Optimal Fluid Flow Research Articles

Biomimetic fetal rotation bioreactor for engineering bone tissues-Effect of cyclic strains on upregulation of osteogenic gene expression.

Cells respond to physiological mechanical stresses especially during early fetal development. Adopting a biomimetic approach, it is necessary to develop bioreactor systems to explore the effects of physiologically relevant mechanical strains and shear stresses for functional tissue growth and development. This study introduces a multimodal bioreactor system that allows application of cyclic compressive strains on premature bone grafts that are cultured under biaxial rotation (chamber rotation about 2 axes) conditions for bone tissue engineering. The bioreactor is integrated with sensors for dissolved oxygen levels and pH that allow real-time, non-invasive monitoring of the culture parameters. Mesenchymal stem cells-seeded polycaprolactone-β-tricalcium phosphate scaffolds were cultured in this bioreactor over 2weeks in 4 different modes-static, cyclic compression, biaxial rotation, and multimodal (combination of cyclic compression and biaxial rotation). The multimodal culture resulted in 1.8-fold higher cellular proliferation in comparison with the static controls within the first week. Two weeks of culture in the multimodal bioreactor utilizing the combined effects of optimal fluid flow conditions and cyclic compression led to the upregulation of osteogenic genes alkaline phosphatase (3.2-fold), osteonectin (2.4-fold), osteocalcin (10-fold), and collagen type 1 α1 (2-fold) in comparison with static cultures. We report for the first time, the independent and combined effects of mechanical stimulation and biaxial rotation for bone tissue engineering using a bioreactor platform with non-invasive sensing modalities. The demonstrated results show leaning towards the futuristic vision of using a physiologically relevant bioreactor system for generation of autologous bone grafts for clinical implantation.

The influence of flap inclination angle on fluid transport at ciliated walls

In optimizing fluid flow at walls, research has turned to artificial cilia to mimic the propulsion of their whip-like beat of a metachronal traveling wave. Recently we developed a pneumatically actuated micro-membrane device which has rows of long flaps positioned off-center on membranes over a row of cavities, much like the comb row of a ctenophore. As little is known about how the flap inclination angle influences the fluid transport near the wall of such devices, this paper presents a detailed modeling and experimental investigation of this question using combined FEM-FVM (finite element method-finite volume method)-based simulations for inclination angles of 0°, 20°, 30°, and 45°. The experimental results agree well with those of the FEM-FVM simulations. Antiplectic fluid transport was observed for flap inclination angles lower than 20° whereas symplectic fluid transport was determined for those higher than 20°. In conclusion, the inclination angle of the flaps decisively affects the fluid transport direction and velocity.

Design and optimization of baffled fluid distributor for realizing target flow distribution in a tubular solar receiver

This paper presents an original study on the design and optimization of baffled fluid distributor for the realization of optimal fluid flow distribution in a tubular solar receiver. The basic idea is to install a perforated baffle in the inlet fluid distributor and to optimize the configuration of orifices on the baffle so as to approach the target flow distribution among downstream parallel tubes. A pressurized-air solar receiver comprising of 45 parallel tubes is used for study, with copper or Inconel 600 used as the filling material.Results show that the final fluid flow distributions realized by the geometrically optimized baffles are in good agreement with the target curves. The peak temperature of the receiver wall can be minimized accordingly with moderate increase in total pressure drop of the receiver system. It is shown that the insertion of a geometrically optimized baffle is generally a practical solution with various features: capable of realizing non-uniform target distribution; small pressure drop increase; compact geometry; flexible and adaptive; easy fabrication with a reasonable cost, etc.

