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Convective Flow (convective + flow)
Selected AbstractsGravity-induced convective flow in microfluidic systems: Electrochemical characterization and application to enzyme-linked immunosorbent assay testsELECTROPHORESIS, Issue 21-22 2004Patrick Morier Abstract A way of using gravity flow to induce a linear convection within a microfluidic system is presented. It is shown and mathematically supported that tilting a 1 cm long covered microchannel is enough to generate flow rates up to 1000 nL·min -1, which represents a linear velocity of 2.4 mm·s -1. This paper also presents a method to monitor the microfluidic events occurring in a covered microchannel when a difference of pressure is applied to force a solution to flow in said covered microchannel, thanks to electrodes inserted in the microfluidic device. Gravity-induced flow monitored electrochemically is applied to the performance of a parallel-microchannel enzyme-linked immunosorbent assay (ELISA) of the thyroid-stimulating hormone (TSH) with electrochemical detection. A simple method for generating and monitoring fluid flows is described, which can, for instance, be used for controlling parallel assays in microsystems. [source] Theoretical and numerical analyses of convective instability in porous media with temperature-dependent viscosityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 10 2003Ge Lin Abstract Exact analytical solutions of the critical Rayleigh numbers have been obtained for a hydrothermal system consisting of a horizontal porous layer with temperature-dependent viscosity. The boundary conditions considered are constant temperature and zero vertical Darcy velocity at both the top and bottom of the layer. Not only can the derived analytical solutions be readily used to examine the effect of the temperature-dependent viscosity on the temperature-gradient driven convective flow, but also they can be used to validate the numerical methods such as the finite-element method and finite-difference method for dealing with the same kind of problem. The related analytical and numerical results demonstrated that the temperature-dependent viscosity destabilizes the temperature-gradient driven convective flow and therefore, may affect the ore body formation and mineralization in the upper crust of the Earth. Copyright © 2003 John Wiley & Sons, Ltd. [source] A note on the universal stability of convective flow with variable viscosityMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 7 2008S. Saravanan Abstract The stability of convective motion of a fluid driven by volumetric heat sources and applied pressure gradient is investigated. The viscosity of the fluid is assumed to depend linearly on temperature. The sufficient conditions for the existence of such a flow are obtained based on the energy inequalities. Copyright © 2007 John Wiley & Sons, Ltd. [source] Changes in convective properties over the solar cycle: effect on p-mode damping ratesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001G. Houdek Measurements of both solar irradiance and p-mode oscillation frequencies indicate that the structure of the Sun changes with the solar cycle. Balmforth, Gough & Merryfield investigated the effect of symmetrical thermal disturbances on the solar structure and the resulting pulsation frequency changes. They concluded that thermal perturbations alone cannot account for the variations in both irradiance and p-mode frequencies, and that the presence of a magnetic field affecting acoustical propagation is the most likely explanation of the frequency change, in the manner suggested earlier by Gough & Thompson and by Goldreich et al. Numerical simulations of Boussinesq convection in a magnetic field have shown that at high Rayleigh number the magnetic field can modify the preferred horizontal length scale of the convective flow. Here, we investigate the effect of changing the horizontal length scale of convective eddies on the linewidths of the acoustic resonant mode peaks observed in helioseismic power spectra. The turbulent fluxes in these model computations are obtained from a time-dependent, non-local generalization of the mixing-length formalism. The modelled variations are compared with p-mode linewidth changes revealed by the analysis of helioseismic data collected by the Birmingham Solar-Oscillations Network (BiSON); these low-degree (low- l) observations cover the complete falling phase of solar activity cycle 22. The results are also discussed in the light of observations of solar-cycle variations of the horizontal size of granules and with results from 2D simulations by Steffen of convective granules. [source] Oxygen transport and consumption by suspended cells in microgravity: A multiphase analysisBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2008Ohwon Kwon Abstract A rotating bioreactor for the cell/tissue culture should be operated to obtain sufficient nutrient transfer and avoid damage to the culture materials. Thus, the objective of the present study is to determine the appropriate suspension conditions for the bead/cell distribution and evaluate oxygen transport in the rotating wall vessel (RWV) bioreactor. A numerical analysis of the RWV bioreactor is conducted by incorporating the Eulerian,Eulerian multiphase and oxygen transport equations. The bead size and rotating speed are the control variables in the calculations. The present results show that the rotating speed for appropriate suspensions needs to be increased as the size of the bead/cell increases: 10 rpm for 200 µm; 12 rpm for 300 µm; 14 rpm for 400 µm; 18 rpm for 600 µm. As the rotating speed and the bead size increase from 10 rpm/200 µm to 18 rpm/600 µm, the mean oxygen concentration in the 80% midzone of the vessel is increased by ,85% after 1-h rotation due to the high convective flow for 18 rpm/600 µm case as compared to 10 rpm/200 µm case. The present results may serve as criteria to set the operating parameters for a RWV bioreactor, such as the size of beads and the rotating speed, according to the growth of cell aggregates. In addition, it might provide a design parameter for an advanced suspension bioreactor for 3-D engineered cell and tissue cultures. Biotechnol. Bioeng. 