Fluid Dynamic Characterization Research Articles

Computational Fluid Dynamics and Experimental Characterization of the Pediatric Pump-Lung.

The pediatric pump-lung (PediPL) is a miniaturized integrated pediatric pump-oxygenator specifically designed for cardiac or cardiopulmonary support for patients weighing 5-20 kg to allow mobility and extended use for 30 days. The PediPL incorporates a magnetically levitated impeller with uniquely configured hollow fiber membranes into a single unit capable of performing both pumping and gas exchange. A combined computational and experimental study was conducted to characterize the functional and hemocompatibility performances of this newly developed device. The three-dimensional flow features of the PediPL and its hemolytic characteristics were analyzed using computational fluid dynamics based modeling. The oxygen exchange was modeled based on a convection-diffusion-reaction process. The hollow fiber membranes were modeled as a porous medium which incorporates the flow resistance in the bundle by an added momentum sink term. The pumping function was evaluated for the required range of operating conditions (0.5-2.5 L/min and 1000-3000 rpm). The blood damage potentials were further analyzed in terms of flow and shear stress fields, and the calculations of hemolysis index. In parallel, the hydraulic pump performance, oxygen transfer and hemolysis level were quantified experimentally. Based on the computational and experimental results, the PediPL device is found to be functional to provide necessary oxygen transfer and blood pumping requirements for the pediatric patients. Smooth blood flow characteristics and low blood damage potential were observed in the entire device. The in-vitro tests further confirmed that the PediPL can provide adequate blood pumping and oxygen transfer over the range of intended operating conditions with acceptable hemolytic performance. The rated flow rate for oxygenation is 2.5 L/min. The normalized index of hemolysis is 0.065 g/100L at 1.0 L/min and 3000 rpm.

Patient based computational fluid dynamic characterization of carotid bifurcation stenosis before and after endovascular revascularization

IntroductionHemodynamic forces play a critical role in determining the molecular phenotype of the endothelial cell and in influencing vascular remodeling. A lesion based computational fluid dynamic (CFD) modeling approach is...

Computational Fluid Dynamics Characterization of a Bioreactor Mixing Device for the Animal Cell Culture

During a cell culture in a bioreactor, the cells are exposed to the shear stresses mainly generated in the culture medium by the mixing device. Beyond a critical shear stress, this exposition induces cell damages. Therefore, the limitation of the shear stress is an important criterion for the design of bioreactors. An accurate modeling of the flow and the induced shear stresses in the medium is a tool to achieve an effective design of a bioreactor. In this work, a new design of a mixing device is considered. The aims of this work are to develop a methodology to study the flow and the induced shear stresses in the device, to study and to model the relation between the flow, the induced shear stresses and the cell viability, to use the developed model as an optimization tool, and to study the design of the bioreactor mixing device and its scale-up. In a first step, the flow and the induced shear stresses in the device are simulated by Computational Fluid Dynamics. In a second step, the model of the influence of the flow and the induced shear stresses on the cell viability is established by a comparison between the computed flow and the induced shear stresses and experimental measurements of cellular viabilities for different impeller rotation speeds. Finally, the influence of another design of the mixing device on the cell viability is studied.

A simple device to test biodiesel process intensification

In this paper, we have studied the KOH catalyzed transesterification reaction of vegetable oil with methanol in a tubular reactor filled with small spheres of stainless steel of different sizes. Three different packed bed configurations have been tested corresponding to different fluid dynamic situations. The first configuration corresponds to the tubular reactor filled with spheres of 2.5 mm of diameters; in the second configuration an opportune amount of spheres of 1 mm has been added to the mentioned spheres of 2.5 mm for filling the void volume of the octahedral cavities between the bigger spheres; in the third configuration an opportune amount of spheres of 0.39 mm has been added to spheres of 2.5 mm for filling the void volume of the tetrahedral cavities between the bigger spheres. The three mentioned configurations give place to the formation of micro-channels with an approximated size of respectively 1000 μm, 500 μm and 300 μm. These systems, subjected to fluid dynamic characterization, have shown a very high local turbulence (static mixer), in particular, when a packed bed reactor with dual size packing is used. Then, kinetic transesterification runs have been made by using the three mentioned packed bed reactors and a very high productivity has been obtained as a consequence of the induced local micro-mixing. A simplified kinetic model has been developed, which is able to describe many runs in batch conditions reported by the literature. This model resulted unsuitable to simulate the continuous runs performed in the described packed bed reactors. Our conclusion is that monophasic models, often proposed in the literature, are not able to describe the kinetic behavior of KOH catalysed transesterification in microchannels devices. At last, the described microchannels device represents, as it will be discussed, an ideal connection between a traditional tubular packed bed reactor and the recently appeared microreactors that are very efficient in mass and energy transfer operations for process intensification.

