Fluid Dynamic Properties Research Articles

Liposome Formation Using a Coaxial Turbulent Jet in Co-Flow.

Liposomes are robust drug delivery systems that have been developed into FDA-approved drug products for several pharmaceutical indications. Direct control in producing liposomes of a particular particle size and particle size distribution is extremely important since liposome size may impact cellular uptake and biodistribution. A device consisting of an injection-port was fabricated to form a coaxial turbulent jet in co-flow that produces liposomes via the ethanol injection method. By altering the injection-port dimensions and flow rates, a fluid flow profile (i.e., flow velocity ratio vs. Reynolds number) was plotted and associated with the polydispersity index of liposomes. Certain flow conditions produced unilamellar, monodispersed liposomes and the mean particle size was controllable from 25 up to >465nm. The mean liposome size is highly dependent on the Reynolds number of the mixed ethanol/aqueous phase and independent of the flow velocity ratio. The significance of this work is that the Reynolds number is predictive of the liposome particle size, independent of the injection-port dimensions. In addition, a new model describing liposome formation is outlined. The significance of the model is that it relates fluid dynamic properties and lipid-molecule physical properties to the final liposome size.

Particle Formation and Product Formulation Using Supercritical Fluids.

Traditional methods for solids processing involve either high temperatures, necessary for melting or viscosity reduction, or hazardous organic solvents. Owing to the negative impact of the solvents on the environment, especially on living organisms, intensive research has focused on new, sustainable methods for the processing of these substances. Applying supercritical fluids for particle formation may produce powders and composites with special characteristics. Several processes for formation and design of solid particles using dense gases have been studied intensively. The unique thermodynamic and fluid-dynamic properties of supercritical fluids can be used also for impregnation of solid particles or for the formation of solid powderous emulsions and particle coating, e.g., for formation of solids with unique properties for use in different applications. We give an overview of the application of sub- and supercritical fluids as green processing media for particle formation processes and present recent advances and trends in development.

Positron emission particle tracking in fluidized beds with secondary gas injection

We apply positron emission particle tracking (PEPT) to a gas–solid fluidized bed with injection of a secondary gas through a centrally arranged nozzle and present a method to compute stationary fluid-dynamic characteristics of the system from the trajectories of a test particle. In order to evaluate this non-invasive method we compare the field of density obtained by PEPT with the density obtained by a traditional, well-established and approved, yet invasive, measurement technique to find good agreement. Besides the penetration depth of the jet region and the opening angle of the jet which are inferred from the density field, we use PEPT to measure quantities whose measurement using traditional methods is rather sophisticated, including the residence time of particles in the jet region and the suspended phase, the coefficients of axial and radial dispersion and the material flux across the jet boundaries. We conclude that PEPT is a reliable and at the same time versatile technique to measure stationary fluid-dynamic properties of dynamical particle systems at spatial resolution only limited by the duration of the measurement.

Force and aspiration analysis of the ADAPT technique in acute ischemic stroke treatment

IntroductionThe development of new revascularization devices has significantly improved recanalization rates and time to reperfusion. A direct aspiration first-pass (ADAPT) technique for stroke thrombectomy was recently shown to be an...

Current status of right ventricular outflow tract reconstruction: complete translation of a review article originally published in Kyobu Geka 2014;67:65-77.

