Trapezoidal Cross-section Research Articles

Channel cross section effect on heat transfer performance of oblique finned microchannel heat sink

In the present work, the effect of channel cross section on the heat transfer performance of an oblique finned micro-channel heat sink was investigated. Water and Al2O3/water nanofluid of volume fraction 0.25% were used as a coolant. The oblique finned microchannels are designed with three channel cross-sections namely square, semicircle and trapezoidal. The primary work of this paper is to study the heat transfer and hydrodynamic characteristics in the oblique finned microchannel. The experimental setup and procedure are validated using water as coolant in a micro-channel heat sink. Heat transfer and flow characteristics are examined for three cross-sections of varying mass flux. The trapezoidal channel cross-section increases the considerable heat transfer rate improvement for both water and nanofluid by 3.133% and 5.878% compared to square and semicircle cross section. Also, the pressure drop is higher in the trapezoidal cross-section over the square and semicircle cross section. This is due to increase in friction loss of trapezoidal cross section. The results indicate that trapezoidal cross-section oblique finned micro-channel is more suitable for heat transfer in the electronic cooling application.

Gland Seal with Soft Packing of Trapezoidal Cross Section and Inside Seating of the Pressure Flange

Results of an analysis of three types of gland seals with soft packing and inside seating of the pressure flange are presented. The packing had a cylindrical or trapezoidal cross section with standard or tapered o-ring gaskets. It was shown that gland seals with packing o-ring gaskets that were pressed beforehand in special matrices or directly in the gland body were most effective.

Enhancement of vorticity reduction by floor splitter in pump sump to improve pump efficiency

The effort to reduce swirls and vortices in pump intake which originated from high vorticity regions in the pumped fluid has been a major task in pump station design because it affects the pump performance and ultimately the energy consumption. In this paper, a numerical study on the influence of cross sectional shape of floor splitter on the effectiveness of vorticity reduction in pump intake was carried out with the aid of computational fluid dynamics (CFD) software. A simulation model setup consisting of a rectangular channel and a column pipe positioned at the downstream of the channel was developed with the incorporation of Reynolds-Averaged Navier–Stokes (RANS) k-∊ turbulence model. The model was tested with the installation of floor splitter at the bottom of the channel directly beneath the column pipe. Four floor splitters with different cross sectional shapes were examined in the simulation. The results showed that the use of floor splitter is effective in reducing flow vorticity. Two of the floor splitter types, which have square and trapezoidal cross sections, produced results similar to the findings in the experiment by Kang et al. (2014) and thus gives some certainties to simulation. Triangular cross section, which was derived from the trapezoidal cross section, exhibited the best overall performance in vortex reduction. On the other hand, another shape derived from the trapezoid, which was a trapezoidal cross section with rounded edges, displayed superior vortex suppression than triangular cross section near pipe entrance but limited to areas without interference from counter flows such as the flow near the back wall. Triangular cross section displayed better performance in the region with counter flows thanks to its sharp apex. These results are helpful to determine our ongoing experimental study as well as actual site installation.

Impact of Trapezoidal Cross Section on Polarization Sensitivity of SNSPD With Ultranarrow Nanowire

The superconducting nanowire single-photon detector (SNSPD) is inherently sensitive to polarization due to its anisotropic nanowire structure. We studied the polarization sensitivity of SNSPDs with ultranarrow nanowires (20–40 nm wide) by simulation and fabricated SNSPDs with 30-nm-wide nanowires. The SNSPD has a maximum system detection efficiency of 20% and a polarization extinction ratio (PER) of 18. The deviation of the PER between the experiment and the simulation can be explained by a trapezoidal cross section of the nanowire.

Comparison of Liquid Water Dynamics in Bent Gas Channels of a Polymer Electrolyte Membrane Fuel Cell with Different Channel Cross Sections in a Channel Flooding Situation

The transport characteristics of water slugs in a bent gas channel of a polymer electrolyte membrane (PEM) fuel cell are numerically studied using the volume of fluid (VOF) method. To investigate the effects of channel cross-sectional shape in a channel flooding situation, the gas channels (GCs) with one rectangular and two trapezoidal cross sections are compared. Parametric studies are also conducted to evaluate the effects of the contact angle of the top and side walls, the contact angle of the gas diffusion layer (GDL) surface, and the air inlet velocity. Considering both of the water volume fraction (WVF) and GDL water coverage ratio (WCR), the trapezoidal channel with open angles of 60 degrees provides the most favorable performance in a channel flooding condition. Among all the top and side wall contact angles considered, the hydrophobic contact angle of 120 degrees shows the best results. Among the three GDL contact angles of 90, 110 and 140 degrees, the hydrophobic GDL contact angle of 140 degrees provides the most favorable water removal characteristics in a channel flooding situation. For all cross-sectional shapes, the water removal rate increases and the liquid water interface shows more complex patterns as the air inlet velocity increases.

