Longitudinal Mass Flow Research Articles

Asymmetric flow effect in a horizontal natural ventilated tunnel with different aspect ratios under the influence of longitudinal fire locations

This paper has analyzed the asymmetric flow effect of fire-induced thermal flow in a horizontal tunnel under the natural ventilation condition by conducting large eddy simulations (LES). The key objective is to reveal and to have a better understanding of the asymmetric flow effect caused by the upstream and downstream tunnel length difference. The mechanism behind it can be explained based on the conservation of mass and dynamic force analysis on the smoke and fresh air. The strength of the asymmetric flow effect is characterized by the mass flow rate of the induced longitudinal flow (net mass flow rate of a cross-section). An empirical correlation to predict the induced longitudinal mass flow rate is proposed. Furthermore, the law of smoke and air flow distribution within a horizontal tunnel is established. The proportion of smoke (or air) flowing out (or coming in) through the opening increase (or decrease) linearly with the increasing distance between that opening to the fire location. The variation of the air flow with the longitudinal fire location in a tunnel is more sensitive than the smoke flow. Results have shown that as the fire approaches the tunnel exit from the middle of the tunnel, the smoke spilling out through this opening is reduced from 50% to 40%, while the fresh air incoming from this opening is increased from 50% to 100% and vice versa.

Numerical simulation on the development of periodic three-dimensional disturbances in a supersonic boundary layer

The results of a numerical study of the development of periodic pulsations in a supersonic boundary layer on a flat plate are presented at a Mach number of 2.5 and a unit Reynolds number of 8×106 m–1. Using the software complex ANSYS, the complete Navier-Stokes equations were solved. Periodic mass flow disturbances with a frequency of 20 kHz were introduced into the boundary layer through a small-diameter hole on the surface of the model. Downstream the profiles of the longitudinal mass flow pulsations were recorded, and spectral analysis of the data was carried out. The main characteristics of the development of unstable disturbances in both physical and wave spaces are obtained.

Onset of the Kelvin-Helmholtz instability in partially ionized magnetic flux tubes

Context. Recent observations of solar prominences show the presence of turbulent flows that may be caused by Kelvin-Helmholtz instabilites (KHI). However, the observed flow velocities are below the classical threshold for the onset of KHI in fully ionized plasmas. Aims. We investigate the effect of partial ionization on the onset of KHI in dense and cool cylindrical magnetic flux tubes surrounded by a hotter and lighter environment. Methods. The linearized governing equations of a partially ionized two-fluid plasma are used to describe the behavior of small-amplitude perturbations superimposed on a magnetic tube with longitudinal mass flow. A normal mode analysis is performed to obtain the dispersion relation for linear incompressible waves. We focus on the appearance of unstable solutions and study the dependence of their growth rates on various physical parameters. An analytical approximation of the KHI linear growth rate for slow flows and strong ion-neutral coupling is obtained. An application to solar prominence threads is given. Results. The presence of a neutral component in a plasma may contribute to the onset of the KHI even for sub-Alfv\'enic longitudinal shear flows. Collisions between ions and neutrals reduce the growth rates of the unstable perturbations but cannot completely suppress the instability. Conclusions. Turbulent flows in solar prominences with sub-Alfv\'enic flow velocities may be interpreted as consequences of KHI in partially ionized plasmas.

High resolution imaging of colliding blast waves in cluster media

Strong shocks and blast wave collisions are commonly observed features in astrophysical objects such as nebulae and supernova remnants. Numerical simulations often underpin our understanding of these complex systems, however modelling of such extreme phenomena remains challenging, particularly so for the case of radiative or colliding shocks. This highlights the need for well-characterized laboratory experiments both to guide physical insight and to provide robust data for code benchmarking. Creating a sufficiently high-energy-density gas medium for conducting scaled laboratory astrophysics experiments has historically been problematic, but the unique ability of atomic cluster gases to efficiently couple to intense pulses of laser light now enables table top scale (1 J input energy) studies to be conducted at gas densities of >1019 particles cm−3 with an initial energy density >5 × 109 J g−1. By laser heating atomic cluster gas media we can launch strong (up to Mach 55) shocks in a range of geometries, with and without radiative precursors. These systems have been probed with a range of optical and interferometric diagnostics in order to retrieve electron density profiles and blast wave trajectories. Colliding cylindrical shock systems have also been studied, however the strongly asymmetric density profiles and radial and longitudinal mass flow that result demand a more complex diagnostic technique based on tomographic phase reconstruction. We have used the 3D magnetoresistive hydrocode GORGON to model these systems and to highlight interesting features such as the formation of a Mach stem for further study.

