In situ characterization of mixing and sedimentation dynamics in an impinging jet ballast tank via acoustic backscatter

Impinging jets are utilized in numerous applications, including nuclear waste treatment, for both the erosion of sediment beds and maintaining particulates in suspension. Pulse‐echo ultrasonic methods offer great potential for the in situ monitoring of critical mixing and settling dynamics, in concentrated dispersions. A non‐active scaled version of a Highly Active Storage Tank at Sellafield, UK, was profiled with an acoustic backscatter system under various jet firing conditions. An advanced analysis technique enabled the direct quantification of dispersion concentration changes from the converted backscatter attenuation. Hence, the erosion and mixing capability of the jets, and settling kinetics were characterized. It was found that jet operation alone provided inadequate localized mixing of eroded sediment. An additional air‐lift process operation was required to hinder the rapid re‐settling of dispersed particulates. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2618–2629, 2017     

CFD-aided prediction of the shape of abrasive slurry jet micro-machined channels in sintered ceramics

The extreme hardness of sintered ceramics makes it difficult to machine them economically. Abrasive slurry-jet micro-machining (ASJM), in which a target is eroded by the impingement of a micro-jet of water containing fine abrasive particles, is a low-cost alternative for micro-machining of sintered ceramic materials without tool wear and thermal damage, and without the use of patterned masks. Existing profile prediction models could not account for changes in the flow field observed in the ASJM of sintered ceramics as channel depth increased. These changes in the flow of abrasive particles fundamentally altered the channel profiles so that the specific erosion rate (mass of material removed per mass of erodent) of the channel centerline decreased with increasing depth and, when machined at 90° incidence, the profiles changed shape. Computational fluid dynamic (CFD) modeling was used to derive a generalized relation between channel geometry and erosive flow (the nonlinearity function), which was used in an existing numerical-empirical model to predict the depths, widths, and shapes of ASJM micro-channels in sintered ceramics; i.e. aluminum nitride (AlN), alumina (Al₂O₃), and zirconium tin titanate (Zn–Sn–TiO₂). The specific erosion rate-particle impact angle and specific erosion rate-particle impact velocity relations, measured for 1 wt%, 10 μm-diameter alumina slurry jet, were used in a CFD model of a first-pass channel to obtain the erosive pattern (erosive efficacy distribution) of the slurry jet within a shallow ceramic channel. This shallow, first-pass erosion pattern was then generalized and used with the nonlinearity function to predict the shapes of deeper channels. The predicted depths in each of the three ceramics at any point on the cross-section were within 6% of those of measured channels up to a depth/width aspect ratio of about 0.5 for nozzle angles of both 90° and 45° in both the forward or backward channel-machining configurations.     

Hydrodynamic characteristics of jet-spouted beds

Jet-spouted beds characterised by high velocity gas jets (above 1.7 U_msl), and shallow bed depths H₀ of around 2 D₁ were investigated on laboratory scale beds and industrial scale beds and the results obtained thereof are correlated and presented in this work. Compared with the classical spouted beds, important differences in bed structure, solid movements and basic hydrodynamic characteristics were observed. The minimum spouting velocity, bed voidage and pressure drop during stabilized spouting are described in terms of dimensionless equations. Bed expansion was used as the basis for the classification of different jet-spouting regimes (incoherent spouting, fast spouting, pneumatic conveying) and changes in the slope of the bed expansion curve are correlated with regime changes. This classification could be useful in the optimization of industrial scale jet-spouted beds. A typically applicable regime of fast spouting was identified.     

