Trapezoidal Channel Research Articles

Experimental Study on Flow and Heat Transfer Characteristics in the Circular-Arc-Shaped Flow Channel

Different parameters of the circular-arc, trapezoidal and equal cross-section-shaped flow channels were analyzed, and the core volume goodness factor was used for the comparison of the three different types of flow channels. During the experiment, the Reynolds number (Re) on the air side ranged from 1200 to 5100. The results showed that the overall heat transfer performance of the three channels in this paper are circular-arc, trapezoidal and equal cross-section in order from good to bad. The overall heat transfer enhancement performance of the circular-arc flow channel is the best, which is 9–26.2% and 3.6–11.8% higher than that of the equal and trapezoidal cross-section flow channels, respectively. This showed that although the divergent flow channel structure reduces the fluid velocity in the flow process, it weakens the convective heat transfer performance in the flow channel. However, this gradually decreasing cross-sectional area improves the downstream heat transfer area and reduces the pressure drop in the flow process, thus promoting the overall heat transfer performance. With the increase in the circular radius (R), both the j and f factors increase, and the highest overall heat transfer performance is obtained at R = 300 mm. The convective heat transfer coefficient increases with the decrease in the inlet height.

Numerical Study on Flow and Heat Transfer Characteristics of Trapezoidal Printed Circuit Heat Exchanger.

Printed circuit heat exchanger (PCHE) is a promising regenerative device in the sCO2 power cycle, with the advantages of a large specific surface area and compact structure. Its tiny and complex flow channel structure brings enhanced heat transfer performance, while increasing pressure drop losses. It is, thus, important to balance heat transfer and flow resistance performances with the consideration of sCO2 as the working agent. Herein, three-dimensional models are built with a full consideration of fluid flow and heat transfer fields. A trapezoidal channel is developed and its thermal–hydraulic performances are compared with the straight, the S-shape, and the zigzag structures. Nusselt numbers and the Fanning friction factors are analyzed with respect to the changes in Reynolds numbers and structure geometric parameters. A sandwiched structure that couples two hot channels with one cold channel is further designed to match the heat transfer capacity and the velocity of sCO2 flows between different sides. Through this novel design, we can reduce the pressure drop by 75% and increase the regenerative efficiency by 5%. This work can serve as a solid reference for the design and applications of PCHEs.

Entropy generation on flow and heat transfer of a reactive MHD Sisko fluid through inclined walls with porous medium

The present research focuses on flow, heat transfer, and entropy production properties in the context of their applications. The use of non-Newtonian materials in biomedical rheological models has garnered considerable attention. Having such practical and potential applications, the current study explores the incompressible, gravity-driven flow of a combustible Sisko liquid down inclined heated permeable walls embedded in a porous medium. The flow is said to be fully developed and modified Darcy’s law is employed to express the porous medium. Such a flow is critical to simulate free-surface flows in trapezoidal reservoirs or channels, and around curved or inclined hulls. The spectral collocation technique with expansions in Chebyshev polynomials was instrumental in achieving numerical solutions. Furthermore, a parametric study is done to explore the behavior of flow, thermal, entropy generation, and Bejan number profiles. The significant outcomes of the current study are that the rise in values of material parameter decreases the velocity, thermal, and entropy generation profiles but increases the Bejan number profile. The upsurge in values of magnetic parameter decreases the velocity and entropy generation profiles but increases the thermal and Bejan number profile. The rise in values of the Frank-Kameneskii parameter increases the Bejan number, thermal, and entropy generation profiles.

