High Energy Dissipation Rate Research Articles

Influence of micromixing and shear on precipitation process in the jet-flow high shear reactors

Micromixing and fluid shear stress significantly affect the nucleation and growth of crystals during the precipitation process. The jet-flow high shear reactor (JFHSR) has strong shear rate and high localized energy dissipation rate, making it promising for applications where the size and the morphology of crystals need to be modified. In this paper, the micromixing properties of JFHSR were first investigated using Villermaux/Dushman method, and the intrinsic correlation among micromixing, shear, and BaSO4 crystals was explored. The results show that the stator, the increased Re and θ, the reduced feed tube diameter and the closer the feed position to the rotor promote micromixing. Excellent micromixing promotes burst nucleation by generating uniform supersaturation, while shear is more likely to provide an environment dominated by the secondary nucleation of fluid shear stress. The correlations of XS, tm (about 10−4 s) and d43,P are obtained, providing guidelines for JFHSR design and application

Hydraulic characteristics of a large rotation-angle baffle-drop shaft through synergetic discharge from dry and wet sides

To enhance the operational capacity and space utilization of baffle-drop shafts, this study improved the traditional baffle-drop shaft by expanding the wet-side space, incorporating large rotation-angle baffles, and installing overflow holes in the dividing wall. A three-dimensional turbulent model was developed using ANSYS Fluent to simulate the hydraulic characteristics of both traditional and new baffle-drop shafts across various flow rates. The simulation results demonstrated that the new shaft design allowed for discharge from both the wet and dry sides, significantly improving operational capacity, with the dry side capable of handling 40% of the inlet flow. Compared to the traditional shaft, the new design reduced shaft wall pressures and decreased the mean and standard deviation of pressure on typical baffles by 21% and 63%, respectively, therefore enhancing structural safety. Additionally, the new shaft achieved a 2%–12% higher energy dissipation rate than the traditional shaft across different flow rates. This study offers valuable insights for the design and optimization of drop shafts in deep tunnel drainage systems.

Three-Dimensional Measurements Of Deformable Oil Droplets In Turbulence

This work introduces an experimental facility designed to generate turbulence with a high energy dissipation rate of up to 0.3 m^2/s^3 , sufficient to induce deformation and fragmentation of oil droplets. The turbulence is produced by opposing arrays consisting of 24 jet streams in total, each with Reynolds numbers ranging from 12,000 to 50,000. Flow regimes are determined using 3D Particle Tracking Velocimetry (PTV) conducted in the center of the octagonal test section. The statistical analysis of the turbulence reveals a nearly homogeneous and isotropic nature. A 3D imaging system, equipped with six high-speed cameras, allows for the reconstruction of droplets using the multiple algebraic reconstruction technique algorithm, fostering both visualization and quantification of interface deformation. Additionally, the system enables the tracking of the breakup process. The presented setup is able to couple the measurements of the droplet shapes with surrounding turbulence in 3D dproplet topology reconstruction coupled with surrounding flow measurements. We demonstrate the capability of our imaging system and reconstruction methods for multiphase flow studies with an example of full 3D droplet topology reconstruction coupled with surrounding flow measurements.

Numerical investigation on characteristics of vortex dissipation in multi-horizontal submerged jets stilling basin.

Multi-horizontal submerged jets stilling basins have been utilized in large-scale water conservancy and hydropower projects due to its stable flow pattern, high energy dissipation rate and less atomization. This study employs vorticity criterion, Q criterion, λ2 criterion and Ω criterion to investigate the characteristics of vortex formation and turbulent dissipation in multi-horizontal submerged jets stilling basins with various configurations, including crest overflowing orifice alone (COO), combination of crest overflowing orifice and mid-discharge orifice (COO-MO) and mid-discharge orifice alone (MO). The results indicate that the Q criterion and λ2 criterion are effective in identifying vortex structure within multi-horizontal submerged jets stilling basin. Specifically, the stronger intensity of vortex structure and vortex dissipation are mainly distributed in the vicinity of the vertical drop, which gradually weakens for the increasing distance to the vertical drop. Furthermore, the intensity and number of vortexes with COO-MO are the largest. This conclusion can provide guidance for energy dissipation and bottom protection of stilling pool.

