Throughflow Velocity Research Articles

Efficient degradation of carbamazepine using a modified nickel-foam cathode (Ni-FM/CNTs) in penetrating electro-Fenton process

A modified nickel-foam (Ni-FM) cathode coated with multi-walled carbon nanotubes (Ni-FM/CNTs) was synthesized for carbamazepine (CBZ) highly energy-efficient degradation in penetrating electro-Fenton. Scanning Electron Microscopy (SEM) and X-ray diffractometer (XRD) test proves that multi-walled CNTs were successfully coated on the surface of nickel foam. The linear sweep voltammetry (LSV) results revealed the greater electrochemical activity of Ni-FM/CNTs compared to Ni-FM. The H2O2 accumulation performance tests showed that Ni-FM/CNTs cathode had higher H2O2 accumulation performance than Ni-FM cathode, and the H2O2 yield of Ni-FM/CNTs was 5.7 times higher than that of Ni-FM after 1 h of electrolysis. The reaction rate of CBZ degradation in penetrating electro-Fenton process was 2.5 times that of planar electro-Fenton process because the flow-through process enhanced O2 mass transfer and promoted the production of H2O2. The Box-Behnken Design response surface method was used to analyze the factors affecting the degradation efficiency of CBZ in the penetrating electro-Fenton process. The CBZ degradation efficiency could reach 100%, and electric energy consumption was 0.4356 Wh/L at current density of 9 mA/cm2, pH = 3, concentration of Fe2+ was 0.3 mM, and the through-flow velocity of 60 mL/min. The quenching experiment and EPR test results confirmed the degradation of CBZ was mainly the oxidation of·OH, and O2-·is the prerequisite for the production of·OH. Eight possible degradation products of CBZ degradation were identified and the probable degradation route was proposed. The ECOSAR program was used to predict the toxicities of CBZ and its degradation products, and the consequences revealed that the electro-Fenton process has a detoxification effect on CBZ, but may also produce more toxic organic compounds than the parent compound.

Seasonal and Interannual Variability of the Subsurface Velocity Profile of the Indonesian Throughflow at Makassar Strait

AbstractAlthough there have been many previous studies that have interpreted the variability of Indonesian Throughflow transport, the processes that determine its vertical structure have rarely been investigated due to limited observations and model inefficiencies. In this study, a regionally coupled model is developed to address this issue. The model adopts an unstructured model grid, with an ~3‐km resolution within the Indonesian seas and straits, and reveals somewhat inconsistent results compared to previous models with coarser resolutions. The results suggest that the seasonal variability of the depth of the Indonesian Throughflow velocity maximum is partially controlled by the seasonally reversed Karimata throughflow, while the remainder primarily originated from the Mindanao–Sulawesi inflow rather than the Sibutu Strait throughflow. The Mindanao–Sulawesi inflow possesses a subsurface velocity core similar to that of the Makassar Strait, with a deep (shallow) maximum during El Niño (La Niña) years that plays a crucial role in determining the downstream Makassar throughflow profile in the interannual time scale. A sensitivity experiment by fixing Indian Ocean boundary condition shows that the impacts from the Indian Ocean might be significant only within the intraseasonal to seasonal time scales.

Heat transfer enhancement of air-cooled heat sink channel using a piezoelectric synthetic jet array

