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Maxwell Model (maxwell + model)

Distribution by Scientific Domains

Engineering	28%
Chemistry	28%

Selected Abstracts

Flow and mass transfer of fully resolved bubbles in non-Newtonian fluids

AICHE JOURNAL, Issue 7 2007
Stefan Radl
Abstract In this work, high-resolution 2-D numerical simulations were performed on the motion of deformable bubbles in non-Newtonian fluids and the associated mass transfer. For that purpose, we have implemented a semi-Lagrangian advection scheme and improved the fluid dynamic calculation by the usage of implicit algorithms. Non-Newtonian fluids are described by generalized Newtonian as well as viscoelastic model fluids. As shear-thinning model we use a Power-Law and a Carreau-Yasuda model, the viscoelastic fluid simulations are based on an Upper-Convected Maxwell model combined with a recently introduced model for the evolution of the effective shear rate. The mathematical challenges arising from the hyperbolic nature of the resulting set of equations are addressed by inclusion of artificial diffusion in the stress equation. In our work, it was found that shear thinning effects have impact on collision rates, and therefore, may influence coalescence of bubbles in non-Newtonian liquids. Furthermore, for the first time, concentration fields of dissolved gas in viscoelastic fluids are presented. The study shows that the fluid elasticity plays a major role for bubble rise velocity, and therefore, mass transfer. As the wake dynamics differ significantly from that in Newtonian liquids, abnormal mixing characteristics can be expected in the bubbly flow of viscoelastic fluids. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source]

Effect of surface roughness on elastohydrodynamic traction.

LUBRICATION SCIENCE, Issue 4 2005
Part
Abstract To investigate the performance of a traction-drive toroidal continuously variable transmission, the traction characteristics under partial elastohydrodynamic lubrication contact were calculated theoretically based on roller test results. A calculation model was constructed for considering the effects of surface roughness on performance. The model incorporated a viscoelastic and elastic-plastic model using a nonlinear Maxwell model to represent the rheological behaviour of the traction fluid. The validity of the model was confirmed by its good agreement with the experimental results described in Part 1 of this paper. Various calculations were made to investigate the effect of surface roughness on traction under the operating conditions of an actual traction drive. The results indicated that the effect of surface roughness on durability could not be ignored. [source]

Global existence for the Vlasov,Darwin system in ,3 for small initial data

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 4 2003
Saïd Benachour
We prove the global existence of weak solutions to the Vlasov,Darwin system in R3 for small initial data. The Vlasov,Darwin system is an approximation of the Vlasov,Maxwell model which is valid when the characteristic speed of the particles is smaller than the light velocity, but not too small. In contrast to the Vlasov,Maxwell system, the total energy conservation does not provide an L2-bound on the transverse part of the electric field. This difficulty may be overcome by exploiting the underlying elliptic structure of the Darwin equations under a smallness assumption on the initial data. We finally investigate the convergence of the Vlasov,Darwin system towards the Vlasov,Poisson system. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Thermo-optic nonlinear response of silver nanoparticle colloids under a low power laser irradiation at 532,nm

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2010
Rouhollah Karimzadeh
Abstract The thermo-optical properties of silver nanoparticles (AgNPs) in the water are investigated under irradiation of a continuous wave (CW) laser at 532,nm. Thermal conductivity of the AgNP colloids is estimated using the Maxwell model. The closed Z-scan measurements reveal thermal contribution for the nonlinear refractive index of the AgNPs. The Z-scan behavior is investigated based on nonlocal thermo-optic process. It is shown that the aberrant thermal lens model is in excellent agreement with the Z-scan experimental results of the sample. A fit allows extracting the values of nonlinear refractive index and thermo-optic coefficient to be ,1.0,×,10,8,cm2/W and ,0.99,×,10,4,W/mK, respectively. Our results suggest that thermal nonlinear effects play an important role in the development of photonic application involving metal nanoparticle colloids and in the investigation of nonlocal nonlinear processes. [source]

The draw ratio,Deborah number diagram: A useful tool for coating applications

POLYMER ENGINEERING & SCIENCE, Issue 3 2006
S. Bourrigaud
The understanding of the basic physical effects of viscoelasticity on drawing performances in the coating process leads to a useful approach to link the rupture of the polymer melt to critical processing conditions. In particular, we show that when solving the drawing problem in the air gap with a simple constitutive equation,like the upper convected Maxwell model,a mathematical inconsistency appears for some drawing parameters. This mathematical instability may be experimentally correlated to the occurrence of melt-rupture, giving rise to a discussion on the effect of viscoelastic properties on drawing performances. Results are given in terms of a diagram representing the maximum drawing ratio Dr with respect to the Deborah number De. A master curve, obtained form experimental results, accounts for the temperature, melt-index, air-gap height, and extrusion output dependences. The limitations of the "universality" of the concept are discussed later. POLYM. ENG. SCI. 46:372,380, 2006. © 2006 Society of Plastics Engineers [source]

Numerical Investigations on the Plastic Memory Effect of PTFE Compounds

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003
Thomas Kletschkowski Dipl.-Ing.
To describe the nonlinear material behaviour of thermoplastic materials via the example of Polytetrafluorethylene (PTFE), a viscoplastic material model of overstress type is proposed. The approach is motivated by a rheological model, consisting of a rate-independent elastoplastic element with an endochronic flow rule and a nonlinear elastic element in parallel connection with a nonlinear Maxwell model. For the generalization to three dimensions, the theory of finite viscoplasticity based on material isomorphisms is applied. To describe the non-isothermal plastic memory effect, thermally induced plastic strains and a scalar back stress (inside the equilibrium branch) are taken into account. [source]

Maxwell Fluid Model for Generation of Stress,Strain Curves of Viscoelastic Solid Rocket Propellants

PROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 4 2010
Himanshu Shekhar
Abstract Solid rocket propellants are modeled as Maxwell Fluid with single spring and single dashpot in series. Complete stress,strain curve is generated for case-bonded composite propellant formulations by taking suitable values of spring constant and damping coefficient. Propellants from same lot are tested at different strain rate. It is observed that change in spring constant, representing elastic part is very small with strain rate but damping constant varies significantly with variation in strain rate. For a typical propellant formulation, when strain rate is varied from 0.00037 to 0.185 per second, spring constant (K) changed from 5.5 to 7.9,MPa, but damping coefficient (D) varied from 1400 to 4,MPas. For all strain rates, stress,strain curve is generated using developed Maxwell model and close matching with actual test curve is observed. This indicates validity of Maxwell fluid model for case-bonded solid propellant formulations. It is observed that with increases in strain rate, spring constant increases but damping coefficient decreases representing solid rocket propellant as a true viscoelastic material. It is also established that at higher strain rate, damping coefficient becomes negligible as compared to spring constant. It is also observed that variation of spring constant is logarithmic with strain rate and that of damping coefficient follows a power law. The correlation coefficients are introduced to ascertain spring constants and damping coefficients at any strain rate from that at a reference strain rate. Correlation for spring constant needs a coefficient "H," which is function of propellant formulation alone and not of test conditions and the equation developed is K2=(K1 - H)×{ln(d,2/dt)/ln(d,1/dt)}+H. Similarly for damping coefficient (D) also another constant "S" is introduced and prediction formula is given by D2=D1×{(d,2/dt)/(d,1/dt)}S. Evaluating constants "H" and "S" at different strain rates validate this mathematical formulation for different propellant formulations. Close matching of test and predicted stress,strain curve indicates propellant behavior as viscoelastic Maxwell Fluid. Uniqueness of approach is to predict complete stress,strain curves, which are not attempted by any other researchers. [source]