Experimental study and turbulence dissipative scale modelling of the rapid micromixing of impinging thin sheets of liquids

Previous studies have shown that the impingement of thin liquid sheets produces high energy dissipation rates due to the release of kinetic energy in a very small mass of liquid (0.0001–0.01 g), even though flowrates are on the order of L/min. Rapid micromixing occurs because the dissipated energy leads to a substantial reduction in the initial segregation size scale of the liquids, which is the single-sheet thickness at impingement (~ 100 μm). In the present study, the micromixing was investigated by following the progress of an acid-base neutralization accompanied by a change in fluorescence intensity of a fluorophore. Micromixing was modeled using a framework that assumes diffusion and reaction of species occur within slabs of fixed thickness (2L). The slabs are fixed in size because the released kinetic energy is dissipated within one turnover time of the large energy-containing eddies produced in the turbulent impingement zone. A simulation, which included a module for calculating the fluorescence intensity, determined 2L for experimental energy dissipation rates (ϵ) ranging from 4×104 to 7.7×106 W/kg. 2L was found to lie in the range of turbulent dissipative scales less than the Taylor microscale but greater than the Kolmogorov microscale. 2L/v′ was found to be a function of ReΛ−1/4 and ν/ϵ1/2, where v′ is the velocity associated with the turbulent kinetic energy, ReΛ is the large-eddy Reynolds number and ν is the kinematic viscosity. Similar to η/Λ, 2L/Λ is a function of ReΛ−3/4, where ηis the Kolmogorov microscale and Λ is the size of the large energy-containing eddies.

ANN based surrogate model for key Physico-chemical effects of cavitation

Intense and localised physico-chemical effects realised by cavitation such as generation of hydroxyl radicals, high-speed jets, and very high energy dissipation rates are being harnessed for a wide range of applications from emulsions, crystallisation, reactions to water treatment and waste valorisation. Single cavity models are typically used to quantitatively estimate such localised effects of cavity collapse. However, these models demand significant computing resources for resolving fast dynamics and therefore are very difficult, if not impossible, to integrate with CFD based cavitation device or reactor scale models. This severely limits the utility of device/ reactor scale models in simulating key applications of interest. In this work, we present, for the first time, artificial neural network (ANN) based surrogate models which accurately represent complex physico-chemical effects of cavity collapse. Recently developed cavity dynamics model was used for generating training data set encompassing both acoustic and hydrodynamic cavitation. Appropriate methodology for training ANN was developed. A shallow three hidden layer dense ANN was found to be more effective for estimating three main effects of cavity collapse: jet velocity, •OH generation and localised energy dissipation rate. The performance of trained ANN was then evaluated by comparing the predictions with the totally unseen data obtained from the cavity dynamics model. The developed ANN was shown to simulate unseen data very well not just within the range of training data (interpolation) but also beyond (extrapolation). Algebraic equations representing ANN are included to facilitate incorporation in device/ reactor scale CFD models. The presented methodology and results will be useful for developing high-fidelity CFD models of cavitation devices/ reactors based on key physico-chemical effects of cavity collapse.

Micromixing and Co-Precipitation in Continuous Microreactors with Swirled Flows and Microreactors with Impinging Swirled Flows

One of the promising methods for process intensification for micromixing, co-precipitation, and crystallization in continuous reactors is the use of vigorous vortices. A combination of the high intensity of the kinetic energy input with the small volume of the micromixing volume allows to concentrate the energy dissipation rate up to 104 W/kg and more. As the embodiment of such an idea, four new types of microreactors with intensively swirled flows were created and studied as a tool for continuous co-precipitation and crystallization. A correlation between residence time and segregation index was found: the smaller residence time, the higher energy dissipation rate and better quality of micromixing. A method for the synthesis of oxides of a number of transition metals in microreactors with intensively swirled flows with subsequent thermal treatment of co-precipitation products has been developed. This method was used to obtain ensembles of nanosized particles of zirconium oxides, as well as calcium and strontium fluorides. In comparison with the currently widely used hydro- and solvothermal methods, the proposed method has high productivity (around 10 m3/day for lab scale device), can significantly reduce the duration of the process, provides low energy consumption, does not require a large number of labor-intensive operations, is technologically advanced and easily scalable.

