Fluid Dynamic Conditions Research Articles

Computational-Aided Approach for the Optimization of Microfluidic-Based Nanoparticles Manufacturing Process

In the last few years, the microfluidic production of nanoparticles (NPs) is becoming a promising alternative to conventional industrial approaches (e.g., nanoprecipitation, salting out, and emulsification-diffusion) thanks to the production efficiency, low variability, and high controllability of the production parameters. Nevertheless, the development of new formulations and the switching of the production process toward microfluidic platforms requires expensive and time-consuming number of experiments for the tuning of the formulation to obtain NPs with specific morphological and functional characteristics. In this work, we developed a computational fluid dynamic pipeline, validated through an ad hoc experimental strategy, to reproduce the mixing between the solvent and anti-solvent (i.e., acetonitrile and TRIS–HCl, respectively). Moreover, beyond the classical variables able to describe the mixing performances of the microfluidic chip, novel variables were described in order to assess the region of the NPs formation and the changing of the amplitude of the precipitation region according to different hydraulic conditions. The numerical approach proved to be able to capture a progressive reduction of the nanoprecipitation region due to an increment of the flow rate ratio; in parallel, through the experimental production, a progressive increment of the NPs size heterogeneity was observed with the same fluid dynamic conditions. Hence, the preliminary comparison between numerical and experimental evidence proved the effectiveness of the computational strategy to optimize the NPs manufacturing process.Graphical

Transport phenomena in pasta drying: a dough-air double domain advanced modeling

In the realm of pasta drying, where precise prediction of temperature and water-content distribution is crucial, the application of modeling and simulation emerges as highly significant. This study endeavors to evaluate operational conditions ensuring the production of a safe, high-quality pasta product. An advanced two-domain model was devised and solved to estimate transport phenomena in both the food and air domains. Unlike conventional models relying on specified interfacial heat and mass transfer coefficients, the proposed model serves as a versatile tool applicable across a broad spectrum of process and fluid-dynamic conditions in real pasta driers. The system of non-linear unsteady-state partial differential equations governing the behavior of a “Rigatone" pasta sample in a drier was solved using the finite elements method to estimate how air characteristics influence drying performance. A pilot-scale drying chamber was used for model validation for inlet air temperature Ta,in=80°C at relative humidity values (RHin) of 50 % and 60 %, with error consistently below 10 %.

Population balance modelling of magnesium hydroxide precipitation: Full validation on different reactor configurations

In this paper, a predictive mono-dimensional (1D) model for Mg(OH)2 precipitation is proposed and its predictive capability is tested. Two different reactor configurations are analyzed and compared, namely a T-mixer and a Y-mixer followed by two consecutive diverging channels and a final coil of constant diameter. Both setups were chosen for their high mixing efficiency. The suspension samples were characterized by Dynamic Light Scattering (DLS), thus obtaining particle size distributions (PSD). The experimental data collected using the T-mixer was used to identify the kinetics parameters set, while the data obtained through the Y-mixer setup was employed to assess the model predictive capability under different fluid dynamics conditions. Computational Fluid Dynamics (CFD) simulations were conducted to characterize the flow fields and the turbulence, which were integrated into the 1D model. Predictions were found to be in good agreement with the experimental data and further improved after introducing a novel correction factor for the aggregation kernel.

Computational fluid dynamics modeling of a discrete feed atomic layer deposition reactor: Application to reactor design and operation

Novel transistor fabrication methods such as area-selective atomic layer deposition (AS-ALD) are crucial to improving nanopatterning, which is essential for facilitating transistor stacking in semiconducting wafers. However, transistor surfaces are subjected to nonuniformities during the initial AS-ALD adsorption reactions that are attributed to steric hindrance effects. To minimize the role of steric hindrance generated by an oversaturation of reagent on the substrate surface, a discrete feed method is proposed for an ALD reactor configuration where reagent is introduced in short pulses through a perpendicular delivery system. An optimal reactor configuration is developed by modifying the inlet geometries of the reactor to ensure ideal fluid dynamics conditions (e.g., minimal vortices, radial flow distribution) are achieved. Detailed computational fluid dynamics simulations demonstrate the performance of the new reactor configuration and operational strategy.

