Local Flow Rate Research Articles

Flow at the Centrifugal Pump Impeller Exit With Circumferential Distortion of the Outlet Static Pressure

The effects of circumferential outlet distortion of a centrifugal pump diffuser on the impeller exit flow were investigated. A fence with sinusoidal width variation was installed at the vaneless diffuser exit. The flow field was measured at the impeller exit with and without the fence, using a hot film probe and an unsteady pressure sensor. Flow parameters varied with the circumferential position and the mean flow parameters plotted against the local flow rate at each circumferential position showed loops along the quasi-steady curves, which were obtained from the result without the fence. Simple theoretical calculations were used to predict the velocity components at the impeller exit with the relative flow angle or total pressure assumed. Good result was obtained when the relative flow angle was assumed to vary quasi-steadily, not constant with the local flow rate. The radial velocity was also reasonably predicted when the total pressure was assumed to vary quasi-steadily. A simple method is proposed to predict the impeller exit flow with downstream blockage in two-step sequence: the first step deals with the diffuser alone to obtain static pressure distribution at the diffuser inlet, while the second step deals with the impeller alone to obtain velocity components distribution at the impeller exit.

03/02604 Potential and cost-effectiveness of CO 2 reductions through energy measures in Swedish pulp and paper mills : Möllersten, K. et al. Energy, 2003, 28, (7), 691–710

At the Tritium Process Laboratory (TPL) in Japan Atomic Energy Research Institute (JAERI), Caisson assembly for tritium safety study (CATS) with 12 m3 of large airtight vessel (Caisson) was fabricated for confirmation and enhancement of fusion reactor safety to estimate the tritium behavior in the case, where the tritium leak accident should happen. One of the principal objectives of the present studies is the establishment of simulation method to predict the tritium behavior after the tritium leak accident should happen in a ventilated room. As for the understanding of initial tritium behavior until the tritium concentration become steady, the precise estimation of local flow rate in a room and time-dependent release behavior from the leak point are essential to predict the tritium behavior by simulation code. The three-dimensional eddy flow model considering, tritium-related phenomena was adopted to estimate the local flow rate in the 50 m3/h ventilated Caisson. The time-dependent tritium release behavior from the sample container was calculated by residence time distribution function. The calculated tritium concentrations were in good agreement with the experimental observations. The primary removal tritium behavior was also investigated by another code. Tritium gas concentrations decreased logarithmically to the time by ventilation. These observations were understandable by the reason that the flow in the ventilated Caisson was regarded as the perfectly mixing flow. The concentrations of tritiated water measured, and indications of tritium concentration by tritium monitors became gradually flat. This phenomena called ‘tritium soaking effect’ was found to be reasonably explained by considering the contribution of the exhaustion velocity by ventilation system, and the adsorption and desorption reaction rate of tritiated water on the wall material which is SUS 304. The calculated tritium concentrations were in good agreement with the experimental observations. The effectiveness of these codes was thus proved.

QUALITY MANIPULATION AND MONITORING IN PROCESSES: PRODUCT-CLIMATE INTERACTION, QUALITY CONTROL

QUALITY MANIPULATION AND MONITORING IN PROCESSES: PRODUCT-CLIMATE INTERACTION, QUALITY CONTROL

Analysis of visitation frequency through particle tracking method based on LES and model experiment.