A Study of Large-eddy Simulation using Statistical and Machine Learning Techniques

The numerical solution of Navier-Stokes (N-S) equations has been found useful in various disciplines during its development, especially in recent years. However, a large-eddy simulation method has been developed to model the subgrid-scale dissipation rate by closing the Navier-Stokes equations. Because the instantaneous and time-averaged statistic characteristics of the subgrid-scale turbulent kinetic energy and dissipation have been studied by large eddy simulation. The purpose of this study is to check the statistical and machine learning of the subgrid-scale energy dissipation. As we know that the current turbulence theory states that the vortex stretching mechanism transports energy from large to small scales and leads to a high energy dissipation rate in a turbulent flow. Hence, a vortex-stretching-based subgrid-scale model is considered regarding the square of the velocity gradient to detect the playing role of the vortex stretching mechanism. The study in this article has shown a two-step process. Considering a posteriori statistic of the velocity gradient is analyzed through higher-order statistics and joint probability density function. Secondly, a machine learning approach is studied on the same data. The results of the vortex-stretching-based subgrid-scale model are then compared with the other two dynamic subgrid models, such as the localized dynamic kinetic energy equation model and the TKE-based Deardorff model. The results suggest that the vortex-stretching-based model can detect the significant subgrid-scale dissipation of small-scale motions and predict satisfactory turbulence statistics of the velocity gradient tensor.

On Characteristics and Mixing Effects of Internal Solitary Waves in the Northern Yellow Sea as Revealed by Satellite and In Situ Observations

This study examines the characteristics, statistics, and mixing effects of internal solitary waves (ISWs) observed in the northern Yellow Sea (YS) during the summers of 2018 and 2019. The mooring stations are located between offshore islands with rough topographic features. Throughout the observation period, the ISWs with vertical displacements of up to 10 m induced prevailing high-frequency (3–10 min period) temperature variations. Synthetic aperture radar (SAR) images showed that the observed ISWs propagate in zonal directions generated around the islands where internal-tide-generating body force is strong. The estimated ISW propagation speed ranges from 0.16 to 0.25 m s−1, which agrees with the Korteweg-de Vries (KdV) model. The ISW intensity exhibits a clear spring-neap cycle corresponding to the local tidal forcing. The constant occurrence of ISWs at low tide suggests an important generation site where the ISWs are tidally generated. The ray-tracing result indicates that this generation site appears to be located at a strait between Dahao and Xiaohao islands. A generalized KdV model successively reproduces the propagation process from the generation site to the mooring station. Following the passage of ISWs, microstructure profiling observations reveal a high turbulent kinetic energy dissipation rate (10−6 W kg−1). The prevalence of ISWs in the study area is believed to play a crucial role in regulating vertical heat and nutrient transport, thereby modulating the biogeochemical cycle.

Study on the Hydraulic Characteristics of the Trapezoidal Energy Dissipation Baffle Block-Step Combination Energy Dissipator