Scratch behavior of glass fiber reinforced polyester matrix composite after solid particle erosion

In current study, the tested material is a glass fiber reinforced polyester matrix composite with one stacking sequence namely [0/90]_s. First of all, the solid particle erosion behavior of composite samples was investigated under various impingement angles (15°, 30°, 45°, 60°, 75°, and 90°, respectively). Eroded composite samples were examined by non‐contact optical profilometer and 3D surface roughness maps were obtained. From optical profilometer results, it was clearly shown that values of erosion crater hole volumes were well suited with erosion rate values versus impingement angles. Maximum and minimum erosion crater hole volumes observed at 60° and 15° impingement angles due to semi‐ductile characteristic of the target material, respectively. After erosion tests, the scratch behavior of composite samples was examined. The results showed that the coefficient of friction was decreased by the increase in impingement angles of 45° and 60°. The maximum scratch hardness value was determined at 60° impingement angle. Scratch damage morphologies were determined by using optical microscope and scanning electron microscope. It was observed that low (15° and 30°) and high (75° and 90°) impingement angles result in remarkably severe surface deformation on the samples. POLYM. COMPOS., 36:1958–1966, 2015. © 2014 Society of Plastics Engineer     

板坯连铸结晶器内流场数值模拟

利用FLUENT软件对1300 mm′230 mm的板坯结晶器建立了三维稳态数学模型,以流体表面流速和射流冲击深度作为主要参考指标,研究了水口的特性及拉速、水口浸入深度对该水口作用下结晶器内流场的影响. 结果表明,A水口作用下具有表面流速大,射流冲击深度小,液面波动大,卷渣的可能性大等特点,且随拉速的增加而逐渐增大;随拉速的增加,结晶器内最大表面流速以0.06 m/s的幅度逐渐增大,射流冲击深度呈减小趋势,在150, 170和190 mm浸入深度下,结晶器液面表面流速最大值分别为0.599, 0.518和0.465 m/s,射流冲击深度分别为385, 410和420 mm,随水口浸入深度的增加,结晶器内表面流速逐渐减小,射流冲击深度逐渐增加;在实际生产过程中,使用A水口时应适当降低拉速、增大水口浸入深度;在高拉速的情况下,需用平行水口替换A水口.     

Chemorheology of thermosetting resins. II. Effect of particulates on the chemorheology and curing kinetics of unsaturated polyester resin

The effect of particulates on both the rheological properties during cure and the curing kinetics of unsaturated resin has been investigated. For the investigation, a general-purpose unsaturated polyester resin was used, with calcium carbonate and clay as inorganic particulates and high-density polyethylene powder as organic particulates. It has been found that, as the particulate content increases, the resin/particulate mixture gives rise to shear-thinning behavior and the rate of cure increases. It has also been found that the CaCO₃ particles helped control shrinkage during cure when the material was subjected to steady shear deformation and that the gel time tη∞ is shorter for mixtures of resin and particulates than for the neat resin alone. Differential scanning calorimetry (DSC) is found useful for determining the curing kinetics of resin/particulate mixtures. We have combined rheological and DSC measurements to obtain a correlation between viscosity and the degree of cure during isothermal curing operations.     

Determination of the crater radius as a function of time of a shaped charge jet that penetrates water

The new technique of measuring radial expansion of a crater as a function of time on a shaped charge jet that penetrates water is explained in this paper. Radial expansion of the crater in the frame of experimentation can, in this case, be easily described with a modified Bernoulli equation under the condition that target strength is weak, the initial radial crater velocity is equal to the axial crater velocity and that the pressure p diminishes from the initial impact pressure p₀, with the ratio of the area a to the initial area a₀ of the impacting jet.     

Impingement Heat Transfer for a Cluster of Laminar Impinging Jets Issuing from Noncircular Nozzles

Abstract:

Results of numerical simulation of the flow and heat transfer characteristics for a semi-confined cluster of laminar air jets impinging normally on a plane wall are presented. A central jet is surrounded by four equally spaced jets of the same configuration. Both circular and noncircular nozzles are considered. The nozzle footprint is displayed in the static pressure, temperature, and local Nusselt number contours on the impingement surface only for relatively short nozzle-to-surface distances. The heat transfer characteristics and performance of circular and noncircular nozzles are compared. It is observed that the Nusselt number based on property values at the jet temperature is relatively insensitive to the temperature difference between the jet and the impingement surface. Also, the local Nusselt numbers are independent of the thermal boundary condition; i.e., the values are nearly the same for both isothermal and uniform heat flux conditions at the target surface. Finally, Nusselt numbers for a single equivalent jet viz. one with the same area as the five nozzles in the cluster combined, are compared for the case of the circular jet.     

