Turbulent Liquid Research Articles

Development of CFD based model for sodium flow boiling in narrow channel akin to SFR fuel subchannel towards high void fraction regimes

The Sodium cooled fast reactor (SFR) is one of the Gen IV reactor type meant for the highest nuclear safety standards. Understanding of flow boiling heat transfer characteristics of liquid sodium is essential under certain postulated events of SFR. This study is intended towards the development of computational fluid dynamics (CFD) based multiphase flow model for the sodium boiling in SFR subchannel using the finite volume method. The numerical simulations have been performed for the basic two-dimensional domain that has a resemblance with the flow subchannel of SFR fuel subassembly. The sodium boiling inception, the nucleate flow boiling regime, and further the forced convective vaporization regime characteristics are numerically predicted by the Eulerian-Eulerian model (two-fluid model) developed using flow regime based modeling within the Algebraic Interfacial Area Density (AIAD) framework for the interfacial closure correlations. The improved non-equilibrium wall boiling model is implemented for wall heat flux partitioning. The liquid turbulence is modeled using a Realizable k-ε model with standard wall function. The CFD simulations are performed for the reference experimental cases of liquid sodium flow boiling in narrow annuli and a tubular channel till high void fraction regimes using the model developed. The predictions of void growth behavior along the axial and in the radial direction depict the dominance of annular flow boiling pattern as observed in sodium flow boiling experiments based on the literature. The numerical predictions for the sodium two-phase flow pressure drop are compared with the experimental results and also with the existing empirical correlations. The mechanistic model-based predictions for boiling heat transfer coefficient are obtained from the wall heat balance model and compared with the available empirical correlations. Also based on the flow parameters predicted the possible flow patterns are identified using the available flow regime maps.

Experimental and numerical investigations of motion and mass transfer of single bubbles in a turbulent flow chamber

Background Gas-liquid mass transfer is a common transport phenomenon in the chemical industry. It is important to relate the mass transfer of single bubbles to the flow of the surrounding liquids. Many research on single bubbles mass transfer is on the experiment where the bubble is free rising in stagnant liquids, resulting a relative low liquid Reynolds number and short residence time. Therefore, the chamber flow is utilized to create a controllable flow field which can keep single bubbles in the chamber for a long period, which enables the accurate determination of the mass transfer coefficient.Methods First, the accuracy of three turbulence models describing the liquid flow in industrial stirred tanks were evaluated, by validating the liquid velocity and turbulent kinetic energy distribution in the chamber with experiments. Then, by coupling the turbulence model, volume of fluid method and several mass transfer models, the bubble motion and mass transfer were simulated. In this coupling approach, five classic models were respectively used to evaluate kL in the turbulent chamber flow.Significant findings This paper provides a reference for the selection of mass transfer model in the liquid flow chamber. The large eddy simulation is typically suitable for calculating turbulent liquid flow in the chamber. By coupling large eddy simulation and volume of fluid method, the mass transfer process of single bubbles in this cavity flow can be predicted. Considering the present partially contaminated and reactive system, Brauer mass transfer model can predict the mass transfer coefficient more accurately than other models.

Large blade impeller application for turbulent liquid–liquid and solid–liquid mixing

AbstractApplication of large blade impellers to turbulent single‐phase and two‐phase mixing is investigated in this work in order to provide a quantitative basis for estimating the possible advantages in industrial mixing operations with respect to fast impeller types. The analysis is based on the discussion of three‐dimensional velocity fields collected in a single‐phase vessel stirred by a Maxblend impeller by stereoscopic particle image velocimetry and of dispersed phase distribution and liquid mixing time obtained in solid–liquid and liquid–liquid systems by electrical resistance tomography. The results highlight that turbulent two‐phase mixing can be efficiently performed in baffled vessels stirred by large blade impellers both in shear‐rate controlled and bulk‐motion controlled processes.