Characterization of fluid dynamics and mass-transfer in an electrochemical oxidation cell by experimental and CFD studies

Flow and mass-transfer in a widely used commercial electrochemical flow cell (DiaCell ®) were investigated by computational fluid dynamics (CFD) simulations and validated by experimental measurements. Both qualitative and quantitative comparisons were made for distinct flow regimes in the Reynolds range between 25 and 2500 (based on the inter-electrode distance and on the superficial velocity in the cell middle cross-section area). A mono-phasic CFD methodology was applied for describing the rather complex bi-phasic phenomena taking place in the electrochemical oxidation of organic compounds, where gases are being formed at both electrodes. The adequacy of this assumption was subjected to validation with experimental results. Transient CFD simulations showed that the flow becomes unsteady at a rather low R e (in the range from 65 to 100) mainly due to the observed flow separation upstream the electrodes region. The pressure-drops determined by CFD agreed very well with the experimental measurements. Good agreement was also obtained between the Sherwood values calculated through CFD and experimentally determined by the limiting current technique. Mono-phasic CFD and experimental limiting current data were used for deriving mass-transfer correlations for the DiaCell ®. These correlations were found to correctly describe S h values determined from galvanostatic (electric current density of 332 A/m 2) electrochemical oxidation of selected organic compounds under mass-transfer controlled operating conditions and a turbulent-developing flow regime. These results suggest that turbulent-developing flow in an electrochemical cell can be sufficiently well described by mono-phasic CFD simulations.

Quantifying Cardiovascular Flow Dynamics During Early Development

The relationship between developing biologic tissues and their dynamic fluid environments is intimate and complex. Increasing evidence supports the notion that these embryonic flow-structure interactions influence whether development will proceed normally or become pathogenic. Genetic, pharmacological, or surgical manipulations that alter the flow environment can thus profoundly influence morphologic and functional cardiovascular phenotypes. Functionally deficient phenotypes are particularly poorly described as there are few imaging tools with sufficient spatial and temporal resolution to quantify most intra-vital flows. The ability to visualize biofluids flow in vivo would be of great utility in functionally phenotyping model animal systems and for the elucidation of the mechanisms that underlie flow-related mechano-sensation and transduction in living organisms. This review summarizes the major methodological advances that have evolved for the quantitative characterization of intra-vital fluid dynamics with an emphasis on assessing cardiovascular flows in vertebrate model organisms.

Thermo- and fluid dynamics characterization of spray cooling with pulsed sprays

A fundamental study is reported here on the spray impingement of pulsed sprays on heated surfaces. The experiments consider simultaneous measurements of surface heat flux and droplet characteristics performed with a Phase Doppler Anemometer (velocity, size and flux) prior to impact, to provide a better insight into the interaction between thermal and fluid dynamic effects during the period of injection. The experimental conditions are relevant for engines at steady rotational speeds between 1800 rpm and 3600 rpm, which are of interest for hybrid configurations, where the IC engine is set to operate at maximum efficiency. The analysis addresses the effects of injection conditions (e.g., duration, frequency and pressure) on the thermodynamic behaviour of the surface. It is observed that the heat flux decreases when the pressure of injection increases, due to dynamic variations of the film induced by interaction with impacting droplets in the film evaporation regime. Results further suggest that, for the range of injection conditions found in real engines, the time variation of the heat transfer during injection depends more on the liquid mass flux than on droplet size and axial velocity. However, when the engine load increases, the mechanism by which heat is removed from the surface varies from thermally controlled to mass diffusion controlled, due to saturation of the atmosphere with gasoline vapour. The time resolved measurements are processed to quantify the critical points of the boiling curves, e.g., the critical heat flux (CHF) at the Nukiyama temperature and the minimum heat flux (MHF) at the Leidenfrost temperature. The dynamic characteristics of those curves are used as an approach to describe the heat transfer mechanisms in pulsed spray systems. It is suggested that multiple droplet interaction alters the thermal behaviour of the target in the sense that both, CHF and MHF, increase in regions of large droplet concentration and when the frequency of injection increases. However, load variations associated with times of injection in the range 5–10 ms, do not produce significant alterations. Analysis shows the likely importance of transient mechanisms occurring at the solid–liquid and liquid–vapour interface in describing the interaction of pulsed sprays with hot surfaces.