Flow and Heat Transfer in a Trapezoidal Cross-Sectional Microchannel Heat Sink Using Nanofluid

In this study, the effects of microchannel number, volume concentration, Reynolds number, and nanofluid type on heat transfer and flow characteristics in the heat sink consisting of trapezoidal microchannels are investigated numerically. Governing equations are solved by assuming three-dimensional, incompressible, steady and laminar flow. The channel material is chosen as copper, and a constant heat flux boundary condition is defined on the upper wall of heat sink. For two different nanofluids, CuO-water and Al2O3-water, investigated parameters are the number of trapezoidal channels (n=3-5) in the heat sink, Reynolds number (Re=200-1500), and volume concentration (=0-4%). Results show that using nanoparticles in base fluid causes to increase both heat transfer coefficient and pressure drop. Heat transfer coefficient increases with increasing number of trapezoidal cross-sectional channel in the heat sink, nanofluid volume concentration and Reynolds number. Pressure drop enhances with enhancing Reynolds number and microchannel number in the heat sink. The nanofluid type and volume concentration do not importantly affect the friction factor. According to the performance index, it is seen that adding CuO nanoparticles in water is convenient, but Al2O3 nanoparticles in water is not appropriate. It is observed that volume concentration for CuO-water nanofluid affects the thermal performance, but volume concentration for Al2O3-water nanofluid does not affect.

Evaluation of the Open Diversion Channel Capacity on Margatiga Dam Construction Project using 6D BIM Analysis

The Margatiga Dam is designed to combine a gravity concrete dam and rockfill with an upright core. In the Margatiga Dam Project, river diversion is carried out in 2 stages. Stage 1 through a trapezoidal open channel with discharge plan of Q10 years approximately 789.10 m3/second and stage 2 with the diversion discharge of Q25 years approximately 976.90 m3/second. During construction, the stage 1 diversion channel is built with a capacity that exceeds the planned design due to the very high water level fluctuations. Moreover, an evaluation is needed regarding the annual plan discharge that passes through stage 1. The Evaluation is based on data from the desk study and 6D BIM analysis. Based on the analysis, the water level is at elevation +19.50. The discharge through the diversion channel on this stage is 884.69 m3/second; this discharge exceeds the planned discharge design for diversion channel stage 1 with an annual Q10 discharge of approximately 789.10 m3/second.

An environmental flow method applied in small and medium-sized mountainous rivers

In small and medium-sized mountainous rivers, there are usually hydropower stations in upper reaches as well as widened and heightened river sections in downstream reaches that are close to settlements. The environmental flow (EF) ensures river connectivity and the survival of aquatic organisms. The Tennant and wetted perimeter methods were used to calculate the minimum EF, and the R2CROSS criteria were used to evaluate the rationality of hydraulic parameters. The result shows that downstream areas with large cross-sections may suffer from shallow water depths, insufficient wetted perimeters, and poor overall connectivity of the water bodies, even under the standard EF discharges. A novel method was proposed to ensure EF and sustain suitable hydraulic conditions. The minimum EF calculated by the Tennant method is adopted as the design flow, and a small trapezoidal trough channel is excavated on the wide riverbed of an artificial river section. The width and depth of the small channel are calculated with Manning's equation. As a study case, this method was applied in the Fenglingang River in Zhejiang Province of China. A trapezoidal groove with a depth of 0.74 m and a bottom width of 0.52 m was excavated in the center of Fenglingang River to sustain EF and maintain river connectivity. This small channel not only prevents the river from cutoff, but also enables the water depth and wetted perimeter to meet the demand of aquatic organisms.

TO ASSESS THE IMPACTS OF HYDRAULIC PARAMETERS OF WATER CHANNEL ON PRE AND POST LINING: A CASE STUDY IN FAISALABAD IRRIGATION ZONE

Water distribution on earth is not constant in its both forms i.e. surface water and groundwater. In many areas, the groundwater availability is changing, making it less available to agriculture for irrigation purposes. Surface water has fresh quality and frequently used for irrigation practices by diverting water from rivers and stream into canals and watercourses. As this scare and valuable resource move into the irrigation structure, a certain part of that water is lost. The losses in the watercourses are much more than those in the main channels and distributaries. So farmer’s face critical shortage of irrigation water issues. In addition to this groundwater pumping is also increasing that is decreasing groundwater table. The conveyance losses in the watercourses can be minimized by applying some lining techniques. To overcome this problem, there is a need to work out of the channel lining that ensures maximum water saving. A detail study has been carried out in the work to calculate the water losses using operational inflow and outflow approach. The losses from the pre and post lining of the canal have been calculated and assess the impacts of hydraulic parameters of the channel after lining the channel to investigate the hydraulic outlet’s performance, seepage water losses from the channel. In this concern, a case study was conducted on channel lining of Faisalabad irrigation zone. The value of the hydraulic parameters (cross-sectional area, flow velocity, wetted perimeters, hydraulic radius, bed slope, and side slope) for the trapezoidal channel have been investigated in this study. For statistical analysis a generalized linear model (exponential) R-language were used in the study. The value of water losses in pre and post lining of three distributary Lagar Disty, Nasrana Disty and Sehti Wala Minor was 2.238, 1.805, 3.008 m3/s/106m2 and 0.385, 0.486, 0.644 m3/s/106m2 respectively. The lowest losses were found in lined channel of LCC (East) Lagar Disty and the highest losses were found in the LCC (West) of Sehti Wala Minor. In this investigation work, the saving of water through lining the channel is also authentic numerically evaluated and authenticated.