Right ventricular outflow tract (RVOT) reconstruction is becoming more prevalent as the number of adult patients who require repeated surgery long after definitive repair of congenital heart defects during childhood has increased. Early primary repair and annulus-preserving surgery have been the two current strategies of RVOT reconstruction from the viewpoint of timing and indications for surgical intervention; however, the long-term outcomes of both procedures remain unknown. Although various materials have been used for pulmonary valve replacement during RVOT reconstruction, deficient durability due primarily to immunological rejection frequently arises, particularly when implanted into young patients. A multicenter study in Japan showed that the clinical outcomes of expanded polytetrafluoroethylene (ePTFE) valved patches/conduits that we developed and manufactured comprised an excellent alternative material for RVOT reconstruction. Such enhanced outcomes might have partly been attributable to the biocompatibility and low antigenicity of ePTFE, and also to the fluid dynamic properties arising from the structural characteristics of a bulging sinus and a fan-shaped valve. However, numerous issues concerning RVOT reconstruction, such as indications for and the timing of definitive repair, as well as the choice of materials for pulmonary valve replacement, must be resolved to achieve better patient prognoses and quality of life. This review describes recent surgical strategies and outstanding issues associated with RVOT reconstruction.

Steady State Thermal Behaviour of Ceramic Wick Structure for Application in Two Phase Heat Transfer Devices

This work reports on results from two phase heat transfer devices assembled with ceramic capillary structure. It is firstly presented the manufacturing of the ceramic wick structures and afterwards the characterization of the morphological-and fluid-dynamical properties of these ceramic wick structures. As closing results, it is presented the thermal behaviour of two different two phase heat transfer devices, i.e. a Capillary Pumped Loop and a Loop Heat Pipe. The properties of the ceramic wick structure are within the desirable range for a correct functioning of these devices, e.g. porosity, pore size and permeability constants ranging from 40 to 60%, from 5 to 30μm and from 10-10 to 10-13m2, respectively. The thermal behaviour tests of the heat transfer devices used power heat load input in range from 10 to 20W and for all devices the evaporator temperature reached steady state condition. Thus, as a result, it can be claimed these ceramic wick structures as successful alternative for assembling capillary evaporator of CPL and LHP.

Thermal behavior of open cell aluminum foams in forced air: Experimental analysis

This paper deals with the study of thermal and fluid dynamics properties of the open cell metal foams. A thermo-fluid dynamic analysis of three different types of aluminum alloy foams, 5, 10 and 20 pores per inch (PPI) was carried out by using a novel ad hoc built instrumentation. In particular, it has been investigated the Heat Transfer Coefficient (HTC*) and the Pressure Drop (PD) under a flow of forced humid air. The influence of the main parameters, temperature of the metal foam and speed of humid air, both on the HTC* and on the PD was examined. Design of experiments (DOE) approach was used as support to interpret the experimental findings and the physical phenomena involved in HTC* and in PD, between foams and air. The analysis permitted to detect the effects of the operational parameters, foam pore size, air flux and temperature on the HTC* and on the PD.

Perturbation of fluid dynamics properties of water molecules during G protein-coupled receptor-ligand recognition: the human A2A adenosine receptor as a key study.

Recent advances in structural biology revealed that water molecules play a crucial structural role in the protein architecture and ligand binding of G protein-coupled receptors. In this work, we present an alternative approach to monitor the time-dependent organization of water molecules during the final stage of the ligand-receptor recognition process by means of membrane molecular dynamics simulations. We inspect the variation of fluid dynamics properties of water molecules upon ligand binding with the aim to correlate the results with the binding affinities. The outcomes of this analysis are transferred into a bidimensional graph called water fluid dynamics maps, that allow a fast graphical identification of protein "hot-spots" characterized by peculiar shape and electrostatic properties that can play a critical role in ligand binding. We hopefully believe that the proposed approach might represent a valuable tool for structure-based drug discovery that can be extended to cases where crystal structures are not yet available, or have not been solved at high resolution.

Industrial applications of supercritical fluids: A review

High pressure technologies involving sub and supercritical fluids offer the possibility to obtain new products with special characteristics or to design new processes, which are environmentally friendly and sustainable. By using high pressure as a processing tool one can also avoid the legal limitations for solvent residues and restrictions on use of conventional solvents in chemical processes. Supercritical fluids are already applied in several processes developed to commercial scale in pharmaceutical, food and textile industries. Extraction of valuable compounds from plant materials and their “in situ” formulation in products with specific properties is one of the very promising applications of high pressure technology. Particle formation using supercritical fluids may overcome the drawbacks of conventional particle size reduction processes. Because of their unique thermo-dynamic and fluid-dynamic properties, dense gases can also be used for impregnation of solid particles, particle coating, foaming etc. Some biochemical and chemical reactions performed in supercritical fluids have already been implemented at industrial scale to obtain products with high added value, while the use of supercritical fluids as heat carriers is a newly emerging field. In our short overview we present some applications and future expected development in the field of sub and supercritical fluids.