The step-type energy dissipator is widely used to construct small- and medium-sized reservoirs with its high energy dissipation rate. In order to further improve its air entrainment characteristics and energy dissipation, and reduce the influence of cavitation, in this paper, we added a trapezoidal energy dissipation baffle block at the convex corner of the traditional step to form a trapezoidal energy dissipation baffle block-step combination energy dissipator. We used a combination of hydraulic model experiments and numerical simulation to study the hydraulic characteristics. The results showed that the trapezoidal energy dissipation baffle block-step combination energy dissipator initial entrainment point, with the increase in flow rate, gradually moved backward. A step horizontal surface pressure change in the cavity recirculation area showed a prominent “V” shape; in front of the trapezoidal energy dissipation baffle block, there was a rising trend, and in the energy dissipation baffle block gap, there was a declining trend. The step vertical surface pressure showed a decreasing trend, and negative pressure appeared near the convex angle. The cross-section velocity distribution presented a trend of being small at the bottom and large at the surface, with a large velocity gradient in the longitudinal section of the energy dissipation baffle block and a small velocity gradient in the longitudinal section of the nonenergy dissipation baffle block. The energy dissipation rate reached more than 70% within the test range, and the energy dissipation rate gradually decreased with the increase in the flow rate. The combined energy dissipator is conducive to reducing the cavitation hazard and improving the energy dissipation effect, providing a reference for engineering design and existing step energy dissipators to remove risks and reinforcement.

Application of turbulence promoter in protein recovery from food wastewater by dynamic shear enhanced ultrafiltration

The expected growth of membrane technology in protein recovery from wastewater is largely impeded by operational non-idealities like concentration polarization and membrane fouling. Two independent concepts, namely, the Dynamic Shear Enhanced (DSE) filtration and turbulence promoters were introduced decades earlier to remediate the problems. However, no systematic effort was undertaken to explore the synergy of the two process intensification schemes. In this study, we have investigated the effects of simple wire-type turbulence promoter on a specific class of DSE membrane modules, the spinning basket filtration units. The maximum flux improvement with synthetic wastewater (i.e., Bovine Serum Albumin (BSA)-water solution) was 445%, whereas for the real dairy effluent, the respective enhancement levelled off at 204%. The lower level of flux enhancement for real wastewater may be attributed to the severe fouling caused by the casein micelle. The increase of power consumption in all promoter-fitted configurations was limited to 9% only. Thus, turbulence promoter-integrated spinning basket group of membrane modules are confirmed to be much superior relative to other devices in protein recovery from wastewater. Our results are also supported by corroborating computational fluid dynamic (CFD) simulations of elevated shear and high turbulent kinetic energy dissipation rates for all promoter-fitted configurations. The present outcomes clearly recommend the application of turbulence promoters in DSE modules to maximally increase the protein recovery from wastewater even at concentrations where the standard cross-flow systems are apprehended to be non-functional.

Numerical Simulations of 2D Hydraulic Jumps by a Parallel SPH Model

Hydraulic jumps are a rapid transition from supercritical to subcritical flow and generally occur in rivers or spillways. Owing to the high energy dissipation rate, hydraulic jumps are widely applied as energy dissipators in hydraulic projects. To achieve efficient and accurate simulations of 2D hydraulic jumps in open channels, a parallel Weakly Compressible Smoothed Particle Hydrodynamics model (WCSPH) with Shepard Density filter was established in this study. The acceleration of the model was obtained by OpenMP to reduce execution time. To further reduce execution time, a suitable and efficient scheduling strategy was selected for the parallel numerical model by comparing parallel speed-ups under different scheduling strategies in OpenMP. Following this, two test cases of uniform flow in open channels and hydraulic jumps with different inflow conditions were investigated to validate the model. The comparison of the water depth and velocity fields between the numerical results and the analytical solution generally showed good agreement, although there was a minor discrepancy in conjugate water depths. The numerical results showed free surface undulation with decreasing amplitude, which is more consistent with physical reality, with a low inflow Froude number. Simultaneously, the Shepard filter was able to smooth the pressure fields of the hydraulic jumps with a high inflow Froude number. Moreover, the parallel speed-up was generally able to reach theoretical maximum acceleration by analyzing the performance of the model according to different particle numbers.

