Laminar pulsatile flow

Laminar pulsatile flow in a tube Flow in a tube is in one direction, parallel to the electrode surface, (taken as the jr-direction). The time-dependent convective-diffusion equation for this geometry is given by equation (10.12). Mass transport to the surface of the electrode is thus determined both by the gradient perpendicular to the surface of the tangential flow, dujdy and the concentration gradient perpendicular to the surface ... 

The laminar pulsatile flow in a plane duct can be treated as the simplest unsteady problem in basic fluid mechanics with applications, for instance, to engineering vibrators [199, 507], In biological and medical fluid mechanics, one meets the pulsating blood flow in arteries and the air flow in lungs. The generalization of such flows was suggested in literature [598, 601], and is of interest for this chapter. 

Nakamura M, Sawada T (1987) Nirmerical study on the laminar pulsatile flow of slurries. J Non-Newtonian Fluid Mech 22 191-206... 

Polystyrene can be easily prepared by emulsion or suspension techniques. Harkins (1 ), Smith and Ewart(2) and Garden ( ) have described the mechanisms of emulsTon polymerization in batch reactors, and the results have been extended to a series of continuous stirred tank reactors (CSTR)( o Much information on continuous emulsion reactors Ts documented in the patent literature, with such innovations as use of a seed latex (5), use of pulsatile flow to reduce plugging of the tube ( ), and turbulent flow to reduce plugging (7 ). Feldon (8) discusses the tubular polymerization of SBR rubber wTth laminar flow (at Reynolds numbers of 660). There have been recent studies on continuous stirred tank reactors utilizing Smith-Ewart kinetics in a single CSTR ( ) as well as predictions of particle size distribution (10). Continuous tubular reactors have been examined for non-polymeric reactions (1 1 ) and polymeric reactions (12.1 31 The objective of this study was to develop a model for the continuous emulsion polymerization of styrene in a tubular reactor, and to verify the model with experimental data. 

The velocity profile across the tube lumen with pulsatile flow is not of the same parabolic form as that found in a steady laminar flow. The velocity profiles oscillate sinusoidally as discussed in detail by Hale et al. [44]. For example. Figure 8.26 shows the velocity profiles, at intervals of 15°, resulting from a simple sinusoidal pressure gradient (cos[mf]) during the half cycle (0°-180°) as for a simple harmonic motion, the second half is the same. 

Although elasticity of vessel walls can significantly compHcate fluid flow analysis, biologically it provides important homeostatic benefits. For example, pulsatile blood flow induces accompanying expansions and contractions in healthy elastic-wall vessels. These wall displacements then influence the flow fields. Elastic behavior maintains the norm of laminar flow that minimizes wall stress, lowers flow resistance, and thus energy dissipation and fosters maximum life of the vessel. In combination with pulsatile flow, distensibility permits strain relaxation of the wall tissue with each cardiac cycle, which provides an exercise routine promoting extended on-line use. 

Laminar flow exposure leads to activation of antioxidant genes in endothelial cell (EC) (21 )and promotes EC survival and quiescence and the secretion of substances that promote vasodilation and anticoagulation (22). Flow induces an increase in oxidative stress in EC, which is dependent on the pulsatile nature of flow (23). 

Thompson, C.A. et al. A novel pulsatile, laminar flow bioreactor for the development of tissue-engineered vascular structures. Tissue Eng., 8,1083, 2002. 

Transport in blood vessels presents another interesting subcase. Here the species involved in mass transfer, typically proteins, have much lower diffusivities than ordinary solutes, of the order 10 to 10 m /s. Flow is generally laminar, and of a pulsatile nature. A further departure from the norm is the complex geometry of the vascular systems, which involves multiple branchings, and constrictions in flow as well as expansions. Because of these complexities, it has become customary to measure local mass transfer coefficients confined to a typical wall area of 1 mm. A host of such measurements has by now been reported. The surprising fact that has emerged from these studies is that irrespective of location or configuration, the vast majority of kc values clusters around a value of IIP m/s. Thus,... 

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