Triangular Channels Research Articles

Topological effects on separation of alkane isomers in metal−organic frameworks

Polymorphism in metal−organic frameworks (MOFs) means that the same chemical building blocks (nodes and linkers) can be used to construct isomeric MOFs with different topological networks. The choice of topology can substantially impact the pore network of the MOF, changing the sizes and shapes of the pores, which has implications for adsorption and separation applications. In this work, we look at the influence of topology in 38 polymorphic MOFs on the separation of linear and branched C4–C6 alkane isomers, a separation of great importance to the petrochemical industry. We find that the MOF Cu2(1,4-benzenedicarboxylate) in nbo topology (nbo-Cu2BDC) has particularly high affinity for linear alkanes due to its small pore size, which excludes the branched isomers. Upon studying this MOF in further detail, we find that it can take either of two conformations: a cubic conformation, which is typical of nbo MOFs, and a unique star conformation that contains 1D triangular and hexagonal channels. The determination of which conformation the MOF will adopt depends on steric effects between the nodes and linkers.

Numerical Simulation of a Proton Exchange Membrane PEM Fuel Cell with Rectangular and Triangular Cross-Section Area Channels

In the present study, the performance of a Proton Exchange Membrane (PEM) fuel cell is numerically simulated for two channels with rectangular and triangular cross-section areas. A series of simulations is carried out to investigate both the influence of the humidity and the temperature of the input gas as two effective parameters on the performance of a PEM, which change from 10% to 100% and 30°C to 60°C, respectively. Numerical results indicate that more moisturized input gas produces a higher output voltage for both geometries. Furthermore, the triangular duct generates a higher output voltage in comparison with the rectangular duct, particularly, in the case of the parallel flow. In addition, the temperature of the input gas remarkably enhances the output voltage of the PEM. A qualitative agreement is achieved by comparing the present results to existing experimental data.

Experimental and Numerical Studies of Two-Phase Flow in Ribbed Periodic Vertical Channel

Pressure drop in a ribbed vertical channel was studied for a two-phase (air and water) flow, different shapes of ribs (triangle, semi-circular, and rectangle) were used in this investigation. An experimental rig was constructed with a test channel having the dimensions (10×3×70 cm) that enabled the flow patterns visual observation. An experimental setup of a two-phase was done for the present investigation, as well as a sum of (150) two-phase data with various flow patterns was determined. The used water superficial inlet velocities were in the range (0.0333 - 0.0888 m/s), and the air superficial inlet velocities were in the range (0.0555 - 0.1666 m/s). The experimental pressure drop according to a smooth plate was (41%, 38%, and 35%) for a channel fitted with semi-circle, rectangular and triangular ribs, respectively. The less pressure drop recorded was in the triangular ribbed channel, which indicates that the triangular shaped ribbed channel is the finest shape among the studied ones to lower the pressure drop. As future work, the numbers and dimensions of ribs can be changed to investigate its effect on the two-phase flow and the pressure drop, another suggestion for the future investigations is to include other fluid to have a three-phase flow, also the inclination angle of the duct can be changed to study its effect.

Predicting seepage from unlined earthen channels using the finite element method and multi variable nonlinear regression

Seepage losses from unlined channels are a major contributor to water loss in the agricultural sector. Quantification of seepage losses can improve water conveyance efficiency and provide solutions to water scarcity. In this study, a numerical simulation method is applied to investigate the factors that affect seepage from earthen channels. SEEP/W software was used to generate finite element method (FEM) solutions of the seepage flow equations. 246 numerical models, including different sections of trapezoidal, rectangular, and triangular earthen channels were studied using FEM. Numerical results are compared to available observation data from Zayandeh-Rud irrigation channels in Iran. Non-linear regression equations for the four empirical seepage equations are obtained from the SPSS statistical software. The results show that nonlinear multivariate regression relationships provide a suitable match for estimating seepage discharge. The accuracy of the suggested nonlinear regression equation in terms of R2 and RE are 0.928 and -2.42 %, respectively. Comparison of the seepage discharge with the empirical relationships showed that the empirical relationships have excessive error.

