Search results for "Viscosity."
showing 10 items of 537 documents
Thermomechanical degradation of filled polypropylene
2003
The main problem in post-consumer plastics recycling is due to the thermomechanical stress acting on the melt during the reprocessing operations. The macromolecules break because of the temperature and of the mechanical stress. The extent of degradation is then correlated to the level of mechanical stress which, in turn, is proportional to the viscosity of the melt. The presence of fillers increases the viscosity of the polymers and then it is expected that the level of thermomechanical degradation of these systems is larger than that of the unfilled material. In this work the thermomechanical degradation kinetic of a polypropylene sample is investigated as a function of the calcium carbona…
Multifunctional polyurethane foams with thermal energy storage/release capability
2020
In this work, polyurethane (PU) insulating panels containing different amounts of a microencapsulated paraffin with a nominal melting temperature of 24 °C, used as phase change material (PCM), were produced. The resulting panels behaved as multifunctional materials able to thermally insulate and simultaneously storing/releasing thermal energy near room temperature. The panels were characterized from a microstructural, thermal and mechanical point of view. Viscosity measurements highlighted an increase in the viscosity values of the PU liquid precursors due to the addition of the capsules, and this could lead to some difficulties during the production stages, especially in the mixing and foa…
Singularity formation and separation phenomena in boundary layer theory
2009
In this paper we review some results concerning the behaviour of the incompressible Navier–Stokes solutions in the zero viscosity limit. Most of the emphasis is put on the phenomena occurring in the boundary layer created when the no-slip condition is imposed. Numerical simulations are used to explore the limits of the theory. We also consider the case of 2D vortex layers, i.e. flows with internal layers in the form of a rapid variation, across a curve, of the tangential velocity.
Singularities for Prandtl's equations.
2006
We used a mixed spectral/finite-difference numerical method to investigate the possibility of a finite time blow-up of the solutions of Prandtl's equations for the case of the impulsively started cylinder. Our toll is the complex singularity tracking method. We show that a cubic root singularity seems to develop, in a time that can be made arbitrarily short, from a class of data uniformely bounded in H^1.
Two-phase flow of liquid–liquid mixture in the range of the water droplet pattern
2002
Abstract Phenomena accompanying flow of water–oil mixture during droplet flow of water in oil have been described. Aims used in the determination of characteristic parameters in two-phase liquid–liquid flow have been presented. The method for calculating the equivalent viscosity and pressure drop during flow of liquid–liquid mixture in the range of the water droplet pattern has been given.
$C^{1,��}$ regularity for the normalized $p$-Poisson problem
2017
We consider the normalized $p$-Poisson problem $$-��^N_p u=f \qquad \text{in}\quad ��.$$ The normalized $p$-Laplacian $��_p^{N}u:=|D u|^{2-p}��_p u$ is in non-divergence form and arises for example from stochastic games. We prove $C^{1,��}_{loc}$ regularity with nearly optimal $��$ for viscosity solutions of this problem. In the case $f\in L^{\infty}\cap C$ and $p>1$ we use methods both from viscosity and weak theory, whereas in the case $f\in L^q\cap C$, $q>\max(n,\frac p2,2)$, and $p>2$ we rely on the tools of nonlinear potential theory.
Local Viscosity in the Vicinity of a Wall Coated by Polymer Brush from Green-Kubo Relations
2008
When fluids are confined in slit pores between parallel walls, their static structures and their dynamical properties exhibit inhomogeneity in the z-direction perpendicular to the wall. Of particular interest are local bulk viscosity η b (z) and shear viscosity η s (z). Here, we discuss an algorithm to estimate these quantities from Green-Kubo relations using equilibrium molecular dynamics. As an application example, a polymer brush (macromolecules end-grafted to a substrate at z= 0) interacting with a solvent formed from point-like particles is given.
Next-to-leading order improved perturbative QCD + saturation + hydrodynamics model for A + A collisions
2014
We calculate initial conditions for the hydrodynamical evolution in ultrarelativistic heavy-ion collisions at the LHC and RHIC in an improved next-to-leading order perturbative QCD + saturation framework. Using viscous relativistic hydrodynamics, we show that we obtain a good simultaneous description of the centrality dependence of charged particle multiplicities, transverse momentum spectra and elliptic flow at the LHC and at RHIC. In particular, we discuss how the temperature dependence of the shear viscosity is constrained by these data.
Collective dynamics in relativistic nuclear collisions
2014
Abstract I will review the current status of describing spacetime evolution of the relativistic nuclear collisions with fluid dynamics, and of determining the transport coefficients of strongly interacting matter. The fluid dynamical models suggest that shear viscosity to entropy density ratio of the matter is small. However, there are still considerable challenges in determining the transport coefficients, and especially their temperature dependence is still poorly constrained.
Flow analysis with 3-dim ultra-relativistic hydro
2009
We review how flow observables of ultra-relativistic heavy-ion collisions are influenced by the initial condition, the description of the fluid dynamical (FD) stage and freeze-out (FO). We discuss the effects of the resolution of the FD treatment, the arising smoothing and numerical viscosity, as well as the consequences of final FO. This final FO stage includes confinement and simultaneous formation of constituent quarks. From the energy and momentum conservation at the FO stage pressure change and flow velocity may occur, which further modifies the observables.