Shear stresses fluid

For any given process, one takes a qualitative look at the possible role of fluid shear stresses. Then one tries to consider pathways related to fluid shear stress that may affect the process. If there are none, then this extremely complex phenomenon can be dismissed and the process design can be based on such things as uniformity, circulation time, blend time, or velocity specifications. This is often the case in the blending of miscible fluids and the suspension of sohds. 

If fluid shear stresses are likely to be involved in obtaining a process result, then one must qualitatively look at the scale at which the shear stresses influence the resiilt. If the particles, bubbles, droplets, or fluid clumps are on the order of 1000 [Lm or larger, the variables are macro scale and average velocities at a point are the predominant variable. 

Each stage of particle formation is controlled variously by the type of reactor, i.e. gas-liquid contacting apparatus. Gas-liquid mass transfer phenomena determine the level of solute supersaturation and its spatial distribution in the liquid phase the counterpart role in liquid-liquid reaction systems may be played by micromixing phenomena. The agglomeration and subsequent ageing processes are likely to be affected by the flow dynamics such as motion of the suspension of solids and the fluid shear stress distribution. Thus, the choice of reactor is of substantial importance for the tailoring of product quality as well as for production efficiency. 

The fluid shear stress actually brings about the mixing process, and is the multiplication of fluid shear rate and viscosity of the fluid [29]. 

Taba, Y., et al. (2000). Fluid shear stress induces lipocalin-type prostaglandin D2 synthase expression in vascular endothelial cells. Circul. Res. 86, 967-73. 

Haidekker MA, L Heureux N, Frangos JA (2000) Fluid shear stress increases membrane fluidity in endothelial cells a study with DCVJ fluorescence. Am J Physiol Heart Circ Physiol 278(4) H1401-H1406... 

Chachisvilis, M., Zhang, Y. L. and Frangos, J. A. (2006). G protein-coupled receptors sense fluid shear stress in endothelial cells. Proc. Natl. Acad. Sci. USA 103, 15463-8. 

NAD(P)H oxidase can also be activated by fluid shear stresses. This is one reason why branched and curved arteries tend to develop atherosclerotic plaques earlier than straight arteries. Using a spin probe to detect 02 , Hwang et al. have demonstrated that monolayer cultures of EC exposed to oscillatory (but not laminar) shear stresses produce the radical using NAD(P)H oxidase.292 A subsequent study showed that XO also responds to oscillatory shear stress.293 Other workers, using BMPO, have detected the flow-induced production of 02 by mitochondria.294... 

Desmopressin stimulates the release from endothelial cells of all the multimeric forms of von Willebrand factor found in normal plasma, including large forms that are not normally present (22). These abnormal multimers can aggregate platelets, particularly at the high levels of fluid shear stress that occur at sites of arterial stenosis. 

For the laminar flow region of Newtonian fluid, shear stress r is equal to the viscosity /t times the velocity gradient du/dy as... 

Kamioka H, Sugawara Y, Murshid SA, Ishihara Y, Honjo T, Takano-Yamamoto T. 2006. Fluid shear stress induces less calcium response in a single primary osteocyte than in a single osteoblast implication of different focal adhesion formation. J Bone Miner Res 21 1012—21. 

In experiments with cultured cells it has been shown that osteocytes, but not periosteal fibroblasts, are extremely sensitive to fluid flow, resulting in increased prostaglandin as well as nitric oxide production [104, 105], Three different cell populations, namely osteocytes, osteoblasts, and periosteal fibroblasts, were subjected to two stress regimes, pulsatile fluid flow and intermittent hydrostatic compression [104], Intermittent hydrostatic compression was applied at 0.3 Hz with a 13-kPa peak pressure. The pulsatile fluid flow was a fluid flow with a mean shear stress of 0.5 Pa with cyclic variations of 0.02 Pa at 5 Hz. The maximal hydrostatic pressure rate was 130 kPa/sec and the maximal fluid shear stress rate was 12 Pa/sec. Under both stress regimes, osteocytes appeared more sensitive than osteoblasts, and osteoblasts more sensitive than periosteal fibroblasts. However, despite the large difference in peak stress and peak stress rate, pulsatile fluid flow was more effective than intermittent hydrostatic compression. Osteocytes, but not the other cell types, responded to 1 hour pulsatile fluid flow treatment with a sustained prostaglandin E2 upregula-... 