Reverse osmosis at elevated temperatures: influence of temperature on degree of concentration polarization and transmembrane flux

A model describing the influence of temperature on longitudinal distribution of the degree of concentration polarization (CP) and transmembrane flux in reverse osmosis systems was developed. The model is based on the following assumptions: (1) membrane morphology is temperature independent; (2) transport characteristics of membranes are invariant with their coordinate; (3) specific water permeability of membranes is based on exponential dependence of viscosity vs. temperature; (4) temperature dependence of membrane rejection is assumed to be linear. The proposed model gives quantitative correlations between the longitudinal mass flow and the CP degree at different operating temperatures. The model enables analyzing the influence of temperature, mass flow, bulk concentration, axial velocity, channel geometry, physical properties and membrane rejection on longitudinal distribution of the degree of CP. This model can be hybridized with sub-models describing driving force, gel resistance, etc., and segmented into a more advanced algorithm for modeling longitudinal variation of characteristics. The model does not contain digital integration and can be easily incorporated into optimization algorithms.

Modeling the influence of temperature on degree of concentration polarization in reverse osmosis systems

A model describing the influence of temperature on degree of concentration polarization is proposed. The model is based on the following assumptions: (1) membrane morphology is temperature-independent; (2) transport characteristics of membrane are invariant with coordinate; (3) specific water permeability of the membrane is based on exponential dependence of viscosity vs. temperature; (4) temperature-dependence of membrane rejection is assumed to be linear. Proposed models permit quantitative correlations of longitudinal mass flow and degree of concentration polarization at different operating temperatures. It enables analysis of the influence of temperature, mass flow, bulk concentration, axial velocity, channel geometry, physical properties and membrane rejection on longitudinal distribution of concentration polarization degree. The submitted model does not contain digital integration and can be segmented into optimization algorithms.

Theoretical Analysis of Concentration Polarization Effect on VOC Removal by Pervaporation

Pervaporation is an innovative membrane-based separation technology for volatile organic compound (VOC) removal from contaminated groundwater. Concentration polarization is a process phenomenon occurring in pervaporation and several other membrane-based separation technologies. Concentration polarization, defined as concentration gradient of permeating solute between the bulk and the region near the membrane surface, becomes a limiting factor in pervaporation separations using high-performance membrane materials in VOC removal operations. Thus, the ability to predict the impact of concentration polarization upon process performance is highly desirable in process design and optimization. A mathematical model was developed to illustrate the interplay between concentration polarization and process performance in pervaporation operation of VOC removal in a membrane channel with rectangular cross section. By incorporating pervaporative mass transfer, laminar hydrodynamics, and boundary-layer theory, the model was built to allow theoretical analysis of the sensitivity of flow velocity, feed concentration, and concentration polarization index (CPI) upon the transmembrane flux and longitudinal mass flow.

Dynamic analysis and optimum design for control of beams with time-dependent changes of length

Structural systems with longitudinal mass flow can be seen in belt-conveyers, running magnetic tapes and flexible manipulators, etc. Transverse vibration problems of flexible longitudinally extensible beams are considered as a special class of vibration problems of structural systems with longitudinal mass flow. The optimum design problem to control the dynamic response of such structural systems is very important from engineering and practical viewpoints, but until now it has not been the subject of much study.

Modeling Concentration Polarization Phenomena for Shell-Side Flow in Ultrafiltration Process

A correlation for the longitudinal mass flow of a dissolved component in terms of the degree of concentration polarization has been developed. The solution developed is applicable to shell-side flow and is based on the assumptions that the flow is to be isothermal, laminar, incompressible, and steady-state. Balance equations for viscous and diffusion boundary layers are the core of the model. Integration of these equations over the control volume of a hexagonal configuration has been carried out. This model permits analysis of the influence of mass flow, bulk concentration, velocity, and channel geometry on the degree of concentration polarization. In addition, it can give the mass flow by using the degree of concentration polarization as an input variable. The solution presented can be segmented and built into a complicated algorithm of a membrane-based process. The solution does not contain digital integration and permits simulation and analysis of the influence of various factors. Calculated data are included.

Modelling concentration polarization phenomena for membrane channel with cylindrical geometry in an ultrafiltration process

A correlation for longitudinal mass flow of dissolved component against degree of concentration polarization has been developed. The developed solution is applicable to tube-side flow and based on the assumptions that the flow is to be isothermal, laminar, incompressible and steady state. Balance equations for viscous and diffusion boundary layers are the core of the model. Integration of these equations over the control volume of the cylindrical configuration has been carried out. This model permits the analysis of the influence of mass flow, bulk concentration, and velocity on the degree of concentration polarization. It can also give mass flow using the degree of concentration polarization as an input variable. The presented solution can be segmented and built into a complicated algorithm of a membrane-based process. The solution does not contain digital integration and permits simulation and analysis of the influence of various factors. The calculated data are included.

Dynamic Behavior and Sensitivity Analysis for Structural Systems with Longitudinal Mass Flow.

