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Macromixing hydrodynamic study in draft-tube airlift reactors using electrical resistance tomography
Farouza Gumery Farhad Ein-Mozaffari Yaser Dahman 《Bioprocess and biosystems engineering》2011,34(2):135-144
The present study summarizes results of mixing characteristics in a draft tube airlift bioreactor using ERT. This technique
offers the possibility for noninvasive and nonintrusive visualization of flow fields in the bioreactor and has rarely been
utilized previously to analyze operating parameters and mixing characteristics in this type of bioreactors. Several operating
parameters and geometric characteristics were examined. In general, results showed that the increase in superficial gas velocity
corresponds to an increase in energy applied and thus, to a decrease in mixing time. This generally corresponded to an increase
in liquid circulation velocity and shear rate values. Bottom clearances and draft tube diameters affected flow resistance
and frictional losses. The influence of sparger configurations on mixing time and liquid circulation velocity was significant
due to their effect on gas distribution. However, the effect of sparger configuration on shear rate was not significant, with
20% reduction in shear rates using the cross-shaped sparger. Fluid viscosity showed a marked influence on both mixing times
and circulation velocity especially in the coalescing media of sugar and xanthan gum (XG) solutions. Results from this work will help to develop a clear pattern for operation and mixing that can help to improve
several industrial processes, especially the ones related to emerging fields of technology such as the biotechnology industry. 相似文献
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Traction forces developed by most cell types play a significant role in the spatial organisation of biological tissues. However,
due to the complexity of cell-extracellular matrix interactions, these forces are quantitatively difficult to estimate without
explicitly considering cell properties and extracellular mechanical matrix responses. Recent experimental devices elaborated
for measuring cell traction on extracellular matrix use cell deposits on a piece of gel placed between one fixed and one moving
holder. We formulate here a mathematical model describing the dynamic behaviour of the cell-gel medium in such devices. This
model is based on a mechanical force balance quantification of the gel visco-elastic response to the traction forces exerted
by the diffusing cells. Thus, we theoretically analyzed and simulated the displacement of the free moving boundary of the
system under various conditions for cells and gel concentrations. This modelis then used as the theoretical basis of an experimental
device where endothelial cells are seeded on a rectangular biogel of fibrin cast between two floating holders, one fixed and
the other linked to a force sensor. From a comparison of displacement of the gel moving boundary simulated by the model and
the experimental data recorded from the moving holder displacement, the magnitude of the traction forces exerted by the endothelial
cell on the fibrin gel was estimated for different experimental situations. Different analytical expressions for the cell
traction term are proposed and the corresponding force quantifications are compared to the traction force measurements reported
for various kind of cells with the use of similar or different experimental devices.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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