Experimental fluid dynamic characterization of a cyclone chamber

An experimental investigation was performed on a laboratory scale model of a gas cyclone separator inserted in a closed/open loop test facility built up to study the flow field of both the gas and solid phase. The cyclone is made entirely by plexiglas in order to allow optical access for velocity measurements through laser Doppler velocimetry. Three velocity components of the gas phase were measured inside the various regions of the apparatus (tangential inlet chamber, cylindrical body and exhaust duct) and a preliminary analysis of the solid phase behaviour has been carried out in some restricted regions of the device, identified as critical for the separation process. Experiments were performed at fixed geometrical swirl number ( S=2.39) in the correspondence of two inlet Reynolds numbers ( Re=3.76×10 4 and 1.25×10 5); glass particles of mean diameter d p=37 μm were added to the fluid flow to simulate the solid phase behaviour. The measurements performed put into evidence the presence of fluid dynamic instabilities (vortex breakdown and precessing vortex core in the exhaust flow) induced by the high swirling motion inside the device and a possible solution to reduce this problem has been identified. Preliminary analysis of the solid phase motion clearly showed the particles behaviour in selected regions of the apparatus and allowed to understand the details of the gas–solid phase separation effects.

Fluid dynamic characterization of operating conditions for continuous flow blood pumps.

As continuous flow pumps become more prominent as long-term ventricular assist devices, the wide range of conditions under which they must be operated has become evident. Designed to operate at a single, best-efficiency, operating point, continuous flow pumps are required to perform at off-design conditions quite frequently. The present study investigated the internal fluid dynamics within two representative rotary fluid pumps to characterize the quality of the flow field over a full range of operating conditions. A Nimbus/UoP axial flow blood pump and a small centrifugal pump were used as the study models. Full field visualization of flow features in the two pumps was conducted using a laser based fluorescent particle imaging technique. Experiments were performed under steady flow conditions. Flow patterns at inlet and outlet sections were visualized over a series of operating points. Flow features specific to each pump design were observed to exist under all operating conditions. At off-design conditions, an annular region of reverse flow was commonly observed within the inlet of the axial pump, while a small annulus of backflow in the inlet duct and a strong disturbed flow at the outlet tongue were observed for the centrifugal pump. These observations were correlated to a critical nondimensional flow coefficient. The creation of a "map" of flow behavior provides an additional, important criterion for determining favorable operating speed for rotary blood pumps. Many unfavorable flow features may be avoided by maintaining the flow coefficient above a characteristic critical coefficient for a particular pump, whereas the intrinsic deleterious flow features can only be minimized by design improvement. Broadening the operating range by raising the band between the critical flow coefficient and the designed flow coefficient, is also a worthy goal for design improvement.

Fluiddynamic characterization of airlift tower loop bioreactors with and without motionless mixtures

In a 60 l airlift tower reactor with outer loop fluiddynamical measurements were carried out in presence of three motionless mixer modules (Type SMV, Sulzer) in water, 0.6%, 0.9% and 1.2% CMC solutions. The global mixing properties were determined in the liquid and gas phases by tracers. Detailed local measurements revealed differences of local flow patterns and mixing properties in the unhindered riser and in the immediate wake of the mixer module. The local liquid velocities were measured by the pseudorandom heat pulse technique. The local bubble velocities were determined by the ultrasound Doppler technique. The dependence of liquid velocity, gas velocity and gas holdup on the superficial gas velocity were determined. The radial profiles of the mean liquid velocities and their standard deviations were evaluated in water and CMC solutions upstream and downstream of the motionless mixer modules. The radial profiles of the mean large-bubble velocities and mean small-bubble velocities and their standard deviations were determined as well. The influence of the presence of the motionless mixers in the riser on these properties was evaluated.