Efficiency of the Longitudinal Fins of Trapezoidal Profile in Motion

The present work is concerned with the heat transfer enhancement and efficiency in the moving longitudinal fins having trapezoidal cross sections. Finding analytical solutions is targeted so that efficiency of trapezoidal fins over the known fin sections can be comparatively searched. It is shown that certain type of trapezoidal fins may have advantageous fin design features. The formulas given in this paper may also be used as benchmark analysis.

INVESTIGATION OF INFLUENCE OF SEPARATOR MAGNETIC SYSTEM CONFIGURATION WITH PERMANENT MAGNETS ON MAGNETIC FIELD DISTRIBUTION IN WORKING AREA

Purpose. To carry out research the influence of magnetic system configuration (shape and size of the permanent magnets) on magnetic field spatial distribution in working area of new structure design magnetic separator with active front surface by numerical methods. Methodology. We have applied the magnetic field numerical simulation for permanent magnets system in absence of electrical current in magnetostatic approximation. We have solved the problem by using finite element method. Research of permanent magnets cross-sectional shape influence made in the two-dimensional formulation using software package Elcut. Research of magnetic field induction spatial (three-dimensional) distribution in new construction magnetic separator working area is conducted using software package COMSOL Multiphysics 3.5a. Results. Magnetic flux density maximum in the immediate vicinity of permanent magnet surface provide magnets with spherical and trapezoidal cross-sectional shape. At a distance from pole surface, where the separation process working, magnetic field density produced by trapezoidal and spherical cross section magnets, substantially lower in comparison with rectangular magnets. Rectangular and rectangular with beveled corners cross-section shape magnets create approximately same magnetic field intensity not significantly different in weight. Analysis of the spatial distribution of magnetic field induction in the working area of a new construction magnetic separator has shown that a strong magnetic field with high magnetic flux density gradient value is formed in the interpolar working volume. Originality. For the first time research of magnetic flux density distribution in working area of new construction magnetic separator is conducted. Developed device feature is complex spatial distribution of magnetic field. Practical value. Results of research can be used for selection of rational parameters of separator magnetic system. Received results also can be used for determination of separator force characteristics.

Numerical simulation on convective thermal loss of a cavity receiver in a solar tower power plant

A numerical simulation model is employed to evaluate the convective thermal loss of a one-point focusing central cavity receiver with a trapezoidal cross-section cubic structure in a solar tower power plant. Due to being laid at the top of the solar tower with a height of several decameters, the cavity receiver is suffering from low temperature and cold wind from its special ambient environment. Consequently, the effect of the natural convection on its thermal performance could not be neglected while the one of the turbulent flow field inside the cavity receiver entering from its aperture is comparably significant. Therefore, a three-dimensional turbulent flow model is established to calculate mixed convection heat loss which is usually used to evaluate the thermal performance. Under the certain wall temperature condition inside the receiver, the receiver laid inclination, the wind incidence angle and wind speed around the receiver are particularly considered in the proposed convection heat loss model. The simulation results show that the trend of mixed convection heat loss changing with the laid inclination is similar to that of natural convection when wind speed is relatively low. The maximum mixed convection heat loss happened in the case of wind direction α=90°, and minimum at α=0°. Under some certain windy condition, mixed convection heat loss may be lower than the natural convection value. In order to explain the variation of mixed convection heat loss, the profiles of flow velocity vector field and the temperature contours around the receiver are illustrated accordingly for each case. Furthermore, the flow pattern and turbulent vortex for the flow field are also presented. Finally, a heat transfer coefficient correlation considering receiver laid inclinations, wind speed and wind incidence angle was proposed to estimate the convection heat loss.