Anti-clogging performance optimization for dentiform labyrinth emitters

It is of great scientific significance to reveal the flow characteristics of dentiform emitters and to optimize the channel structure of emitters to improve the anti-clogging properties of emitters, which contribute to improving the working performance of irrigation systems. The study was carried out using computational fluid dynamics (CFD) simulations, combined with the physical test in the laboratory. First, this paper analyzes the distributions of flow velocity, kinetic energy in turbulence, and physical particle trajectories inside the different structural emitters based on CFD simulations, and based on the simulation results, a dentiform emitter optimization scheme was proposed, and two-channel structures, including the structurally improved emitter, were arranged to conduct indoor tests for verification. The result shows that the maximum kinetic energy in turbulence in the flow channel appeared in the main flow area and that the area of strongest energy dissipation in turbulence was at the tooth tip. The main flow area was largest for the emitter with the triangular channel, and the turbulence energy of the low-speed region was highest for the circular trapezoidal structure. The results suggested a scheme for further optimization of the dentiform emitter. For the optimized channel structure, the maximum value of turbulent kinetic energy was increased by about 19–101% compared with the other four flow channels. The area of the main flow region and the kinetic energy in turbulence in the low-speed area in the emitter were increased. In addition, the range of kinetic energy in turbulence was increased by 52–200% in the low-speed region of the channel. The transport rate of physical particles was increased, and the transport distance and residence time of the particles were reduced. The physical test results show that the optimized channel structure emitter achieved a decrease in the clogging probability compared with the other four structures. Therefore, increasing the area of the main flow region and the low-speed area in the flow channel is an effective physical way of physically improving the anti-clogging performance of the emitter.

Inertial focusing in triangular microchannels with various apex angles.

We consider inertial focusing of particles in channels with triangular cross sections. The number and the location of inertial focusing positions in isosceles triangular channels can change with varying blockage ratios (a/H) and Reynolds numbers (Re). In triangular channels, asymmetric velocity gradient induced by the sloped sidewalls leads to changes in the direction and the strength of the inertial lift forces. Therefore, varying the configuration (specifically, angle) of the triangular cross section is expected to lead to a better understanding of the nature of the inertial lift forces. We fabricated triangular microchannels with various apex angles using channel molds that were shaped by a planing process, which provides precise apex angles and sharp corners. The focusing position shift was found to be affected by the channel cross section, as expected. It was determined that the direction of the focusing position shift can be reversed depending on whether the vertex is acute or obtuse. More interestingly, corner focusing modes and splitting of the corner focusing were observed with increasing Re, which could explain the origin of the inertial focusing position changes in triangular channels. We conducted fluid dynamic simulations to create force maps under various conditions. These force maps were analyzed to identify the basins of attraction of various attractors and pinpoint focusing locations using linear stability analysis. Calculating the relative sizes of the basins of attractions and exhaustively identifying the focusing positions, which are very difficult to investigate experimentally, provided us a better understanding of trends in the focusing mechanism.

Thermohydraulic performance study of different square baffle angles in cross-corrugated channel

Cross-corrugated channels implementing high heat transfer performance are proper to employ in plate fin heat exchangers. In this work, the heat transfer, pressure drop and thermohydraulic performance in the cross-corrugated triangular channels having rectangle baffles with different settlement angles are numerically researched. Ansys-Fluent program is performed to solve Navier Stokes and energy equations by using k-ε turbulence model in numerical calculations. While air inlet temperature employed as working fluid is 293 K, wall surface temperature values of the lower corrugated duct are taken as constant 373 K. The constant rectangle baffle height and apex angle of the corrugated channel are utilized as 0.5 H and 60°, respectively. Re number range analyzed in this work is 1000–6000 while the rectangle baffle settlement angles are 30°,45°,60° and 90°. Numerical results are agreed with 3.53% deviation according to experimental study existed in literature. The attained results are exhibited as mean Nu number, fluid temperature and pressure variations for each rectangle baffle angle. Contour distributions of the temperature and velocity vector are also evaluated for different Re numbers and rectangle baffle angles. The Num value for the corrugated channel with rectangle baffle of 90° angle is 52.8% higher than that of the 60° for the Re = 6000. Also, for Re = 1000 the value of the pressure drop is 65.97% lower in the corrugated triangular channel with 60° rectangle baffle angle than that of 90° angle.

