Unsteady-state Flow Research Articles

Gas–liquid–powder flow in moving particles: Operational and non-operational regimes

An experimental study has been carried out for gas–liquid–powder–solid four-fluid flow in a packed bed. This system simulates the complex flow conditions in an ironmaking blast furnace which involves the upward flow of gas and unburnt coal/char and the downward flow of coke and molten iron and slag. It is shown that depending on the flow conditions, both steady and unsteady state flows can be observed, giving the so-called operational and non-operational regimes. The effects of solid, liquid, powder and gas flow conditions on the two regimes have been quantified. The non-operational regime stems from the flooding caused by high superficial gas and liquid velocities, and powder mass flux and/or hanging caused by high powder mass flux and low gas velocity. The operational regime expands with an increase in solid velocity, and contracts with an increase in gas and liquid velocities and/or powder mass flux.

Parametric study of unsteady-state flow modulation in trickle-bed reactors

Unsteady-state liquid flow modulation (periodic operation) was investigated for hydrogenation of alpha-methylstyrene to cumene in a hexane solvent over 0.5% Pd on alumina spheres. This test reaction was run under both gas and liquid reactant-limited conditions. It is shown that periodic liquid flow modulation can alter the supply of liquid and gaseous reactants to the catalyst and result in reactor performance different from that obtained under steady-state conditions. The effect of key parameters such as extent of gas/liquid limitation, total cycle period, cycle split, and liquid mass velocity were investigated experimentally to demonstrate the cause–effect relationships in periodic operation. Performance enhancement was observed for a wide range of operating conditions under gas reactant limitation. It was strongly dependent upon the extent of catalyst wetting under liquid-limited conditions. The feasibility of achieving improved reactor performance is shown to depend on the extent of reactant limitation, the cycle period and split, mean liquid mass velocity, and the improvement of liquid maldistribution by periodic operation. Moreover, performance enhancement is dependent upon the induced flow modulation frequency and this is discussed in relation to the natural frequency of the governing process.

Automatic Control Valve–Induced Transients in Operative Pipe System

In most cases, the final configuration of complex pipe networks is attained simply by connecting subsystems initially designed to work separately. Thus, automatic control valves (ACV) are often installed in the confluence nodes where the subsystems meet. The present paper deals with the response and hydraulic behavior of ACVs, topics on which data are scarce. More precisely, attention is focused on transients, which occur in a water-distribution pipe system in operation due to the action of an ACV, both from an experimental and numerical point of view. The aim of the water-hammer field tests is to enlarge the amount of the experimental data concerning unsteady-state flow processes in operating pipe systems. The numerical model extends to field conditions and ACVs laboratory work on the hydraulic characterization of valves and the unsteady-state friction simulation.

Simple waves on a shear gas flow in a channel of constant cross section

The plane-parallel unsteady-state shear gas flow in a narrow channel of constant cross section is considered. The existence theorem of solutions in the form of simple waves of a set of equations of motion is proved for a class of isentropic flows with a monotone velocity profile over the channel depth. The exact solution described by incomplete beta-functions is found for a polytropic equation of state in a class of isentropic flows.

Free-surface flow of hyperconcentrations

A mixture of fluid and solid particles with high sediment concentration (hyperconcentration) is described by a non-Newtonian rheological model incorporating the yield stress, a linear (viscous) stress, and a quadratic (turbulent-dispersive) term. Unsteady flow of hyperconcentration down an inclined plane is studied: first the set of equations governing the flow are derived, then velocity profiles for steady uniform motion are illustrated. The solution for unsteady state flow is obtained in term of permanent waves; their speed is derived and the possible surface profiles are illustrated as functions of a dimensionless parameter describing the relative importance of the linear and quadratic term. When the viscous stress overwhelms the turbulent-dispersive one, earlier relations for a Bingham fluid are recovered. It is shown that more types of gravity currents are possible than in a Newtonian fluid; these include some cases of permanent waves propagating up a slope.