Characterising highly active nuclear waste simulants

Reprocessing of spent nuclear fuel produces a highly active liquor (HAL) waste stream, which is typically stored over extended periods of many years in waste tanks equipped with extensive heat exchange capability. Over time, particulates are known to precipitate from the HAL within these tanks. Particle simulants provide a route for understanding the physical behaviour of these HAL solids under different agitation and transfer conditions. Particle and dispersion characterisation techniques are used here to understand the behaviour of two types of simulant HAL solids, viz. caesium phosphomolybdate (CPM) and zirconium molybdate (ZM), in dispersion. Distinct properties are established for CPM and ZM and compared to a common oxide particle material titanium dioxide (TiO₂). The results of this study highlight the influence of key aspects of the HAL particulates, such as size and shape, on relevant solid–liquid properties such as sedimentation and rheology. The influence of bulk liquid properties such as electrolyte concentration and pH is also investigated. The results indicate various possible behaviours within the tanks which may impact the storage, remobilisation and pipeline transport of this class of nuclear waste.     

Experimental and numerical characterization of viscous flow and mixing in an impinging jet contactor

The laminar flow in an impinging jet contactor is examined as a first step toward the development of new technology for fast mixing of viscous fluids. The flow, velocity, and stretching fields in an impinging jet contactor are quantified for low Reynolds number flow using three-dimensional numerical simulations and particle image velocimetry measurements. Computational and experimental velocity fields are in close agreement, as quantified by the velocity probability density functions. Two steady-state flow regimes are found to exist: for jet Reynolds numbers (Re_j) < 10, the jets do not impinge and the velocity field scales linearly with Reynolds number; for Re_j > 10, the jets begin to impinge and recirculation regions form above and below the impingement point. The magnitude of the rate-of-strain tensor is calculated as a function of Re_j. While areas of essentially zero stretching occupy most of the flow domain, very high rates of stretching occur at specific locations in the flow. The maximum and average rates of stretching in the contactor increase roughly linearly as a function of Reynolds number. Mixing simulations show that no mixing occurs for the steady flow in a symmetric-jet contactor. However, mixing is improved substantially by a slight modification of the impinging jet geometry that disrupts geometric symmetry.     

Emissions from the combustion of polystyrene,styrene and ethylbenzene under diverse conditions

This experimental study contrasts the products of incomplete combustion (PIC) of polystyrene, a widespread solid waste, with those from the combustion of its predominant pyrolyzate, styrene. The study also included ethylbenzene, as it has been reported to convert to styrene extensively and extremely fast in combustion conditions. Emissions were compared from: (i) steady-state combustion of vaporized ethylbenzene in premixed flames, (ii) steady-state combustion of polystyrene powders in a drop-tube furnace, (iii) batch combustion of fixed beds of polystyrene in a muffle furnace, and (iv) batch combustion of pools of liquid styrene in a muffle furnace. PICs, sampled in post-combustion zones, included unburned hydrocarbons, with emphasis to polycyclic aromatic hydrocarbons (PAH), particulates, CO₂ and CO. Yields of major PIC were compared to underscore the differences in the underlying physics of premixed and non-premixed (diffusion) flames. Combustion of polystyrene and styrene in diffusion flames generated soot at any nominal global (bulk) equivalence ratio, no matter how fuel-rich or fuel-lean. On the other hand, combustion of ethylbenzene in premixed flames did not generate any soot up to its soot onset limit, which typically occurs well-within the fuel-rich domain. However, conditions that were not conducive to the formation of soot did not preclude the presence of other PIC, such as PAH.     