Experimental Investigation on Heat Transfer of Supercritical Water Flowing in the Subchannel with Grid Spacer in Supercritical Water-Cooled Reactor

Experimental investigations on the heat transfer performance of supercritical water flowing in the subchannel of supercritical water-cooled reactor (SCWR) simulated by a triangular channel were conducted at pressures of 23–28 MPa, mass flow rates of 700–1300 kg·m−2·s−1, and inner wall surface heat fluxes of 200–600 kW·m−2. An 8 mm diameter fuel rod with a 1.4 pitch to diameter ratio was used. The effects of pressure, mass flow rate, and heat flux on the heat transfer performance under the resistance of a standard grid spacer were analyzed. Experimental results showed the significant positive influence of the grid spacer on the supercritical water in the subchannel. Moreover, in the presence of the grid spacer, the parameters influenced the heat transfer with different degrees of strengthening reaction. In view of the phenomenon in the tests, the rule of the supercritical heat transfer was further revealed by the comparison between empirical formulas and experimental data. This paper mainly studied the positioning grid function and the fluid flow characteristics downstream of the subchannel under the influence of the standard grid spacer and the impact mechanism of each parameter on the whole heat transfer process coefficient.

Numerical study on flow and pressure drop characteristics of a novel type asymmetric wall-flow diesel particulate filter

In order to reduce the pressure drop and regeneration cost of diesel particulate filters (DPFs), and improve the power and economic performance of the diesel engines, a novel type of asymmetric channel wall-flow filter was proposed, including the regular hexagonal and triangular channels, as well as the rectangular channels. A one-dimensional mathematical model was built to study the flow characteristics, especially pressure drop performance, for this type of particulate filter, as well as a square symmetric and a square asymmetric channel filter for comparison. The effects of exhaust gas flow rate, cell density, wall thickness, and aspect ratio were numerically accessed. The results show that the novel asymmetric channel filter can effectively reduce the lifetime pressure drop by increasing the utilization ratio of the filtration wall and the filtration area. Specially, with the novel asymmetric channel structure, the wall pressure drop is considerably reduced owing to a lower mean wall penetration velocity. Furthermore, the depth layer and soot layer pressure drops of the novel type filter are much lower than those of the square symmetric channel filter owing to the smaller penetration velocity and thinner thickness of the soot layer, nearly the same as those of the square asymmetric channel filter. Additionally, the filter with a smaller aspect ratio can slightly reduce the pressure drop, so it can be practically applied if the distribution of the inlet gas is uniform. The novel asymmetric channel filter can meet the current and future demand for miniaturization and light-weighting of particulate filters, and has excellent market adaptability.

Numerical analysis of triangular labyrinth side weir in triangular channel

ABSTRACT Labyrinth side weir is a type of lateral weirs which used for diversion of flow and head regulator in the sewage system, irrigation and drainage engineering. Discharge coefficient of labyrinth side weir is more than linear side weirs. An investigation has been carried out by many researchers on labyrinth side weirs with rectangular parent channel. In this study, computational Fluid Dynamics (CFD) volume of fluid method was used to investigate the coefficient of discharge of triangular labyrinth side weirs in the triangular straight main channel. Dimensionless parameters like dimensionless nape height h/p, Froude number, the Apex angle of triangular labyrinth side weir, dimensionless weir width and included angle of triangular parent channel affecting on the coefficient of discharge of triangular labyrinth side weirs obtained from CFD simulations are used for an empirical equation. The surface profile also studied for triangular labyrinth side weirs. Comparison of simulation results and experimental results have a good agreement. According to the results, coefficient of discharge of 45° labyrinth side weir is higher than 60° and 90° labyrinth side weirs.

Modelling of condensation pressure drop for R134a and R134a-lubricant-mixtures in multiport flat tubes

This paper presents the results of an experimental investigation on pressure drop characteristics for R134a and R134a-lubricant mixtures in multiport flat tubes (MPFT). An experimental facility has been set up, carefully validated and used to determine the pressure drop value in the two-phase flow regime inside extruded MPFT with hydraulic diameters from 0.91 mm to 0.53 mm with either triangular or rectangular channel cross sections with and without an axial fin structure. Based on the investigation published in Knipper et al. (2019), the operating parameters have been varied within a broad range to ensure a high degree of reliability and comparability to pressure drop correlations. In addition, the nominal oil content has been varied between 0 and 7% by weight. A good agreement of the pressure drop data with several correlations can again be confirmed for most of the flat tubes. With respect to the urgent need for reliable correlations regarding low liquid only Reynolds numbers (Relo=800−5000), the authors present an approach based on the Cavallini et al. (2006) correlation that is also considering the surface roughness of the tube. For both, pure R134a and R134a-PAG-oil-mixtures, a good agreement with the newly determined data can be achieved and, thus, an enlarged range of applicability can be stated.