Intellection of Transport Mechanism of Multi-Mixtures in the Vertical Pipe by Air Lifting System for Deep Sea Manganese Nodules

ABSTRACT In an air lift pumping system, the air is gradually lifted within the vertical lifting pipe by the injection of air into the fully developed sea water pipe. When the water velocity is greater than the settling velocity of nodules, the manganese nodules are floated with water in the lifting pipe. In this type of transporting mechanism of multi-mixture in the pipe, unsteady state flow should be considered due to the unstable behavior of air flow. Therefore, we have developed unsteady state transport model in pipe and analyzed for the flow of multi-mixture of air, sea water, and manganese nodules. From the results of these studies, we have proposed the system configurations of development of manganese nodules on deep seabed, that can be instantly operated in laboratory as well as pilot scales.

燃料集合体信頼性実証試験 ＢＷＲ高燃焼度８×８燃料集合体熱水力試験

Nuclear Power Engineering Corporation (NUPEC) has completed the proving test for thermal-hydraulic performance of high burnup 8×8 fuel assembly. The high-burnup 8×8 fuel is a new type of BWR fuel assembly. New concepts such as ferrule type spacer and a large diameter central water rod are introduced in order to improve the thermal margin and reactor shut down margin for the higher uranium enrichment. The purpose of this test is to prove the thermal-hydraulic performance of this fuel and to verity the current BWR thermal-hydraulic design base.The tests were carried out in an out-of pile test facility that can simulate the high pressure and high temperature conditions of BWRs. An electrically heated test assembly simulated a BWR fuel bundle on full scale.The current BWR design method was compared with measured thermal-hydraulic data (data for critical power under steady state and unsteady state conditions, pressure drop and flow induced vibration of fuel rod). It was verified that the current BWR core design base has the enough reliability.

Water Control in Producing Wells: Influence of an Adsorbed-Polymer Layer on Relative Permeabilities and Capillary Pressure

Summary To determine modifications of oil/water two-phase-flow properties after injection of water-soluble polymers, unsteady-state flow experiments were performed on both water- and oil-wet (silanetreated) sandstones. The same imbibition cycle (water displacing oil) under the same conditions was performed on the same core, first without any polymer and then after polyacrylamide had been adsorbed within the core. The capillary pressure was measured directly along the core by use of water- and oil-wet semipermeable membranes, while relative permeabilities were determined from the measurement of the saturation profile (by gamma ray absorption), outlet fluid production, and pressure drop. The action of adsorbed polymer on relative permeabilities was found to be the same with both water- and oil-wet cores (i.e. a selective reduction of the relative permeability to water with respect to the relative permeability to oil). The trend was somewhat different for the capillary pressure. For the case of water-wet sandstones, the capillary pressure remained positive but increased dramatically after polymer adsorption. Because the polymer has little effect on the interfacial tension (IFT), this effect was attributed to the reduction of pore-throat size caused by macromolecule adsorption and to a possible improvement of the wettability of the core to water. For the case of oil-wet sandstone, the capillary pressure curve moved from negative to positive values, indicating that, in addition to pore-size restriction, the wettability of the core changed after polymer adsorption. This wettability change also induced a dramatic drop in residual oil saturation (ROS).

Process dynamics for overflow devices of rectangular, circular, parabolic and triangular shape — loss prevention applications

The problem of unsteady-state liquid flow across overflow devices of various shapes has been investigated. Dimensionless efflux times to evacuate a given amount of liquid from an upstream vessel or basin through an overflow conduit or weir as a function of dimensionless height of the liquid crest were computed for four specific overflow device shapes: rectangular, circular, parabolic and triangular. Analytical expressions were developed for this purpose in all cases except circular. Generalized comparison charts were developed for the cases of (1) equal flow areas of the overflow devices and (2) equal maximum flow capacities. Two examples illustrating application of the equations and charts developed in this paper to loss prevention scenarios are also presented.