Investigation of the Hydraulic Characteristics of Flap Gates at the End of Trapezoidal Channels

Investigation of the Hydraulic Characteristics of Flap Gates at the End of Trapezoidal Channels

On the micro-PIV accuracy and reliability utilizing non-Gaussian particle images

Optical investigations of the dynamics of concentrated suspensions, such as in blood flows (Fitzgibbon et al. in Biophys J 108(10):2601–2608, 2015. http://doi/org/10.1016/j.bpj.2015.04.013) or slurry flows (Li et al. in Ocean Eng 163(October 2017):691–705, 2018. http://doi/org/10.1016/j.oceaneng.2018.06.046), are challenging due to reduced optical accessibility. Furthermore, the suspension particle image size can strongly deviate from the optimal particle image size for PIV measurements. Optical accessibility can be achieved by refractive index matching of surface labelled suspension particles. This results in particle images that are transparent in the particle image centre, but fluoresce at the particle image rim, resulting in ring-shaped particle images. In the present study, the influence of the particle image size on the cross-correlation result of such ring-shaped particle images is compared with Gaussian and plateau-shaped particle images. Particles of Gaussian image shape result from fully labelled particles with small image diameters and are commonly used in PIV measurements. Such particles are also utilized for the determination of the continuous phase velocities in the experimental part of the present study. With increasing image diameter, fully labelled particles are observed to assume plateau-shaped particle images. Monte Carlo simulations of synthetically generated images show that ring-shaped particle images have a superior behaviour, i.e. they assume a reduced displacement estimation error for noisy as well as for noise-free image data, compared to Gaussian and plateau-shaped particle images. This is also true for large particle image diameters when particle images are intersected at interrogation window borders or when different values of nonzero particle image displacements are considered. The detectability is similar for all three particle image shapes as long as particles do not intersect with the interrogation window border. Interestingly, for intersected particles of large image diameter, ring-shaped particle images show a slightly improved detectability compared to particle images of Gaussian and plateau shape. Furthermore, the detectability is insensitive against a nonzero particle image displacement. The usage of refractive index matched, ring-shaped particle images results in a good optical accessibility of the suspension. This allows to perform simultaneous cross-correlation evaluations on large ring-shaped particle images and fluid tracers with Gaussian particle images that are two orders of magnitude smaller compared to suspension particle images. Velocity measurements are taken on a suspension containing 5 vol% surface labelled, refractive index matched 60 upmu hbox {m} polymethylmethacrylate (PMMA) particles. Simultaneously, upmuPIV measurements of the carrier liquid flow are performed utilizing 1.19 upmu text {m} fluorescent polystyrene (PS) particles. Measurement results reveal a parabolic shape of the velocity profiles of both phases with a mean slip velocity of 7.4% at the position of maximum streamwise velocity in a 580 upmu text {m} high trapezoidal channel. An error analysis confirms the presence of these slip velocities within a 68.5% confidence interval. A measurement uncertainty in the order of magnitude of {mathcal {O}}(10^{-1} mathrm{px}) is reached for both fluid tracers and suspension particles. Overall, the present study demonstrates theoretically and experimentally that the usage of suspension particles with ring-shaped images is superior compared to Gaussian and plateau-shaped particle images of the same size. Additionally, the present study demonstrates that the usage of ring-shaped particle images allows to investigate suspension bulk dynamics by measuring velocity fields of both the suspended and the continuous phase simultaneously and with an overall uncertainty that is in the same order of magnitude as for standard upmuPIV measurements.Graphic abstract