In vivo measurement of gas flow in human airways with hyperpolarized gas MRI and compressed sensing.

Hyperpolarized (HP) (3) He and (129) Xe are two gases with different fluid dynamic properties, which can be used as tracers for airflow measurement in the lungs with phase contrast velocimetry MRI sequences. In this work, in vivo measurements of velocity maps of airflow in the upper airways and first bronchi of healthy volunteers were obtained with both gases and compared. To reduce the acquisition time, a Compressed Sensing (CS) based acquisition and reconstruction algorithm was developed and optimized for flow measurement in three directions by including the sparsity of the complex difference images as prior knowledge. CS simulations on retrospectively under-sampled images demonstrated a better reconstruction with the inclusion of the complex difference terms in the cost function. The technique was then validated with a prospective acquisition study providing artifact free maps with acceleration factors up to 3. The presented technique opens up the possibility to map velocity inside human lungs. The results are of interest for the validation of computational fluid dynamics flow simulations and for understanding the spatio-temporal evolution of airflow patterns in the airways in vivo with different gas mixtures.

Fluid–solid interaction based morphological investigation of hyperelastic stenotic structure under turbulent pulsatile flow

The accumulation of low density lipoproteins, which form different geometrical stenotic structures, affects not only the blood fluid dynamics but also the structural properties of the arterial wall. A fluid structure interaction study was conducted to investigate the morphology of the stenotic structure in a two-dimensional axisymmetric arterial model. Three different stenotic structures were subjected to turbulent flow. Using pulsatile velocity and pressure waveforms as the physiological boundary conditions, the fluid dynamic and structural properties of an arterial wall with a hyperelastic material model were calculated.

Multi physics network simulation of a solenoid dispensing valve

Multi-physics modelling is often required to establish simulation models taking into account all significant effects in a complete technical system. In a solenoid dispensing valve the involved physical effects are electro-magnetic (coil and magnet interaction), fluid flow and fluid structure interaction. It is challenging and time consuming to establish a full model description of these different effects even by using the most up-to-date Computational Fluid Dynamics (CFDs) software tools. This article therefore presents an alternative approach using network simulation methods for modelling of a dispensing valve using the simulation software SABER (Synopsys). To create the model, the different parts of the valve and the relevant physical effects occurring therein are described by partial differential equations and implemented as lumped elements. The lumped elements are then linked together to form a complete model of the dispensing valve including electrical, mechanical and fluid dynamic properties. A comparison with experimental data obtained from a real valve is presented at the end of the paper to discuss and validate the model. In particular the correct prediction of the dispensed liquid volume in dependence of the main parameters like pressure and opening time are considered. Using ab initio simulation deviations of the predicted dispensed liquid volume from the experimental results in the range 0.65–7.4% was found for different actuating pressures at valve opening times larger than 20ms.

The Magnetic Nanoparticle Movement in Magnetic Fluid Characterized by the Laser Dynamic Speckle Interferometry

A dual scanning laser speckle interferometry experiment was designed to observe the dynamic behavior of the magnetic fluid actuated by a magnetic field. In order to improve the spatial resolution of the dynamic speckle measurement, the phase delay scanning was used to compensate the additional phase variation which was caused by the transverse scanning. The correlation coefficients corresponding to the temporal dynamic speckle patterns within the same time interval scattering from the nanoparticles were calculated in the experiment on nanoscale magnetic clusters. In the experiment, the speckle of the magnetic nanoparticle fluid movement has been recorded by the lens unmounted CCD within the interferometry strips, although the speckle led to the distinguished annihilation of the light coherence. The results have showed that the nanoparticle fluid dynamic properties appeared synergistically in the fringe speckles. The analyses of the nanoparticle′s relative speed and the speckle pattern moving amount in the fringes have proved the nanoparticle’s movement in a laminar flow in the experiment.