Gas-Cap Effects in Pressure-Transient Response of Naturally Fractured Reservoirs

Summary This paper presents a theoretical framework of gas-cap effects in naturally fractured reservoirs. General pressure solutions are derived for both pseudosteady-state and unsteady-state matrix-fracture interporosity flow. Deviation from the fracture or fracture-matrix response occurs as the gas-cap effect is felt. Anomalous slope changes during the transition period depend entirely on the contrast between the fracture anisotropy parameter,λ1, and matrix-fracture interporosity parameter, λ, and between the total gas-cap storage capacitance (1 − ω1) and oil-zone matrix storage (1 − ω). A composite double-porosity response is observed for ω1 ≤ ω1c and 1.0 ≤ λ1/λ ≤ 1000. A triple-porosity response is observed for ω1 ≥ ω1c and 140 < ωλ1/λ < 1.0E05.

Effects of Heterogeneity and Anisotropy on Probe Measured Permeabilities

Abstract Numerical simulations and laboratory experiments were used to study effects of heterogeneity and anisotropy on probe measured permeabilities. Simulation results show that the geometric factors for unsteady-state flow measurements are not different from the ones obtained for steady-state. Effects of a nearby flow barrier on probe measured permeability are studied experimentally and numerically, and it is concluded that the effect of a local flow barrier is negligible when the barrier is located farther than one-half of a probe-tip diameter from the probe. Probe measured permeability on a damaged formation is profoundly affected by the damaged zone thickness. Working with geometric factors, a methodology to obtain undamaged and damaged zone permeabilities, and damaged zone thickness is developed. To obtain such information uniquely three measurements with three different probe tip sizes are required. The effects of anisotropy on probe measured permeability are also investigated by introducing tensorial permeability for probe measurements. Several simulation runs were performed for different anisotropy ratios at various cross-bedding angles. Results are presented in the form of dimensionless parameters that can be used to determine depositional dip angle and permeabilities in the principal directions.

Brownian Particle Adsorption in Unsteady-State Viscous Flows in Pores

In this study, an idealized pore model is used to examine the salient features of Brownian particle adsorption onto the inner pore walls in unsteady-state flow. An important example is the expansion/contraction of the alveolar region of the lung that gives rise to the unsteady-state gas flow and can have a significant effect on the transport and adsorption of submicron particles. An idealized pore model with an oscillating outer wall is developed to systematically study fluid and Brownian particle motion as well as adsorption. The unsteady-state gas flow is derived in a general way using a Fourier series representation of the oscillating outer wall in order to simulate various patient specific breathing patterns. The Smoluchowski–Chandrasekhar equation is used to describe the convective-diffusion of a solution of non-interacting Brownian particles. A perturbation method is adopted to obtain analytical solutions for the Brownian particle concentration and flux behavior. The leading order solution describes pure unsteady-state diffusion, while the first-order solution takes into account the effects of fluid convection. As expected, the adsorption of Brownian particles is enhanced during inhalation cycles and is reduced during exhalation cycles. An interesting feature of the first-order solution is the appearance of local particle concentration maximum (“hot spots”) between the wall and centerline of the pore due to large zero-order concentration gradients in those regions. These solutions can be used to maximize or minimize deposition by controlling the various parameters such as breathing pattern, flow rate, and particle concentration. We also summarize the general domains of the problem of Brownian particle motion for unsteady-state flows in pores.

非定常河川水質混合の数値計算モデルの開発

A mathematical model was developed to predict the un-steady state two dimensional distribution of pollutant discharged from non-point and point sources to a natural water channel. The model was composed of the hydrodynamic and dispersion models.A hydrodynamic model was formulated following Leendertes procedure and modified to be able to apply on un-steady state flow resulted from rainfall run-off. And the dispersion model derived according to Peaceman and Rachford nonlinear formulation was made considering two-dimensional movement of dissolved pollutant in meandering non-uniform river.Hydrological concentration of the study area were examined on site where the longitudinal dispersion coefficient of fluid practicles was determined by measuring the peak dye concentration, for hydrodynamic model as well as dispersion model.The computational procedures were tested on the study site of Seom-jin river, Korea. The result of the application of this model was analyzed and presented in this paper.