Effect of cone angles on single-phase flow of a laboratory cyclonic-static micro-bubble flotation column: PIV measurement and CFD simulations

Combination of cyclonic flotation and conventional column flotation is a novel column flotation technology. A cyclonic-static micro bubble flotation column (FCSMC) using this technology significantly improves recovery rate during flotation. However, the mechanism of cyclonic separation still remains black box. This paper presents CFD simulations on single-phase to find how different the reversal cone, a key part in cyclonic flotation unit in FCSMC, can affect the fluid flow, then corresponding mineral processing efficiency. PIV measurement is established for simulations validation. RSM-S turbulent model is used to obtain hydrodynamic characteristics in FCSMC. 38-, 48-, 58-, 68-degree cone angle cases are explored. Results show that three kinds of vortexes exist in a laboratory FCSMC: spiraling-up quasi-free vortex near wall, spiraling-up quasi-forced vortex near column axis and spiraling-down quasi-forced vortex between wall and axis of column. The vortexes are greatly affected by the angle of the reversal cone. In the column flotation unit, diameter and flux of quasi-forced vortex spiraling down increase while quasi-forced vortex spiraling up decreases with the angle increasing from 38° to 68°. Smaller angle generates larger overflow in cyclonic flotation unit. Both tangential velocity and centrifugal intensity in cyclonic flotation unit decrease. Disordered fluid flow in cyclonic flotation unit is generated under too small cone angle, like 38°. Besides, under too large cone angle, like 68°, centrifugal intensity in column flotation unit increases and quasi-forced vortex spiraling up flux in cyclonic flotation unit decreases or disappears. So the separation environment is deteriorated. Among the four degrees, optimal fluid flow of the laboratory cyclonic-static micro bubble flotation column can be maintained under an angle of 48°.

3D CFD modelling and optimization of single‐phase flow in rotating packed beds

Rotating Packed Beds (RPBs) are novel reactors used for intensification of mass transfer and mixing since they provide adjustable centrifugal force to simulate high gravity. In this work, in order to analyze and optimize fluid flow in RPBs, a three‐dimensional single‐phase flow was simulated and validated with previous experimental data. The results show that pressure drop increases with an increasing gas flow rate and rotation speed, and reveal the distribution of total pressure and velocity magnitude. A RPB with radial gas inlet, one of the generic types of RPBs, which is widely applied in the chemical industry but has poor gas distribution on the surface of packing, was optimized using various baffles. The width, distance, shape, and opening porosity of the baffles were examined by adopting a criterion, and their effect on gas distribution was illustrated. Finally, a possible optimum structure of the RPB was formulated under optimal operational conditions.

Advanced Amine Process Technology Operations and Results from Demonstration Facility at EDF Le Havre

Abstract Alstom Power and The Dow Chemical Company have jointly developed an Advanced Amine Process (AAP) utilizing Dow's advanced amine solvent formulation UCARSOL™ FGC-3000 for the capture of CO2 from fossil fuel power plant-generated flue gas. This development effort includes the use of facilities to address operational issues such as energy efficiency and solvent management, along with environmental factors such as emissions and wastes. A new demonstration facility has been constructed in Le Havre, France, through a partnership between Alstom and Electricite de France (EDF) with support from ADEME, the French Environment and Energy Management Agency. This facility is designed to capture 25 tonnes of CO2/day at a 90% capture rate on a slip- stream flue gas from a hard coal-fired power plant. The EDF-Le Havre demonstration plant is equipped with flue gas conditioning for controlling the water content, temperature and SOx level of the incoming flue gas stream. The CO2 absorber column contains structured packing selected for optimal CO2 capture efficiency and fluid flow characteristics. The exiting flue gas passes through a water wash section designed to capture residual amine emissions. Amine solvent management comprises an amine reclamation system and assisted by an on-site amine solvent analytical laboratory. The quality of the incoming flue gas, the exiting flue gas and CO2 product gas streams are assessed through various gas sample locations in the pilot plant. Amine solvent sampling is available at various locations throughout the amine circulation loop as well as the liquid discharge locations for waste assessment. Additionally, the EDF facility is also equipped with an oxygen stripper to study the impact on solvent degradation. The current status of the Alstom Advanced Amine Process at EDF will be discussed in this paper. The presented results include the performance of the UCARSOL™ FGC-3000 amine solvent evaluated under varied process conditions in an advanced flow scheme set-up. The test campaign comprised several series of tests, including energy consumption at varied liquid-to-gas flow ratios (L/G) in the absorber while maintaining 90% CO2 removal, the effect of varying process conditions at a set solvent circulation rate, and the effect of different absorber intercooling and recirculation configurations on energy consumption. Results show that the advanced flow scheme effectively reduced power and energy demand by over 30% at a 90% CO2 capture rate versus a conventional process scheme with MEA solvent.