Influence of the coupling matrix B on the interactive buckling of FML-FGM columns with closed cross-sections under axial compression

The study of the coupled instabilities of thin-walled columns with trapezoidal and square cross-sections, which are made of Functionally Graded Materials (FGMs) and Fibre Metal Laminates (FMLs) is presented in the paper. It is assumed that each column wall is made of a stack of nine FML layers and/or a single FGM (Al-TiC) and/or ceramics (TiC). The GLARE 3 type FML part was made of an alternate sequence of Al 2024-T3 and even GFR prepreg layers where aluminium was always the outer layer. In the case of the FGM layer, volume fractions of ceramics and the metal distribution throughout the layer thickness are described by a simple power law. It is assumed that the columns are subjected to axial compression and simple supported at their loaded edges. All constituent materials obey Hooke’s law. The effect of temperature influence is neglected. To determined governing equations of considered FML-FGM structures the classical laminate plate theory (CLPT) is used. The solution to the problem of the non-linear buckling of hybrid thin-walled structure is based on the Koiter’s theory. An interaction of the global buckling mode with two local buckling modes is taken into account. In order to derive the equilibrium equations of FML-FGM profiles, the full Green’s strain tensor and the second Piola-Kirchhoff’s stress tensor have been adapted. The presented solution seems to be especially important as the authors have not found no earlier studies on the coupled buckling of thin-walled FML-FGM structures with closed cross-sections.

Effect of Air and Water Inlet Velocities on Liquid Water Droplet Behaviors in a PEMFC Trapezoidal Gas Channel

In a PEMFC gas channel with a trapezoidal cross-section, the effect of air and water inlet velocities on water removal characteristics is numerically studied via the volume of fluid(VOF) method. When the channel wall contact angle is 60 degrees, the air inlet velocities higher than 2.5 m/s are advantageous to obtain lower GDL surface water coverage ratio(WCR). The WCR increases as the wall contact angle increases to 90 or 120 degrees due to the relatively lower surface tension force. In overall, WCR decreases as the air inlet velocity increases and WCR increases as the water inlet velocity increases.

Transitional flow of non-Newtonian fluids in open channels of different cross-sectional shapes

This work investigated the prediction of transitional flow of non-Newtonian fluids in open channels. A number of empirical methods are available in the literature, which purport to predict the frictional losses associated with the transitional flow in open channels of different shapes, but with no conclusive guidelines. Therefore, a large experimental database for non-Newtonian flow in flumes of rectangular, triangular, semi-circular and trapezoidal cross-sections at slopes varying from 1° to 5° was used to achieve this objective. Aqueous suspensions of bentonite and kaolin clay and solutions of carboxymethyl cellulose (CMC) of various concentrations were used to span a wide range of rheological characteristics. The steady shear stress–shear rate behaviour of each test fluid was measured using in-line tube viscometry. In this work, predictive models of transitional flow in triangular, semi-circular and trapezoidal channels, as well as a combined model applicable to all four channels of shapes were established. The method used to establish these models is based on the Haldenwang [19, 22] model. Based on a detailed comparison of the extensive experimental data with model velocities was conducted for power law, Bingham plastic and yield shear-thinning fluids, it was found that the combined model adequately predicted transition for all shapes tested in this work with an acceptable level of reliability.

A cost model with several hydraulic constraints for optimizing in practice a trapezoidal cross section

Open channel structures are essential to infrastructure networks and expensive to manufacture. Optimizing the design of channel structures can reduce the total cost of a channel's length, including costs of lining, earthwork, and water lost through seepage and evaporation. The present research aims to present various optimization models towards the design of trapezoidal channel cross section. First, a general resistance equation was applied as a constraint. Next, a genetic algorithm (GA) was used to determine the optimal geometry of a trapezoidal channel section based on several parameters, i.e., depth, bottom width, and side slope. Eight different models were proposed and evaluated with no other constraint besides financial cost as well as with a normal depth, flow velocity, Froude number, top width, and by ignoring the cost of seepage. Numerical outcomes obtained by the GA are compared to previous studies in order to determine the most efficient model. Results from a single application indicate that the restriction of depth, velocity, and Froude number can increase the total cost, while restriction of the top width can decrease the cost of the construction. Also, the solution for various example problems incorporating different discharge values and bed slopes caused increase and decrease in cost, respectively.