On locating the obstruction in the upper airway via numerical simulation

The fluid dynamical properties of the air flow in the upper airway (UA) are not fully understood at present due to the three-dimensional (3D) patient-specific complex geometry of the airway, flow transition from laminar to turbulent and flow-structure interaction during the breathing cycle. It is quite difficult at present to experimentally measure the instantaneous velocity and pressure at specific points in the human airway. On the other hand, direct numerical simulation (DNS) can predict all the flow properties and resolve all its relevant length- and time-scales. We developed a DNS solver with the state-of-the-art lattice Boltzmann method (LBM), and used it to investigate the flow in two patient-specific UAs reconstructed from CT scan data. Inspiration and expiration flows through these two airways are studied. The time-averaged first spatial derivative of pressure (pressure gradient), ∂p/∂z, is used to locate the region of the UA obstruction. But the time-averaged second spatial derivative, ∂2p/∂z2, is used to pinpoint the exact location of the obstruction. The present results show that the DNS-LBM solver can be used to obtain accurate flow details in the UA and is a powerful tool to locate its obstruction.

Correlation between nasal airflow characteristics and clinical relevance of nasal septal deviation to nasal airway obstruction

Since the imbalance of the nasal cavities due to nasal septal deviation (NSD) is a commonly observed anatomic variation in healthy adults, clinicians must often decide whether or not it is clinically relevant to the symptoms of nasal airway obstruction (NAO). Main reason for this is a lack of data correlating the symptoms of NAO with objective findings. The aim of our study is to find the correlation between fluid dynamic parameters and the anatomy of nasal cavity with NSD by numerical simulation. We generated 6 computational models of nasal cavities with NSD were created from computed tomographic images: 3 symptomatic patients with NAO and 3 asymptomatic patients. Computational fluid dynamics (CFD) was used to simulate steady inspiratory airflows in each nasal cavity model and compare the fluid dynamic properties of each. In the symptomatic cases, the pressure drop from the naris to the end of the septum was larger, and more uneven flow partitioning was observed. Local maximum velocity and wall shear stress were higher in the symptomatic group than in the asymptomatic group. The symptoms of NAO seem to be related more to the nasal resistance from the naris to the end of the septum than to the total nasal resistance from naris to nasopharynx. Factors correlated with NAO by CFD can be used as elements in patient-specific objective diagnostic tools for NAO in the presence of NSD.

Motion of rigid aggregates under different flow conditions

The response of rigid aggregates to different flow fields is investigated theoretically using model clusters with realistic three-dimensional structure composed of identical spherical primary particles. The aim is to relate the main fluid dynamic properties of the system with the geometry and morphology of the aggregates. Our simulations are based on Stokesian dynamics. The dilute limit of a colloidal aggregate system was studied, where aggregates are very far from each other, and hence, mutual inter-aggregate interactions are negligible. The motion of aggregates is characterized in terms of translational mobility and angular velocity, and the ability of simple models, based on either the simplified aggregate geometry or the concept of permeability, to capture the main features of the motion is examined.

Prototyping a Ferrofluid-Cooled Transformer

This paper presents the work conducted on prototyping a step-up/step-down, single-phased, low-power, and medium-voltage electrical transformer cooled by a fluid with colloidal magnetic nanoparticles. The magnetic and fluid dynamic properties and the heat capacities of the ferrofluid (magnetic nanofluid) and that of the regular coolant (UTR-40 transformer oil) were experimentally determined and comparatively evaluated. Mathematical models for the electromagnetic field and the heat transfer were defined and numerically solved to assess the capacity of the transformer to sustain the working conditions. The simulation results were utilized to improve the design of a prototype, where the UTR-40 regular coolant is replaced by ferrofluid. The numerical simulation results and the experiments evidence the superior performance of the prototype.