As ventilation efficiency in a room is not always uniformly distributed, an index for measuring ventilation efficiency at a concerned point or in a concerned local domain is required. Local ventilation efficiency is often represented by the rate of the averaged concentration of the local domain to that of exhausted air from the room. From the age theory of air, it is well known that the averaged concentration in a room corresponds to the mean staying time of contaminant. Evaluating the domain-averaged concentration (Cdomain) means evaluating the average staying time of the contaminant in the domain. It can be only one part of the whole room and can be considered as an occupied zone. Visitation frequency (VF) and the average staying time of the contaminant for one visitation in the local domain (Tp) are introduced to analyze the average staying time of the contaminant in the local domain. The value of VF is strongly affected by the position of the local domain in the room; that is, the position of the local domain in the whole flow field of the room. Tp represents the property of the flow pattern in the local domain. As the indication of VF and Tp represent the mechanism for forming the domain-averaged concentration, they are deeply related to local purging flow rate, which represents the airflow rate for defining the domain-averaged concentration. As VF and Tp are related to the contaminant transportation property, it is effective to analyze them by particle tracking method. A CFD method of large eddy simulation (LES) was thereby carried out in this study. The prediction result by LES is also validated by a precise model experiment. In this paper, the detailed analysis of VF and Tp is carried out on the basis of the particle tracking method utilizing the LES result in order to clarify the mechanism of the domain-averaged concentration. The analyzed room has one supply inlet and one exhaust outlet. A clear re-circulating flow, generated by the forced ventilation, is observed in the room. The value of VF is examined with three types of local domains in the room model. In the room model, VF shows a value of 5.70 when the local domain occupies half of the room. It becomes smaller when the size of the local domain is reduced.

Catalytic heat generating element for autonomous domestic heating systems

New heat-conducting metal porous reinforced catalysts were developed to manufacture a catalytic heat generating element (CHGE) of 25 kW power. The element was subjected to thermophysical, hydraulic and ecological testing. Local temperature and gas flow rates were determined in different places of the outer catalytic bed surface. We have estimated impact of the convective and radiant transfer in total CHGE heat generation. Dynamics of CHGE startup was studied. A prototype of the catalytic water boiler supplied with a CHGE of 25 kW power was manufactured and tested. The boiler provides below yield of toxic waste: CO 5–10 ppm, NO x traces, CH 4 10–20 ppm, CO 2 10 vol.%, the other gases 89.5 vol.%. CHGE is promising as a device for ecologically safe heat production for household appliances.

Local cerebral blood flow during lithium-pilocarpine seizures in the developing and adult rat: role of coupling between blood flow and metabolism in the genesis of neuronal damage.

Coupling between local cerebral blood flow and local cerebral metabolic rate for glucose is involved in the pathogenesis of epilepsy-related neuronal damage in the adult brain; however, its role in the immature brain is unknown. Lithium-pilocarpine-induced status epilepticus is associated with extended damage in adult rats, mostly in the forebrain limbic areas and thalamus, whereas damage was moderate in 21-day-old rats (P21) or absent in P10 rats. The quantitative autoradiographic [14C]iodoantipyrine technique was applied to measure the consequences of lithium-pilocarpine status epilepticus on local cerebral blood flow. In adult and P21 rats, local cerebral blood flow rates increased by 50% to 400%; the highest increases were recorded in regions showing damage in adults. At P10, local cerebral blood flow rates decreased by 40% to 60% in most areas, except in some forebrain regions showing no change during status epilepticus. In areas injured when status epilepticus was induced in adults, a strong hypermetabolism (Fernandes et al., 1999) not matched by comparable local cerebral blood flow increases was present in rats of all ages, whereas in damage-resistant areas, local cerebral metabolic rate for glucose and local cerebral blood flow remained coupled in the three age groups. Thus, the level of coupling between blood flow supply and metabolism is not involved in seizure-related brain damage in the developing brain, which appears to be resistant to the consequences of such a mismatch.

Velocity distributions and volume flow rates in the nip and translational regions of a co-rotating, self-wiping, twin-screw extruder

Velocity measurements were carried out in the nip and translational regions of a co-rotating, self-wiping, twin-screw extruder using laser Doppler anemometry. Significantly higher values of axial and tangential velocity components were measured in the nip region, indicating that the fluid accelerated as it moved through the nip. The local volume flow rates in the nip and translational regions were calculated from the measured velocity field. The volume flow rate in the nip was about four times higher than that in the translational region, indicating the positive displacement character of the nip region. The total volume flow rate calculated over the entire cross-section of the extruder was in agreement with the experimentally measured volume flow rate.