Numerical study of the effect of channel geometry on the performance of Magnetohydrodynamic micro pump

Magnetohydrodynamic micropumps received more attention due to its applications in pumping of biological and chemical specimens, such as blood, DNA, and saline buffers. In this paper the MHD flow in different cross section microchannels has been numerically investigated with different electromagnetic boundary conditions. Square, rectangular, circular and trapezoidal cross section microchannels have been used to explore the effect of channel geometry on the MHD micropump operation. The study covers a selected range of applied electric currents and magnetic flux to show their effects on MHD flow. Thermal characteristics of MHD flow have been also studied by calculation the temperature distribution through MHD micropump region. The results obtained show a considerable effect of channel geometry, the applied electric and magnetic fields on the velocity and flow rate. The circular cross section micropump gave higher velocity and flow rate compared with other cross sections, and there is a slight increase in temperature due to small effect of Joule heating.

Optimal isosceles trapezoid cross section of laterally loaded piles based on friction soil arching

The paper presents a novel analytical solution to determine an optimal isosceles trapezoid cross-section of stabilizing piles subjected to the lateral load. In view of the pile-soil interaction mechanical analysis on the friction soil arching between the adjacent stabilizing piles, a general mechanical model for analyzing the behavior of the laterally loaded stabilizing piles with isosceles trapezoid cross-section is put forward. The reasonable net pile spacing expression for all kinds of isosceles trapezoid section piles is established via the analytical deduction, and it indicates that there is a positive relationship between the reasonable net pile spacing and gradient of pile sidewall. In consideration of the strength failure possibility in the apex of friction soil arching, the complete expressions of both the gradient of pile sidewall and corresponding reasonable net pile spacing of stabilizing piles can be established. The case study of Jinle landslide verifies that the reasonable pile spacing obtained by the presented model is slightly greater than that of the conventional design scheme, which shows that the stabilizing piles with optimal isosceles trapezoid cross-section can results in reducing the investment of the whole stabilizing piles.

Numerical Analysis of Liquid Water Removal Characteristics in a PEMFC Gas Channel with Trapezoidal Cross-section

The water removal characteristics in a PEMFC trapezoidal gas channel are investigated with the volume of fluid (VOF) method. For the case of wall contact angle of 60 degree, liquid water attaches on the top wall and moves toward the exit. In contrast, liquid water moves along the channel side corner or GDL surface irregularly for the higher wall contact angles. The hydrophillic wall contact angle of 60 degrees provides more favorable diffusion of reactants to cathode reaction sites as the GDL surface water coverage ratio approaches zero even if the water flow rate increases.

25 nm Single-Crystal Silicon Nanowires Fabricated by Anisotropic Wet Etching.

We report a top-down method for fabricating ultra-high aspect ratio single-crystal silicon nanowires. The fabrication method is based on the standard photolithography technique and anisotropic wet etching of the single-crystal silicon in KOH solution. SiO₂ mask nanolines used for patterning single-crystal silicon nanowires are formed by the undercut etching of thin SiO₂ layer in buffered hydrofluoric solution. The minimum width of the SiO₂ mask nanolines are 50 nm. The length of SiO₂ mask nanolines is 2 cm. The single-crystal silicon nanowires have been successfully transferred from the SiO₂ mask nanolines by KOH anisotropic wet-chemical etching. The minimum width of the silicon nanowire has obtained to be 25 nm. The fabricated single-crystal silicon nanowires have trapezoidal and triangular cross sections, which are useful for applications in nanoelectronic and nanophotonic elements.

Designing an Optimized Novel Femoral Stem

After total hip arthroplasty, there would be some problems for the patients. Implant loosening is one of the significant problems which results in thigh pain and even revision surgery. Difference between Young's modulus of bone-metal is the cause of stress shielding, atrophy, and subsequent implant loosening. In this paper, femoral stem stiffness is reduced by novel biomechanical and biomaterial design which includes using proper design parameters, coating it with porous surface, and modeling the sketch by the software. Parametric design of femoral stem is done on the basis of clinical reports. Optimized model for femoral stem is proposed. Curved tapered stem with trapezoidal cross-section and particular neck and offset is designed. Fully porous surface is suggested. Moreover, Designed femoral stem analysis showed the Ti6Al4V stem which is covered with layer of 1.5 mm in thickness and 50% of porosity is as stiff as 77 GPa that is 30% less than the stem without any porosity. Porous surface of designed stem makes it fix biologically; thus, prosthesis loosening probability decreases. By optimizing femoral stem geometry (size and shape) and also making a porous surface, which had an intermediate stiffness of bone and implant, a more efficient hip joint prosthesis with more durability fixation was achieved due to better stress transmission from implant to the bone.