2008;99: 99,107. © 2007 Wiley Periodicals, Inc. [source] Ultrafiltration characteristics of pegylated proteinsBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2006Jessica R. Molek Abstract There is growing clinical interest in the use of pegylated recombinant proteins with enhanced stability, half-life, and bioavailability. The objective of this study was to develop a quantitative understanding of the ultrafiltration characteristics of a series of pegylated proteins with different degrees of pegylation. Sieving data were compared with available theoretical models and with corresponding results for the partition coefficient in size exclusion chromatography (SEC). The sieving coefficients of the pegylated proteins depended not only on the protein size and the total molecular weight of the polyethylene glycol (PEG) but also on the number of PEG chains. This is in sharp contrast to the partition coefficient in SEC, which was uniquely determined by the total molecular weight of the PEG and protein. This difference is due to the deformation and/or elongation of the PEG chains caused by the convective flow into the membrane pores, an effect that is not present in SEC. These results provide important insights into the transport and separation characteristics of pegylated proteins. © 2006 Wiley Periodicals, Inc. [source] Modeling O2 transport within engineered hepatic devicesBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2003Randall E. McClelland Abstract Predicting and improving oxygen transport within bioartificial liver (BAL) devices continues to be an important engineering challenge since oxygen is one of the critical nutrients necessary for maintaining hepatocyte viability and function. Such a computational model would not only help predict outcomes but it would also allow system modifications to be analyzed prior to developing experimental protocols. This would help to facilitate future design improvements while reducing both experimental time and capital resource costs, and is the focus of the current study. Specifically, a computational model of O2 transport through collagen and microporous collagen ECMs is analyzed for hollow fiber (HF), flat plate (FP), and spheroid BAL designs. By modifying the O2 boundary conditions, hepatocyte O2 consumption levels, O2 permeability of the ECM, and ECM void fractions, O2 transport predictions are determined for each system as a function of time and distance. Accuracy of the predictive model is confirmed by comparing computational vs. experimental results for the HF BAL system. The model's results indicate that O2 transport within all three BAL designs can be improved significantly by incorporating the enhancement technique. This technique modifies a diffusion-dominant gel ECM into a porous matrix with diffusive and convective flows that mutually transport O2 through the ECMs. Although tortuous pathways increase the porous ECM's overall effective length of O2 travel, the decreased transport resistances of these pathways allow O2 to permeate more effectively into the ECMs. Furthermore, because the HF design employs convective flow on both its inner and outer ECM surfaces, greater control of O2 transport through its ECM is predicted, as compared with the single O2 source inputs of the flat plate and spheroid systems. The importance of this control is evaluated by showing how modifying the O2 concentration and/or transfer coefficients of the convective flows can affect O2 transport. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 12,27, 2003. [source] Perfusion seeding of channeled elastomeric scaffolds with myocytes and endothelial cells for cardiac tissue engineeringBIOTECHNOLOGY PROGRESS, Issue 2 2010Robert Maidhof Abstract The requirements for engineering clinically sized cardiac constructs include medium perfusion (to maintain cell viability throughout the construct volume) and the protection of cardiac myocytes from hydrodynamic shear. To reconcile these conflicting requirements, we proposed the use of porous elastomeric scaffolds with an array of channels providing conduits for medium perfusion, and sized to provide efficient transport of oxygen to the cells, by a combination of convective flow and molecular diffusion over short distances between the channels. In this study, we investigate the conditions for perfusion seeding of channeled constructs with myocytes and endothelial cells without the gel carrier we previously used to lock the cells within the scaffold pores. We first established the flow parameters for perfusion seeding of porous elastomer scaffolds using the C2C12 myoblast line, and determined that a linear perfusion velocity of 1.0 mm/s resulted in seeding efficiency of 87% ± 26% within 2 hours. When applied to seeding of channeled scaffolds with neonatal rat cardiac myocytes, these conditions also resulted in high efficiency (77.2% ± 23.7%) of cell seeding. Uniform spatial cell distributions were obtained when scaffolds were stacked on top of one another in perfusion cartridges, effectively closing off the channels during perfusion seeding. Perfusion seeding of single scaffolds resulted in preferential cell attachment at the channel surfaces, and was employed for seeding scaffolds with rat aortic endothelial cells. We thus propose that these techniques can be utilized to engineer thick and compact cardiac constructs with parallel channels lined with endothelial cells. