characteristics of the junction are determined mainly by the size of the central coupling region of the waveguides and the electrical parameters of the dielectric in the junction, the measurements are of a local nature.

EFFECT OF HEIGHT AND ORIENTATION OF INTERFERING BUILDINGS ON WIND LOADS ON TALL BUILDINGS

The research work presented in this paper investigates the effect of interference on wind loads on a tall building (instrumented building) having rectangular cross-sectional shape due to the presence of two interfering buildings close to the instrumented building. The effect of interference on the instrumented building is studied with the variation of height and relative orientation of the interfering buildings with respect to the instrumented building. Wind tunnel experiments are undertaken using five component force balance load cell and the results are reported in the form of X-Y plots. The effect of interference in both shielding as well as enhancing the wind load on the instrumented building, is seen to increase with the increase in the height of the interfering building. Negative drag force is also observed in few cases where shielded part of the instrumented building is large. Value of torsion on the instrumented building is observed to be as high as ten times of that in the isolated case.

Optimization of Three- and Single-Phase AC HTS Cables Design by Numerical Simulation

This paper presents the results of calculation of ac HTS cables designs optimized by the values of hysteresis and eddy current losses. The superconducting elements of the cables are 2G HTS tapes. The program we developed and used allowed the variation of both the cable shape and its internal structure. There have been considered nonsectioned and sectioned cables having two variants of geometry-the axially symmetrical coaxial and extended rectangular cross-sectional shape. It has been shown that the internal structure optimization allows decreasing of ac losses in several times for both cross-sectional shapes. Due to the compensation of the perpendicular magnetic field component, the characteristics of flat three-phase cables turn out to be close of those with the axially symmetrical cross-sectional shape. In this case, the rectangular cross-sectional shape allows obtaining better mass, dimensional, and mechanical parameters and better cooling conditions of phases. The cables sectioning allows an essential reduction of ac losses. But, the latter is possible only when there is a uniform current distribution over the sections, i.e., at a very exact design calculation.

Synthesis of self-assembled rectangular-shaped polyaniline nanotubes and their physical characteristics

Abstract We reports synthesis of polyaniline (PANI) nanotubes with a rectangular cross-sectional shape by simply changing both molar ratio of organic dopant acid to monomer and reaction time. The PANI nanotubes were fabricated with a controlled rectangular pore structure by an in-situ chemical oxidation polymerization process in the absence of surfactant and template. Morphology of citric acid (CA)-doped PANI was observed via scanning electron microscopy and transmission electron microscopy. Fourier transform infrared spectroscopy and X-ray diffraction confirmed chemical structure and hydrogen bonding between amine group of PANI and hydroxyl and carboxyl group of CA, is the driving force for this self-assembly.

Three-Dimensional Analysis of the Contact Pattern between the Cortical Bone and Femoral Prosthesis after Cementless Total Hip Arthroplasty.

The cementless stem Excia (B. Braun, Melsungen, Germany) implant has a rectangular cross-sectional shape with back-and-forth flanges and a plasma-sprayed, dicalcium phosphate dihydrate coating from the middle to proximal portion to increase initial fixation and early bone formation. Here, the conformity of the Excia stem to the femoral canal morphology was three-dimensionally assessed using computed tomography. Forty-three patients (45 hips) were examined after primary total hip arthroplasty with a mean follow-up of 27 ± 3 months (range: 24–36 months). Spot welds occurred at zone 2 in 16 hips and at zone 6 in 24 hips, with 83% (20/24 hips) of those occurring within 3 months after surgery. First- (n = 12 hips), second- (n = 32), and third- (n = 1) degree stress shielding were observed. The stem was typically in contact with the cortical bone in the anterolateral mid-portion (100%) and posteromedial distal portions (85%). Stress shielding did not progress, even in cases where the stems were in contact with the distal portions. The anterior flange was in contact with the bone in all cases. The stability of the mid-lateral portion with the dicalcium phosphate dihydrate coating and the anterior flange may have inhibited the progression of stress shielding beyond the second degree.