High energy dissipation rates from the impingement of free paper-thin sheets of liquids: A study of the coefficient of restitution of the collision

The micromixing time of impinging thin liquid sheets depends upon the energy dissipation rate, which is typically104 to 106 W/kg. The energy dissipation rate in the impingement zone is a function of the coefficient of restitution (COR) of the collision. In this study theCOR was investigated both theoretically and experimentally. An analytical expression was developed that consists of a term that accounts for an inelastic collision of impinging sheets and a term that quantifies the “elasticity” imparted to the collision once the critical velocity for backflow is reached. The theoretical results were compared with experiments that determined theCOR by measuring the velocity of single sheets and mixed sheets. Not only do the experimental results show a jump in theCOR at the critical velocity, as predicted by theory, but calculated values of theCOR from the analytical expression compare well with measured values.

Hard vs soft impacts in oscillatory systems' modeling revisited.

An application of soft and hard impact models to represent vibro-impact systems is reconsidered. The conditions that the two collision models have to satisfy to be equivalent in terms of energy dissipation are discussed and key features of the resulting soft impact models are demonstrated. Then, it is examined what effect will be exerted on the behavior of a vibro-impact system when an additional elastic-damping element and external forcing are used. Both methods are shown to yield the same results for a stiff base with a low rate of energy dissipation; however, when the soft impact model is applied to either the base with low stiffness or even the stiff base with a high rate of energy dissipation, different results are obtained than in the case of the hard impact model.

Liquid hydrodynamics in a gas-liquid vortex reactor

A gas–liquid vortex reactor (GLVR) is considered one of the promising Process-Intensified Equipment for applications that require high mixing and mass transfer efficiency. To gain understanding of the fundamentals of GLVR operation, the gas–liquid hydrodynamics in the GLVR has been investigated by high-speed imaging, digital images analysis and cross correlation. Gas bubbles and liquid ligaments are observed in the GLVR over a wide operating window. The dynamic liquid layer thickness in the GLVR chamber varies in the range of 26–36 mm. The instantaneous and time-average velocity fields of the liquid phase are obtained with a guaranteed high signal-to-noise ratio (cross correlation peak ratio higher than 10), allowing the analysis of liquid turbulent properties including the turbulent kinetic energy and its dissipation rate. Results show that the high turbulent kinetic energy dissipation rate ranging from 23 to 114 m2/s3 contributes to a high mixing and mass transfer efficiency in the GLVR.

Hard versus soft impact modeling of vibro-impact systems with a moving base

Soft and hard impact models applied to modeling of vibro-impact systems with a moving base are discussed. The conditions under which two collision models are equivalent in terms of equal energy dissipation are derived. These conditions differ from those presented in the literature. It is shown that in the case of a stiff, harmonically moving base with a low rate of energy dissipation, both methods yield the same results, but an application of the soft impact model to either the base with low stiffness or even the stiff base with a high rate of energy dissipation leads to different results from the ones for the hard impact model.

Crystal Growth, Dissolution, and Agglomeration Kinetics of Sodium Chlorate

The analysis, development, and implementation of novel complex industrial crystallization processes requires kinetic knowledge of not only crystal growth and nucleation but also breakage, dissolution, and agglomeration processes. In this work, the crystal growth, dissolution, and agglomeration kinetics of sodium chlorate (NaClO3) in aqueous solutions are estimated via seeded batch experiments with in-line particle size distribution measurements. Contrary to previous works, the growth/dissolution kinetics are expressed in terms of the fundamental driving force of crystallization calculated from the activity of supersaturated solutions. The activity-based driving force is roughly 2-fold higher than the commonly used representation, which assumes ideal solutions. By fitting experimental desupersaturation data to mechanistic and empirical growth models, we show that the growth of sodium chlorate is surface integration controlled and is best described by a two-dimensional birth and spread surface nucleation mechanism. The dissolution of sodium chlorate crystals is diffusion controlled and is ∼4 times faster than the growth at an equal initial driving force. Particle agglomeration is substantial in the early stages of crystallization experiments, likely due to a strong increase in the particle number due to initial breeding secondary nucleation upon seeding. The agglomeration rate constant increases with supersaturation and decreases at higher energy dissipation rate (by increased agitation) due to a strong decrease in the efficiency of interparticle collisions. Seeding with material of different sizes does not influence the agglomeration rate constant, although substantial amount of small particles was present in all seeding materials.

