Channel Of Variable Cross Section Research Articles

Numerical analysis of catalytic reaction kinetics in methanol steam reformer with variable cross-sectional channel

ABSTRACT Methanol steam reforming (MSR) is a hydrogen production method recognized for its low harmful emissions and high cost-effectiveness. In this study, a three-dimensional numerical model of MSR within channels of variable cross-section. A quantitative relationship between local equilibrium constants and channel structural parameters was established based on the partial pressures of the components. Additionally, the mechanisms by which variable cross-sectional channel structural parameters regulate MSR reaction performance were quantitatively analyzed, considering fluid dynamics, hydrogen production efficiency, and chemical kinetics rates. The results indicate that the kinetic rate of MSR and local equilibrium constants are significantly influenced by the modulation of variable cross-sectional channel structural parameters, with a maximum variation of 50.6%. A positive correlation between methanol conversion rate and the local equilibrium constant of MSR was observed. Utilizing channel structural parameters to enhance MSR led to an 8.75% increase in methanol conversion rate within the same reaction volume. These conclusions may provide theoretical support for regulating volumetric reactions through variable cross-sectional channel structural parameters.

Pore-scale flame oscillations and patterns of upstream combustion wave propagation in a one-layer porous burner

Upstream propagation of filtration combustion wave in a one-layer porous burner is studied experimentally using thermal imaging and high-speed filming. The burner is the one-layer packed bed of spheres modeling porous media and providing optical access to the flame. This design allowed us to study macroscopic propagation of the combustion wave as well as non-stationary flame behavior at the pore scale. Experimental results demonstrate that upstream propagating combustion wave forms non-uniform porous medium temperature distribution in transverse direction which consists of hot areas separated by low-temperature regions. Macroscopic flame propagation can be accompanied by oscillations of some flame fragments at the pore scale. The mechanism of these pulsations is identical to the flames with repetitive extinction and ignition in narrow channels with external heating. Experimental results suggest that large scale evolution of the thermal wave affects the non-stationary behavior of the flame fragments at the pore scale and vice versa. The interplay between pore-scale and macro-scale processes manifests itself in the multiple repetitions of some patterns of the combustion wave propagation. Two most typical and common patterns are described and discussed. These patterns are step-wise transition of the flame fragment into the upstream pore and transition through the series of flame oscillations with repetitive extinction and ignition. It is shown that highly simplified one-dimensional model describes flame propagation in externally heated variable cross-section channel with heat conducting walls is capable to describe main features of these two patterns. Parametric study allows to predict the effect of problem parameters on the regions of existing of one or another pattern of upstream flame propagation.Novelty and Significance StatementThis paper presents new experimental data on temperature characteristics of upstream propagating filtration combustion wave in a one-layer porous burner. For the first time the patterns of combustion wave propagation uniting macro-scale processes of the thermal wave propagation and oscillations of the flame fragments at the pore scale are described on the basis of experimental data and numerical modeling. Results obtained for the one-layer burner can apparently be generalized to the case of combustion in three-dimensional porous media and packed beds. These results are significant because extend fundamental knowledge on porous media combustion by information on pore- and macro- scale flame dynamics as well as on the interplay of these scales. Experimental results can also be useful for validation of pore-resolved numerical simulations actively developed in the last decade.

The Performance and Fabrication of 3D Variable Cross-Section Channel for Passive Microfluidic Control.

Passive fluid control has mostly been used for valves, pumps, and mixers in microfluidic systems. The basic principle is to generate localized losses in special channel structures, such as branches, grooves, or spirals. The flow field in two-dimensional space can be easily calculated using the typical Stokes formula, but it is challenging in three-dimensional space. Moreover, the flow field with periodic variable cross-sections channeled of polyhedral units has been neglected in this research field due to previous limitations in manufacturing technology. With the continuous progress of 3D printing technology, the field of microfluidic devices ushered in a new era of manufacturing three-dimensional irregular channels. In this study, we present finite analysis results for a periodic nodular-like channel. The experiments involve variations in the Reynold number (Re), periodic frequency, and comparative analyses with conventional structures. The findings indicate that this variable 3D cross-section structure can readily achieve performance comparable to other passive fluid control methods in valve applications. A 3D model of the periodic tetrahedron channel was fabricated using 3D printing to validate these conclusions. This research has the potential to significantly enhance the performance of passive fluid control units that have long been constrained by manufacturing dimensions.