In the last decade, active devices, such as synthetic jets have been intensively studied for electronics cooling. The present study experimentally and computationally investigates heat transfer performance of synthetic jet arrays used in heat sink channels. The heat sink of the present study consists of multiple flow channels that are parallel to one another. The channel walls behave like fins in that their tops are exposed to the flow. The jets are designed to impinge on the tops and sides of those fins to augment heat transfer. The current study employs a single channel of the heat sink to investigate heat transfer augmentation performance by the jets. The oscillating diaphragms that create the jets are driven by a piezo-bow operating at its second resonant vibrational mode to generate a large oscillatory displacement at a high working frequency. The frequency for this study is 1240 Hz and the measured displacement of the jet-driving diaphragm is 0.5 mm. The corresponding peak velocity of each jet is around 45 m/s and the total power consumption is 1.6 W when operating with 20 jets. Heat transfer experiments using jet arrays of different jet orifice configurations are conducted in a single narrow channel that represents one of the channels of a multi-channel heat sink. With a through-flow velocity of 14.7 m/s driven by a centrifugal fan, the synthetic jet arrays with square orifices achieve 9.3% enhancement on heat transfer coefficient averaged over the entire fin (channel wall) surface, compared to the value for a case with through-flow only. When the channel through-flow velocity decreases to 8 m/s spatially-averaged heat transfer enhancement by the jets is 21.7%; again, averaged over the entire fin (channel wall) surface. In a computational study, the jet diaphragm movement is realized with a dynamic mesh available within the commercial software package ANSYS Fluent. Computed surface-average Nusselt numbers show good agreement with the experimental data, differing by no more than 10%. The numerical study was performed to quantify the effects of system parameters, such as the jet and channel flow rates and orifice-to-fin-surface distance, on heat transfer performance over different sections of the channel (fin) wall. According to the results of the numerical study, the synthetic jets have a strong cooling effect on the channel wall tip region, the nearest surface to the jet orifice, and a weaker effect on the channel side surfaces. It is found that the synthetic jet can enhance locally-averaged heat transfer coefficients at the fin tip by up to 413%, compared to a case with cooling by channel through-flow only.

Critical comparison of electrostatic effects on hydrodynamics and heat transfer in a bubbling fluidized bed with a central jet

In many industrial processes, electrostatic charges are inevitable and affect the hydrodynamic behavior and heat transfer ability of chemical equipment. A comprehensive study of the electrostatic effect on bubble behavior, particle fluctuation velocity and heat transfer coefficient in the fluidized bed with a central jet has been evaluated in this paper by Eulerian-Eulerian two-fluid model coupled with electrostatic model and energy model. The simulated voidage profiles at different positions, bubble detachment time and initial bubble diameter are compared with experimental results from the literature without charge. The bubble behaviors including bubble frequency and bubble numbers, combined with particle fluctuation parameters are analyzed in both charged and uncharged system. The electrostatic effect on two kinds of heat transfer coefficients is quantitatively compared, namely bubble to emulsion phase heat transfers based on the gas throughflow velocity and gas-solid local heat transfer coefficient. Simulation results show that electrostatic charges decrease bubble numbers and granular temperature, whereas the averaged heat transfer coefficients are enhanced. Overall, the electrostatic effect on the hydrodynamic and heat transfer characteristics can be revealed.

Investigations on Twisted Blade for Axial Microfan

By ‘Radial Equilibrium’ principle, an equation was derived to describe the radial distribution of the throughflow velocity, by which a design approach was proposed for the twisted blade of axial microfan. This approach can take into consideration the influence of the radial gradient for the throughflow velocity at the impeller’s outlet, which is different from the traditional design approach for large fans assuming the throughflow velocity remains radially unchangeable. By this design approach, attempt was made on the design for an axial microfan by choosing different twisted powers so as to obtain different shapes of twisted blades and their respective aerodynamic performance was numerically investigated. Compared to the corresponding straight blade and the twisted blade designed by the traditional approach, this new twisted blade can not only enlarge the stable operating range but also improve the flow pressure, which contributes to the improvement of the blade’s aerodynamic performance.

On the Convection in a Porous Medium with Inclined Temperature Gradient and Vertical Throughflow. Part I. Normal Modes

In this analysis, we apply the methods of the theory of linear absolute and convective instabilities to studying the destabilization of transverse modes in a model of convection in an extended horizontal layer of a saturated porous medium with inclined temperature gradient and vertical throughflow. In this first part of the analysis, normal modes are treated and neutral curves are obtained for a variety of values of the horizontal Rayleigh number, Rh, and the Peclet number, Qv. The computations are performed by using a high-precision pseudo-spectral Chebyshev-collocation method. Our results compare well with the results found in the literature for the critical values of the vertical Rayleigh number. It is shown that the horizontal temperature gradient effect, inducing a Hadley circulation, is stabilizing for any fixed value of the throughflow velocity. The throughflow effect is stabilizing, for each of the values of Rh = 0, 10, 20, 30. For higher values of Rh = 40, 50, 60 considered, the influence of increasing throughflow on the stability is mixed. For a vanishing horizontal temperature gradient the critical normal mode is non-oscillatory, for all the values of throughflow. In all the cases of a non-zero horizontal temperature gradient and a non-zero throughflow considered, the critical normal mode is oscillatory, and the oscillatory frequency is an increasing function of both Rh and Qv.