Characterizing Mist Distribution in Through-Tool Minimum Quantity Lubrication Drills

Abstract The mist distribution is a critical factor in through-tool minimum quantity lubrication (MQL) drilling since a small amount of lubricant is used. However, it has rarely been discussed because of the difficulty in measuring the mist flow experimentally. In this paper, an optical approach is developed to approximate the mist distribution by using high-speed images from multiple angles. Drill bits with two through-tool channel shapes (circle and triangle) and three helix angles (0 deg, 30 deg, and 45 deg) are 3D printed for mist distribution analysis. Furthermore, computational fluid dynamics (CFD) is conducted to investigate the underlying physics behind mist flow variations. The results show that, in the circular channel, the mist is concentrated near the periphery; the low concentration region shifts away from the chisel point as the helix angle increases. For the triangular channel, the mist is concentrated near three vertices but is less affected by the helix angle. Furthermore, based on the CFD solution, high mist concentration tends to be in low-velocity regions and vice versa. This study confirms a noticeable difference of mist flow distribution in different through-tool channel designs.

Modeling and experimental study of a triangular channel solar air heater

In this study, a pilot plant of a triangular channel solar air heater with a U-turn airflow pattern was constructed and its performance was investigated using a developed model and experimental data under different operating conditions. A new equivalent radiation-convection circuit was developed as the most sophisticated part of the model. Based on the circuit, a mathematical model with minimal simplifying assumptions was developed to predict the performance of the heater. Compared with the results of an integral model of overall energy balance equations, the developed model showed a 50% reduction of error in prediction of thermal efficiency and outlet air temperature. The maximum thermal efficiency of the system could be obtained at an air mass flow rate of 0.045 kg/s (i.e. mass flux of 8.18 kg/m2.s). Considering the air pressure drop (as the most important penalty) and outlet air temperature, the highest thermohydraulic performance was obtained at a channel internal peak angle of 60°. Besides, the results indicated that to achieve a certain thermal efficiency, the presented solar air heater requires less surface area than that of a flat plate solar air heater for the same input solar radiation.

Reorientable fluorinated aryl rings in triangular channel Fe-MOFs: an investigation on CO2–matrix interactions

Flexible aryl rings in fluorinated Fe-MOFs point C–F dipoles towards the corner of triangular channels capturing efficiently CO2 molecules.

Numerical investigation on geometric configurations affecting seepage from unlined earthen channels and the comparison with field measurements

In this study, a numerical simulation is applied to investigate the effective factors on the seepage from the earthen channels. To authenticate the information at hand, some of the earthen channels in the Zayandeh-Rud irrigation network in Iran and Gediz watershed in Turkey were studied. 246 numerical models, including different sections of trapezoidal, rectangular and triangular earthen channels, were performed using the finite elements method (FEM). The results showed that, for a numerical simulation, a width of 15 times wider than the top width of the water surface in the channel would be required for the modelling of the left and right lateral boundaries. The comparison of the seepage with empirical relationships showed that the empirical relationships have too much error in the seepage estimation, however, Moritz’s relation with the coefficient of determination (R2) of 0.373 was better than the others. The linear and nonlinear multivariate regression relationships provide a suitable match for the seepage discharge estimation. The wetted perimeter has been distinguished as an effective parameter in the seepage from the channels, yet the channels side slope has a low impact on the seepage.