Thermal Performance of V-Shaped and X-Shaped Ribs in Trapezoidal Cooling Channels

Convective heat transfer enhancement using rib turbulators is effective for turbine blade internal cooling. Detailed heat transfer measurement of X-shaped ribs in a trapezoidal cooling channel was experimentally conducted using infrared thermography. The novel X-shaped ribs were designed by combining two V-shaped ribs, and more secondary flows generated by the X rib delivered higher heat transfer enhancement. The Reynolds numbers in this study were 10,000, 20,000, and 30,000. These ribs were installed on two opposite walls of a trapezoidal channel in a staggered arrangement. The rib pitch-to-height ratios were 10 and 20, and the rib height-to-hydraulic diameter ratio was 0.128. Results indicated that higher heat transfer distribution was observed in the vicinity of the shorter base in the trapezoidal channel. The full X-shaped ribs and the V-shaped ribs demonstrated the highest Nusselt number ratios among all the cases. Although full X-shaped ribs contributed to higher heat transfer improvement due to intensified secondary flows, they also caused significant pressure loss. Therefore, the cutback X-shaped ribs were proposed by removing a segment in the rib at either upstream or downstream region. Consequently, the upstream cutback X-shaped rib and the V-shaped rib produced the highest thermal performance in this trapezoidal channel.

Comparative Study on Thermos-Hydraulic Performance of Different Cross Section Shapes of Microchannels with Supercritical CO2 Fluid

The influence of the cross section shape of microchannels on the thermos-hydraulic performance of the supercritical CO2 fluid is an important issue in the design of industrial compact heat exchangers, but few studies have been conducted about this issue. In this paper, comparative studies of the flow and heat transfer performance of SCO2 fluid in horizontal microchannels with circular, semicircular, rectangle, and trapezoidal cross sections were conducted numerically. The comparison is based on the same hydraulic diameter and length for all channel types and is carried out under the same mass flux, outlet pressure, and wall heat flux. The fluid bulk temperature in this analysis ranges from 285 K to 375 K, which covers the pseudocritical point of SCO2. The results show that the circular channel has the highest average heat convection coefficient, while the trapezoidal channel has the worst convective heat transfer performance under the same hydraulic diameter and boundary conditions. The results also indicate that the effect of cross section shape on the heat convection coefficient is significantly greater than that on the channel pressure drop, and the existence of the corner region in the cross section, especially the acute angle, will weaken the heat transfer performance.

Numerical investigation on the behavior of combining open-channel flow

Open-channel flow is known as fluid flow with an open atmospheric surface. It has become an important issue especially when measuring the flow rate and depth of water as part of environmental management schemes. Many efforts have been made by the previous researchers to investigate the behavior of water flow. However, most studies on water flow have only been carried out in a straight prismatic main channel, either in a trapezoidal and rectangular type of channel section with lateral branch of angle of 90<sup>o</sup>. In this study, the general equations of combining open-channel flow for trapezoidal and V-shaped channels are modified in the form of nonlinear polynomial equations. The proposed equations are solved using Newton-Raphson procedure to determine the upstream flow depth. All the computations and analysis of the behavior of water flow depth influenced by Froude number and flow rate ratio are performed using graphical user interface, which is designed in MATLAB software. Comparative analysis shows that the modified equations agree well with the experimental data as reported in the literature. The trapezoidal channel demonstrates the highest value of flow depth as the Froude number and flow rate ratio increase; thus, it has potential to avoid water overflow.