Numerical analysis and simulation experiment of lithospheric thermal structures in the South China Sea and the Western Pacific

The asthenosphere upwelled on a large scale in the western Pacific and South China Sea during the Cenozoic, which formed strong upward throughflow and caused the thermal structure to be changed obviously. The mathematical analysis has demonstrated that the upward throughflow velocity may have varied from 3×1011 to 6×1012 m/s. From the relationship between the lithospheric thickness and the conductive heat flux, the lithospheric heat flux in the western Pacific should be above 30 mW/m2, which is consistent with the observed data. The huge low-speed zone within the upper mantle of the marginal sea in the western Pacific reflects that the upper mantle melts partially, flows regionally in the regional stress field, forms the upward heat flux at its bottom, and causes the change of the lithospheric thermal structure in the region. The numerical simulation result of the expansion and evolution in the South China Sea has demonstrated that in the early expansion, the upward throughflow velocity was relatively fast, and the effect that it had on the thickness of the lithosphere was relatively great, resulting in the mid-ocean basin expanding rapidly. After the formation of the ocean basin in the South China Sea, the upward throughflow velocity decreased, but the conductive heat flux was relatively high, which is close to the actual situation. Therefore, from the heat transfer point of view, this article discusses how the upward heat flux affects the lithospheric thermal structure in the western Pacific and South China Sea. The conclusions show that the upward heat throughflow at the bottom of the lithospheric mantle resulted in the tectonic deformation at the shallow crust. The intensive uplifts and rifts at the crust led to the continent cracks and the expansion in the South China Sea.

F302 A NEW DESIGN APPROACH FOR TWISTED BLADE OF AXIAL MICROFAN(Components-1)

By 'Radial Equilibrium' principle, an equation is derived to describe the radial distribution of the throughflow velocity, by which a design approach is proposed for the twisted blade of axial microfan. This approach can take into consideration the influence of the radial gradient for the throughflow velocity at the impeller's outlet, which is different from the traditional design approach for large fans assuming the throughflow velocity remains radially unchangeable. By this design approach, attempt is made on the design for an axial microfan by choosing different twisted powers so as to obtain different shapes of twisted blades and their respective aerodynamic performance is numerically investigated. Compared to the corresponding straight blade and the twisted blade designed by the traditional approach, this new twisted blade can not only enlarge the stable operating range but also improve the flow pressure, which contributes to the improvement of the blade's aerodynamic performance.

Measurement and analysis of three-dimensional flow in a centrifugal fan volute with large volute width and rectangular cross-section

Among all the elements of a centrifugal fan, the volute is the one that has the lowest flow efficiency. Therefore, improving the performance of the volute is an efficient way to improve the total performance of a centrifugal fan. To contribute a better understanding of the flow structure in the fan volute, the three-dimensional flow in a centrifugal fan volute with a large volute width and rectangular cross-section has been measured in detail by means of five-hole probe at three different flowrates. The time-average swirling and throughflow velocity, static and total pressure distributions on eight cross-sections in the throughflow direction of the volute are presented. The results show the formation and development of the flow in the fan volute of this type, indicate the variation of flow parameters, and discover some peculiar flow phenomena different from the traditional understanding. On the basis of the experimental results, the main hydraulic losses in this kind of fan volute have been preliminarily classified and analysed. The results show that the traditional one-dimensional design method of the volute should be further improved as it is only based on the law of momentum moment conservation and the ideal assumption that the distribution of flow parameters are uniform at the volute inlet.

Mesocosm seepage experiment to restore the buffering capacity of acidified wet heath soils

Soils of wet heathlands have lost their buffering capacity as a result of acidification, eutrophication, and desiccation. Many characteristic plant species have disappeared from these ecosystems because of the unfavourable soil conditions. Restoration projects should aim at counteracting the negative effects of acidification in particular. Blocking of drainage ditches to increase groundwater influence and lime application to improve soil pH and buffering capacity have been applied in many restoration projects in the Netherlands, but with varying success. In this mesocosm experiment, the restoration of the soil buffering capacity of degraded wet heath soil was studied. Groundwater with low or high calcium and bicarbonate concentrations and low or high flow velocities was applied to soil columns filled with wet heath soil. Measurements of the nutrient concentrations in soil pore water and soil extractions revealed that restoration of the soil buffering capacity was optimal at both high calcium concentrations and high through-flow velocity. It was concluded that high concentrations of calcium are more effective than high flow velocity in the reloading of the buffer capacity. Furthermore, the restoration was limited to the soil layers that were in direct contact with the groundwater, which stresses the need for higher groundwater levels in degraded wet heathlands.