Numerical Simulation of Stepped Spillways with Front Step Deformation

In order to solve the flood discharge problem of both small- and medium-sized warping dams in the Loess Plateau, a stepped spillway scheme, based on an ecological bag, to achieve full-section water flow and energy dissipation has been proposed in this paper. The hydraulic and energy dissipation characteristics of a stepped spillway layout scheme were studied using 3D numerical simulation. As the height of the dams is low and the spillways are short, the research has shown that the traditional single-step layout scheme leads to a low overall energy dissipation rate due to the small amount of energy dissipated in the initial steps. As a result of this, this paper has put forward two kinds of step layout schemes such as the shunt type and the staggered type for the initial steps. Through analysis of the flow state, the pressure distribution, and the total energy dissipation rate, the results have shown that shunt type and staggered type with front step deformation produced an obvious mixing of the water flow, fewer negative pressure areas, and a higher energy dissipation rate. The optimal energy dissipation rate of the staggered type reached 87.75%, and the maximum energy dissipation rate was increased by 27.97%.

Regenerating Hair in Prevascularized Tissue Space Formed by a Controllable Foreign Body Reaction

AbstractIntracutaneous transplantation of trichogenic cells is a currently endorsed strategy to realize hair regeneration in vivo. However, skin is not the most advantageous transplant site due to the robust mechanical property and deficient physiological perfusion. Herein, a subcutaneous space made of prevascularized collagen fibers (PVCF) generated by controlling the duration of in situ foreign body reaction is reported. In contrast to skin, an optimally preprogrammed PVCF presents a larger tissue volume (171 mm3), low Young's modulus (1/2‐fold), high flexibility high mechanical energy dissipation rate (1.3‐fold), highly permeable surface structure, and plentiful vascular network. Remarkably, cells transplanted into PVCF suffer less apoptosis and necrosis, and generate more mature hairs (≈289 per site) than that in intracutaneous transplantation (≈177 per site). The RNA‐sequencing profiling indicates similar trends under molecular level. This work provides a promising strategy to improve graft site microenvironment physiologically and mechanically, with a low‐cost and simple fabrication process.

Observations of Flow Separation and Mixing around the Northern Palau Island/Ridge

AbstractTurbulent mixing adjacent to the Velasco Reef and Kyushu–Palau Ridge, off northern Palau in the western equatorial Pacific Ocean, is examined using shipboard and moored observations. The study focuses on a 9-day-long, ship-based microstructure and velocity survey, conducted in November–December 2016. Several sections (9–15 km in length) of microstructure, hydrographic, and velocity fields were acquired over and around the reef, where water depths ranged from 50 to 3000 m. Microstructure profiles were collected while steaming slowly either toward or away from the reef, and underway current surveys were conducted along quasi-rectangular boxes with side lengths of 5–10 km. Near the reef, both tidal and subtidal motions were important, while subtidal motions were stronger away from the reef. Vertical shears of currents and mixing were stronger on the northern and eastern flanks of the reef than on the western flanks. High turbulent kinetic energy dissipation rates, 10−6–10−4W kg−1, and large values of eddy diffusivities, 10−4–10−2m2s−1, with strong turbulent heat fluxes, 100–500 W m−2, were found. Currents flowing along the eastern side separated at the northern tip of the reef and generated submesoscale cyclonic vorticity of about 2–4 times the planetary vorticity. The analysis suggests that a torque, imparted by the turbulent bottom stress, generated the cyclonic vorticity at the northern boundary. The northern reef is associated with high vertical transports resulting from both submesoscale flow convergences and energetic mixing. Even though the area around Palau represents a small footprint of the ocean, vertical velocities and mixing rates are several orders magnitude larger than in the open ocean.