Euler-Euler/RANS modeling of solid-liquid flow in stirred tanks: A comprehensive model validation

Simulations of solid–liquid flow on industrial scales are feasible within the Euler-Euler / RANS approach. The reliability of this approach depends largely on the closure models applied to describe the unresolved phenomena at the particle scale, in particular the interfacial forces. In this work, a set of closure models reviewed previously for this kind of application (Shi and Rzehak, 2020) is further validated by comparing the predictions to a recent experiment on stirred-tank flows (Sommer et al., 2021), which focuses on dilute suspensions. The dataset used for validation comprises 14 different experimental cases, covering a wide range of particle Reynolds number, impeller Reynolds number, and particle Stokes number. For each case, simulation results on the solid velocity and volume fraction as well as liquid velocity and turbulence are compared with the experimental data. It turns out that by and large the experimental data are reasonably well reproduced. However, the measurements show a small but clear effect of modulation of the liquid phase turbulence by the particles. Therefore, several particle-induced turbulence (PIT) models based on the available literature are assessed as well. Our results indicate a reduction in the predicted fluctuations by all PIT models, which improves the results in cases with turbulence suppression but deteriorates those with turbulence augmentation.

Effect of Structural Optimization of Scrubbing Cooling Rings on Vertical Falling Film Flow Characteristics.

In order to study the influence of the structural optimization of the scrubbing cooling ring in the scrubbing cooling chamber on the flow characteristics of the vertical falling film, the flow characteristics of the turbulent falling film in the rising section of the development region at different internal platform heights of the scrubbing cooling ring and a high Reynolds number were studied by FLUENT software. First, the correctness of the model was verified by the maximum error of simulation and experimental results of no more than 9.836%. Then, the distribution of liquid film thickness (δ), velocity (V), and turbulence intensity (Iz) at 0° of the tube in the axial direction x = 0–500 mm were calculated and obtained when the platform height (H) was 0–30 mm and the liquid film Reynolds number (Rel) = 1.1541 × 104–3.4623 × 104. The results showed that δ in the entrance region increased sharply due to the “jet” effect with solid wall constraints formed by the structure of the water inlet pipe and the scrubbing cooling ring. On the contrary, the liquid film in the fully developed region showed a stable fluctuation trend due to the weakening of the “jet” effect. When H = 30 mm, the change of δ was relatively stable and the change of Iz was small, indicating that this platform height is conducive to the stable and uniform distribution of the liquid film. In addition, when Rel < 1.1541 × 104, the liquid film was unstable due to the low flow rate and insufficient cohesion of the liquid film, but V increased slightly. In addition, with the increase of Rel, δ did not change significantly along the axial direction, that is, the Plateau–Rayleigh hindered the growth of δ. Finally, the empirical formula for δ applicable to Rel = 1.1541 × 104–3.4623 × 104 at the axial fixed position was fitted for the first time.

Creation of turbulence in polyatomic gas flow via an intermolecular potential

Turbulence in gases and liquids manifests in the form of spontaneously developing chaotic dynamics in a laminar flow without any measurable external disturbances. For gas flows, we propose that turbulence is created by the average effect of an intermolecular potential, leading to a system of equations with novel coupling between density and momentum. Numerical simulations show that turbulent dynamics in this system emerges spontaneously in the absence of external disturbances, in agreement with observations. In addition, the time-averaged kinetic energy spectra of our numerical solutions decay at the Kolmogorov rate, which is also an intriguing feature of observed turbulent flows.