The cycle of instability: stress release and fissure flow as controls on gully head retreat

AbstractGully head and wall retreat has commonly been attributed to fluvial scour and head collapse as a result of soil saturation, sapping or piping. The empirical evidence to substantiate these conceptual models is sparse, however, and often contradictory. This paper explores the hydrological and mechanical controls on gully head and wall stability by modelling the hydrology, stability and elastic deformation of a marl gully complex in Granada Province, south‐east Spain. The hydrological and slope‐stability simulations show that saturated conditions can be reached only where preferential fissure flow channels water from tension cracks into the base of the gully head, and that vertical or subvertical heads will be stable unless saturation is achieved. Owing to the high unsaturated strengths of marl measured in this research, failure in unsaturated conditions is possible only where the gully head wall is significantly undercut. Head retreat thus requires the formation of either a tension crack or an undercut hollow. Finite‐element stress analysis of eroding slopes reveals a build up of shear stress at the gully head base, and a second stress anomaly just upslope of the head wall. Although tension cracks on gully heads have often been attributed to slope unloading, this research provides strong evidence that the so called ‘sapping hollow’ commonly found in the gully headwall base is also a function of stress release. Although further research is needed, it seems possible that ‘pop out’ failures in river channels may be caused by the same process. The hydrological analysis shows that, once a tension crack has developed, throughflow velocity in the gully headwall will increase by an order of magnitude, promoting piping and enlargement of this weakened area. It is, therefore, possible to envisage a cycle of gully expansion in which erosion, channel incision or human action unloads the slope below a gully head, leading to stress patterns that account for the tension crack and a stress‐release hollow. The tension crack promotes faster throughflow, encouraging hollow enlargement and piping, which undercut the gully head. The tension crack permits the development of positive pore‐water pressures behind the gully head, leading either to failure or contributing to toppling. Finally the debris may be eroded by fluvial action, unloading a new section of slope and completing the cycle of gully head retreat. Copyright © 2001 John Wiley & Sons, Ltd.

Experimental Measurements of Rotordynamic Forces Caused by Front Shroud Pump Leakage

Unsteady forces generated by fluid flow through the impeller shroud leakage path of a centrifugal pump were investigated. Different pump shroud geometries were compared, and the effect of leakage path inlet swirl (pump discharge swirl) on the rotordynamic forces was examined for various ratios of fluid throughflow velocity to impeller tip speed. A short axial length leakage path reduced the measured forces, while curvature appeared to increase the destabilizing forces when inlet swirl was present. It was observed that changing the inlet swirl velocity does not appear to significantly affect the measured forces for a given leakage flow coefficient, but any nonzero inlet swirl is destabilizing when compared to cases with no inlet swirl.

Influence of pressure, fluidization velocity and particle size on the hydrodynamics of a freely bubbling fluidized bed

The hydrodynamics have been studied in a cold, freely bubbling, pressurized fluidized bed. The bed has a cross-section of 0.2 m×0.3 m and was operated at pressures between 0.1 and 1.6 MPa and at excess gas velocities of 0.2 and 0.6 m/s. The bed material was silica sand with a mean particle diameter of d p =0.45 mm. Comparisons were made with previous results obtained with particles of d p =0.7 mm. The hydrodynamic results are similar for the two different particle sizes when plotted vs the excess gas velocity. The results also show that the bed expansion, bubble rise velocity, bubble volume fraction and visible bubble flow rate fall on single curves if plotted vs a dimensionless potentially available drag force, while the bubble frequency, the mean pierced length and the through-flow velocity of gas through the bubble do not. The dimensionless drag force is a suitable scaling parameter as long as the particles do not respond to the gas-phase velocity fluctuations and as long as the dense phase does not expand. At high pressures, an increased gas–particle interaction, in combination with turbulent fluctuations in the gas phase, can be used to explain the increased bubble instability, with a corresponding increased bubble splitting and dense phase expansion. The gas–particle interaction also increases with decreasing particle size, which may help explain the maximum stable bubble size for group A particles observed by many workers.