Heat transfer and pressure drop evaluation of different triangular baffle placement angles in cross-corrugated triangular channels

Plate heat exchangers have a widespread usage and the simplest parallel plate channel structures. Cross-corrugated ducts are basic channel geometries used in the plate heat exchangers. In this study, the increasing of heat transfer from the cross-corrugated triangular ducts by inserting triangular baffles with different placement angles into the channel upper side and pressure drop have been numerically investigated. Numerical calculations have been carried out to solve Navier-Stokes and energy equations by employing k-? turbulence model as 3-D and steady with ANSYS-FLUENT program. While inlet temperature of the air used as working fluid is 293 K, constant surface temperature values of the the lower corrugated channel walls are 373 K. The height of the baffle and apex angle of the corrugated duct have been taken constant as 0.5 H and 60?, respectively. Investigated Reynolds number range is 1000-6000 while the baffle placement angles are 30?, 45?, 60?, and 90?. Numerical results of this study are within 3.53% deviation with experimental study existed in literature. The obtained results have been presented as mean Nusselt number temperature and pressure variations of the fluid for each baffle angle. The temperature and velocity vector contour distributions have been also assessed for different Reynolds numbers and baffle angles. The value of the Num for the corrugated channel with 60? baffle angle is 8.2% higher than that of the 90? for the Re = 4000. Besides, for Re = 1000 the value of the pressure drop is 39% lower in the channel with 60? baffle angle than that of 90?.

Solutions of transition problems in exponential channels

ABSTRACT Transition problems in a smooth open-channel flow consist of a solution of the third- or higher-degree algebraic equations to determine the choke-free or post-choking depths at downstream and upstream sections, respectively. Graphical solutions of trapezoidal, circular and exponential channels and analytical solution for rectangular channels have been obtained in the past. However, these solutions are cumbersome and so are difficult for field applications. In the present work, a general transition problem in exponential channels has been formulated in terms of alternate-depth ratio. A governing algebraic equation representing incipient choking condition has been derived for the exponential channel (rectangular, parabolic and triangular). Furthermore, the method of applying the same to calculate the choke free and post-choking depth at downstream and upstream sections has been presented in this paper. Exact solutions for the case of rectangular and parabolic channels have been obtained. After observing, the impossibility of exact solutions for triangular channels and the cumbersome nature of the solutions for rectangular and parabolic channels, empirical solution for the post-choking depth at upstream section has been carried out for the exponential channel. The empirical relation between the shape factor and upstream Froude number for the incipient condition has been obtained for all channel types. The result shows that for , the absolute error in is less than 1% in all channel types, while for , this value goes up to 1.1%, 1.6% and 1.8% for rectangular, parabolic and triangular channels, respectively. These empirical solutions are simple for field applications with negligible error. The methodologies presented in this paper have been corroborated using examples from various sources.

Jet direction in bubble collapse within rectangular and triangular channels.

A vapor bubble collapsing near a solid boundary in a liquid produces a liquid jet that points toward the boundary. The direction of this jet has been studied for boundaries such as flat planes and parallel walls enclosing a channel. Extending these investigations to enclosed polygonal boundaries, we experimentally measure jet direction for collapsing bubbles inside a square and an equilateral triangular channel. Following the method of Tagawa and Peters [Phys. Rev. Fluids 3, 081601 (2018)10.1103/PhysRevFluids.3.081601] for predicting the jet direction in corners, we model the bubble as a sink in a potential flow and demonstrate by experiment that analytical solutions accurately predict jet direction within an equilateral triangle and square. We further use the method to develop predictions for several other polygons, specifically, a rectangle, an isosceles right triangle, and a 30^{∘}-60^{∘}-90^{∘} right triangle.

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.

The influence of channel geometry on the pressure drop in automotive catalytic converters: Model development and validation

This paper presents a detailed physics based model for the pressure drop through a honeycomb substrate for several channel shapes and void fractions. A CFD-based computational model of a single channel is used to study the pressure drop when flow is entering, passing through and leaving the substrate. An extensive set of 3D computational experiments covering square, hexagonal and triangular channel cross-sections, void fractions from 0.39 to 0.84 and channel Re from 95 to 1284 is used. It is shown that altering the void fraction changes the pressure drop at the inlet and outlet of the substrate, however, its effect on the friction factor inside the substrate is minor. The resulting model can be used either as a semi-empirical lumped model for pressure drop and in 3D full-scale simulations with a porous medium representing the substrate. A validation for the velocity profile in a full scale monolith with experimental data available in the literature is carried out and an excellent agreement is observed. The proposed model significantly improves the prediction of the flow distribution across the substrate, which has remained unaddressed historically by existing models and is the most important effect required to make accurate predictions of heat distribution, conversion efficiency and others in full-scale simulations.