Mass Flow Velocity Research Articles

Effect of emplaced nZVI mass and groundwater velocity on PCE dechlorination and hydrogen evolution in water-saturated sand

The effect of nZVI mass loading and groundwater velocity on the tetrachloroethylene (PCE) dechlorination rate and the hydrogen evolution rate for poly(maleic acid-co-olefin) (MW=12K) coated nZVI was examined. In batch reactors, the PCE reaction rate constant (3.7×10−4Lhr−1m−2) and hydrogen evolution rate constant (1.4 nanomolLhr−1m−2) were independent of nZVI concentration above 10g/L, but the PCE dechlorination rate decreased and the hydrogen evolution rate increased for nZVI concentration below 10g/L. The nonlinearity between nZVI mass loading and PCE dechlorination and H2 evolution was explained by differences in pH and Eh at each nZVI mass loading; PCE reactivity increased when solution Eh decreased, and the H2 evolution rate increased with decreasing pH. Thus, nZVI mass loading of <5g/L yields lower reactivity with PCE and lower efficiency of Fe° utilization than for higher nZVI mass loading. The PCE dechlorination rate increased with increasing pore-water velocity, suggesting that mass transfer limits the reaction at low porewater velocity. Overall, this work suggests that design of nZVI-based reactive barriers for groundwater treatment should consider the non-linear effects of both mass loading and flow velocity on performance and expected reactive lifetime.

High-cadence observations of spicular-type events on the Sun

Chromospheric observations taken at high cadence and high spatial resolution show a range of spicule like features, including Type I, Type II (as well as RBEs and RREs) and those which seem to appear within a few seconds, which if interpreted as flows would imply mass flow velocities in excess of 1000 km/s. This article seeks to quantify and study rapidly appearing spicular type events. We also compare the MOMFBD and speckle reconstruction techniques in order to understand if such spicules are more favourably observed using a particular technique. We use spectral imaging observations taken with the CRISP on the Swedish 1 m Solar Telescope. Data was sampled at multiple positions within the Halpha line profile for both an ondisk and limb location. The data is host to numerous rapidly appearing features which are observed at different locations within the Halpha line profile. The feature's durations vary between 10 and 20 s and lengths around 3500 km. Sometimes, a time delay in their appearance between the blue and red wings of 3 and 5 s is evident, whereas sometimes they are near simultaneous. In some instances features are observed to fade and then re emerge at the same location several tens of seconds later. We provide the first statistical analysis of these spicules and suggest that these observations can be interpreted as the LOS movement of highly dynamic spicules moving in and out of the narrow 60 mA transmission filter used to observe in different parts of the Halpha line profile. The LOS velocity component of the observed fast chromospheric features, manifested as Doppler shifts, are responsible for their appearance in the red and blue wings of Halpha line. Additional work involving data at other wavelengths is required to investigate the nature of their possible wavelike activity.

Assessment of Cavitation Models for Flows in Diesel Injectors With Single- and Two-Fluid Approaches

Several recent cavitation models for the analysis of two-phase flows in diesel injectors with single- and two-fluid modeling approaches have been evaluated, including the Saha–Abu-Ramandan–Li (SAL), Schnerr–Sauer (SS), and Zwart–Gerber–Belamri (ZGB) models. The SAL model is a single-fluid model, while the other two models have been implemented with both single- and two-fluid approaches. Numerical predictions are compared with experimental results available in literature, qualitatively with experimental images of two-phase flow in an optically accessible nozzle, and quantitatively with measured mass flow rates and velocity profiles. It is found that at low injection pressure differentials there can be considerable discrepancy in the predictions of the vapor distribution from the three models considered. This discrepancy is reduced as the injection pressure differential is increased. Implementation of the SS and ZGB models with single- and two- fluid approaches yields noticeable differences in the results because of the relative velocity between the two phases, with two-fluid approach providing better agreement with experimental results. The performance of the SS and ZGB models implemented with the two-fluid approach is comparable with the SAL single-fluid model, but with significantly more computational time. Overall, the SAL single-fluid model performs comparatively better with respect to the other two models.