Further accuracy and convergence results on the modeling of flows down inclined planes by weighted-residual approximations

We study the reliability of two-dimensional models of film flows down inclined planes obtained by us [Ruyer-Quil and Manneville, Eur. Phys. J. B 15, 357 (2000)] using weighted-residual methods combined with a standard long-wavelength expansion. Such models typically involve the local thickness h of the film, the local flow rate q, and possibly other local quantities averaged over the thickness, thus eliminating the cross-stream degrees of freedom. At the linear stage, the predicted properties of the wave packets are in excellent agreement with exact results obtained by Brevdo et al. [J. Fluid Mech. 396, 37 (1999)]. The nonlinear development of waves is also satisfactorily recovered as evidenced by comparisons with laboratory experiments by Liu et al. [Phys. Fluids 7, 55 (1995)] and with numerical simulations by Ramaswamy et al. [J. Fluid Mech. 325, 163 (1996)]. Within the modeling strategy based on a polynomial expansion of the velocity field, optimal models have been shown to exist at a given order in the long-wavelength expansion. Convergence towards the optimum is studied as the order of the weighted-residual approximation is increased. Our models accurately and economically predict linear and nonlinear properties of film flows up to relatively high Reynolds numbers, thus offering valuable theoretical and applied study perspectives.

Hydrodynamic and metallurgical characterization of industrial flotation banks for control purposes

An industrial flotation circuit consisting of five parallel rougher flotation banks, each bank provided with 9 cells of 42.5 m 3, was characterized. The air flow rate delivered over the cross-sectional area was directly measured using a simple device that provides a continuous measurement of local gas flow rate. The range of superficial gas rate was 0.8–1.2 cm/s. Gas holdup was measured using a pulp sampler providing estimations of local gas holdup of 15–22%. Bubble size distribution was measured using the UCT bubble size analyzer and the mean bubble size was compared with direct observations of the bubble size distribution near the pulp/froth interface. The Sauter average bubble size observed was 0.9–1.1 mm. The effective residence time of the liquid and solid phases was evaluated from residence time distribution (RTD) measurements, using radioactive tracers. The mean solid residence time was 5% lower than the mean liquid residence time. RTD of non-floatable mineral was also evaluated at different particle size classes. Measurements of grade, solid percentage and particle size profiles from the top to the bottom of different cells along the bank gave a complete diagnosis of particle distribution and mixing. The use of compressed air and the effect of pulp level on the bank flotation kinetics was evaluated. Thus, a useful correlation between mass recovery and enrichment ratio from industrial flotation cells was found for control purposes.

Investigation of Channel Formation Due to Random Packing in a Burning Waste Bed

Obtaining energy from sustainable sources such as waste and biomass has required a significant extension of combustion technology. Many of the advanced technologies are based on thermal treatment in gas-solid packed-bed systems such as gasifiers, incinerators and biomass furnaces. In this paper channel formation in a packed bed of fuel solids as a result of the random packing process has been investigated. Channelling causes a severely uneven distribution of the primary airflow through a packed fuel bed and results in poor combustion performance of the furnace. By assuming Furnas packing, a general relationship is derived between the bed porosity and the particle size distribution and the proposed methodology is tested against limited experimental data. A probability density function (PDF) of truncated Gaussian type is assumed for the random size distribution at local areas within the bed and the local bed porosity is calculated accordingly. Then by solving the fluid flow equations through the porous bed, flow rate profiles are obtained at the top surface of the bed. Two particulate systems were investigated as a function of change in bed height and pressure drop through the grate. Depending on bed height and pressure drop through the grate, maximum local flow rate at the top surface of the bed can be 1.5 ∼ 2 times higher than the minimum flow rate for the particulate system with a narrower size range (2.5 mm–18 mm) while the ratio of the maximum to minimum flow rate can reach as high as 8 ∼ 32 for the particulate system with a wider size range (0.677 mm–20 mm). Visualization of the velocity profile inside the bed reveals that flow passages are slightly curved in some areas but straight in others. The largest channel observed presents a ‘perfect’ straight passage of airflow running from the very bottom of the bed to the very top of the bed. Channelling inside a burning bed of solid waste in a large-scale travelling grate incinerator plant was also investigated using a unique in-house prototype instrument. The result shows that the combustion processes within the bed were dominated largely by the circles of formation and subsequent collapse of channels.