Numerical Analysis of the Effect of Trapezoidal Baffles Inside Fuel and Air Channels on the Performance of a Planar-Type Solid Oxide Fuel Cell

Abstract This paper investigates the effect of trapezoidal baffles inside a planar-type solid oxide fuel cell. To achieve the objective, four cases are proposed: (1) simple planar geometry as a base case, (2) trapezoidal baffles inside the fuel channel, (3) trapezoidal baffles inside the air channel, and (4) trapezoidal baffles in both fuel and air channels. The height of the trapezoidal baffles inside the channels of the solid oxide fuel cell increases along the direction of the fluid flow. The numerical investigation is based on a three-dimensional computational fluid dynamics (CFD) model that takes into account the phenomenon of mass transfer, heat transfer, species transport, and electrochemical reactions. A detailed comparison of the performance between the four cases of the fuel cell is provided in terms of power density, fluid flow, species concentration, temperature distributions, and electric fields at a variable current density and a fixed power density of 3000 W/m2. The results show that the power density, the velocity, the availability of the hydrogen and oxygen species on the electrodes-electrolyte interfaces increases for case 2, case 3, and case 4, respectively, in comparison to case 1. Finally, the average temperature of the electrode–electrolyte interface is reduced with the baffles, and it is concluded that the configuration with baffles inside the air channel (case 3) shows better results in terms of the increment of the power density and the decrement of the average temperature.

ENERGY, ENTROPY AND EXERGY ANALYSES OF HYBRID NANOFLUID FLOW IN A TRAPEZOIDAL CHANNEL

This study presents energy, entropy, and exergy analyses of Al2O3-Cu/water hybrid nanofluid flow in a trapezoidal cross-sectioned channel under a turbulent regime (104<Re<105) for the first time. Understanding the main source of the entropy generation along the channel, also obtaining the total entropy variation of hybrid nanofluid comparing to single nanofluids (Al2O3/water and Cu/water) and base fluid is pursued objective. In other to perform these aforementioned analyses, a realistic model, in which all formulas are derived, is developed and thermodynamic concepts such as exergy efficiency and exergy destruction for hybrid nanofluid flow in a non-circular cross-sectioned channel are discussed for the first time. Results obtaining from the analyses of both hybrid and single nanofluids have been compared and discussed for volumetric concentrations of 1.0% and 2.0%. As a result, it is obtained that 2.0% volume concentration hybrid nanofluid offers the best convective heat transfer performance with 34% enhancement and best exergetic performance. Furthermore, hybrid nanofluid has the lowest entropy generation value.

Ridge-channel AlGaN/GaN normally-off high-electron mobility transistor based on epitaxial lateral overgrowth

A ridge-channel AlGaN/GaN high-electron mobility transistor (HEMT) utilizing selective-area growth and epitaxial lateral overgrowth (ELO) technique is proposed in this work to achieve high-performance normally-off devices. It has a c-plane platform for the source and the drain contacts, and sidewalls of lattice plane for the gate contact. The sidewalls have characteristics of weak polarization and thin barrier, which are advantageous for realizing normally-off operation. Two ridge HEMTs with triangular and trapezoid channel are designed. Theoretical simulation demonstrates a threshold voltage of 0.03 V for the sidewall channel with reduced polarization and barrier thickness, and a threshold voltage of 1.1–1.3 V for the ridge HEMTs assuming no polarization charge in sidewall channel. The ridge-channel device also exhibits high saturation drain current. The ELO-based ridge-channel opens a new way to achieve normally-off AlGaN/GaN HEMT.

Discharge estimation for trapezoidal open channels applying fuzzy transformation method to a flow equation

Abstract The aim of this paper is to implement fuzzy logic theory in order to estimate the discharge for open channels, which is a well-known physical problem affected by many factors. The problem can be solved by the Manning equation but the parameters present uncertainties as to their true-real values. Especially, the Manning n roughness coefficient, which is an empirically derived coefficient, presents quite a high variation for different substrates. With the help of fuzzy logic and utilizing a fuzzy transformation method, it is possible to include the uncertainties of the problem in the calculation process. In this case, it is feasible to estimate the discharge, putting more emphasis on different uncertainty rates of the Manning roughness coefficient, while the rest of the parameters remain with constant or zero uncertainty level. By taking different α-cut levels, it is shown that the methodology gives realistic and reliable results, presenting with great accuracy the variations of the water discharge for trapezoidal open channels. In this way, a possible underestimation or overestimation of the actual physical condition is avoided, by helping engineers and researchers to obtain a more comprehensive view of the real physical conditions, and thus make better management plans.