A comparison between the hydrodynamic characteristics of 3D-printed polymer and etched silicon microchannels

The use of 3D-printing as a microfabrication approach has potential to address contemporary challenges in microfluidic applications including rapid prototyping, complex channel layouts and sealing. The hydrodynamic characteristics of 3D-printed embedded microchannel arrays have been experimentally examined in this paper. Conventional silicon fabrication processes using deep reactive ion etching techniques (DRIE) and wet-etching (KOH) are used as a benchmark for comparison. Rectangular, trapezoidal and circular cross-sectional shapes were considered. The channel arrays were 3D-printed in vertical and horizontal orientations, to examine the influence of print orientation on channel characteristics. These characteristics included cross-sectional area (CSA), surface features and pressure-flow behavior. The etched silicon channels were found to be dimensionally superior, with channel-to-channel variances in CSA of 2.7 and 5.0 % for DRIE and KOH, respectively. The 3D-printed microchannel arrays demonstrated larger variance in CSA (6.6–20 %) with the vertical printing approach yielding greater dimensional conformity than the horizontal. The 3D-printed microchannel arrays had a consistently smaller value of CSA than the nominal, with a noticeable feature of the horizontal approach being additional sidewall roughness leading to shape distortion. The hydrodynamic measurements revealed the etched silicon microchannel arrays to be in agreement with laminar flow theory (within ±10 % for DRIE and KOH, respectively) using the nominal geometric data. 3D-printing in a vertical orientation produced lower fidelity channels with differences of up to 24.5 % between the actual printed geometry and the nominal input. Horizontally printed microchannels were found to have significantly larger differences of up to 103.8 %. Using the measured geometric data, theory provided a reasonable prediction of the hydrodynamic performance of the printed channels. It was concluded that vertical 3D-printing is superior to the horizontal 3D-printing approach for creating microchannel arrays to transport fluids. This finding is useful to practitioners using 3D-printing for microfabrication and rapid turnaround microfluidic applications.

Fabrication of Cu–Zr–Ti thick film metallic glass structure by double metal mask lift-off process

In micro-electro-mechanical systems (MEMS) technology, one of the conventional patterning methods used for metallic thin films is the lift-off process using a photoresist material. However, there is concern regarding the photoresist material generating gas due to the long-term annealing or the high power used in sputter deposition. Thin-film amorphous alloys, such as thin-film metallic glass (TFMG), when used in the device, become crystallized by such heating and outgassing during sputtering. Unlike photoresist material, a metal mask does not generate gas during sputtering. However, a metal mask is subject to deformation by the stress in the sputtered film on the mask. The pattern shape of the TFMG structure can thus collapse due to this mask deformation. Its cross-sectional shape then deviates significantly from a rectangle. We propose a novel lift-off process using a double metal mask for reducing changes in the cross-sectional shape, and maintaining the amorphous nature of the TFMG structure. The characteristic of the double metal mask lift-off process is duplication of the metal mask for restraint of the lower metal mask deformation. Since nearly all of the sputtered material is deposited on the upper metal mask, the material is only minimally deposited onto the lower metal mask. In this work, the double metal mask lift-off process was compared with the conventional lift-off process, and important points for using the double metal mask lift-off process were elucidated. Using the double metal mask lift-off process, a very thick amorphous TFMG structure could be obtained, as compared to the conventional lift-off process. To maintain the rectangular cross-sectional shape of the structure, it was found to be necessary to decrease the height of the double metal mask, as compared to the conventional lift-off process, in anticipation of upper metal mask deformation.

Fuzzy robust nonlinear control approach for electro-hydraulic flight motion simulator

A fuzzy robust nonlinear controller for hydraulic rotary actuators in flight motion simulators is proposed. Compared with other three-order models of hydraulic rotary actuators, the proposed controller based on first-order nonlinear model is more easily applied in practice, whose control law is relatively simple. It not only does not need high-order derivative of desired command, but also does not require the feedback signals of velocity, acceleration and jerk of hydraulic rotary actuators. Another advantage is that it does not rely on any information of friction, inertia force and external disturbing force/torque, which are always difficult to resolve in flight motion simulators. Due to the special composite vane seals of rectangular cross-section and goalpost shape used in hydraulic rotary actuators, the leakage model is more complicated than that of traditional linear hydraulic cylinders. Adaptive multi-input single-output (MISO) fuzzy compensators are introduced to estimate nonlinear uncertain functions about leakage and bulk modulus. Meanwhile, the decomposition of the uncertainties is used to reduce the total number of fuzzy rules. Different from other adaptive fuzzy compensators, a discontinuous projection mapping is employed to guarantee the estimation process to be bounded. Furthermore, with a sufficient number of fuzzy rules, the controller theoretically can guarantee asymptotic tracking performance in the presence of the above uncertainties, which is very important for high-accuracy tracking control of flight motion simulators. Comparative experimental results demonstrate the effectiveness of the proposed algorithm, which can guarantee transient performance and better final accurate tracking in the presence of uncertain nonlinearities and parametric uncertainties.