Choanoflagellate and choanocyte collar‐flagellar systems and the assumption of homology

The similarities between the choanoflagellates and the choanocytes of sponges have been discussed for more than a century yet few studies allow a direct comparison of the two. We reviewed current knowledge of the collar and flagellum and compared their structure and function in the choanoflagellate Monosiga brevicollis and the sponge Spongilla lacustris. Collar microvilli were of similar length and number, but the shape of the collar differed between the two cells. In Monosiga, collars were flared and microvilli were joined by a single band of glycocalyx mid-way along their length; in Spongilla, collars formed a tube and microvilli were joined by a mesh of glycocalyx. Monosiga flagella beat at least four times faster than those in Spongilla. Flagellar vanes were found in both cell types. In both cells, the flagella and so probably also the vanes maintained moving points of contact with the microvilli, which suggested that collars and flagella were integrated systems rather than independent units. There were fundamental differences in how the collar and flagella interacted, however. In Spongilla, the flagellum bent upon contact with the collar; the flagellar amplitude was fitted to the collar diameter. In Monosiga, the flagellar amplitude was unaffected by the collar; instead the collar diameter appeared fitted to the flagellum. These differences suggest that though choanocytes and choanoflagellates are similar, homology cannot be taken for granted. Similarities in collar-flagellum systems separated by 600 million years of evolution, whether maintained or convergent, suggest that these form important adaptations for optimizing fluid flow through micro-scale filters.

Second-law analysis of fluid flow over an isothermal moving wedge

In this study, entropy generation minimization (EGM) was employed to optimize fluid flow and heat transfer over a moving wedge. Governing partial differential equations including continuity, momentum and energy are reduced to ordinary ones using similarity variables and solved numerically. The novelty of this study is to consider the effects of the moving wedge parameter λ, to find the stable system via entropy generation minimization (EGM) method. The results indicated that as the slope of the wedge increases, the absolute values of the optimum moving wedge parameter λo grow as well. Moreover, it was found that the minimum value of entropy generation happens for the negative values of λo which gets smaller as Falkner–Skan power law parameter m increases.

Optimal fluid flow enhanced mineralization of MG-63 cells in porous chitosan scaffold

This study confirms the effects of flow rate in a perfusion culturing system on the maturation and mineralization of osteoblast-like MG-63 cells within genipin cross-linked chitosan scaffolds exhibiting distinct porous structures. The scanning electron microscopy revealed that chitosan scaffold exhibited homogeneous and interconnected pore structures with an average size of 100μm. Perfusion of medium increased the cell viability, cellular distribution and secreted high level of type I collagen in first developmental period. Alkaline phosphatase (ALP) activity and osteocalcin (OCN) content of osteoblast culture in chitosan scaffold displayed maximal level at 0.24mL/min of perfusion fluid rate. Calcium content analysis revealed a significant enhancement of deposited minerals on scaffold after 21d cultured under flow perfusion. These results may be concluded that appropriate flow shear stress accelerated cellular differentiation and mineralization in 3D scaffolds. Therefore, dynamic culturing is a valuable and convenient tool for applications in the generation of three-dimensional bone tissue in vitro, and flow rate is an important operational factor.