Numerical analysis of heat transfer characteristics in ribbed two-passed channel with varied cross section

The mid-chord region of turbine blades typically employs internal cooling channels to enhance heat transfer. However, traditional internal cooling channels are mostly designed in the form of straight channels, and studies based on it may not address the needs of variable cross section channels. Therefore, this study investigates the effect of rib configurations in variable cross section channels on channel performance. First, the cross sectional area of the two-passed channels is modified by altering the inclination angle of the dividers (−3°, 0°, and +3°). The flow pattern and heat transfer features within a two-passed channel with variable cross section under four different rib configurations of NP, NN, PN, and PP are investigated using numerical simulation. N denotes the ribs rotated 45° clockwise relative to the flow direction, while P denotes the ribs rotated 45° counterclockwise. Subsequently, the optimal rib configuration within the variable cross sectional two-passed channels is determined for Reynolds numbers ranging from 10 000 to 50 000. Results show that, at +3°, the PP exhibits the maximum decrease of up to 18.2% in transfer performance factor (TPF), while at −3°, the NN shows the maximum decrease of up to 12.7%. It is evident that the optimal rib configuration for two-passed channels under different divider inclinations is not consistent. At +3°, the NP exhibits the best TPF, while at −3°, the PP demonstrates the optimal TPF. This study provides insights into selecting appropriate rib configurations when the cross sectional area of internal channels within turbine blades varies. Compared to the studies that have focused on traditional straight channels, the research provides guidance for the design of ribbed two-passed channels with varied cross section.

Computer modeling of supersonic gas flow in variable cross-section channels using OpenFOAM

Computer modeling of supersonic gas flow in variable cross-section channels using OpenFOAM

Direct stochastic simulation of a rarefied gas flow in channels of variable cross section

Direct stochastic simulation of a rarefied gas flow in channels of variable cross section

Buoyancy influences on local heat transfer characteristic of supercritical LNG across the pseudo-phase transition in variable cross-section horizontal channels

The regasification process within the printed circuit heat exchanger (PCHE) channel for supercritical liquefied natural gas (S-LNG) will produce a large temperature difference. This process is considered a pseudo-phase transition process, and the resulting density difference driving buoyancy has a crucial action in influencing the heat transfer and flow of S-LNG. Three horizontal variable cross-section channels are established to examine the buoyancy impact on the local heat transfer and flow of S-LNG within the pseudo-phase transition process in the PCHE channel. It comprehensively analyzes the buoyancy impact on local heat transfer and flow under different channel shapes and mass flow rates. The findings demonstrated that the eddy blockage caused by buoyancy mainly acts on the top of the channel and mainly occurs in the liquid-like and pseudo-critical regions, resulting in the deterioration of local heat transfer on the upper and lower walls of the channel. The hybrid channel achieves the intended design goal, and the diverging channel is almost unaffected by buoyancy. The overall performance evaluation criterion (PEC) is used to evaluate the thermal and hydraulic performance of each channel under different mass flow rates. The data show that the diverging channel has the best thermal and hydraulic performance, and its PEC can reach 1.28. The hybrid channel also achieves the expected effect, and its PEC can reach 1.09.