Comparison of microsac and VCO diesel injector nozzles in terms of internal nozzle flow characteristics

A computational study focused on the inner nozzle flow and cavitation phenomena has been reported in this paper in order to investigate the two most common types of diesel injector nozzles at the present: microsac and valve covered orifice (VCO). The geometrical differences among both types of nozzles are mainly located at the needle seat, upstream of the discharge orifices. In the case of microsac nozzles there is a small volume upstream of the discharge orifices which is not present in VCO nozzles. Due to these geometrical differences among both type of nozzles, differences in the inner flow and the cavitation development have been found and analysed in this research. For the study, two cylindrical nozzles with six orifices and the same outlet diameter have been experimentally characterized in terms of mass flow rate. These measurements have been used to validate the CFD results obtained with the code OpenFOAM used for the analysis of the internal nozzle flow. For the simulations, two meshes that reproduce the microsac and VCO nozzles seat geometry while keeping the same geometry at the orifices have been built. The simulations have been carried out with a code previously validated and able to simulate cavitation phenomena using a homogeneous equilibrium model (HEM) and with RANS approach for the turbulence modelling (RNG k–ε).For the computational study, three injection pressures and different geometries simulating different needle lifts have been used. The comparison among nozzles has been made in terms of mass flow, momentum flux and effective velocity and in terms of other non-dimensional parameters which are useful for describing the inner nozzle flow: discharge coefficient (Cd), area coefficient (Ca) and velocity coefficient (Cv). The analysis performed by studying and comparing the particularities of the flow in each nozzle has been useful in order to explain the experimental differences found in terms of mass flow rate and critical cavitation conditions.One of the main conclusions of this study is the higher influence of the needle on the mass flow, momentum and injection velocity results for the VCO nozzle as compared to the microsac one. Hence, whereas in the first one these variables scale with the needle lift value, in the second one there is an intermediate needle lift from which they stop being influenced by the presence of the needle.Furthermore, the study has also revealed important differences in the proneness to produce cavitation and its morphology. For the VCO nozzle, cavitation phenomenon occurs only in the upper part of the orifice inlet. However, for the microsac nozzle cavitation appears both at the upper and the lower part of the nozzle orifice entrance.

Analysis of the steady state hydraulic behaviour of the ITER blanket cooling system

The blanket system is the ITER reactor component devoted to providing a physical boundary for plasma transients and contributing to thermal and nuclear shielding of vacuum vessel, magnets and external components. It is expected to be subjected to significant heat loads under nominal conditions and its cooling system has to ensure an adequate cooling, preventing any risk of critical heat flux occurrence while complying with pressure drop limits.At the University of Palermo a study has been performed, in cooperation with the ITER Organization, to investigate the steady state hydraulic behaviour of the ITER blanket standard sector cooling system. A theoretical–computational approach based on the finite volume method has been followed, adopting the RELAP5 system code. Finite volume models of the most critical blanket cooling circuits have been set-up, realistically simulating the coolant flow domain. The steady state hydraulic behaviour of each cooling circuit has been investigated, determining its hydraulic characteristic function and assessing the spatial distribution of coolant mass flow rates, velocities and pressure drops under reference nominal conditions.Results obtained have indicated that the investigated cooling circuits are able to provide an effective cooling to blanket modules, generally meeting ITER requirements in term of pressure drop and velocity distribution, except for a couple of circuits that are being revised.

Transformation and intensification of tornado-like flow in a narrow channel during elongation of an oval dimple with constant area

Reynolds averaged Navier–Stokes equations closed using the Menter shear-stress-transfer model have been numerically solved on multiblock intersecting structured grids of various scales. The obtained solution has been used to analyze the separated flow past an elongated oval dimple oriented at 45± on the wall of a narrow plane-parallel channel and to study transformation of the flow with increasing dimple aspect ratio at constant depth and spot area. It is established that, at a dimple width below one-third of the equivalent dimple diameter, intensification of the generated helical vortices observed when the transverse flow velocity exceeds 80% of the average mass flow velocity is accompanied by decrease in the level of hydraulic losses below that in an otherwise identical channel with an equivalent spherical dimple.