Osteocytes also rapidly release nitric oxide in response to stress [160, 105] and this NO response seems to be required for the stress-related prostaglandin release [105]. Therefore, the behavior of osteocytes compares to that of endothelial cells which regulate the flow of blood through the vascular system, and also respond to fluid flow of 0.5 Pa with increased prostaglandin and nitric oxide production [79]. The response of endothelial cells to shear stress is likely related to their role in mediating an adaptive remodeling of the vasculature, so as to maintain constant endothelial fluid shear stress throughout the arterial site of the circulation [99],... 

Mi. L.Y., Basu, M., Fritton, S.P., Cowin, S.C. (2004a) Analysis of avian bone response to mechanical loading Part One Distribution of bone fluid shear stress induced by bending and axial loading, in preparation. 

Reich, K.M., Gay, C.V., Frangos, J.A. (1990) Fluid shear stress as a mediator of osteoblast cychc adenosine monophosphate production. Journal of Cellular Physiology 143, 100-104... 

Weinbaum, S., Cowin, S.C., Zeng, Y. (1991) A model for the fluid shear stress excitation of membrane ion channels in osteocytic processes due to bone strain. Advances in Bioengineering. Editor R. Vanderby, Jr. 317-320. American Society of Mechanical Engineers, New York... 

Fluid shear stress Product of shear rate and viscosity, which is responsible for many mixing phenomena in the tank. 

First ask yourself if there is any role for fluid shear stresses in determining and obtaining the desired process result. About half of the time the answer will likely be no. That is the percentage of mixing processes where fluid shear stresses either have no effect or seem to have no effect on the process result. In these cases, mixer design can be based on pumping capacity, blend time, velocities and other matters of that nature. Impeller type location and other geometric variables are major factors in these types of processes. 

However, if the answer to this first question is yes there is an effect of fluid shear stresses on the process, then there needs to have a second question asked. Is it at the micro-or macroscale that the process participants are involved And, of course, it may be both. 

Fleming, I., Bauersachs, J., Fisslthaler, B., and Busse, R. 1998. Ca2+-independent activation of the endothelial nitric oxide synthase in response to tyrosine phosphatase inhibitors and fluid shear stress. Circ. Res. 82 686-695. 

Osteoblasts subjected to fluid shear increase expression of the early response gene, c-fos, and the inducible isoform of cyclooxygenase, COX-2, two proteins linked to anabolic response of bone to mechanical stimulation. Flow-induced responses in osteoblasts are mediated by inositol triphosphate intracellular calcium release. Flow-mediated stress is reported to induce both PGE2 and NO production. Fluid shear stress stimulates NO release by two distinct pathways a G-protein and calcium-dependent phase sensitive to flow gradients, and a G-protein and calcium-independent pathway stimulated by sustained flow. 

Khachigian LM, Resnick N, Gimbrone MA Jr, Collins T. Nuclear factor-KB interacts functionally with the platelet-derived growth factor B-chain shear-stress response element in vascular endothelial cells exposed to fluid shear stress. / Clin Invest. 1995 96 1169-1175. 

Li S, Kim M, Hu YL, Jalai S, Schlaepfer DD, Hunter T, Chien S, Shyy JY. Fluid shear stress activation of focal adhesion kinase. Linking to mitogen-activated protein kinases. / Biol Chem. 1997 272 30455-30462. 

McAllister TN, Du T, Frangos JA. Fluid shear stress stimulates prostaglandin and nitric oxide release in bone marrow-derived preosteoclast-like cells. Biochem Biophys Res Comm. 2000 270 643-648. 

Resnick N, Collins T, Atkinson W, Bonthron DT, Dewey CF Jr, Gimbron MA. Platelet-derived growth factor B chain promoter contains cis-acting fluid shear-stress responsive element. Proc Natl Acad Sci USA. 1993 90 7908. 

The cone-and-plate viscometer is an in vitro flow model used to investigate the effects of bulk fluid shear stress on suspended cells. Anticoagulated whole blood specimens (or isolated cell suspensions) are placed between the two platens (both of stainless steel) of the viscometer. Rotation of the upper conical platen causes a well-defined and uniform shearing stress to be applied to the entire fluid medium as described by Konstantopolous et al. (1998). The shear rate (y) in this system can be readily calculated from the cone angle and the speed of the cone using the formula i/ = where y is the shear rate in sec-1, mis the... 

The mechanical force most relevant to platelet-mediated thrombosis is shear stress. The normal time-averaged levels of venous and arterial shear stresses range between 1-5 dyn/cm2 and 6 10 dyn/cm2, respectively. However, fluid shear stress may reach levels well over 200 dyn/cm2 in small arteries and arterioles partially obstructed by atherosclerosis or vascular spasm. The cone-and-plate viscometer and parallel-plate flow chamber are two of the most common devices used to simulate fluid mechanical shearing stress conditions in blood vessels. 

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