The dynamic behaviors of the structural systems with longitudinal mass flow are very important from engineering points of view. However, they have not been studied so detailly, especially in general manners for various structures with different boundary conditions. In this study, structural systems with longitudinal mass flow were considered as flexible moving beams in longitudinal direction, and the flexible moving beams were taken as the longitudinal mass flow inside the idealized massless pipes with the same rigidity of the beams and a method of dynamic analysis was derived. And complex eigenvalue analysis and dynamic stability analysis of non-cyclic and cyclic structural systems were held by following the dynamic analysis method and considerations on dynamic behaviors and stability were taken for various boundary conditions from view points of energy and property matrices etc. It is known that the dynamic stabilities mainly depend upon such parameters as mass fiow's velocities, tensions, elastic modulus and cross sectional areas etc. A method of sensitivity analysis of complex eigenvalues with respect to such parameters was also presented here. Then we showed an application of the sensitivities which may extend the stable areas. Based on the presented methods, numerical examples of complex eigenvalues and sensitivities are obtained and examined and the applications of the sensitivities are also discussed to show the effectiveness of the method.

A Study on Dynamic Response Analysis of Beams with Time-dependent Change of Their Lengths.

The dynamic problems of beams whose lengths change with time in longitudinal direction are often found in industrial manipulator systems. However, characteristic matrices of such system depend on time and the dynamic response analysis becomes very complex. Some works on such problems have been done for stringsre(1)-(4), But there are not so many about the dynamic response analysis for beams with time-dependent changes of their lengths(5)-(8). Though dynamic unstability may possible occur in such problems and be significant in practical problems but it has not been studied fully yet. Then the aim of this study is to present a convenient and effective dynamic response analysis method for such moving beams with time-dependent change of their lengths by making use of the developed method of dynamic analysis in our previous works for vibrating beams with longitudinal mass flow and to examine the dynamic behaviors through numerical examples by the method. Comparisions of the results by the proposed method with exprimental results done by us and with ones in other typical analytical study are made to confirm the validity and effectiveness of the method.

The Effect of Two-Dimensional Surface Roughness on the Load-Carrying Capacity of a Thin Compressible Gas Film

The influence of two-dimensional surface roughness on a very low clearance gas bearing slider is analyzed for conditions typical of current and near term hard disk data storage products. A model lubrication equation including finite width effects, compressibility and molecular slip is first developed and expressed in terms of the product variable, Z = PH. The analytical solution is then obtained by a combined variation of parameters and perturbation expansion method. Results obtained show that the product variable, which is proportional to longitudinal mass flow per unit depth, is not influenced by the details of surface roughness but is instead influenced by the statistics of the roughness distribution. The gas film pressure, however, is found to be a function of both the roughness details and statistics. The bearing load support is increased by the surface roughness, with the roughness first influencing the load through a second order effect.

Resistive ballooning modes in helical axis stellarators with longitudinal mass flow

The magnetohydrodynamic equilibrium equation for magnetic confinement systems with helical symmetry and longitudinal plasma flow is derived. The incompressible resistive ballooning mode equation for systems with a coordinate of symmetry and rigid longitudinal flow is also derived. A reduced equation is then obtained by expanding the ballooning mode equation for a system with a large field period length compared with the plasma cross section. An analytic solution is obtained for a model equilibrium with circular flux surfaces. In the limit of small longitudinal velocity, the static mode width and growth rate scaling as the resistivity to the one-third power are recovered. For small growth rates and large longitudinal velocity, these growth rates are driven by the interaction of the magnetic curvature and the centrifugal force with the radial pressure and mass density gradient, respectively, and scale linearly with the resistivity at a reduced level.

DIFFERENT RATES TRANSLOCATION OF14C-L-α-ALANINE (U) AND TRITIATED WATER IN THE XYLEM VESSELS OF TOMATO PLANTS

A solution of 5 mM 14C-L-α-alanine in tritiated water was allowed to perfuse the xylem vessels of tomato stem segments. In each stem segment an exponential distribution gradient for THO was found, the slope of which was dependent on the length of the stem segment and the perfusion velocity. Nearly all the THO was retained in the stem segment whereas a great amount of 14C-alanine could be recollected. Thus the 14C-alanine was recollected in a solution of other water molecules than those it was introduced in. A similar phenomenon could be observed, if 14C-L-α-alanine or 14C-D-sucrose dissolved in THO were allowed to flow through a Sephadex G-10 column. The results clearly demonstrate, that mass flow in xylem vessels goes along with exchange and diffusion-like processes. Moreover experimentally they show that different velocities for the movement of organic solutes and THO in other long distance translocation systems (sieve tubes) – as reported in literature – need in no way be in conflict with an assumed longitudinal mass flow of their contents.