Channel Of Variable Cross Section Research Articles

Lattice Boltzmann method simulations about shale gas flow in contracting nano-channels

Shale matrix consists of numerous interconnected nanoscale slit pores with size ranging from 4 nm to 200 nm, naturally resulting in variable cross-section scenarios for shale gas transport. Understanding the behavior of shale gas flow in variable cross-section channels would have practical benefits to further reveal the gas flow mechanism. Herein, using multiple-relaxation time lattice Boltzmann method (LBM) simulations, we investigate the flow characteristic of shale gas in sudden and gradual contraction channels. The influences of Knudsen number and cross-section shrinking coefficient on the shale gas transport are discussed in details. We find that the relationship between centerline velocity and Knudsen number is dependent on the gas flow regime. The nonlinear pressure deviation shows a negative correlation with the Knudsen number. The slip mass flux and the second-order permeability correlation factor are found to have positive correlations with the cross-section shrinking coefficient, demonstrating that the shale gas apparent permeability would be underestimated without considering the influence of cross-section contraction. Moreover, we reveal that the shrinking of pore channel has a great influence on Knudsen minimum effect. A high cross-section shrinking coefficient and dramatically varied cross-section type will lead to a low critical Knudsen number of Knudsen minimum effect. The LBM results and insight obtained here would be conductive to understanding shale gas transport in contracting nano-channels.

Numerical Study of Detonation Wave Propagation in the Variable Cross-Section Channel Using Unstructured Computational Grids

The work is dedicated to the numerical study of detonation wave initiation and propagation in the variable cross-section axisymmetric channel filled with the model hydrogen-air mixture. The channel models the large-scale device for the utilization of worn-out tires. Mathematical model is based on two-dimensional axisymmetric Euler equations supplemented by global chemical kinetics model. The finite volume computational algorithm of the second approximation order for the calculation of two-dimensional flows with detonation waves on fully unstructured grids with triangular cells is developed. Three geometrical configurations of the channel are investigated, each with its own degree of the divergence of the conical part of the channel from the point of view of the pressure from the detonation wave on the end wall of the channel. The problem in consideration relates to the problem of waste recycling in the devices based on the detonation combustion of the fuel.

Nonlinear wave dynamics in self-consistent water channels

We study long-wave dynamics in a self-consistent water channel of variable cross-section, taking into account the effects of weak nonlinearity and dispersion. The self-consistency of the water channel is considered within the linear shallow water theory, which implies that the channel depth and width are interrelated, so the wave propagates in such a channel without inner reflection from the bottom even if the water depth changes significantly. In the case of small-amplitude weakly dispersive waves, the reflection from the bottom is also small, which allows the use of a unidirectional approximation. A modified equation for Riemann waves is derived for the nondispersive case. The wave-breaking criterion (gradient catastrophe) for self-consistent channels is defined. If both weak nonlinearity and dispersion are accounted for, the variable-coefficient Korteweg–de Vries (KdV) equation for waves in self-consistent channels is derived. Note that this is the first time that a KdV equation has been derived for waves in strongly inhomogeneous media. Soliton transformation in a channel with an abrupt change in depth is also studied.

Methodology of experimental determining the combustion efficiency of fuel mixture flows in channels of variable cross-section

The physically validated approaches to the setting of an experiment are presented and the methodological aspects of an analysis of experimental data for establishing the distinctive features of the fuel mixture combustion in variable-cross-section channels are considered. The special features of determining the fuel combustion efficiency coefficient in subsonic and supersonic flows are considered with account for heat removal into the channel walls. The effect of the fuel combustion efficiency coefficient on the distributions of gasdynamic and thermodynamic parameters along the length of the internal ducts of channels of different configurations is analyzed. The results of the testing of the techniques proposed against an experimental investigation of gaseous hydrogen combustion in high-enthalpy air flows are presented. The results obtained and the mathematical models developed can be used at the stage of computational and experimental investigations of the working process in promising power plants.