Laser Velocimeter Measurements in the Pump of an Automotive Torque Converter: Part II—Unsteady Measurements

The unsteady velocity field found in the pump of an automotive torque converter was measured using laser velocimetry. Velocities in the inlet, mid-, and exit planes of the pump were investigated at two significantly different operating conditions: turbine/pump rotational speed ratios of 0.065 and 0.800. A data organization method was developed to visualize the three-dimensional, periodic unsteady velocity field in the rotating frame. For this method, the acquired data are assumed to be periodic at synchronous and blade interaction frequencies. Two shaft encoders were employed to obtain the instantaneous angular position of the torque converter pump and turbine at the instant of laser velocimeter data acquisition. By proper “registration” of the data, visualizing the transient interaction effects between the stator and the pump, and between the pump and the turbine, was possible. Results showed strong cyclic velocity fluctuations in the pump inlet plane as a function of the relative stator-pump position. Typical percent periodic fluctuations in the through flow velocity were 70 percent of the average throughflow velocity. The upstream propagation influence of the turbine on the pump exit plane flow field was seen to be smaller. Percent periodic fluctuations of the throughflow velocity were typically 30 percent. The effect of the stator and turbine on the midplane flow field was seen to be negligible. The incidence angle at the pump inlet fluctuated by 27 and 14 deg for the 0.065 and 0.800 speed ratios, respectively. Typical slip factors at the exit were 0.965 and fluctuated by less than 1 percent.

Experimental and Computational Results From the NASA Lewis Low-Speed Centrifugal Impeller at Design and Part-Flow Conditions

The NASA Lewis Low-Speed Centrifugal Compressor (LSCC) has been investigated with laser anemometry and computational analysis at two flow conditions: the design condition as well as a lower mass flow condition. Previously reported experimental and computational results at the design condition are in the literature (Hathaway et al., 1993). In that paper extensive analysis showed that inducer blade boundary layers are centrifuged outward and entrained into the tip clearance flow and hence contribute significantly to the throughflow wake. In this report results are presented for a lower mass flow condition along with further results from the design case. The data set contained herein consists of three-dimensional laser velocimeter results upstream, inside, and downstream of the impeller. In many locations data have been obtained in the blade and endwall boundary layers. The data are presented in the form of throughflow velocity contours as well as secondary flow vectors. The results reported herein illustrate the effects of flow rate on the development of the through flow momentum wake as well as on the secondary flow. The computational results presented confirm the ability of modern computational tools to model the complex flow in a subsonic centrifugal compressor accurately. However, the blade tip shape and tip clearance must be known in order to properly simulate the flow physics. In addition, the ability to predict changes in the throughflow wake, which is largely fed by the tip clearance flow, as the impeller is throttled should give designers much better confidence in using computational tools to improve impeller performance.

Analysis of Throughflow Velocity in Two-Dimensional Fluidized Bed Bubbles

The formation of gas bubbles is one of the most characteristic phenomena of fluidized beds. Many unique properties of fluidized beds can be related directly to the presence of bubbles and are dominated by their behavior. Therefore, accurate prediction of parameters such as bubble shape and size, voidage variation and throughflow are practically important. In the present analysis, an approximate model, based on a strongly idealized picture of the bubble formation has been presented. The bubbling gas fluidized bed has regions of low solids density comprised of gas pockets or voids. The observed voids exhibited a variety of shapes (Halow and Nicoletti, 1992), depending upon the material and fluidization velocity. In the low-velocity experiments with the finer materials, rounded voids are observed. However, with coarser materials, voids were typically large and bluntnosed. In the image analyses work, reported by Gautam (1989), in a bed operating slightly above the incipient fluidization, elongated bubbles (a > b, as shown in Figure 1) were observed for glass beads (sp. gravity = 2.5) of mean diameter 500 μm and flattened bubbles (a < b) were seen for mean particle diameter of 350 μm. Also, he noticed the dependence of throughflow velocity on the elongation of the bubble as it traverses up the bed. Additionally, throughflow velocity was found to be independent of the excess gas flow rate through the bed. The digitized image of a typical bubble (refer Gautam et al., 1994) which shows that the bubble were elongated in the vertical direction and were more elliptical than circular. Therefore, description of a bubble on the basis of just one diameter, either the horizontal or the vertical or an equivalent diameter, as has been done by many researchers in the past, is rather incomplete. It is inferred from the present work that the bubble aspect ratio plays an important role in predicting an accurate gas flow through the bubble.