Fluiddynamic characterization of airlift tower loop bioreactors with and without motionless mixtures

Fluiddynamic characterization of airlift tower loop bioreactors with and without motionless mixtures

Fluid dynamics characterization of a pneumatic bed using a spouted bed type solid feeding system

AbstractThe development of a bed is reported, in which characteristics from spouted beds and pneumatic conveying are combined. The apparatus can be described as a pneumatic transport bed modified by the introduction of a recirculation process for inert materials, which leads to a final configuration akin to that of spouted beds. The dependency of the particle recirculation rates on the air flow rates and on the distance between the air inlet and the lower end of the central tube (z0) was investigated. Also studied was the variation of the total pressure drop with air flow rate, for different loads of inert materials (glass spheres, dp = 2.8 mm) and different z0 values.

Characterization of MOCVD fluid dynamics by laser velocimetry

The process of metalorganic chemical vapor deposition (MOCVD) is critically dependent on the fluid dynamics of the reacting and carrier gases. Quantitative understanding of the basic fluid dynamics associated with a reactor design is central to the application of engineering techniques to achieve design improvements in efficiency, bulk production and growth uniformity. A laser velocimetry (LV) system has been adapted specifically to acquire such quantitative information for the low Reynolds number mixed convective flows commonly encountered in MOCVD reactors. The instrument uses three color-separated wavelengths of an argon-ion laser to make three simultaneous independent orthogonal measurements of the flow field at specified interior locations. The technique is noninvasive, provides high spatial resolution, and is compatible with reactors operating at growth temperatures. The fluid dynamics of a horizontal MOCVD reactor used for GaAs growth were characterized by laser velocimetry measurements. The full three-component LV system was employed to determine a three-dimensional map of the flow field inside the quartz reactor vessel. Data have been obtained from the vessel both at room temperature and heated to growth temperature by RF induction. The two cases were compared to evaluate the effects of gravity-induced convection and buoyancy. Significant convective effects were found in the heated reactor, while fluidic switching effects were observed during room temperature operation. Instrumentation details and flow field measurements are presented.

A viscous pump bioreactor

The fluid dynamic design and characterization of a low mechanical stress agitator and bioreactor vessel for large-scale bioprocessing using anchorage dependent mammalian cells is considered. The complex and fragile nature of mammalian cells puts stringent constraints on the design of agitators for stirred tank bioreactors. Traditional agitators have difficulty meeting the competing requirements of fluidization and mixing while maintaining low enough mechanical stress levels to avoid cell damage. A rotating disc agitator design is proposed. Flow visualization and laser Doppler velocimeter measurements reveal fluidization of microcarriers with a gentle (low turbulence level), highly three-dimensional flow characterized by good mixing at low hydrodynamic shear stress levels.

Fluid Dynamic Characterization of Sudden-Expansion Ramjet Combustor Flowfields x

Experimental studies pertinent to axisymmetric, sudden-expansion dump combustor configurations for integral rocket-ramjet missiles have been performed under cold flow test conditions. These studies have included surface flow visualization, measurements of total and static pressures, and gas sampling within a representative combustor duct. Flow visualization tests, using a surface oil flow technique, vividly demonstrated the complex nature of the flow recirculation region downstream of the dump station. Gas concentration measurements of simulated fuel-air mixing were made in the combustor duct using an on-line gas analysis system with a quadrupole mass spectrometer. Combustor flowfield studies were made for test configurations with and without mechanical flameholding devices. Direct correlations between cold flow mixing data and measurements of combustion efficiency from direct-conned ramburner tests were made as a function of combustor Sen«fh-todiameter ratio.