Design of a continuous device for ethoxylation reaction: The choice between micro and milli scale

A laminar flow model was developed to investigate the reaction kinetics of 1-dodecanol ethoxylation promoted by KOH, elaborating the data collected in microreactors. A generic laminar flow model was coded, and a sensitivity analysis was conducted highlighting the good flexibility of the model to simulate a wide range of conditions. Ethylene oxide diffusivity and liquid mixture viscosity were determined by applying existing correlations, carefully considering the change in viscosity with ethylene oxide conversion, temperature, and feed ethylene oxide/1-octanol ratio. The model was tested on literature data obtaining in every case good results. The obtained kinetic data were demonstrated to be in line with the ones obtained in separate investigations conducted in a fed-batch reactor, demonstrating that there was a real need in adopting the laminar flow reactor approach, as it allowed to retrieve of more precise information about the intrinsic kinetics of the ethoxylation reaction, when working with microreactors, compared with the ones obtainable with a plug-flow ideal fluid-dynamic model. The developed model was used to simulate the behavior of a milli-reactor (this device allows to reach sufficient productivity for industrial application) and it was forecasted the possibility to use continuous ethoxylation milli-reactors using fluid-dynamic conditions characterized by a high Reynolds number (>10000).

Development of a low-cost pseudo-fuel spray combustion chamber for gas injection analysis of two-stroke dual-fuel engines

The present work is aimed to model, design, build and experimentally characterize a low-cost pseudo-fuel spray combustion chamber (SCC) for gas injection analysis of two-stroke dual fuel engines. The novel SCC, operating at low pressure and with a pseudo-fuel, was capable to reproduce, under equivalent fluid-dynamic conditions, the operating behavior of a full-scale engine combustion chamber. A mathematical model, based on AVL Boost®, was developed to simulate pressure, mass flow rate, velocity and momentum rate within the system. Then, according to these numerical results, the SCC was built and experimentally characterized. Its main element was a velocimetric chamber provided with four optical accesses to perform imaging analysis (PIV and LIF) on pseudo-fuel sprays. In conclusion, this article may be a useful guide to build a new type of low-cost pseudo-fuel spray combustion chamber for gas injection analysis of two-stroke dual-fuel engines, avoiding dangerous (because of high pressures and temperatures involved) and expensive full-scale studies.

3D Numerical Analysis of a Phase Change Material Solidification Process Applied to a Latent Thermal Energy Storage System

The techniques for releasing thermal energy accumulated in periods of high availability to meet the demand in periods of low energy supply contribute to the continuity of the cycles involved in thermodynamic processes. In this context, phase change materials are capable of absorbing and releasing large amounts of energy in relatively short periods of time and under specific operating conditions. However, phase change materials have low thermal conductivity and need to be coupled with high-thermal-conductivity materials so that the heat flux can be intensified and the energy absorption and release times can be controlled. This work aims to numerically study the solidification process of a phase change material inserted into a triplex tube heat exchanger with finned copper walls to intensify the thermal exchange between the phase change material and the cooling heat transfer fluid, water, that will receive the energy accumulated in the material. This work proposes the 3D numerical modeling of the triplex tube heat exchanger with finned walls and meets the need for numerical models that allow for the analysis of the full geometry of the latent heat thermal energy storage system and the thermal and fluid dynamic phenomena that are influenced by this geometry. Results of the temperature, liquid fractions and velocity fields during phase transformations are presented, analyzed and validated with experimental data, presenting average errors of below 5%. The total material discharge time was approximately 168 min, necessary for the complete solidification of the phase change material, with water injected into the triplex tube heat exchanger at a flow rate of 8.3 L/min and a temperature of 68 °C. The solidification process occurred more slowly in the same direction as the length of the triplex tube heat exchanger, and from 80% of the material in the solid state, the difference between the solidification time for z = 0 and z = 480 mm was 30 min. The fluid dynamic conditions developed in the latent heat thermal energy storage system promoted a maximum negative heat flux of −6423 w/m2 to the annular internal surface and −742 w/m2 to the annular external surface, representing a heat removal process nine times less intense on the external surface. The total energy released to the cooling heat transfer fluid was 239.56 kJ/kg.