Granulation Technology Experiments of Novel Mesoporous Composite Water Purification Material

A novel mesoporous composite water purification material was synthesized from natural zeolite to possess certain water purification properties as well as in proper particle size range for optimal fluid flow, particle retention and mass transfer in fixed bed applications. The meerschaum was used as the framework material in the experimental manufacturing procedure, polyethylene alcohol with carboxylic methylic cellulose was used as cohesive reagent, and H2O2 as bubble-forming agent. And the resulted granular product has good abrasion resistance ability with the measured impact breaking time reaching 12 hours. In addition, its decoloring rate is only 4.4% lower and its CODcr removing is only 13.2% lower than those of the original powder product, respectively. As a whole, the granulation potential and significantly expands the zeolite wastewater treatment application range with (only is not necessary) minor reduction of its treatment efficiency.

Numerical Study of Capillary Flow in Microchannels With Alternate Hydrophilic-Hydrophobic Bottom Wall

A two-dimensional numerical simulation of flow in patterned microchannel with alternate layers of different sizes of hydrophilic and hydrophobic surfaces at the bottom wall is conducted here. The effect of specified contact angle and working fluid (de-ionized (DI) water and ethanol) on capillary phenomena is observed here. The volume of fluid method is used for simulating the free surface flow in the microchannel. Meniscus profiles with varying amplitude and shapes are obtained under the different specified surface conditions. Nonsymmetric meniscus profiles are obtained by changing the contact angles of the hydrophilic and hydrophobic surfaces. A meniscus stretching parameter is defined here and its relation to the capillary phenomena in the microchannel is discussed. Flow variation increases as the fluid traverses alternately between the hydrophilic and hydrophobic regions. The pattern size and the surface tension of the fluid are found to have significant influence on the capillary phenomena in the patterned microchannel. Smaller pattern size produces enhanced capillary effect with DI water, whereas no appreciable gain is observed for ethanol. The magnitude of maximum velocity along the channel height varies considerably with the pattern size and the contact angle. Also, the rms velocity is found to be higher for smaller alternate patterned microchannel. The meniscus average velocity difference at the top and bottom walls increases for a dimensionless pattern size of 0.6 and thereafter it decreases with the increase in pattern size in the case of DI water with hydrophilic-hydrophobic pattern. Using such patterned microchannel, it is possible to manipulate and optimize fluid flow in microfluidic devices, which require enhanced mixing for performing biological reactions.

Anterior-to-posterior wave of buccal expansion in suction feeding fishes is critical for optimizing fluid flow velocity profile

In fishes that employ suction feeding, coordinating the timing of peak flow velocity with mouth opening is likely to be an important feature of prey capture success because this will allow the highest forces to be exerted on prey items when the jaws are fully extended and the flow field is at its largest. Although it has long been known that kinematics of buccal expansion in feeding fishes are characterized by an anterior-to-posterior wave of expansion, this pattern has not been incorporated in most previous computational models of suction feeding. As a consequence, these models have failed to correctly predict the timing of peak flow velocity, which according to the currently available empirical data should occur around the time of peak gape. In this study, we use a simple fluid dynamic model to demonstrate that the inclusion of an anterior-to-posterior wave of buccal expansion can correctly reproduce the empirically determined flow velocity profile, although only under very constrained conditions, whereas models that do not allow this wave of expansion inevitably predict peak velocity earlier in the strike, when the gape is less than half of its maximum. The conditions that are required to produce a realistic velocity profile are as follows: (i) a relatively long time lag between mouth opening and expansion of the more posterior parts of the mouth, (ii) a short anterior portion of the mouth relative to more posterior sections, and (iii) a pattern of movement that begins slowly and then rapidly accelerates. Greater maximum velocities were generated in simulations without the anterior-to-posterior wave of expansion, suggesting a trade-off between maximizing fluid speed and coordination of peak fluid speed with peak gape.