Numerical investigation of mixed convection of nanofluid flow in a trapezoidal channel with different aspect ratios in the presence of porous medium

In this study, a numerical investigation of mixed convection of nanofluid flow in a trapezoidal channel with two different aspect ratios of 0.3 and 0.5 with the presence of porous media is investigated. The present study was based on Ri = 0.1, 1, and 10 and used water-Al2O3 nanofluid in ϕ= 0–3% as the working fluid. Also, metal foam made of aluminum alloy in Darcy numbers 10−2, 10−3, and 10−4 is used for the porous medium, and the thermal equilibrium model is used to simulate the porous medium. The finite volume method and the single-phase model are applied. Nusselt number diagrams for different porous heights are obtained in different Darcy and Richardson numbers for the lower and upper walls of the channel. The results show that with the decrease in Richardson number, the local and NuAveincreases. In addition, a fully filled channel with a porous medium does not yield satisfactory results for the lower wall, but the results are desirable for the upper wall. The highest heat transfer occurs in the 90% porous height range. Aspect ratio of 0.3 predicts more heat transfer than aspect ratio of 0.5. As the height of the porous medium increases, the NuAve goes through an upward-downward trend, with two heights of 10% and 90% of the turning points in this upward and downward trend. As the percentage of porous height increases, the Darcy number changes on the heat transfer rate exhibit unique behaviors.

How soil texture, channel shape and cross‐sectional area affect moisture dynamics and water loss in irrigation channels

AbstractTo enhance the utilization efficiency of farmland irrigation water and reduce the leakage of water conveyance channels, the leakage process of channels was simulated dynamically. The simulated results were compared with data measured in laboratory experiments, and the performance of the model was evaluated. The results indicated that the simulated values of the model were consistent with the observation values, and the R2 values varied between 0.91 and 0.99. In addition, based on the laboratory experiments, a water supply system (Mariotte bottles) and soil box were built using plexiglass. Three influencing factors, namely, the channel form, soil texture and channel cross‐sectional area, were varied to observe and calculate the resulting cumulative infiltration amount, infiltration rate and wetting front migration distance. HYDRUS‐3D software was used to solve the three‐dimensional soil water movement equation under different initial conditions. The results demonstrated that the U‐shaped channel was more effective than the trapezoidal channel in increasing the utilization efficiency of the water resources. A U‐shaped channel with a small channel cross‐sectional area should be adopted and the soil particle size should be prioritized in the construction of water conveyance channels for farmlands. The simulation results were in agreement with the observed results, which indicates that HYDRUS‐3D is a reliable tool that can accurately simulate the soil moisture movement in water conveyance channels. The research results can provide a reference for the design and operation of farmland irrigation systems.

Featured Collection Introduction: National Water Model III

Featured Collection Introduction: National Water Model III

Assessment of Artificial Intelligence Models for Estimating Lengths of Gradually Varied Flow Profiles

The study of water surface profiles is beneficial to various applications in water resources management. In this study, two artificial intelligence (AI) models named the artificial neural network (ANN) and genetic programming (GP) were employed to estimate the length of six steady GVF profiles for the first time. The AI models were trained using a database consisting of 5154 dimensionless cases. A comparison was carried out to assess the performances of the AI techniques for estimating lengths of 330 GVF profiles in both mild and steep slopes in trapezoidal channels. The corresponding GVF lengths were also calculated by 1-step, 3-step, and 5-step direct step methods for comparison purposes. Based on six metrics used for the comparative analysis, GP and the ANN improve five out of six metrics computed by the 1-step direct step method for both mild and steep slopes. Moreover, GP enhanced GVF lengths estimated by the 3-step direct step method based on three out of six accuracy indices when the channel slope is higher and lower than the critical slope. Additionally, the performances of the AI techniques were also investigated depending on comparing the water depth of each case and the corresponding normal and critical grade lines. Furthermore, the results show that the more the number of subreaches considered in the direct method, the better the results will be achieved with the compensation of much more computational efforts. The achieved improvements can be used in further studies to improve modeling water surface profiles in channel networks and hydraulic structure designs.