A Human Ovarian Tumor & Liver Organ-on-Chip for Simultaneous and More Predictive Toxo-Efficacy Assays.

In oncology, the poor success rate of clinical trials is becoming increasingly evident due to the weak predictability of preclinical assays, which either do not recapitulate the complexity of human tissues (i.e., in vitro tests) or reveal species-specific outcomes (i.e., animal testing). Therefore, the development of novel approaches is fundamental for better evaluating novel anti-cancer treatments. Here, a multicompartmental organ-on-chip (OOC) platform was adopted to fluidically connect 3D ovarian cancer tissues to hepatic cellular models and resemble the systemic cisplatin administration for contemporarily investigating drug efficacy and hepatotoxic effects in a physiological context. Computational fluid dynamics was performed to impose capillary-like blood flows and predict cisplatin diffusion. After a cisplatin concentration screening using 2D/3D tissue models, cytotoxicity assays were conducted in the multicompartmental OOC and compared with static co-cultures and dynamic single-organ models. A linear decay of SKOV-3 ovarian cancer and HepG2 liver cell viability was observed with increasing cisplatin concentration. Furthermore, 3D ovarian cancer models showed higher drug resistance than the 2D model in static conditions. Most importantly, when compared to clinical therapy, the experimental approach combining 3D culture, fluid-dynamic conditions, and multi-organ connection displayed the most predictive toxicity and efficacy results, demonstrating that OOC-based approaches are reliable 3Rs alternatives in preclinic.

The effect of fluid dynamics conditions and combustion reactions on the performance and heat and mass transfer distribution of dual-phase oxygen transport membranes

A 3-D model based on CFD approach was developed to explore the effect of fluid dynamic conditions and combustion reactions on oxygen transport, in which the distribution of parameters such as oxygen partial pressure, temperature, velocity, and oxygen permeability were considered. After meshing the geometric model with poly-hexcore method, a series of user defined functions written in C++ were compiled and hooked to FLUENT to solve for oxygen permeation of dual-phase oxygen transport membranes. The results showed that oxygen permeability can be improved by pressurizing the feed side or vacuuming the permeate side, and the increased kinetic effect under evacuation conditions can increase the oxygen permeability by 69.85% at a vacuum pressure of 10 kPa and by 270.94% at 90 kPa. Due to the phenomenon of differential concentration polarization, the effect of oxygen concentration on oxygen permeability is more significant when the oxygen concentration on the feed side is lower than 0.17. Combustion reaction of CH4 promotes oxygen permeation, and the effect of the gap height between the fuel inlet and membrane is determined by several trade-off factors including momentum effects, reaction rate and temperature, and optimal oxygen permeability is achieved with a gap height of 3 mm.

Impact of drug release in USP II and in-vitro stomach on pharmacokinetic: The case study of immediate-release carbamazepine tablets

The in-vitro reproduction of the real physiological conditions that occur along the gastrointestinal (GI) tract would be the optimum for the dissolution and release testing of pharmaceutical formulations for oral intake. In this study a method for the automated reproduction of the real pH conditions that occurs in the gastric cavity and a device that mimics the same forces exerted by the internal walls of the stomach are presented. Commercial immediate-release carbamazepine tablets were tested in conventional (USP II) and unconventional apparatuses. The gastric pH and the fluid dynamic conditions are factors to be carefully considered since they both affect the drug release profiles. Finally, a PBPK model was used to predict the evolution of plasma drug concentrations knowing the experimental in-vitro GI release behavior. It was found that, for immediate-release carbamazepine tablet, the gastric drug release does not have a major impact on the plasmatic drug concentration.