Dynamical characteristics of an electrically actuated microbeam under the effects of squeeze-film and thermoelastic damping

The static and dynamic behavior of a MEMS subjected to thermoelastic and squeeze-film effects is investigated. We analyse the various engineering aspects which interact in a slender fixed–fixed microbeam; major attention is devoted to the modeling of such a multiphysics system, including the mechanical, electrical, thermoelastic and fluid-dynamic properties with their couplings. The static solution is obtained numerically by a finite-difference technique. The variation of the static deflection with respect to the voltage increment, in the presence of geometric nonlinearites, is studied first. Numerical results on the magnitude of thermoelastic damping (TED) and squeeze-film damping are obtained and examined with a parametric analysis. The effect of different relaxation times imposed on the TED, both in pull-in and non pull-in regime, is studied. The squeeze-film damping is modeled by means of the Reynolds equation and the large pressure regime is investigated. We then present a comparison between the different sources of damping, evaluating their relative contribution to the system.

Conditional flow field statistics of jet-in-hot-coflow flames

The conditional velocity field of the Delft jet-in-hot-coflow flames is studied by the simultaneous application of planar laser-induced fluorescence of the OH radical (OH-PLIF) and particle image velocimetry (PIV). The goal of this study is to assess the role of turbulence on chemical processes in the Delft jet-in-hot-coflow flames and similar setups, that are characterised by the presence of a turbulent jet that issues into a slower-moving and much less turbulent surroundings of combustion products. An important result is that the conditional velocity field (conditional on the presence of a strong OH signal) is very different from the non-conditional velocity field at the same location. These jet-in-hot coflow flames are thus characterised by a strong intermittency, and experience a very different flow field and flow time scales than one would expect from the local mean velocity and scalar field. An other result following from the local velocity data is that the average conditional strain perpendicular to the flame surface is neither compressive nor extensive. This is caused by to the orientation of the principle strains and that of the flame interface. One millimetre inward to the jet, from the edge of the fuel-rich side of the OH contours, the average strains do become compressive, and the pdf of normal strain becomes considerably wider. In light of these results, the closure of the mean chemical source term by introducing a single (unconditional) turbulent time scale seems to be an invalid approach. Furthermore, it demonstrates that the fluid dynamic properties of the coflow stream are decisive for the applicability of these setups to the study of turbulence-chemistry interaction in industrial combustion processes.

Fluid-dynamic properties and wetting behavior of coating inks for roll-to-roll production of polymer-based solar cells

In the last decade, semiconducting and conducting materials were developed that can be processed by solvent-based deposition to form functional layers or complete electronic devices. These materials are typically synthesized in laboratory scale quantities and tested on small spin-coated substrates, whereas the final goal is to produce them on flexible substrates in a continuous roll-to-roll process. To enable a fast scale up and optimization, fluid-dynamic properties have to be known. Here, we present viscosity and surface tension data for typical material systems, applied in polymer-based solar cells. Materials presented include water-based polymer dispersions (hole-conducting and high-conductive PEDOT:PSS types), solvent-based anorganic nanoparticle dispersions (silver nanoparticle ink, hole-blocking ZnO nanoparticle ink), and dissolved organic molecules and polymers (P3HT:PCBM photoactive blend). Predictive models are proposed to approximate viscosity and surface tension for these materials at various compositions. As well, corona treatment is used to modify the surface energy of P3HT:PCBM and described as a function of web speed and corona power. The importance of material properties is demonstrated by predicting stable conditions for a slot-die coating process. A simple drying simulation highlights the possibility of using property models to investigate wetting problems.