Effect of nanofluids on heat transfer characteristics of an aerodynamic swirl nozzle for isothermal and isoflux conditions

ABSTRACT Achieving axisymmetric boundary conditions in turbulent swirl flows and predicting thermo-fluidic behaviours within a nozzle is often a challenge due to the difficulties of measurement diagnostics. Adding nanoparticles to ase fluids exacerbates the complexity because of the regeneration of effective properties of the fluid medium. As such, this study numerically investigates the flow and thermal characteristics for the effect of swirl and nanofluids of incompressible turbulent liquid jets. The results show that the axial and tangential velocity profiles for water-based nanofluids resemble to those for water in no-to-high swirl flows. The surface Nusselt number for strong swirl flow reduces with axial distances at isothermal wall condition, and the Nusselt number is strongly dependent on types of nanofluid for isoflux condition. Water-based nanofluids cause higher heat transfer compared to Dowtherm+Al2O3 and Syltherm800+ Al2O3. The average Nusselt number and the pressure drop are found to be the largest for 10% volume fraction. The increase of thermal-hydraulic performance factor for nanofluids after nozzle convergence is steeper for highly swirling flow than for non-swirling and medium swirling cases. A strong turbulent kinetic energy is observed immediately after the nozzle converging section for all nanofluid cases and Dowtherm+Al2O3 shows relatively uniform distributions across the nozzle.

Laser-induced microjet-assisted ablation for high-quality microfabrication

Liquid-assisted laser ablation has the advantage of relieving thermal effects of common laser ablation processes, whereas the light scattering and shielding effects by laser-induced cavitation bubbles, suspended debris, and turbulent liquid flow generally deteriorate laser beam transmission stability, leading to low energy efficiency and poor surface quality. Here, we report that a continuous and directional high-speed microjet will form in the laser ablation zone if laser-induced primary cavitation bubbles asymmetrically collapse sequentially near the air-liquid interface under a critical thin liquid layer. The laser-induced microjet can instantaneously and directionally remove secondary bubbles and ablation debris around the laser ablation region, and thus a very stable material removal process can be obtained. The shadowgraphs of high-speed camera reveal that the average speed of laser-induced continuous microjet can be as high as 1.1 m s−1 in its initial 500 μm displacement. The coupling effect of laser ablation, mechanical impact along with the collapse of cavitation bubbles and flushing of high-speed microjet helps achieve a high material removal rate and significantly improved surface quality. We name this uncovered liquid-assisted laser ablation process as laser-induced microjet-assisted ablation (LIMJAA) based on its unique characteristics. High-quality microgrooves with a large depth-to-width ratio of 5.2 are obtained by LIMJAA with a single-pass laser scanning process in our experiments. LIMJAA is capable of machining various types of difficult-to-process materials with high-quality arrays of micro-channels, square and circle microscale through-holes. The results and disclosed mechanisms in our work provide a deep understanding of the role of laser-induced microjet in improving the processing quality of liquid-assisted laser micromachining.

Collapse of Coherent Large Scale Flow in Strongly Turbulent Liquid Metal Convection.

The large-scale flow structure and the turbulent transfer of heat and momentum are directly measured in highly turbulent liquid metal convection experiments for Rayleigh numbers varied between 4×10^{5} and ≤5×10^{9} and Prandtl numbers of 0.025≤Pr≤0.033. Our measurements are performed in two cylindrical samples of aspect ratios Γ=diameter/height=0.5 and 1 filled with the eutectic alloy GaInSn. The reconstruction of the three-dimensional flow pattern by 17 ultrasound Doppler velocimetry sensors detecting the velocity profiles along their beam lines in different planes reveals a clear breakdown of coherence of the large-scale circulation for Γ=0.5. As a consequence, the scaling laws for heat and momentum transfer inherit a dependence on the aspect ratio. We show that this breakdown of coherence is accompanied with a reduction of the Reynolds number Re. The scaling exponent β of the power law Nu∝Ra^{β} crosses eventually over from β=0.221 to 0.124 when the liquid metal flow at Γ=0.5 reaches Ra≳2×10^{8} and the coherent large-scale flow is completely collapsed.