Kelvin-Helmholtz instability in coronal mass ejecta in the lower corona

We model an imaged Kelvin-Helmholtz (KH) instability on a coronal mass ejecta (CME) in the lower corona by investigating conditions under which kink ($m = 1$) and $m = -3$ magnetohydrodynamic (MHD) modes in an uniformly twisted flux tube moving along its axis become unstable. We employ the dispersion relations of MHD modes derived from the linearised magnetohydrodynamic equations. We assume real wave numbers and complex angular wave frequencies, namely complex wave phase velocities. The dispersion relations are solved numerically at fixed input parameters (taken from observational data) and various mass flow velocities. It is shown that the stability of the modes depends upon four parameters, the density contrast between the flux tube and its environment, the ratio of the background magnetic fields in the two media, the twist of the magnetic field lines inside the tube, and the value of the Alfv\'en Mach number (the ratio of the tube velocity to Alfv\'en speed inside the flux tube). For a twisted magnetic flux tube at a density contrast of $0.88$, background magnetic field ratio of $1.58$, and a normalised magnetic field twist of $0.2$, the critical speed for the kink ($m = -3$) mode (where $m$ is the azimuthal mode number) is $678$ km\,s$^{-1}$ just as it is observed. The growth rate for this harmonic at KH wavelength of $18.5$ Mm and ejecta width of $4.1$ Mm is equal to $0.037$ s$^{-1}$, in agreement with observations. KH instability of the $m = -3$ mode may also explain why the KH vortices are seen only at the one side of arising CME. The good agreement between observational and computational data shows that the imaged KH instability on CME can be explained in terms of emerging KH instability of the $m = -3$ MHD mode in twisted magnetic flux tube moving along its axis.

New design aspects of cooling scheme for SST-1 plasma facing components

PFC of SST-1 comprising of baffles, divertors and passive stabilizers have been designed and fabricated for a maximum heat load up to 1.0MW/m2. In operational condition, SST-1 divertors and passive stabilizers are expected to operate with a heat load of 0.6 and 0.25MW/m2, respectively. During plasma operation, the heat loads on PFC are required to be removed promptly and efficiently. Thereby the design of an efficient cooling scheme becomes extremely important for an efficient operation of PFC. PFCs are also baked up to 350°C in order to remove absorbed moistures and other gases.3D thermal analysis of PFC using ANSYS has been carried out to ensure its thermal stability. The cooling parameters have been calculated according to average incident flux on divertors and passive stabilizers. Engineering design demonstrated the required mass flow rate and velocity for cooling water in each sub-connection are optimized to be 0.43kg/s and 5.5m/s for efficient heat extraction under steady state heat load. Maximum temperature which PFC could be maintained is 355°C and is well within threshold limits of material property degradation. The header distribution, modeled using AFT fathom, resulted for required parameters within maximum 5% of deviation.

Fluid Analysis and Improved Structure of an ATEG Heat Exchanger Based on Computational Fluid Dynamics

In this study, a numerical model has been employed to analyze the internal flow field distribution in a heat exchanger applied for an automotive thermoelectric generator based on computational fluid dynamics. The model simulates the influence of factors relevant to the heat exchanger, including the automotive waste heat mass flow velocity, temperature, internal fins, and back pressure. The result is in good agreement with experimental test data. Sensitivity analysis of the inlet parameters shows that increase of the exhaust velocity, compared with the inlet temperature, makes little contribution (0.1 versus 0.19) to the heat transfer but results in a detrimental back pressure increase (0.69 versus 0.21). A configuration equipped with internal fins is proved to offer better thermal performance compared with that without fins. Finally, based on an attempt to improve the internal flow field, a more rational structure is obtained, offering a more homogeneous temperature distribution, higher average heat transfer coefficient, and lower back pressure.

Investigation the effects of injection pressure and compressibility and nozzle entry in diesel injector nozzle’s flow

Investigating nozzle’s orifice flow is challenging both experimentally and theoretically. This paper focuses on simulating flow inside diesel injector nozzle via Ansys fluent v15. Validation is performed with experimental results from Winkhofler et al (2001). Several important parameters such as mass flow rate, velocity profiles and pressure profiles are used for this validation. Results include the effects of contraction inside nozzle’s orifice, effect of compressibility; effect of injection pressures and several orifice entries are also simulated in this study. To consider the effect of compressibility, a user defined function used in this simulation. The Cavitation model which is used in this simulation is Singhal et al. (2002) cavitation model. Presto discretization method is used for Pressure equation and second upwind discretization method is used for Momentum equation. Converging Singhal et al. cavitation model is very challenging and it needs several efforts and simulations.

Review of Electrostatic Sensor Applications

Electrostatic sensors have a simple but robust structure, which can detect the electric charge from moving charged particles. Measurement of the dry particle mass flow rate, velocity, and concentration in a conveyor are the main areas of sensor application. This paper considers the measurement methods and techniques that utilize electrostatic sensors for instrumentation. The most significant applications of the sensor are reviewed and a newly developed technique in particle sizing using the spatial filtering method is explained. The results of the study re-emphasize the flexibility, reliability and cost-effective features of the electrostatic sensor for industrial applications.