Wave Dynamics in the Channels of Variable Cross-Section

Wave Dynamics in the Channels of Variable Cross-Section

Formation of an overdriven detonation wave in the flow of methane–oxygen mixtures in a variable cross section channel

The formation of an overdriven detonation wave in methane-oxygen mixtures in an axially symmetrical channel with a variable cross section was experimentally investigated. The ignition of gas mixture was carried out using the spark gap, located at the closed end of the channel. To create the overcompressed shock detonation wave, the decay of the stationary detonation wave was performed at the transition to the channel of a larger cross section. The created complex of shock wave and flame front, moving behind it, propagated in a channel with conical narrowing. The formation of the overdriven detonation wave, with parameters exceeding the parameters of Chapman–Jouguet stationary detonation by a few times, was registered at the outlet of conical narrowing. The rates and pressures on the front of the detonation wave were determined, depending on the mixture composition. The sizes of detonation cells, diagrams of compression waves propagation, flame front, and detonation wave in a combustion chamber, depending on the mixture composition, were presented.

Flow of a Methane Vapor–Drop Mixture in a Channel of Variable Cross Section

Results of numerical investigation of the dynamics of a methane vapor–drop mixture in a channel of variable cross section are presented. Calculations were performed on the basis of a one-velocity, one-temperature model in the diffusion approximation with the use of the scheme of a nonequilibrium phase transition. A computational method was verified by comparison of the results of calculations of the dynamics of a water vapor flow with experimental data. The temperature fields and the partial density of the condensate in a Laval nozzle were determined depending on the temperature of the flow at the input of the channel and on the pressure drop in it.

Conceptual bases of creation of the membrane device of tubular type for studying the in bioreactors

In this study, methods for intensifying micro- and ultrafiltration processes by controlling the concentration-polarization effect are considered and studied. The negative effect of concentration polarization on the process of separation of the filtered liquid and on the membrane surface is described (due to the increase in concentration, the selectivity and specific productivity of the membrane surface decrease). The physical picture of the flowing phenomena in a flat membrane channel with known geometric dimensions is considered, four sections with different effects on the filtration process are identified. The equation of material balance is analyzed by introducing boundary conditions into the criterion equation of material balance, with the aim of finding opportunities for mass transfer. It is revealed that the mass transfer coefficient km decreases, due to the growth of the thickness of the boundary layer. The main parameters significantly influencing the process of microfiltration are the flow rates G of the initial solution, the mass transfer coefficient km, and with decreasing km decreases and G. The analysis of theoretical and experimental data is carried out showing that the decisive role in the course of the microfiltration process is played by the motion regime of the initial solution, Physical-chemical properties, geometry of the membrane channel. The prospects for using the pulsating field in bioreactors and the need for a conceptual approach for the development of promising membrane devices are grounded. The need to create membranes of complex geometric shapes with the possibility of placing turbulent devices in them and the possibility of moving them relative to each other is considered, creating channels of variable cross-section, which will lead to the appearance of a sufficient number of possibilities for creating hydrodynamic instabilities of various intensities. The article touches upon the application of pulsation regimes of destruction or loosening of the polarization layer by means of reciprocating motion of the concentrate, periodic membrane regeneration by tangential pulsating flow or by using reverse pumping.

Effect of Surface Energy Pulses on Supersonic Flow in a Channel of Variable Cross Section

The influence of a surface pulse-periodic supply of energy on the formation of shock-wave structures in a plane channel of variable cross section has been studied. Energy is supplied to the constant cross-section units of the channel with the flow Mach number M = 2. The time-average supplied power corresponds to the combustion of hydrogen with the excess-air coefficient from 1 to 10. The problem is solved within the framework of the Euler equations. A dimensionless approach is used to analyze the effect of sources. The applicability of the analytical relations obtained is confirmed by numerical solution of two-dimensional Euler equations.

Математическая модель и численная методика расчёта на основе ENO-схем течений в каналах переменного сечения с горением

Математическая модель и численная методика расчёта на основе ENO-схем течений в каналах переменного сечения с горением

The formation of an overdriven detonation wave in the flow of methane-oxygen mixtures in a channel of variable cross section

Formation of an overdriven detonation wave in methane-oxygen mixtures in a channel was investigated experimentally The gas mixture was ignited by a spark gap, located at the closed end of the combustion chamber. To create the overdriven detonation wave, a decay of the stationary detonation wave in the transition to a channel with a larger cross-section was carried out. Then, a complex of a shock wave and flame front moved into the channel with converging section. Formation of the overdriven detonation wave with parameters several times greater than those of the Chapman-Jouguet detonation was recorded at the outlet of the conical section. The velocities of the detonation front depend upon the composition of the mixture.

