Elastic Flow rate

Equation (52) allows us to estimate the impact of viscoelastic braking on the capillary flow rate. As an example, we will consider that the liquid is tricresyl phosphate (TCP, 7 = 50 mN-m t = 0.07 Pa-s). The viscoelastic material is assumed to have elastic and viscoelastic properties similar to RTV 615 (General Electric, silicone rubber), i.e., a shear modulus of 0.7 MPa (E = 2.1 MPa), a cutoff length of 20 nm, and a characteristic speed, Uo, of 0.8 mm-s [30]. TCP has a contact angle at equilibrium of 47° on this rubber. 

As previously mentioned in this article, liquid behavior presents an immense sanely ol puzzling problems that arc dilhcult to comprehend and hence diflicult to forecast precisely. As jusl one example, in the study of large drops of liquid at high flow rates, the inertia of the drops and the surrounding fluids play an iniporiaiii role. When such drops arc propelled toward one another, they may coalesce into a single drop or may rebound like a pair of elastic balls, a phenomenon that is partially (but not fully dependent upun ihc comparative velocities of the two drops. 

Estimation of Fluid Elasticity s Contribution to Flow Rate (Velocity) Characteristics of Flow.47... 

Thus, the problem of flow of a viscoelastic fluid between two flat parallel plates one of which is moving in a direction transverse to the main flow is reduced to a solution of simplified system (7) at boundary conditions (1). Analysis of relationships (7) for specific boundary conditions indicates that the problem is reduced to the case of a non-Newtonian viscous fluid. In other words, the velocity profile v(y) is determined only by viscous characteristics of the media and the effect of high-elasticity properties of the melt upon velocity (flow rate) characteristics of the flow can be neglected. 

Rheodynamics of non-linear viscous fluids flowing in circular channels with moving walls is described most comprehensively in 1S-34). With respect to the above conclusion (see sect 2.2.1) that the high elasticity of a melt influences insignificantly flow rate parameters of a flow, the combined shear is discussed in 24128-30,341 on the basis of a general approach to the analysis of viscosimetric flows developed by B. Colleman and W. Noll. 

Fig. 12.4, the melt is forced into a converging flow pattern and undergoes a large axial acceleration, that is, it stretches. As the flow rate is increased, the axial acceleration also increases, and as a result the polymer melt exhibits stronger elastic response, with the possibility of rupturing, much like silly putty would, when stretched fast. Barring any such instability phenomena, a fully developed velocity profile is reached a few diameters after the geometrical entrance to the capillary. 

Measurement techniques of the elastic moduli, 388 Mechanical behaviour and failure, 819 Mechanical comfort, 879 Mechanical properties of solid polymers, 383 various materials, 389 Melt/Melting, 167, 700 elasticity, 316 expansion, 97 flow index, 801, 802 flow rate diagram, 801 fracture, 578 number, 579 strength, 799, 812 Merkel number, 59 Mesogenic groups, 34 in the main chain, 177 side-chain, 179 Mesogenic polymers, 172... 

Chemical vapor deposition (CVD) is an atomistic surface modification process where a thin solid coating is deposited on an underlying heated substrate via a chemical reaction from the vapor or gas phase. The occurrence of this chemical reaction is an essential characteristic of the CVD method. The chemical reaction is generally activated thermally by resistance heat, RF, plasma and laser. Furthermore, the effects of the process variables such as temperature, pressure, flow rates, and input concentrations on these reactions must be understood. With proper selection of process parameters, the coating structure/properties such as hardness, toughness, elastic modulus, adhesion, thermal shock resistance and corrosion, wear and oxidation resistance can be controlled or tailored for a variety of applications. The optimum experimental parameters and the level to which... 

Sometimes, this expectation is not met. At high flow rates, there can be hydrodynamic instabilities that lead to secondary flows which ruin the rheological measurement. Such instabilities occur in Newtonian fluids, due, for example, to inertial effects, such as those in Poiseuille flow at Reynolds numbers exceeding 2000 (Drazin and Reid 1981). For some complex fluids, even at low Reynolds number there are instabilities that are driven by elastic effects (Larson 1992). 

Peristaltic devices with a variable drive speed can provide a wide range of flow rates, typically 0.2—5.0 mL min-1, in several channels, each with a different flow rate if necessary. Partial damping is inherent in these fluid propulsion devices due to tube elasticity. 

A second way of looking at forced expiration is with a maximum expiratory flow-volume (MEFV) curve, which describes maximum flow as a function of lung volume during a forced expiration (Fig. 12). In healthy human subjects, flow rates or flow-volume curves reach a maximum and will not increase with additional effort after the lungs have emptied 20-30% of their volume (Fry and Hyatt, 1960). This phenomenon of flow limitation is due to airway compression over most of the lung volume. Thus, flow rate is independent of effort and is determined by the elastic recoil force of the lung and the resistance of the airways upstream of the collapse point. In obstructive diseases of the lung this curve is shifted to the left, whereas restrictive diseases shift the curve in the opposite direction (also shown in Fig. 12). 

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