Experimental and numerical analysis of variable cross-section channel liquid cooling plate for server chips thermal management

Utilizing high-performance chips results in increased heat generation, necessitating more effective heat dissipation method. To address challenges in microchannel liquid cooling plates for server chips cooling the study presents the variable cross-section channel liquid cooling plate designs. To investigate the effect of channel structure on the performance of liquid cooling plate, two types of samples, one featuring side wall ribs and bottom cavities (SC) and the other featuring side wall ribs and bottom waves (SW), are evaluated through experimental analyses under various heating power and flow rate conditions. Comparing their performance to a conventional rectangular channel (RC) liquid cooling plate, their heat transfer and flow attributes were assessed. Finally numerical analysis was conducted to investigate the flow behavior inside the channel and extreme performance prediction were made using the numerical study. Results demonstrate that the SC and SW designs outperform the RC in terms of heat transfer capabilities, despite having the weaker flow characteristics. Under 300 W heat source power, the SW variants enable the heat source surface temperature to stay below 77.8 °C with a 194 mL/min flow rate. Notably, the SW variant showcases lower average heat source surface temperature and demonstrates lower pressure drop compared to the SC variant. As the flow rate increases, the heat transfer efficiency of the SW variant is further amplified while simultaneously highlighting the relatively suboptimal flow behavior of the SC variant. Predictive numerical models underscore that the SW variants offers improved thermal performance when subjected to high heat source power scenarios. Remarkably, under the heat source power of 500 W, a mere augmentation in flow rate proves sufficient to reduce the heat source temperature below the prescribed threshold value. The combination design of side wall ribs and bottom waves should enable a low cost, simple and high efficiency electronics cooling.

Flows structure and intensity during liquid and body oscillations in variable cross-section channel

The present study investigates the intensity and structure of averaged flows at oscillating fluid flow in a vertical axisymmetric channel of variable cross-section. The results demonstrate that oscillating of the fluid induces the formation of strong flows throughout each of the channel segments. The magnitude of these flows is contingent upon the influence of a free oscillating solid body. The results indicate that the presence of a spherical body in the channel has the effect of either intensifying or weakening the fluid’s flow rate in response to both the amplitude of the oscillation and the body’s relative position within the channel.

Oscillatory Dynamics of a Spherical Solid in a Liquid in an Axisymmetric Variable Cross Section Channel

Oscillatory Dynamics of a Spherical Solid in a Liquid in an Axisymmetric Variable Cross Section Channel

Cell-Based Modeling of Tissue Developing in the Scaffold Pores of Varying Cross-Sections.

In this work, we present a mathematical model of cell growth in the pores of a perfusion bioreactor through which a nutrient solution is pumped. We have developed a 2-D vertex model that allows us to reproduce the microscopic dynamics of the microenvironment of cells and describe the occupation of the pore space with cells. In this model, each cell is represented by a polygon; the number of vertices and shapes may change over time. The model includes mitotic cell division and intercalation. We study the impact of two factors on cell growth. On the one hand, we consider a channel of variable cross-section, which models a scaffold with a porosity gradient. On the other hand, a cluster of cells grows under the influence of a nutrient solution flow, which establishes a non-uniform distribution of shear stresses in the pore space. We present the results of numerical simulation of the tissue growth in a wavy channel. The model allows us to obtain complete microscopic information that includes the dynamics of intracellular pressure, the local elastic energy, and the characteristics of cell populations. As we showed, in a functional-graded scaffold, the distribution of the shear stresses in the pore space has a complicated structure, which implies the possibility of controlling the growth zones by varying the pore geometry.

Numerical and experimental study on efficient optimization of variable cross-section battery thermal management systems using an improved flow resistance network model

Air-cooled systems are widely used for cooling of battery packs in electric vehicles. Optimization method combined with the flow resistance network (FRN) model is effective for system design. However, the local pressure loss of divergence and convergence ducts in the traditional FRN model is ignored, leading to large error when applying the model in systems with variable cross-section channels. In this study, the local loss coefficients of the contractive and diffusive channels are derived and the improved FRN model is developed for velocity calculation of variable cross-section air-cooled systems. The improved model is verified using computational fluid dynamics method. Based on the improved FRN model, the cross-section width distribution of the divergence duct is calculated from the given flow rate distribution. The shape of the divergence deflector is optimized by adjusting the flow rate distribution and using the improved model. The results indicate that the temperature difference of the battery cells decreases by more than 84% after the optimization, with the maximum temperature decreasing by more than 3.8 K. Furthermore, the optimized system performs better than those in the previous studies. Also, experiments are carried out to verify the effectiveness of the developed optimization method based on the improved FRN model.