High resolved Optical Emission Spectroscopy as accurate physics methodology for plasma freestream temperature characterization

In this work the hypersonic plasma flow generated by SCIROCCO hypersonic facility has been experimentally characterized as test case, using a high resolved Optical Emission Spectroscopy (OES) during a high enthalpy test campaign. The CIRA methodology to measure roto-translational and NO vibrational temperatures of a free jet via analyses performed in the Ultra Violet spectral range has been improved and a comparison between experimental data and Computational Fluid Dynamics (CFD) simulations has been carried out. The revised methodology estimates the roto-translational and vibrational temperatures using high definition spectroscopy carried out at conditions of high values of pressure and enthalpy.In particular, attention is mainly focused on the NO emission band at Non-Local Thermal Equilibrium (NLTE) conditions in the hypersonic flight regime which means equilibrium between the molecular rotational and translational degrees of freedom but not between the roto-translational and vibrational degrees of freedom. Three tests at high enthalpy hypersonic conditions (23.8, 24.0 and 26.0 MJ/kg at a total pressure of about 2.5 bars) have been investigated and experimental data have been compared with numerical simulations in order to verify sensitivity of the method in estimating the small variation in NO roto-translational and vibrational temperatures by changing slightly the total enthalpy fluid-dynamic conditions. The current work presents a high definition spectral method which can be used to determine the temperature of NLTE hypersonic free jets, and may serve as a benchmark in determining the accuracy of various numerical models dedicated to these flow regimes.

Multiphysics Design of an Automotive Regenerative Eddy Current Damper

This research presents a finite element multi-physics design methodology that can be used to develop and optimise the inherent functions and geometry of an innovative regenerative eddy current (REC) damper for the suspension of B class vehicles. This methodology was inspired by a previous work which has been applied successfully for the development of an eddy current (EC) damper used for the same type of applications. It is based on a multifield finite element coupled model that can be used to fulfil the electromagnetic, thermal, and fluid dynamic field properties and boundary conditions of a REC damper, as well as its non-linear material properties and boundary conditions, while also analysing its damping performance. The proposed REC damper features a variable fail-safe damping force, while electric power is advantageously regenerated at high suspension frequencies. Its damping performance has been benchmarked against that of a regular hydraulic shock absorber (selected as a reference) by analysing the dynamic behaviour of both systems using a quarter car suspension model. The results are expressed in terms of damping force, harvested power, thermal field, comfort and handling, with reference to ISO-class roads. The optimisation analysis of the REC damper has suggested useful guidelines for the harmonisation of damping and regenerative power performances during service operation at different piston speeds.

The use of ultrasound-assisted precipitation for the production of micro-sized crystals with a narrow CSD

The presented study takes into account the recognition of the ultrasounds parameters’ impact on (i) the obtained product characteristic features (like CSD, size, shape, etc.), (ii) kinetics of precipitation, as well as (iii) precipitation efficiency. The experimental research has been based on CaF2 precipitation, carried out in a stirred tank reactor (STR), where the turbulence intensity was increased by the use of ultrasounds (US). As an US generator, the ultrasonic bath has been introduced to the reaction system. The ranges of the analyzed US parameters were as follows (i) power PUS = 150–300 W, (ii) frequency fUS = 40 and 59 kHz, and (iii) sonication time τ = 9, 30 s. The results were compared with the data obtained in previous investigations provided in silent conditions. It has been shown that the use of US-assisted methods may promote the achievement of solid crystals with a decreased particle size, narrowly distributed, together with a significant reduction of agglomerated clusters. It has been also explained that the conscious selection of both US parameters and fluid dynamic conditions may stimulate the process in such a way to obtain the product with pre-defined characteristics.