Effect of circumferential outlet distortion on the flow characteristics at the impeller exit of a centrifugal pump

Centrifugal impellers are exposed to downstream circumferential outlet distortions due to non-axisymmetric volutes or diffusers. This paper explores the effect of circumferential outlet distortion on the flow characteristics at the impeller exit of a centrifugal pump. A fence with non-uniform height was installed at the vaneless diffuser exit to create the outlet distortion, and then unsteady velocity and static pressure were measured at the impeller exit. The instantaneous and mean flow fields at the impeller exit varied with the circumferential position. Plots of the flows against the local flowrate showed hysteretic loops that deviated from the quasi-steady curves obtained from the flows without the fence. When the assumption of quasi-steady variation was applied to the present impeller-diffuser interaction, the prediction for the total and static pressure was reasonable but showed a phase difference for the absolute velocity.

Evidence for a major role of skeletal muscle lipolysis in the regulation of lipid oxidation during caloric restriction in vivo.

A lipolytic process in skeletal muscle has recently been demonstrated. However, the physiological importance of this process is unknown. We investigated the role of skeletal muscle lipolysis for lipid utilization during caloric restriction in eight obese women before and after 11 days of very low-calorie diet (VLCD) (2.2 MJ per day). Subjects were studied with indirect calorimetry and microdialysis of skeletal muscle and adipose tissue in order to analyze substrate utilization and glycerol (lipolysis index) in connection with a two-step euglycemic-hyperinsulinemic (12 and 80 mU/m(2). min) clamp. Local blood flow rates in the two tissues were determined with (133)Xe-clearance. Circulating free fatty acids and glycerol decreased to a similar extent during insulin infusion before and during VLCD, and there was a less marked insulin-induced reduction in lipid oxidation during VLCD. Adipose tissue glycerol release was hampered by insulin infusion to the same extent ( approximately 40%) before and during VLCD. Skeletal muscle glycerol release was not influenced by insulin before VLCD. However, during VLCD insulin caused a marked (fivefold) (P < 0.01) increase in skeletal muscle glycerol release. The effect was accompanied by a fourfold stimulation of skeletal muscle blood flow (P < 0.01). We propose that, during short-term caloric restriction, the reduced ability of insulin to inhibit lipids, despite a preserved antilipolytic effect of the hormone in adipose tissue, is caused by an augmented mobilization of fat from skeletal muscle, and that a physiological role of muscle lipolysis provides a local source of fatty acids.

Analysis of heat transfer during mist chilling of a packed bed of spheres simulating foodstuffs

Heterogeneity of heat transfer was studied in a packed bed of 8 mm spheres cooled by a two-phase flow composed of air and fine ( 8 μm diameter) water droplets. Local heat fluxes in the packed bed were measured in both single- and two-phase flow and analyzed as a function of water mass flow rate, the surface temperature of the spheres and air velocity. Heat transfer was enhanced in the two-phase flow: the maximum value rose to 2.8 under experimental conditions. The study shows that heat transfer depends on several factors: axial position, temperature difference, water mass flow rate and air velocity. A marked heterogeneity of heat transfer was demonstrated and was correlated with the local mass flow rate of the collected water.