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Effective Diffusivities and Convective Coefficients for CaO-CaSO4 and CaO-CaCl2 PelletsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 1 2004C. Akosman Abstract Diffusion and convective flow in the pores of pellets formed by compressing mixtures of calcined limestone and CaSO4/CaCl2 powders have been studied experimentally by using the single pellet moment technique. The experiments were conducted in a diffusion cell by flowing nitrogen gas (carrier) through both faces of the pellet. Limestone powder was calcined in an atmosphere of N2 at 800,°C and mixed with CaSO4/CaCl2 for diffusion experiments. Effective diffusivity of helium has been estimated by exposing the upper face of the pellet to a pulse of and matching the response peak on the lower face of the pellet with theoretical expressions. The values of the effective diffusivities increased with temperature, but decreased with increasing CaSO4/CaCl2 content in the pellet. The convective flow contribution to the diffusion flux was found to increase with increasing pressure drop across the pellet. [source] Fluid flow and heat transfer of opposing mixed convection adjacent to downward-facing, inclined heated platesHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2009Kenzo Kitamura Abstract Experimental investigations were carried out for opposing mixed convective flows of air adjacent to downward-facing, inclined heated plates. The experiments covered the ranges of the Reynolds and modified Rayleigh numbers from ReL=400 to 4600 and RaL*=1.0×107 to 5.4×108, and the inclination angles from ,=15 to 75° from horizontal. The flow fields over the plates were visualized with smoke. The results showed that a separation of forced boundary layer flow occurs first at the bottom edge of the plate, and then the separation point shifts toward upstream with increasing wall heat flux, and finally, reaches the top edge of the plates. It was found that the separations at the bottom and top edges are predicted with a non-dimensional parameter (GrL,*/ReL2.5)=0.35 and 1.0, respectively. The local heat transfer coefficients of the inclined plates were also measured and the results showed that the minimum coefficients appear in the separation region. Moreover, it was revealed that forced, natural, and combined convective flows can be classified by the non-dimensional parameter (GrL,*/ReL2.5). © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Pub- lished online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20233 [source] Modeling O2 transport within engineered hepatic devicesBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2003Randall E. McClelland Abstract Predicting and improving oxygen transport within bioartificial liver (BAL) devices continues to be an important engineering challenge since oxygen is one of the critical nutrients necessary for maintaining hepatocyte viability and function. Such a computational model would not only help predict outcomes but it would also allow system modifications to be analyzed prior to developing experimental protocols. This would help to facilitate future design improvements while reducing both experimental time and capital resource costs, and is the focus of the current study. Specifically, a computational model of O2 transport through collagen and microporous collagen ECMs is analyzed for hollow fiber (HF), flat plate (FP), and spheroid BAL designs. By modifying the O2 boundary conditions, hepatocyte O2 consumption levels, O2 permeability of the ECM, and ECM void fractions, O2 transport predictions are determined for each system as a function of time and distance. Accuracy of the predictive model is confirmed by comparing computational vs. experimental results for the HF BAL system. The model's results indicate that O2 transport within all three BAL designs can be improved significantly by incorporating the enhancement technique. This technique modifies a diffusion-dominant gel ECM into a porous matrix with diffusive and convective flows that mutually transport O2 through the ECMs. Although tortuous pathways increase the porous ECM's overall effective length of O2 travel, the decreased transport resistances of these pathways allow O2 to permeate more effectively into the ECMs. Furthermore, because the HF design employs convective flow on both its inner and outer ECM surfaces, greater control of O2 transport through its ECM is predicted, as compared with the single O2 source inputs of the flat plate and spheroid systems. The importance of this control is evaluated by showing how modifying the O2 concentration and/or transfer coefficients of the convective flows can affect O2 transport. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 12,27, 2003. [source] | |||||||||||||