Combined Effects of the Turbulence and Interfacial Momentum Transfer on Two-Phase Turbulent Bubbly Flows

Abstract The paper studies one-way and two-way coupling interactions between the liquid turbulence and bubbles' presence in bubbly jets. One-way coupling focuses on jet with low void fraction in which the bubbles have no significant effect on the hydrodynamic liquid fields in comparison to the single-phase jet. It sets out to model the interfacial momentum transfer identifying the turbulent contribution and its effect on the bubbles' dynamics and phase distribution. Two-way coupling considers jets with high void fractions where the liquid turbulence is altered by the bubbles which in turn influence the interfacial momentum transfers. This paper aims to improve the two-fluid model closures by implementing in computational fluid dynamics code a three-equation turbulence model and new interfacial momentum transfer closures. A benchmark of turbulence models combined with different interfacial exchange modeling is achieved to highlight the strong couplings between the interfacial forces, the phase distribution and the hydrodynamic fields of both phases.

Predicting the diameters of droplets produced in turbulent liquid–liquid dispersion

AbstractThe droplet size distribution in liquid–liquid dispersions is a complex convolution of impeller speed, impeller type, fluid properties, and flow conditions. In this work, we present threea priorimodeling approaches for predicting the droplet diameter distributions as a function of system operating conditions. In the first approach, called the two‐fluid approach, we use high‐resolution solutions to the Navier–Stokes equations to directly model the flow of each phase and the corresponding droplet breakup/coalescence events. In the second approach, based on an Eulerian–Lagrangian model, we describe the dispersed fluid as individual spheres undergoing ongoing breakup and coalescence events per user‐defined interaction kernels. In the third approach, called the Eulerian–Parcel model, we model a sub‐set of the droplets in the Eulerian–Lagrangian model to estimate the overall behavior of the entire droplet population. We discuss output from each model within the context of predictions from first principles turbulence theory and measured data.

Simultaneous coupling of fluidized granular activated carbon (GAC) and powdered activated carbon (PAC) with ultrafiltration process: A promising synergistic alternative for water treatment

Ultrafiltration (UF) has been extensively employed in current water treatment practice, during which limited removal for soluble contaminants and membrane fouling remain two perennial hurdles to efficient operation. This study proposed a promising approach by simultaneous coupling of fluidized granular activated carbon (GAC) and PAC with UF process, whereby PAC was responsible for improving effluent quality, and fluidized GAC was targeted for mitigating UF fouling and PAC deposition. The operational performance of such integrated GAC-PAC-UF system was systemically evaluated in a lab-scale setup. The results showed that fluidized GAC particles with larger size appeared highly effective in removing PAC deposition and fouling formed by surface water. PAC addition improved the effluent quality mainly by adsorbing humic acid-like substances. More importantly, energy consumption by GAC fluidization was found to be at least an order-of-magnitude lower than conventional fouling control methods employed in UF. Furthermore, redundancy analysis revealed that the key mechanism for UF fouling mitigation was tied to GAC particle momentum, whereas inorganic fouling mitigation was mostly achieved by GAC-induced liquid turbulence. It is expected that such integrated GAC-PAC-UF process proposed should be technically feasible and economically viable, potentially achieving high permeate quality and reducing membrane fouling with limited energy requirement.

A multiscale methodology for small-scale bubble dynamics in turbulence

We formulate in this paper a multiscale numerical framework that handles small-scale bubble dynamics in turbulence. Our framework involves bubbles with arbitrary density ratios with the carrier phase. We use a Moving Reference Frame method that follows a bubble to deal with a fast rising of bubbles present at high density ratios between the phases. We use a Proportional Integral Derivative controller to handle an additional acceleration term in the governing equations that stems from the change of a coordinate system from a fixed to a non-inertial one. Our framework accounts for the fact that the dynamics of bubbles are significantly influenced by the unsteadiness of the small-scale turbulent liquid fluctuations that modify the bubble shapes and alter their motion. In addition, we improve and speed up, with at least two orders of magnitude in computational time, the numerical framework recently proposed by Milan et al. (2020). The developed numerical framework can capture processes occurring at time scales even smaller than the Kolmogorov times. It can be applied to droplets, bubbles or particle systems in both laminar and turbulent flows, using any general DNS technique that handles two-phase flows.