Математическая модель аэродинамики сушильных камер с вертикально-поперечной циркуляцией

In the article, from the standpoint of aerodynamics considered the concept of a mathematical model of the circulation channels marketing chambers of variable cross section with a vertically transverse circulation. Factors affecting the uniformity of the air flow in the pile of lumber. Developed analytical mathematical model of the motion of drying agent on the side channel of variable cross section. Revealed that the parameters of the lateral channel of the drying chamber of variable cross section does not depend on the temperature and humidity of the circulating air, and hence from the "rigidity" of the drying mode.

Effect of the variable cross-section channel on performance of a cusped field thruster at low power

The cusped field thruster has drawn much attention from many institutions due to its wide thrust range, high impulse, and long lifetime. However, lots of experimental results reveal that the cusped field thruster at low power has a poor performance. A cusped field thruster with a variable cross-section channel by putting a ceramic spacer in the channel is introduced in this paper, aimed at improving the thruster performance at low power. The DSMC results validate that the upstream atom density can be increased by a spacer, especially near the wall. Based on simulated results, spacers are put into different positions of the channel. The experimental results show that a suitable spacer can enhance thruster performance at low power, which can be confirmed by the results that the anode efficiency can achieve 40% at 400 V anode voltage and 20 sccm gas flow rate by contrast to 35% without a spacer under the same condition.

Shock Wave Instability in a Channel with an Expansion Corner

2D and 3D transonic flows in a channel of variable cross-section are studied numerically using a solver based on the Reynolds-averaged Navier–Stokes equations. The flow velocity is supersonic at the inlet and outlet of the channel. Between the supersonic regions, there is a local subsonic region whose upstream boundary is a shock wave, whereas the downstream boundary is a sonic surface. The sonic surface gives rise to an instability of the shock wave position in the channel. Computations reveal a hysteresis in the shock position versus the inflow Mach number. A dependence of the hysteresis on the velocity profile given at the inlet is examined.

Fluid-flow features in a plane channel of variable cross section with high clutter for obstacles of various shapes

Fluid-flow features in a plane channel of variable cross section with high clutter for obstacles of various shapes

Detonation Wave Parameters in a Variable Cross Section Channel in Gas Mixture of Methane with Oxygen and Nitrogen

Detonation Wave Parameters in a Variable Cross Section Channel in Gas Mixture of Methane with Oxygen and Nitrogen

Numerical and Analytical Estimation of Parameters of Pulsed Energy Sources Which Do Not Lead to Locking of Supersonic Flow in Channels of Variable Section

In this paper the pulse energy supply into the channel of variable cross section was studied. The approximate formulas were obtained for the value of the input energy, corresponding to the maximal distance which the shock wave from a pulsed power source reached upstream, as well as full power, energy supply period corresponding to the conditions of closing the channel. The applicability of the analytical relationships is confirmed by numerical calculations based on the Euler equations in a quasi one-dimensional approximation

Rarefied gas flow through a long rectangular channel of variable cross section

The method, proposed previously by other authors, is applied here to calculate a mass flow rate of rarefied gas through a long rectangular channel of variable cross-section aspect ratio. The gas flow through this channel is generated by the pressure and/or temperature gradient. The method is based on the results obtained previously on the basis of the kinetic equation and it requires very modest computational efforts. As a demonstration of its application some examples of the mass flow rate calculations for the isothermal and non-isothermal flows through the channels with variable rectangular cross sections are given. The analytical expressions in the case of the hydrodynamic and free molecular flow regimes are proposed.

Acoustic oscillations excited in a variable cross-section channel under annular boiling conditions

Acoustic oscillations excited in a variable cross-section channel under annular boiling conditions

The condition of steady-state flow in a channel of variable cross section in the presence of heat supply and kinetic energy dissipation

An expression for maximum permissible entropy gain is obtained and the condition of passage via the velocity of sound is found for the steady-state flow of an ideal gas in a channel of variable cross section in the presence of heat supply and kinetic energy dissipation. Particular flow examples are considered.