Evaluation of Step-Shaped Solenoidal Coils for Current-Enhanced SMES Applications

This paper investigates a step-shaped solenoidal coil for current-enhanced superconducting magnetic energy storage (SMES) applications. Three performance evaluation factors related to the coil inductance, critical current and energy storage capacity are extracted to analyze and evaluate the energy storage characteristics of the step-shaped solenoidal coil. As compared to a conventional solenoidal coil with rectangular cross-sectional shape, the step-shaped one could obtain the same energy storage capacity with reduced tape usage amount; it also improves the critical current significantly. To suit various high-current application conditions such as low-voltage direct-current power transmission, four feasible application schemes of sole step-shaped coil, semi-step-shaped coil, sub-step-shaped coil, and sub-semi-step-shaped coil are explored and discussed.

A dimensional comparison between embedded 3D-printed and silicon microchannels

The subject of this paper is the dimensional characterization of embedded microchannel arrays created using contemporary 3D-printing fabrication techniques. Conventional microchannel arrays, fabricated using deep reactive ion etching techniques (DRIE) and wet-etching (KOH), are used as a benchmark for comparison. Rectangular and trapezoidal cross-sectional shapes were investigated. The channel arrays were 3D-printed in vertical and horizontal directions, to examine the influence of print orientation on channel characteristics. The 3D-printed channels were benchmarked against Silicon channels in terms of the following dimensional characteristics: cross-sectional area (CSA), perimeter, and surface profiles. The 3D-printed microchannel arrays demonstrated variances in CSA of 6.6-20% with the vertical printing approach yielding greater dimensional conformity than the horizontal approach. The measured CSA and perimeter of the vertical channels were smaller than the nominal dimensions, while the horizontal channels were larger in both CSA and perimeter due to additional side-wall roughness present throughout the channel length. This side-wall roughness caused significant shape distortion. Surface profile measurements revealed that the base wall roughness was approximately the resolution of current 3D-printers. A spatial periodicity was found along the channel length which appeared at different frequencies for each channel array. This paper concludes that vertical 3D-printing is superior to the horizontal printing approach, in terms of both dimensional fidelity and shape conformity and can be applied in microfluidic device applications.

Influence of operational parameters on the performance of PEMFCs with serpentine flow field channels having different (rectangular and trapezoidal) cross-section shape

The effect of operational parameters on the performance of PEMFCs by using serpentine flow field channels with different (rectangular and trapezoidal) cross-section shape has been investigated. More than cell temperature and pressure, reactant humidification temperature (Tha,c) has a significant influence on the effect of serpentine channels with trapezoidal cross-section on cell performance. The high capability of water removal by serpentine channels with trapezoidal cross-section positively affects the fuel cell performance when the water content in the system is high, as in the case of the reactant humidification temperature higher than cell temperature (Tc). On the contrary, when the water content in the cell is low, as in the case of Tha,c = Tc, the high ability of water removal of serpentine channels with trapezoidal cross-section results in a less effective membrane/cathode hydration. Conversely, the effect of Tha,c on the performance of the cell with serpentine channels with rectangular cross-section is negligible.

J2220102 薄膜金属ガラスCu-Zr-Tiを用いた二軸駆動マイクロミラーデバイスの製作と駆動([J222-01]マイクロ・ナノ材料創成とそのデバイス応用(1))

In Micro Electro Mechanical Systems (MEMS) technology, structure of amorphous alloy thin film is manufactured by sputter deposition and lift-off process. But its thickness is not uniform because lift-off masking material block off. The structure thickness of amorphous alloy thin film is low in the vicinity of lift-off masking material, and its cross-sectional shape is not rectangular. For these problems, we proposed new fabrication method of thick film structure of metallic glass with the sputtering jig, which combines projection surfaces and spacers. As this application, we have successfully fabricated two-axis scanning micro mirror device with thin film metallic glass Cu-Zr-Ti, which have uniform film thickness, rectangular cross-sectional shape and electrical factors. However, the sample was not able to be driven in driving test, because the torsion bar of sample had been broken for Cu-Zr-Ti crystallization. In this paper, we proposed low temperature production process which is not to crystallize Cu-Zr-Ti. And we have succeeded in fabricating and driving the two-axis scanning micro mirror device.