Direct measurement of porous media local hydrodynamical permeability using gas MRI

The concept of hydraulic permeability is at the core of modeling single phase or multi-phase flow in heterogeneous porous media, as it is the spatial distribution of the permeability that primarily governs the behavior of fluid flow in the medium. To date, the modeling of fluid flow in porous media has been hampered by poor estimates of local permeability. Magnetic Resonance Imaging is well known for its ability to measure non-invasively the local density and flow rate of different fluids saturating porous media [1,2]. In this paper we demonstrate the first non-invasive method for the direct measurement of a single projection of the local permeability tensor of a porous medium using gas-phase MRI. The potential for three-dimensional imaging of the medium permeability is also discussed. The limitations of the method are listed and results are presented in a model porous medium as well as in a real oil reservoir rock.

Simulation study of intentional tritium release experiments in the caisson assembly for tritium safety at the TPL/JAERI

At the Tritium Process Laboratory (TPL) in Japan Atomic Energy Research Institute (JAERI), Caisson assembly for tritium safety study (CATS) with 12 m 3 of large airtight vessel (Caisson) was fabricated for confirmation and enhancement of fusion reactor safety to estimate the tritium behavior in the case, where the tritium leak accident should happen. One of the principal objectives of the present studies is the establishment of simulation method to predict the tritium behavior after the tritium leak accident should happen in a ventilated room. As for the understanding of initial tritium behavior until the tritium concentration become steady, the precise estimation of local flow rate in a room and time-dependent release behavior from the leak point are essential to predict the tritium behavior by simulation code. The three-dimensional eddy flow model considering, tritium-related phenomena was adopted to estimate the local flow rate in the 50 m 3/h ventilated Caisson. The time-dependent tritium release behavior from the sample container was calculated by residence time distribution function. The calculated tritium concentrations were in good agreement with the experimental observations. The primary removal tritium behavior was also investigated by another code. Tritium gas concentrations decreased logarithmically to the time by ventilation. These observations were understandable by the reason that the flow in the ventilated Caisson was regarded as the perfectly mixing flow. The concentrations of tritiated water measured, and indications of tritium concentration by tritium monitors became gradually flat. This phenomena called ‘tritium soaking effect’ was found to be reasonably explained by considering the contribution of the exhaustion velocity by ventilation system, and the adsorption and desorption reaction rate of tritiated water on the wall material which is SUS 304. The calculated tritium concentrations were in good agreement with the experimental observations. The effectiveness of these codes was thus proved.

Estimation of NOx Emissions in Thermal Power Plants Using Neural Networks

In this paper a neural network-based strategy is proposed for the estimation of the NOx emissions in thermal power plants, fed with both oil and methane fuel. A detailed analysis based on a three-dimensional simulator of the combustion chamber has pointed out the local nature of the NOx generation process, which takes place mainly in the burners’ zones. This fact has been suitably exploited in developing a compound estimation procedure, which makes use of the trained neural network together with a classical one-dimensional model of the chamber. Two different learning procedures have been investigated, both based on the external inputs to the burners and a suitable mean cell temperature, while using local and global NOx flow rates as learning signals, respectively. The approach has been assessed with respect to both simulated and experimental data.

Hypervascularization in the magnocellular nuclei of the rat hypothalamus: relationship with the distribution of aquaporin-4 and markers of energy metabolism.