The Rehydration Ability of Whey Ingredients

The purpose of this research was to studythe ability of whey protein concentrates (WPC) and whey permeate produced with ultrafiltration of cheese whey to rehydrate. The products studied were cheese whey concentrate witha PDM percentage of 80% (WPC-80), and cheese whey permeate, both produced under the conditions of the PJSC Dairy “Voronezhsky”.WPC-80 and the whey permeate dissolution processes were studied using microscopy. Water-impermeable hydrophobic layers were formed at the boundary, preventing water penetration into dry particles. The result was a higher dissolution timeforWPC-80 compared with whey permeate. When WPC-80 came into contact with water,it initially formed an obtuse wetting angle with a slow change over time. Whey permeate reached the equilibrium wetting angle more quickly. Quickreconditioning of WPC moisture content required avoiding capillary penetration of water, which created a turbulent liquid flow. The application of these ingredients in different food industry areas can reduce the costs for finished products, contribute to cost-effectiveness, increase the total production, and reduce environmental risks.&#x0D; Keywords: whey protein concentrate, whey permeate powder, water-wetting, dissolution

Mass transfer intensification through increased surface wetting and liquid turbulence using 3D printing structured packing for CO2 capture

Mass transfer intensification through increased surface wetting and liquid turbulence using 3D printing structured packing for CO2 capture

Numerical Investigation of Turbulence Production Under Two-Phase Flow in a Simulation of Electrical Submersible Pump Performance

Abstract Investigating the characteristics of gas–liquid two-phase flow in a centrifugal pump is critical for evaluating pump performance. In this study, a numerical simulation was performed to understand the effects of gas–liquid turbulence formation in the impeller channels on the performance of a single-stage centrifugal pump. The focus was on the inlet gas volume fraction (IGVF) at constant flowrate and constant impeller speed on the flow structure in the impeller and the pressure surging characteristics. The correlation between Reynolds shear stress and turbulent kinetic energy on pump performance is shown by examining pressure, velocity, turbulent kinetic energy, and gas volume fraction (GVF). The model verification is verified using the theoretical pump pressure head determined by the manufacturer, which demonstrated adequate uncertainty (μ&amp;lt;5%) for a flowrate of 250 L/min. The results show a 9.41% decrease in wall shear stresses when the in-situ GVF varies between 1% and 10%. Wall shear stresses combined with circulation resulted in a 3.76% decrease in turbulent kinetic energy, while the contribution of turbulence to pump performance degradation is minimal. Other factors such as gas entrapment, impeller inlet blockage due to bubble coalescence, pressure gradient, and bubble size had a much greater impact on performance. The performance decreased dramatically by 26.53% when the GVF increased from 1% to 10%. The proposed flow structure can be further investigated together with the wall shear stress and circulation phenomena, such as vorticity and shear layers in the context of two-phase flow.

Use of new similarities Bl and Blturb. to optimize the calculation and selection of heat exchange equipment for working with nanofluid coolants