CONSISTENT LOCAL ERROR COMPUTATIONS PART I: THEORY

In Part I of this paper we examine the notion of invariant quantities in problems encountered in computational mechanics. These invariant quantities are then used to verify results obtained by numerical techniques. Examples in rigid-body dynamics, elastostatics and unsteady-state heat flow are presented. In Part II, we use the invariant quantities to compute consistent local errors in a finite-element analysis.

A Graphical Method for Storage Coefficient Determination from Quasi-Steady State Flow Data

A simple, approximate but practical graphical method is proposed for estimating the storage coefficient independently from the transmissivity value, provided that quasi-steady state flow data are available from a pumping test. In the past, quasi-steady state flow distance-drawdown data have been used for the determination of transmissivity only. The method is applicable to confined and leaky aquifers. The application of the method has been performed for various aquifer test data available in the groundwater literature. The results are within the practical limits of approximation compared with the unsteady state flow solutions.

Unsteady-state flow induced by a well in a deformable stratum interacting with the adjacent rocks

Unsteady-state plane radial flow induced by a well in a thin deformable stratum is studied taking into account the stratum interaction with the adjacent rocks. The stratum permeability is assumed to depend on the lateral deformation. The behavior of the well productivity properties for harmonic reservoir pressure oscillations and after pressure drawdown in a bilayered stratum is analyzed. Steady-state well behavior under these conditions was studied in [1]. A qualitative estimate of the well productivity variation due to a stepwise pressure change in an adjacent stratum was previously derived in [2].

Particle Reentrainment from a Fine Powder Layer in a Turbulent Air Flow

ABSTRACT Particle reentrainment from a fine powder layer was investigated both in a steady-state flow and in an unsteady-state (accelerated) flow. Experiments were conducted in a rectangular channel, where a powder layer of fly ash was placed. The average air velocity was increased at a constant rate in the range of 0.01–0.6 m/s2 up to a certain velocity and, thereafter, it was maintained at the velocity. The reentrainment flux was measured automatically by an electrostatic method. Microscopic observation showed that small aggregates were reentrained randomly from the surface of the powder layer, and then the reentrainment gradually progressed through the depth of the powder layer. Through these processes, surface renewal of the powder occurred. The experimental results also showed that the distribution of adhesive strength (wall shear stress) was approximated by a log-normal distribution. Further, the time-delay of the reentrainment was found to be represented by two simple exponential functions with dif...

Modeling of blood rheological behavior in unsteady-state shearing flows

Issues of blood flow modeling under unsteady-state conditions at moderate shear rates are considered using a blood rheological model accounting both for the viscoelastic properties and the thixotropy caused by erythrocyte aggregation. The resulting shear stress versus time relations for single shear rate steps and the dependence of the complex viscosity components on the shear rate amplitude in oscillating shear flow show good qualitative correspondence with the experimental data reported in the literature.

Studies of instability of two-phase flows in parallel channels

Experiments were carried out to determine boundaries of unsteady-state flows of a two-phase water-air mixture in three parallel vertical channels. It is shown that under certain conditions of parallel operation of individual channels self-sustained fluctuations of the pressure drop can appear and that interchannel interations can lead to unstable two-phase flow regimes with stable hydrodynamic characteristics of the individual channels and the whole system. It is shown that these fluctuations are caused by nonlinear characteristics of the two-phase flow.

Modeling of vortex structures on the lateral surface of a cylinder in a longitudinal flow

The problem of generation of vortex structures by ejection of a jet through an annular slot on a cylindrical surface in a longitudinal flow is considered. Results of modeling of large-scale vortices and their effect on local characteristics of the wall boundary layer are presented. The modeling is based on numerical integration of the Navier-Stokes equations in an axisymmetric formulation. An unsteady-state flow with separation and entrainment of vortices by the main stream is obtained. The decrease in the friction drag achievable in devices of this kind is estimated.