Spherical Resorcinol‐Formaldehyde Resin Testing for Cesium Removal from Hanford Tank Waste Simulant

Abstract

A new spherical form of resorcinol‐formaldehyde (RF) resin was tested for efficacy of cesium removal from Hanford tank waste. Two spherical RF formulations, prepared by varying curing temperature, were tested. Both resins had a tight particle size distribution and a high degree of sphericity. Small‐scale column testing (on ～20‐mL resin beds) was conducted evaluating the cesium load profile with AZ‐102 simulated tank waste and the cesium elution profile using 0.5 M HNO₃ eluant. The load and elution profiles were compared in side‐by‐side testing with ground‐gel RF resin and SuperLig® 644, the Waste Treatment Plant baseline ion exchanger. Although breakthrough capacity was not as high as the other resins tested, the spherical RF resin met plant cesium loading requirements with the AZ‐102 simulant matrix. Excellent reproducibility of cesium load and elution was demonstrated over three process cycles with no evidence of degraded performance. Residual cesium on the resin beds after elution was nearly a factor of 10 lower than that of the ground‐gel RF and SuperLig^® 644.     

Mass transfer from crystalline surfaces in a turbulent impinging jet part I. Transfer by erosion

Mechanical erosion from two crystalline coating materials, naphthalene and trans-cinnamic acid, in submerged turbulent impinging jets of water has been studied. In the absence of diffusion, the observed erosion rates in the wall jet region vary linearly with wall shear stress. Threshold shear stress values below which erosion may be neglected have been defined for both coating materials. Erosion rates in the impingement region also depend on the shear stress which, depending on the crystalline grain size, may interact with pressure forces.     

Flow behaviors of a large spout-fluid bed at high pressure and temperature by 3D simulation with kinetic theory of granular flow

Flow behaviors of a large spout-fluid bed (I.D. 1.0 m) at high pressure and temperature were investigated by Eulerian simulation. The gas phase was modeled with k − ε turbulent model and the particle phase was modeled with kinetic theory of granular flow. The development of an internal jet, gas-solid flow patterns, particle concentrations, particle velocities and jet penetration depths at high pressure and temperature at different operating conditions were simulated. The results show that the bed operated at an initial bed height larger than the maximum spoutable bed height resembles the flow patterns of jetting fluidized beds. The radial profiles of particle velocities and concentrations at high temperature and pressure have the similar characteristic shapes to those at ambient pressure and temperature. The particle concentrations and velocities appear to depend on the bed heights when increasing pressure while keeping the gas velocities and temperature constant. The particle velocities in the lower region of the bed increase with increasing pressure, while they tend to decrease in the middle and upper regions of the bed. The particle concentrations have an opposite dependency with increasing pressure. They decrease in the lower region of the bed but increase in the middle and upper regions of the bed. Besides, the jet penetration depths are found to increase with increasing pressure.     

Identification of the mechanisms that drive the toxicity of TiO2 particulates: the contribution of physicochemical characteristics

This review focuses on outlining the toxicity of titanium dioxide (TiO₂) particulates in vitro and in vivo, in order to understand their ability to detrimentally impact on human health. Evaluating the hazards associated with TiO₂ particles is vital as it enables risk assessments to be conducted, by combining this information with knowledge on the likely exposure levels of humans. This review has concentrated on the toxicity of TiO₂, due to the fact that the greatest number of studies by far have evaluated the toxicity of TiO₂, in comparison to other metal oxide particulates. This derives from historical reasons (whereby the size dependency of particulate toxicity was first realised for TiO₂) and due to its widespread application within consumer products (such as sunscreens). The pulmonary and dermal hazards of TiO₂ have been a particular focus of the available studies, due to the past use of TiO₂ as a (negative) control when assessing the pulmonary toxicity of particulates, and due to its incorporation within consumer products such as sunscreens. Mechanistic processes that are critical to TiO₂ particulate toxicity will also be discussed and it is apparent that, in the main, the oxidant driven inflammatory, genotoxic and cytotoxic consequences associated with TiO₂ exposure, are inherently linked, and are evident both in vivo and in vitro. The attributes of TiO₂ that have been identified as being most likely to drive the observed toxicity include particle size (and therefore surface area), crystallinity (and photocatalytic activity), surface chemistry, and particle aggregation/agglomeration tendency. The experimental set up also influences toxicological outcomes, so that the species (or model) used, route of exposure, experiment duration, particle concentration and light conditions are all able to influence the findings of investigations. In addition, the applicability of the observed findings for particular TiO₂ forms, to TiO₂ particulates in general, requires consideration. At this time it is inappropriate to consider the findings for one TiO₂ form as being representative for TiO₂ particulates as a whole, due to the vast number of available TiO₂ particulate forms and large variety of potential tissue and cell targets that may be affected by exposure. Thus emphasising that the physicochemical characteristics are fundamental to their toxicity.     