The problem of correct, exact calculation and selection of the optimal heat exchange equipment at use in it of nanoliquid heat carriers was investigated in the work. Classical numerical equations, which are widely used in the calculation and selection of heat exchangers with nanofluids, especially at temperatures above 50 °C, give an error of (15–20) % or more. This leads to the fact that the selected heat exchange equipment may not work efficiently with excessive consumption of thermal energy. A new approach to heat transfer processes is considered, taking into account the theory of J. Businesque, which gives an idea of turbulent viscosity and thermal conductivity, as well as comparing the resistance of the coolant flow to the nanoparticle with surface forces and considering turbulent fluid as Newtonian. It is shown that the consideration of the behavior of a nanoparticle in a turbulent liquid coolant without taking into account surface forces is inaccurate and erroneous. The physical content of the previously obtained new numbers of similarity Bl and Blturb is considered and the possibility of their effective application in the new numerical equation obtained by us for the calculation of heat exchangers using nanofluid coolants is shown. The existing express method of estimating the efficiency of nanorluids use in heat exchangers on the basis of classical numerical equations is analyzed and a new express method on the basis of a new numerical equation and new numbers of similarity Bl and Blturb is proposed. The proposed express calculation method shows that a mixture of H2O + EG (60:40) improves the heat transfer properties of water by + 12.86 %, and a mixture of (H2O + EG (60:40) + 1.5 % TiO2) and (milk) + 0.5 % pumpkin seed oil) – by +16.75 %, which corresponds to the experiments and our calculations, and the known express method based on classical numerical equations shows a deterioration of – 4.5 % and, accordingly, by – 1.2 %. An example of calculating the optimal shell-and-tube heat exchanger according to the new algorithm when heating milk with hot water with the addition of mixtures (H2O + EG (60:40) + 1.5 % TiO2) and accordingly (milk + 0.5 % pumpkin seed oil) fully confirms the correctness of the new express –method.

Turbulence-induced formation of emulsion gels

Emulsion gels have a wide range of applications. We report on a facile and versatile method to produce stable emulsion gels with tunable rheological properties. Gel formation is triggered by subjecting a mixture containing aqueous colloidal particle (CP) suspensions and water-immiscible liquids to intense turbulence, generated by low frequency (20 kHz) ultrasound or high-pressure homogenization. Through systematic investigations, requisite gel formation criteria are established with respect to both formulation and processing, including ratio/type of liquid pairs, CP properties, and turbulence conditions. Based on the emulsion microstructure and rheological properties, inter-droplet bridging and CP void-filling are proposed as universal stabilization mechanisms. These mechanisms are further linked to droplet-size scaling and sphere close-packing theory, distinctive from existing gel-conferring models. The study thereby provides the foundation for advancing the production of emulsion gels that can be tailored to a wide range of current and emerging applications in the formulation and processing of food, cosmetics or pharmaceutical gels, and in material science.

A conservative level set method for liquid-gas flows with application in liquid jet atomisation

In this paper, a methodology for modelling two-phase flows based on a conservative level set method in the framework of finite volume method is presented. The novelty of the interface capturing method used here lies on the advection of level set which is solved with a WENO scheme and corrected with a novel re-initialisation method for retaining its signed distance function character. The coupling with the volume of fluid method is done with a simple algebraic approach, and with the new algorithm the accumulated mass conservation errors remain reasonably low. The paper presents a unique coupling between the level set method and the Eulerian-Lagrangian Spray Atomisation approach for modelling spray dispersion in liquid atomisation systems. The method is shown to have good accuracy providing similar results to other numerical codes for the classical tests presented. Preliminary results are also shown for three-dimensional simulations of the primary break-up of a turbulent liquid jet obtaining results comparable to direct numerical simulations. Consequently, the coupled method can be used for simulating various two-phase flow applications offering an accurate representation of the interface dynamics.

Sediment wear prediction model of ZG06Cr13Ni4Mo turbine guide vane in sediment-laden hydropower station

The guide vane of a hydraulic turbine in any sediment-laden hydropower station is one of the components most seriously affected by sediment abrasion. Damage to a guide vane can significantly impact stable operation and energy characteristics of the unit, and it is thus essential to address and effectively manage this problem. In this study, the k-ε solid–liquid two-phase turbulence model and sample algorithm were used to numerically simulate the sand-water flow through the entire passage of a hydraulic turbine and sand samples were subsequently collected from the hydropower station to examine the sediment abrasion damage to turbine’s guide vane, which was made of ZG06Cr13Ni4Mo. Thereafter, calculation and test results were used to establish a prediction model for sediment abrasion of hydraulic turbine guide vane. These research findings could provide guidance for improved hydraulic turbine design and could thus contribute to the optimized operation of sediment-laden hydropower stations.