Inquest of material dissipation from cavitation bubble in laser-irradiated solid–liquid interface

The role of fluid dynamical phenomena – shockwaves and cavitation bubble for laser irradiation in liquid/solid–liquid interface – is thoroughly investigated in the literature considering idealized fluid dynamical conditions. The dynamics outside the cavitation bubbles are mostly ignored in laser-irradiated pure liquids. But this proves pivotal at the solid–liquid interface when entities from ablated targets are dispersed in liquids from an early breakdown via an explosive boiling, diffusion-assisted mass transfer through cavitation bubble wall or via releasing of trapped nanomaterials from a cavitation bubble collapse. The localized conditions (pressure and temperature) of these ablated species found outside the cavitation bubble favors chemical interactions for underwater-pulsed laser-induced material processing. To gain an insight into the materials dispelling from the cavitation bubble, a simplified model is employed to extract the localized conditions (pressure and temperature) in liquid, diffusion coefficient and diffusion-assisted distance traversed by the laser-ablated agglomerates.

High-Versatility Left Ventricle Pump and Aortic Mock Circulatory Loop Development for Patient-Specific Hemodynamic In Vitro Analysis.

The importance of experimental setups able to reproduce cardiac functions was well established in the field of clinical innovations. The mock circulatory loops acquired rising relevance, and the possibility to have a complete reproduction of different and specific fluid dynamic conditions within the setup is pivotal. A system with enough versatility to reproduce the physiologic range of both flows and pressures is required. This study describes the design of a versatile setup composed by a custom pulsatile left ventricular pump system and a 3D-printed mock circulatory loop for the in vitro analysis of a patient-specific case of an aortic complex. The performances of the pump were validated first with a set of test flow profiles. It was demonstrated that the system was able to cover a wide range of aortic and mitral flows. Second, the pump system was inserted within the full mock circulatory loop. A patient-specific case was reproduced, both in terms of flow and pressure profiles. A successful validation of the flow and pressure waveforms was obtained by using patient-specific in vivo data from magnetic resonance analysis.

Simulación termofluidodinámica en un molde de colada continua de acero

In the present study, a 3D multiphysics mathematical model was solved using the finite volumes method to predict the phenomena of fluid flow and heat transfer in a continuous casting mold of 20CrMnTi steel billets. The results showed the high cooling capacity of the system for the formation of a progressive and uniform solid layer that begins very close to the meniscus and reaches a thickness of 10 % of the section of the casting at the exit of the mold. At the exit of the SEN, the liquid steel underwent a reflux with a depth of 0.45 m measured from the meniscus. Some of the rising reflux reached the meniscus and descended, infiltrating the walls of the mold. Velocities less than 0.2 m/s, in the upper zone of the mold, and great penetration of the steel jet, in the center of the mold, were observed. It was concluded, based on what is described in the literature, the following: a) the thickness of the solidified crust, at the exit of the mold, is sufficient to avoid breakage in the piece due to the ferrostatic pressure exerted by the liquid steel, c) The fluid dynamic conditions that occur in the upper zone of the mold can be counterproductive for the transfer of heat in the meniscus and the dissipation of overheating in the steel.

The shape of wave-packets in a three-layer hydrodynamic system

The article is devoted to the problem of wave-packet propagation in a three - layer hydrodynamic system "layer with a hard bottom - layer - layer with a cover stratified by density. The current research on selected topics is reviewed. The mathematical formulation of the problem is given in dimensionless form and contains the equations of fluid motion, kinematic and dynamic conditions on the contact surfaces, as well as the boundary conditions on the lid and on the bottom. Using the method of multiscale developments, the first three approximations of the studied problem are obtained, of which the first two are given in the article, because the third approximation has a cumbersome analytical form. The solutions of the first approximation and the variance relation are presented. The evolution equations of the circumferential wave-packets on the contact surfaces are derived in the form of the nonlinear Schrodinger equation on the basis of the variance relation and the conditions for the solvability of the second and third approximations. A partial solution of the nonlinear Schrodinger equation is obtained after the transition to a system moving with group velocity. For the first and second approximations, the formulas for the deviations of the contact surfaces are derived, taking into account the solution of the nonlinear Schrodinger equation. The conditions under which the shape of wave-packets on the upper and lower contact surfaces changes are derived. The regions of familiarity of the coefficients for the second harmonics on the upper and lower contact surfaces for both frequency pairs, which are the roots of the variance relation, are presented and analyzed. Also, for both frequency pairs, different cases of superimposition of maxima and minima of the first and second harmonics, in which there is an asymmetry in the shape of wave packets, are graphically illustrated and analyzed. All results are illustrated graphically. Analytical transformations, calculations and graphical representation of results were performed using a package of symbolic calculations and computer algebra Maple.