Bayesian regularization neural networks for optimizing fluid flow processes

This paper details the application of neural networks and evolutionary strategies for shape optimization problems. These, commonly grouped under the name soft computing methods, are quite recent methods and in demand for application to engineering optimization tasks. For complex problems, like in non-convex optimization, such heuristic techniques are able to outperform conventional optimization methods. We show that the use of progressive network models can yield satisfactory results when optimizing engineering relevant applications. Numerical examples are given.

Tailored operative technique for Chiari type I malformation using intraoperative color Doppler ultrasonography.

We describe an operative technique for Chiari Type I malformation that uses color Doppler ultrasonography as a guide for performing patient-specific posterior fossa decompressions. The technique has been used since 1999 in more than 300 operations. On the basis of real-time anatomic and physiological measurements, the following goals of surgery were monitored: 1) adequate decompression of the cervicomedullary junction; 2) creation of a retrocerebellar space of 8 to 10 cm(3) volume; and 3) establishment of optimal cerebrospinal fluid flow between the cranial and spinal compartments. The size of the craniectomy was tailored to conform to the area of cerebellar impaction as demarcated by compressed subarachnoid spaces. A laminectomy was not performed unless the cerebellar tonsils were herniated below C1. Before opening the dura, color Doppler ultrasonography imaging was invaluable in planning operative strategies. A simple duraplasty without additional steps was found to be appropriate treatment in occasional patients with minimal tonsillar herniation (5-8 mm). In all other cases, it was necessary to perform an internal decompression that included lysis of the arachnoid and shrinkage of the cerebellar tonsils to achieve the goals of surgery. Optimal cerebrospinal fluid flow through the foramen magnum in anesthetized, prone patients was found to have the following characteristics: a peak velocity of 3 to 5 cm/s, bidirectional movement, and a waveform exhibiting vascular and respiratory variations. The attainment of surgical goals was confirmed in most patients by postoperative neuroimaging. Color Doppler ultrasonography imaging is an important technological advance that permits the neurosurgeon to tailor the steps of Chiari surgery according to patient-specific variables. The success of this technique depends on the mastery of a new and sophisticated monitoring modality.

A MATHEMATICAL MODEL FOR LAMINAR DISPLACEMENT OF ONE NON-NEWTONIAN FLUID BY ANOTHER IN HORIZONTAL CONCENTRIC ANNULI

This paper develops a mathematical model and a computational algorithm, which enable the prediction of laminar displacement efficiency in concentric horizontal annuli. Power-law model is used to characterize rheological properties of both displaced and displacing fluids. This model allows a careful investigation of individual effects of various parameters such as fluid rheology, flow geometry and displacement rate on the displacement efficiency. Simulated results demonstrate the dominant influence of rheological properties of displaced and displacing fluids on the laminar displacement efficiency. The model can be used to optimize fluid flow parameters in chemical process designs.

Cannula Selection and Cannulation Techniques for Nonpulsatile Mechanical Ventricular Assistance

The successful use of mechanical ventricular assistance is, in large part, dependent upon easy insertion of well designed inflow and outflow cannulas. This manuscript describes a family of cannulas specifically designed for use in a nonpulsatile ventricular assist device (VAD) circuit. Although a variety of commercially available cannulas can be employed in a nonpulsatile VAD circuit, the cannulas described in this manuscript possess a number of unique design features. The reinforced thin-walled design and end hole construction optimize fluid flow characteristics in both the inflow and outflow cannula. The extended length allows the cannulas to transverse the skin at a point far distant from the mediastinum, reducing the potential for ascending cannula site infection. The purpose of this manuscript is not to review all cannulas available for nonpulsatile VAD circuits, but rather to describe in detail a family of cannulas that are ideal VAD cannulas based on their design characteristics. In addition individual cardiac surgeons implant very few of these devices annually. Thus the advantages and disadvantages of common cannulation sites and a proven technique for cannula insertion will also be presented.