CFD SIMULATION ON DIFFERENT GEOMETRIES OF VENTURIMETER

This paper describe an analytical approach for comparison of four different models to describe the velocity, pressure, turbulence and mass flow rate taken place in the venturimeter and graph are plotted. Venturimeter are most commonly used for flow meters for measuring volumetric or mass flow rate and velocity of fluid flowing through the venturimeter. Hence are also know as variable head meters. Variable head meters work on the principle that a variation of the flow rate through a constriction with a constant cross-sectional area causes a pressure drop suffered by the fluid as it flows through the constriction. The pressure drop is related to the flow rate, and hence variations of the pressure drop can be used to measure variations in the flow rate. Fluent soft ware was used to plot the characteristics of the flow of fluid through the flow meter and gambit software was used to design the 2D model. Two phase computational fluid dynamic calculation, using K-Epsilon model were employed. The numerical results were validated against experimental data from the literature and were found to be in good agreement. The pressure recovery is better in the venturi meter.

Flow behavior of non-spherical particle flowing in hopper

Ellipsoidal particles flowing in the hopper were simulated by using the discrete element method (DEM), and described by the multi-element method. The contact detection algorithm and equations for ellipsoidal particle motion in hopper were developed. And the simulation results were confirmed by experiment. Additionally, the mass flow rate, pressure distribution and velocity distribution of two kinds of particles were examined. The results show that the mass flow rate of ellipsoidal particles is smaller than that of spherical particles. There is a maximum value of pressure drop at the top of the junction. Besides, the pressure drop decreases with the discharging time increasing. The velocity of spherical particle is larger than that of ellipsoidal.

Optimum design of the injection nozzle system of a three-drive jigger dyeing machine

A jigger dyeing machine is used to dye fabric across the width, which enables the fabric to be passed back and forth in a perfect dyeing bath. A three-drive jigger dyeing machine contains an injection nozzle system. The flowfield inside the injection nozzle system was computed using ANSYS CFX software and was evaluated by mass flow rate, velocity, and pressure. The injection nozzle system was observed by installing two different division plates and by changing the diameter and distance of the outlet holes to improve dyeing efficiency. The division plates have slits and holes help to distribute the dye liquid evenly over all the holes. The standard deviations of the mass flow rate of the division plates with slits and holes were 0.000551 and 0.000368, respectively. The effects of distance and diameter of the outlet holes were analyzed and evaluated by mass flow rate and standard deviation. The developed injection nozzle system of the jigger machine has more uniform mass flow rate. A diameter of 5 mm for the outlet holes and a distance of 50 mm between them were selected to manufacture a prototype. The prototype of the injection nozzle system of the three-drive jigger machine was manufactured and tested. The test results were compared with the computational results from the developed three-drive jigger dyeing machine, the original three-drive jigger dyeing machine, and a classic jigger dyeing machine.

Numerical Simulation of Distribution of Discharged Gas Fire Extinguishing Agent in High Velocity Flow Field

This paper studied the concentration distribution of gas extinguishing agent numerically in high velocity flow field. Civil aircraft power plant compartment has been a difficult area for its high velocity flow field formed after fire happens. Focusing on this issue, certain results, such as mass flow rate of agent gas, total mass of agent and extinguishing efficiency were presented. A typical apparatus of fire extinguishing system was set up, and its fire-fighting efficiency was evaluated. Critical ratio of mass flow rate and flow velocity, gas discharge time and locations of gas sample tubes were recommended. The results and data can provide a practical way in fire extinguishing system evaluation in civil aircraft power plant compartment.

Centrifugal Reactive-Molecular Distillation from High-Boiling-Point Petroleum Fractions. 1. Mathematical Modeling, Screening Variables, and Experimental Validation

The modeling and simulation of the reactive-molecular distillation process (centrifugal type-CRMD) to upgrade high-boiling-point petroleum fractions is presented in this work. A case study is presented for an atmospheric petroleum residue (673.15 K+) of “W” crude oil. The use of the Plackett–Burman and fractional factorial designs (2IV4–1) permitted the evaluation of the effects of the independent variables (evaporator temperature, feed flow rate, percent weight of catalyst, feed temperature, condenser temperature, rotor speed, and system pressure) on the dependent variables: film thickness, surface evaporation rate, distillate mass flow rate, concentration profiles, and velocity profiles. The results showed that the independent variables, the evaporator temperature and the percent weight of catalyst, were relevant operational conditions for the performance of the CRMD process reaching a conversion of the feedstock about 65% at 3 wt % of catalyst and 64% at 5 wt % of catalyst in the distillate stream and ...