The influence of fluid dynamics on the selectivity of fast gas–liquid reactions in methanol

One important strategy for process intensification is the enhancement of yield and selectivity in fast gas–liquid reactions, like oxidations, hydrogenations or halogenations. However, the interplay between fluid dynamics and competitive chemical reactions has not yet been understood to an extent that allows tailoring the flow and concentration fields for intensified reactions. To understand the interplay, the fluid dynamic conditions surrounding Taylor bubbles rising in an organic solvent are studied and compared to data of aqueous systems from the literature. The local flow fields are measured using Particle Image Velocimetry (PIV) and compared to spectroscopically derived selectivity data of a competitive consecutive gas–liquid reaction. The general rising behavior of Taylor bubbles in methanol is confirmed to be similar to those of bubbles in aqueous systems. However, as surface active agents do not affect the interface mobility in organic solvents, the local flow structures in the bubble wake differ significantly from those of bubbles rising in water, impacting the mixing behavior. Finally, the flow fields are compared to the concentration fields of the main and side products. Thereby, a decisive influence of the fluid dynamics on yield and selectivity becomes apparent, unveiling the potential for process intensification.

Standing shock prevents propagation of sparks in supersonic explosive flows

Volcanic jet flows in explosive eruptions emit radio frequency signatures, indicative of their fluid dynamic and electrostatic conditions. The emissions originate from sparks supported by an electric field built up by the ejected charged volcanic particles. When shock-defined, low-pressure regions confine the sparks, the signatures may be limited to high-frequency content corresponding to the early components of the avalanche-streamer-leader hierarchy. Here, we image sparks and a standing shock together in a transient supersonic jet of micro-diamonds entrained in argon. Fluid dynamic and kinetic simulations of the experiment demonstrate that the observed sparks originate upstream of the standing shock. The sparks are initiated in the rarefaction region, and cut off at the shock, which would limit their radio frequency emissions to a tell-tale high-frequency regime. We show that sparks transmit an impression of the explosive flow, and open the way for novel instrumentation to diagnose currently inaccessible explosive phenomena.

CFD analysis of a multiplatform catamaran by means of a web-based application: Experimental data comparison for a fully automated analysis process

The recently introduced LincoSim Web Based High Performance Computing (HPC) Cloud Platform for Automatic Virtual Towing Tank Analysis, which is based on open-source Reynolds Averaged Navier-Stokes (RANS) solvers (Salvadore & Ponzini, 2019), is herein applied to the hydrodynamic assessment of a catamaran vessel. An experimental data campaign was used to assess the effect of the demihull separation distance on the catamaran's resistance for a given demihull shape. The results of the comparison between the experimental and the automatically generated numerical ones are presented and discussed in the present work. The comparison is quite rich including data for a reference monohull, three demihull separations and two displacements conditions, each with the Froude number ranging from 0.145 to 0.904. The set of the experimental data acquired for the model scaled catamaran are the total resistance, the sinkage and the dynamic trim. Nevertheless, also the wave fields at three given locations are considered in the towing tank experiments in order to assess not only the effect on the hull, but also on the catamaran's wake field. The agreement between computational and experimental quantities is good for both the hull-related and flow-related ones, confirming the ability of the developed automated tool to discern between favorable and detrimental fluid dynamic conditions and to efficiently rank performances also for multihulls. Notably, thanks to the availability of numerical data for both model and full scale, also the effectiveness of the extrapolation process has been assessed.