Effect of bubble coalescence on throughflow velocity in a 2-D fluidized bed

A theoretical analysis is presented of the effect of bubble coalescence on throughflow gas velocity. In order to predict the motion of interacting two-dimensional circular bubbles, bubble velocity is approximated by adding to its rise velocity in isolation the velocity that the particulate phase would have at the position of the nose if the other bubble were absent. It is inferred that throughflow gas velocity is significantly increased during bubble interaction as compared with the case of single isolated bubbles. Also, it was found that a lateral motion of the rear bubble is induced if the interaction bubbles are not vertically aligned.

Navier-Stokes Analysis of the Pump Flow Field of an Automotive Torque Converter

A three-dimensional, incompressible, viscous flow code, developed by NASA AMES (INS3D) using the pseudo-compressibility method, is modified for torque converter flow field computations. The code is used to predict the velocity and pressure fields in the pump of an automotive torque converter. Numerical results are compared to measured static pressure and velocity distributions. Results show that: 1) the code can fairly well predict the Cp distribution, the distribution of the through-flow velocity, and the secondary flow field, 2) pump rotation has a major effect on the secondary flow field and on the mass-averaged total pressure loss, and 3) inlet velocity profiles have a profound effect on the mass-averaged total pressure loss.

An Experimental Investigation of Throughflow Velocities in Two-Dimensional Fluidized Bed Bubbles: Laser Doppler Anemometer Measurements

Detailed nonintrusive measurements have been made to determine the throughflow velocity in isolated fluidized bed bubbles. In air-fluidized beds, the throughflow component has been rather neglected and measurements of the visible bubble flow alone have, therefore, failed to clarify the overall distribution of gas flow between the phases. A single component fiber optic laser Doppler anemometer was used to map the fluid flow through a bubble rising in a two-dimensional bed. The bed was fluidized at a superficial velocity slightly higher than incipient. The conditioned sampling technique developed to characterize the periodic nature of the bubble phase flow revealed that the throughflow velocity in two-dimensional beds increases linearly with increasing distance from the distributor, thereby enhancing the convective component in the interphase mass transfer process. Bubble growth was accounted for and the end-effects were minimized. Dependence of the bubble throughflow on the elongation of the bubble was observed thus confirming the theoretical analysis of some previous investigators. However, experimental evidence presented in this paper showed that the existing models fail to accurately predict the convective component in the bubble phase of two-dimensional fluidized beds.

Influence of pressure and fluidization velocity on the hydrodynamics of a fluidized bed containing horizontal tubes

An experimental investigation of the influence of horizontal tubes on the bubble behaviour and through-flow velocity of gas inside bubbles was carried out and the influence of pressure and fluidization velocity was studied. The visible bubble flow rate and the gas velocity through the bubbles were measured simultaneously in a pressurized fluidized bed, using capacitance and Pitot-static pressures probes respectively. Silica sand with a mean particle diameter of 0.7 mm was fluidized at pressures between 01. and 1.6 MPa, in a bed of 0.2 × 0.3 m cross-section. Six different horizontal tube configurations were used and comparisons were made with results obtained in the same bed operated without tubes. The results from the bed with tubes show that the influence of pressure and fluidization velocity is basically the same as in the bed without tubes; an increase in pressure and fluidization velocity increases the bubble activity. At low excess gas velocities, the influence of immersed tubes on the bubble behaviour is less pronounced than at high excess gas velocities. Measurements and visual observations show that a small tube pitch gives a more uniform distribution of the visible bubble flow over the bed cross-section. At a combination of high pressure, high excess gas velocity and a large tube pitch, a preferred bubble path was observed in the centre of the bed cross-section. The pressure probe measurements show that the through-flow velocity of gas inside the bubbles is in most cases higher when tubes are present in the bed. The through-flow velocity consistently decreases with increasing pressure in the bed without tubes. The tendency is largely the same at a low excess gas velocity when tubes are present, but at a high excess gas velocity the through-flow velocity first decreases and then increases as the pressure is increased.