In the magnocellular nuclei of the hypothalamus, there is a rich vascular network for which the function remains to be established. In the supraoptic nucleus, the high vascular density may be one element, which together with the water channel aquaporin-4 expressed in the astrocytes, is related to a role in osmoreception. We tested the osmoreception hypothesis by studying the correlation between vascular and cellular densities in the paraventricular nucleus and the supraoptic nucleus. Whether aquaporin-4 is likely to contribute to osmoreception was tested by studying the distribution in the magnocellular nuclei of the hypothalamus. The high vascular density may also reflect a high metabolic activity due to the synthesis of vasopressin and oxytocin. This metabolic hypothesis was tested by studying the regional cytochrome oxidase histochemistry, the local cerebral blood flow, and the density of glucose transporter type-1 in the supraoptic and paraventricular nuclei. All the magnocellular nuclei were characterized by an extended and intense aquaporin-4 labelling and a weak cytochrome oxidase histochemistry. The highest vascular density was found in the supraoptic nucleus and the magnocellular regions of the paraventricular nucleus. The local cerebral blood flow rates were surprisingly low in the paraventricular nucleus and the supraoptic nucleus in comparison to the cerebral cortex. Furthermore in these nuclei, the antibody for glucose transporter type-1 revealed two populations of vessels differing by their labelling intensity. The similarities observed between the different nuclei suggest that, in the hypothalamus, all magnocellular regions sense the plasma osmolarity. The low local cerebral blood flow, and the patterns of glucose transporter type-1 labelling and cytochrome oxidase histochemistry suggest that the high vascularization of these hypothalamic nuclei is not related to a high metabolic capacity in basal conditions.

Flow Simulation in Stochastic Porous Media

A family of gamma distributions can be used to model the pore size distributions in a range of stochastic porous media. Our simu lator generates distributional and net flow data for different fluid flow regimes through such networks. The outputs from the simu lation show strong relationships between mean flow and the variance of pore radii for turbulent, laminar, molecular and capillary flow. We observe also affine relationships between the coefficient of variation of local flow rate and the variance of pore radii for each of the above flow modes.

Calcium mass transport and sandstone diagenesis during compaction-driven flow: Stevens Sandstone, San Joaquin basin, California

Sediment compaction provides a limited source of fluids for diagenesis and drives fluid flow at average rates of only ∼1 mm/yr. Nevertheless, many geochemical and petrographic studies of diagenesis provide evidence of significant mass transport in systems where fluid flow appears to be compaction driven. This apparent discrepancy could arise because diagenetic studies generally are concerned with relatively permeable petroleum reservoirs. Focused fluid flow through permeable zones could increase local flow rates and allow mixing of fluids from different sources. This study uses the Stevens Sandstone of the San Joaquin basin to explore the potential diagenetic effects of fluid focusing during compaction-driven flow over a 5 m.y. period. Reactive-transport simulations incorporate a new kinetic expression for plagioclase dissolution and suggest that rate-limited plagioclase dissolution drove calcium enrichment of pore fluids and caused precipitation of calcite, kaolinite, and albite. In spite of the importance of this rate-limited reaction, simulations show that influx of fluids from compacting shale could limit the distribution of calcite and kaolinite in adjacent sandstones. Although calcium mass transport is predicted on a scale of kilometers, upward flow of calcium-rich fluids from deep beds does not significantly increase calcite volume relative to closed-system predictions. Increased transverse dispersivity increases mixing, which further limits precipitation of calcite and kaolinite. Results are consistent with field observations of fluid chemistry, although simulations account for

Simulation analysis of substrate utilization in the mammary gland of lactating cows.

A kinetic modelling approach was developed and investigated with the aim of predicting the utilization of major substrates in the mammary gland and milk secretion rates in the lactating cow at varying concentrations of substrate in arterial blood. The model includes kinetic equations of transport and metabolism of glucose, acetate, free amino acids and free fatty acids in secretory cells and a phenomenological description of autoregulation of local blood flow, in which an energy criterion of control has been used. The predicted relationships between the rate of milk secretion and glucose levels in the blood are consistent with experimental results. Differential stimulation of alpha-lactalbumin synthesis causes increments in local blood flow and milk secretion rate in the model. The results of the study suggest that there is no simple relationship between the level of substrates in the blood and milk yield and contents of fat and protein in milk. This is because the effect on production of varying patterns of substrate concentrations in the blood is mediated by network interactions at the level of secretory cell metabolism and microcirculation. However, dynamic modelling provides a rational framework for developing such predictive tools.