Erosion behaviour of B4C-based ceramic composites

In this paper, TiO₂ was introduced into boron carbide and B₄C-based ceramic composites were obtained by uniaxial hot pressing. The mechanical properties, relative density and erosion behaviour of B₄C-based ceramic composites were investigated. X-ray analysis showed that the fabricated composites were composed of B₄C, TiB₂ and C phases. SEM technique was employed to observe the original polished surfaces and the eroded surfaces of B₄C-based ceramic composites. The effect of impingement angle, impact velocity of SiC erodent particle, relative density and phase ratio on the erosion rate of B₄C-based ceramic composites was determined. It was found that the erosion rate of B₄C-based ceramic composites increased with increasing of impingement angle and erodent particle velocity. The relative density and phase ratio influenced the erosion rate of B₄C-based ceramic composites significantly by influencing their mechanical properties.     

Wear by particulates

A review is presented of practical situations where wear by particulates can occur. In certain flow regimes, wear occurs by erosion of material due to impingement of the particles. The dependence of erosive wear on flow parameters, particle properties and material properties is discussed, and suggestions are made for reducing this type of wear.     

Wear on tubes by jet impingement in a fluidized bed

This study investigated wear on heat-transfer tubes resulting from impingement of particles entrained by a jet in a fluidized bed. The particular application is the fluidized-bed boiler for the Liquid Metal Fast Breeder Reactor in which a steam-tube failure might cause a high-velocity jet, accelerate particles, and erode adjacent tubes.Croloy and 304 SS tubes immersed in a fluidized bed were subjected to impingement wear from a sonic-jet issuing through a 1.17 mm diam. hole. Wear on target tubes was severe (when spaced near the leak source (1.6 cm)). With spacings of 20 cm, wear was scarcely measurable, being less than 0.002 cm/min.Impingement wear was measured in beds of rounded nickel, angular magnesia and angular iron. Results clearly show that increasing the hardness or angularity of particles increases impingement wear rate.An analysis of impingement wear was performed to project results of room-temperature tests to actual conditions. At 800 K and 1400 kPa, wear is projected to occur at 3 – 5 times the rate measured in tests.     

Erosion Behavior of Gelcast Fused Silica Ceramic Composites

In this paper, the characteristics of solid particle erosion on fused silica ceramics are investigated. Gelcasting, a near net shape forming process, is adopted for the fabrication of ceramics. Three types of ceramics with a combination of pure fused silica, fused silica+5 wt% silicon nitride (Si₃N₄)?+?1 wt% boron nitride (BN) and fused silica+5 wt% silicon nitride (Si₃N₄) +1 wt% alumina (Al₂O₃) are prepared at a constant 52 vol% solid loading, 10 wt% monomer content and 10:1 monomer ratio. Different impingement angles (30^o, 45^o, 60^o and 90^o) and three impact velocities (86 m/s, 101 m/s and 148 m/s) were chosen to examine the behavior of erosion on gelcasted ceramics using SiO₂ particles as erodent. The maximum rate of erosion is obtained at normal impingement angle (90^o), which shows the brittle nature of ceramics. The impact velocity and angle of impingement have an appreciable effect on erosion rate. Resistance to erosive wear is found to have improved with the inclusion of reinforcements in the fused silica ceramics. The erosion rates of different ceramics are compared. Ceramic composite with a combination fused silica+5 wt% Si₃N₄+ 1 wt% BN shows the highest resistance to wear. The surface roughness and morphology of the eroded surfaces have also been studied.