A catastrophic debris flow in the Wenchuan Earthquake area, July 2013: characteristics, formation, and risk reduction

In the Wenchuan Earthquake area, many co-seismic landslides formed blocking-dams in debris flow channels. This blocking and bursting of landslide dams amplifies the debris flow scale and results in severe catastrophes. The catastrophic debris flow that occurred in Qipan gully (Wenchuan, Southwest China) on July 11, 2013 was caused by intense rainfall and upstream cascading bursting of landslide dams. To gain an understanding of the processes of dam bursting and subsequent debris flow scale amplification effect, we attempted to estimate the bursting debris flow peak discharges along the main gully and analyzed the scale amplification process. The results showed that the antecedent and triggering rainfalls for 11 July debris flow event were 88.0 mm and 21.6 mm, respectively. The event highlights the fact that lower rainfall intensity can trigger debris flows after the earthquake. Calculations of the debris flow peak discharge showed that the peak discharges after the dams-bursting were 1.17–1.69 times greater than the upstream peak discharge. The peak discharge at the gully outlet reached 2553 m3/s which was amplified by 4.76 times in comparison with the initial peak discharge in the upstream. To mitigate debris flow disasters, a new drainage channel with a trapezoidal V-shaped cross section was proposed. The characteristic lengths (h1 and h2) under optimal hydraulic conditions were calculated as 4.50 m and 0.90 m, respectively.

TECHNICAL AND MORPHOLOGICAL MODEL OF CHALCOLITHIC CHOPPING TOOLS OF THE RUSSIAN-KARELIAN TYPE FROM KARELIA AND THE UPPER VOLGA REGION

The article addresses chopping tools (axes, adzes, and gouges) from the Chalcolithic peatbog sites at Sakhtysh, Karelia, associated with the Volosovo culture. This group was first separated on the basis of technological and typological criteria, and their connection with the Volosovo component of these culturally and temporally heterogeneous sites was later verified with a detailed spatial analysis. The main traits of the Volosovo tools match those of the Russian-Karelian type, found in Russian Karelia at Chalcolithic sites with Asbestos and Porous Ware. The analysis of preforms suggests that their production followed a certain technological and typological model. The basic type of tool had a trapezoid or triangular cross-section, which was formed at the knapping stage and could then be transformed into a half-oval. Knapping was done with the punch technique, also evidenced by axes with a tetrahedral cross-section, widespread in the Neolithic of northern, central, and eastern Europe. The Volosovo chopping tools at sites with asbestos ware in the Upper Volga region and Karelia, then, follow the same single technological tradition. Its distribution area cannot be delimited thus far, but it could extend beyond that of the axes with a tetrahedral cross-section.

Prediction of the discharges within exponential and generalized trapezoidal channel cross-sections using three velocity points

A free over-fall can be used as a flow metering hydraulic structure with a single depth measurement of the end. Due to that, theoretical and experimental research has been undertaken on free over-falls with various approaches for different cross-sectional shapes. This paper presents a new and relatively simple theoretical approach for computing the end depth ratio (EDR) and the end depth discharge (EDD) relationships for exponential and generalized trapezoidal channel cross-sections at free over-falls for sub-critical flow regime. The exponential channel is a general channel cross-section which is defined mathematically with a single exponential equation where five widely known prismatic shapes can be generated (rectangular, parabolic, semi-parabolic, triangular and semi-triangular). Similarly, the generalized trapezoidal channel is a geometric shape that is defined mathematically with the 2nd degree equation where seven widely known prismatic channel cross-sectional shapes can be generated (rectangular, triangular, semi-triangular, trapezoidal, semi-trapezoidal, inverted triangular (∆) and semi-inverted triangular). This suggested theoretical approach uses three velocity points at the end (brink) section and the continuity equation to obtain the EDR. To verify the proposed EDR and EDD relationships, relevant experimental and theoretical study results were gathered and statistically examined through the percentage difference and the correlation coefficient (R2). The computed results show very close agreements with the earlier works. For engineers in practice, simple equations are also generated to estimate the direct discharges (Q) using the end depth (ye) for each of the above mentioned channel cross-sections.