Numerical simulation of compressible gas flow in flat channels in the narrow channel approximation

In this paper, numerical simulation of a compressible gas in plane channels of constant and variable cross-section is performed within the framework of two-dimensional parabolized Navier-Stokes equations. The "narrow channel approximation" model is used for the numerical solution of the uranation system.A number of transformations are described in detail, such as de-dimensioning the equation system, reducing the considered area to a square, as well as thickening the calculated points in large gradients of gas dynamic parameters. Flow conservation conditions are used to determine the pressure gradient.An effective method is given for simultaneously determining the pressure gradient and the longitudinal velocity, then other gas dynamic parameters stable for subsonic and supersonic flows, as well as a method for determining the critical flow rate for solving Laval nozzle problems.The results of methodical calculations are presented, with the aim of verifying the effectiveness of the developed calculation methodology, as well as confirming the reliability of the results obtained by comparing them with data from other authors

Broaden the sound absorption band by using micro-perforated plate back cavities with different cross-sectional areas

In finite size micro-perforated plate structure, the cross-sectional area size of back cavity will affect the resonant frequency of structure. Based on transfer matrix and the characteristics of acoustic propagation in variable cross-section channel, the sound absorption characteristics of the double-layer micro-perforated plate structure with variable cross-section back cavity are studied and analyzed, and a theoretical analysis model of the variable cross-section back cavity micro-perforated plate structure is established. By comparing the theoretical model with the finite element model, the effect of abrupt changes in the cross-sectional area of the back cavity on the noise reduction performance is obtained. As for the double-layer micro-perforated plate in this paper, the bigger the cross-sectional area of back cavity of inner micro-perforated plate, the lower the frequency of first peak absorption coefficient of structure will be and the higher the frequency corresponding to second absorption coefficient peak of structure. Utilizing this feature, a combined micro-perforated plate structure is designed, which has back cavities with different inner cross-sectional areas, and ultimately broadening the structural sound absorption band. Additionally, through using 3D printing technology to produce samples and conducting experimental tests in the impedance tube. Experiments show that the structure can achieve an absorption coefficient of more than 0.8 within the frequency range of 500–1650 Hz, which further improving the noise reduction performance of the MPP structure. The feasibility of variable-sectional back cavity structure for the design of low-frequency and broadband noise reduction absorber is verified.

A novel cathode flow field for PEMFC and its performance analysis

A good flow field design is important to the proton exchange membrane fuel cell (PEMFC) performance, especially under a high current density region, which is dominated by concentration polarization. Motivated by the variable cross-section channel idea, in this study, a novel flow field containing a converging-diverging (C-D) pattern is proposed. A three-dimensional multiphase model is established to study its performance. The numerical results show that it outperforms the conventional straight channel and only depth-variant channel. In the novel flow field the enhanced under land cross flow and higher effective mass transfer coefficient both improve the reactant transport. The effects of operating conditions, like stoichiometric ratio and operating pressure, on cell output performance are studied. It is found that a higher promotion rate can be obtained by increasing the stoichiometric ratio, but increasing the operating pressure has little effect. The droplet dynamic behavior in the C-D channel and straight channel are studied, and the results prove the better drainage capability of the novel flow field.

К вопросу о принципе наименьшего действия при течении несжимаемой жидкости в осесимметричном канале переменного сечения

A formulation of the principle of least action is proposed as applied to the stationary motion of a non-viscous, non-heat-conducting, incompressible fluid in an axisymmetric channel of variable cross section. As a result of solving the variational problem corresponding to this principle, a connection was found between the components of the velocity vector, which made it possible to determine the shape of the channel in which the implementation of the principle of least action is ensured, and the flow parameters both in the channel itself and in the initial outflow region - the region that forms the flow in some conditional section of the entrance to the channel

Numerical Analysis of Flow-Induced Vibration and Noise Generation in a Variable Cross-Section Channel

Numerical Analysis of Flow-Induced Vibration and Noise Generation in a Variable Cross-Section Channel