Application of fracture mechanics for energetic effects predictions while wood sawing

In the classical approach, energetic effects (cutting forces and cutting power) of wood sawing process are generally calculated on the basis of the specific cutting resistance, which is in the case of wood cutting the function of more or less important factors. On the other hand, cutting forces (or power—more interesting from energetic point of view) could be considered from a point of view of modern fracture mechanics. Cutting forces may be employed to determine not only toughness but also shear yield strength, which are then applied in the models. Furthermore, forecasting of the shear plane angle for the cutting models, which include fracture toughness in addition to plasticity and friction, broadens possibilities of energetic effects modelling of the sawing process even for small values of the uncut chip. Mentioned models are useful for estimation of energetic effects of sawing of every kinematics. However, for band saws and circular sawing machines, the chip acceleration power variation as a function of mass flow and tool velocity ought to be included in analysis of sawing at larger cutting speeds.

Equilibrium and dynamic studies for adsorption of boron on calcium alginate gel beads using principal component analysis (PCA) and partial least squares (PLS)

AbstractIn this paper, boron removal from aqueous solutions by adsorption on calcium alginate gel beads was investigated. Based on the batch tests, calcium alginate gel beads demonstrated a good capacity of adsorption; the maximum capacity obtained was 121 mg/g at pH 6. The aim of this paper is the study of analytical tools for extracting more analytical information from a few experiments. Principal component analysis (PCA) was employed to perform a comparative analysis between different isotherms obtained by varying the percentage of alginate on the adsorbent beads. The calculated fraction of the cumulative sum of squares for all the components (R2X(cum)) and the predictive reliability model based on the value of the correlation coefficient of cross validation (Q2 (cum)) obtained were 0.9639 and 0.8523, respectively. Dynamic system study using 20 different columns was carried out. Partial least squares (PLS) modeling are applied to characterize the effect of the experimental variables on the adsorption process. Some of the descriptors studied were the initial boron concentration (Co), adsorbent mass (m), pH, column diameter (dc), column depth (Z) and superficial flow velocity (U0). Experimental adsorptions were compared against predicted adsorptions and a correlation coefficient (r2) of 0.9927 was obtained.

Second Law Analysis of Al2O3-Water Nanofluid Turbulent Forced Convection in a Circular Cross Section Tube with Constant Wall Temperature

The present paper proposes an analysis based on the second principle of thermodynamics applied to a water-Al2O3 nanofluid. The nanofluid flows inside a circular section tube subjected to constant wall temperature. The aim of the investigation is to understand, by means of an analytical model, how entropy generation within the tube varies if inlet conditions, particles concentration, and dimensions are changed. To gather these information is of fundamental importance, in order to optimize the nanofluid flow. The results show that according to the inlet condition, there is a substantial variation of the entropy generation, particularly when Reynolds number is kept constant there is an increase of entropy generation, whereas when mass flow rate or velocity are taken constant, entropy generation decreases.

Study of the influence of the needle lift on the internal flow and cavitation phenomenon in diesel injector nozzles by CFD using RANS methods

It is well known that cavitation phenomenon in diesel injector nozzles has a strong influence on the internal flow during the injection process and spray development. However, its influence on the flow during needle opening and closing remains still unclear due to the huge difficulties related to performing experiments at partial needle lifts.In this paper, an extended computational study has been performed in a multi-hole nozzle modeling 10 different fixed needle lifts. The internal flow has been modeled with a continuum nozzle flow model that considers the cavitating flow as a homogeneous mixture of liquid and vapour. Due to high Reynolds numbers, turbulence effects have been taken into account by RANS methods using a RNG k–ε model.Firstly, the code has been validated against experimental data at full needle lift conditions in terms of mass flow, momentum flux and effective velocity, showing a fairly good agreement with experimental results.Once the code has been validated, it has been possible to study in depth the internal nozzle flow and its characteristics at the outlet at different partial needle lifts. Nevertheless, not only the main flow features have been explained, but also the cavitation appearance and the turbulence development, which present huge differences between the different needle lifts simulated.