СРАВНИТЕЛЬНЫЙ АНАЛИЗ ЭФФЕКТИВНОСТИ ПАРАЛЛЕЛЬНЫХ ВЫЧИСЛЕНИЙ ПО ЯВНЫМ И НЕЯВНЫМ РАЗНОСТНЫМ СХЕМАМ ДЛЯ ЗАДАЧ ВЫЧИСЛИТЕЛЬНОЙ АЭРОДИНАМИКИ

One of the main areas of parallel computing application is solving of computational aerodynamicsproblems. The paper considers parallel modeling of gas dynamics with quasi-onedimensionalsystem of equations. The system describes the gas flow through a channel with variablecross section using implicit and explicit difference schemes. The purpose of this work is tostudy the methods efficiency for organizing parallel computations with implicit and explicit differenceschemes for solving internal aerodynamics problems. The article presents a comparativeanalysis of the proposed parallel models for quasi-one-dimensional equations system of gas dynamics.The system describes flows in a channel of variable cross section. Various parallel algorithmsare used to solve systems of such type numerically. The method of splitting by physical processesis used for an implicit difference scheme. To suppress the solution oscillations a smoothingoperator at the correction stage is introduced in calculations according to the scheme of the predictor-corrector type. In scheme fractional steps the parallel scalar sweep algorithm is used tosolve tridiagonal systems with the parametric unknown choice. Besides to compare scheme mentionedabove a parallel algorithm is constructed for McCormack's explicit scheme. Such algorithmis widely used in computational aerodynamics. Parallel computations are held by computingstructures with distributed memory and by another one – with linear switching dependence betweencomputing devices of the working field. The paper presents time estimations for each computingstage (both by implicit and explicit difference schemes). It helped to calculate the developedparallel algorithms efficiency. It is concluded that the acceleration factor in explicit scheme dependslinearly on the computing devices number.

Numerical solution of a singularly perturbed boundary value problem of supersonic flow transformed to the modified best argument

When solving problems of aerodynamics, researchers often need to numerically solve singularly perturbed boundary value problems. In some cases, the problem can be reduced to solving a boundary value problem for an ordinary differential equation. Then it is possible to apply various numerical methods such as the grid method, the shooting method, as well as a number of projection methods, which, in turn, can form the basis of the finite element method. The grid method requires solving a system of algebraic equations, that are often nonlinear, which leads to an increase in the calculation time and to the difficulties in convergence of the approximate solution. According to the shooting method, the solution of boundary value problem is reduced to solving a certain set of Cauchy problems. When solving stiff Cauchy problems, implicit schemes are used as a rule, but in this case the same difficulties arise as for the grid method. The transformation of the problem to the best argument λ, calculated tangentially along the integral curve, makes it possible to increase the efficiency of explicit numerical methods. However, in cases where the growth rate of integral curves is close to exponential, the transformation to the best argument is not efficient enough. Then the best argument is modified in such a way as to smooth out this flaw. This paper investigates the application of modified best argument to the solution of the boundary value problem of an aerodynamic flow movement in case when the gas is injected at supersonic speed into a channel of variable cross-section.

INTENSIFICATION AND STUDY OF HEAT TRANSFER AND FRICTION IN THE PLATE HEATING SURFACES OF THE KMS-2 AIR HEATER WITH A PRESSURE GRADIENT

A numerical study of heat transfer and friction in the heat exchanger channels in the presence of a variable pressure gradient is performed. The research was carried out in software complexes (Code_Saturne, Salome). The results of the validation of the research method are presented and they showed that the deviation of the numerical simulation results from the calculation data according to the known criterion equations is within the error of generalization of the experimental data by the criterion equations. According to the results of studies at Red=3000, Red=4177, Red=6000, it was found that the average value of the heat transfer coeffi cient of the channel of variable cross-section is up to 20 % higher than for the channel at dp/dx0. At the same time, the thermal-hydraulic effi ciency of the alternating channel (L=117 mm, l=58.5 mm, n=2) in the initial section at x =0...0.08 is lower than in the channel with dp/dx>0 by 26.7 %, and at x =0.08...1 it is higher by 5 ... 15 %, at dp/dx