Measuring anisotropic thermal conduction in polyisobutylene following step shear strains

Iddir, Hadjira; Venerus, David C.; Schieber, Jay D.

doi:10.1002/aic.690460319

Cited by 8 publications

(15 citation statements)

References 18 publications

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“…15,18,19 In a previous study, we reported the first quantitative measurements of anisotropic thermal conduction in a polymer liquid following a step shear deformation. 20,21 These results showed thermal conduction was enhanced in the flow direction and decreased in the vorticity direction, relative to the equilibrium level. Birefringence (anisotropy of the refractive index tensor) measured in the same flow allowed us, using a combination of eqs 2 and 3, to verify indirectly the stress-thermal rule for a polymer melt in shear flow.…”

Section: Introductionmentioning

confidence: 86%

“…Birefringence (anisotropy of the refractive index tensor) measured in the same flow allowed us, using a combination of eqs 2 and 3, to verify indirectly the stress-thermal rule for a polymer melt in shear flow. 20,21 In a similar study on a cross-linked polymer subjected to simple elongation, 22 we reported measurements of the thermal diffusivity tensor and tensile stress that provided direct evidence for the stress-thermal rule. Validity of the stressthermal rule, eq 2, indicates that deformation-induced anisotropies in mechanical and thermal transport in polymers are governed by polymer chain orientation on a common length scale.…”

Section: Introductionmentioning

confidence: 90%

“…Validity of the stressthermal rule, eq 2, indicates that deformation-induced anisotropies in mechanical and thermal transport in polymers are governed by polymer chain orientation on a common length scale. [20][21][22] This observation could have profound implications on theoretical modeling because it provides guidance on the level of course graining necessary to describe anisotropic thermal conductivity. In addition, many of the results from molecular models of polymer dynamics to predict rheological behavior can, if eq 2 is generally valid, be immediately used to develop models for flow-induced anisotropic thermal conductivity.…”

Section: Introductionmentioning

confidence: 99%

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Measurements of Flow-Induced Anisotropic Thermal Conduction in a Polyisobutylene Melt Following Step Shear Flow

et al. 2005

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Flow-induced anisotropic thermal conduction in a polyisobutylene melt subjected to shear deformations is studied experimentally. Time-dependent measurements of the full (four components) thermal diffusivity tensor following step shear strain flow are presented. These data were obtained with a novel experimental setup based on the optical technique of forced Rayleigh scattering. Birefringence and stress measurements are made for the same flow, and the well-known stress-thermal rule is found to be satisfied. Thermal diffusivity data and stress data are used to test directly the stress-thermal rule, which is also satisfied for the two cases considered. Consideration of stress-thermal coefficients from the present and previous studies gives preliminary evidence that flow-induced anisotropic thermal conduction is a universal phenomenon for flexible polymers.

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Section: Introductionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

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Measurements of Flow-Induced Anisotropic Thermal Conduction in a Polyisobutylene Melt Following Step Shear Flow

et al. 2005

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“…How do we need to generalize the concepts of thermal conductivity and heat capacity in complex fluids undergoing flow? Pioneering experiments on anisotropic heat flow have been performed by Venerus, Schieber and coworkers [Venerus et al (1999); Broerman et al (1999); Iddir et al (2000); Venerus et al (2004); Schieber et al (2004); of heat capacity have been discussed by Hütter et al (2009).…”

Section: Closurementioning

confidence: 99%

On the stupendous beauty of closure

Öttinger

2009

Preprint

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Closure seems to be something rheologists would prefer to avoid. Here, the story of closure is told in such a way that one should enduringly forget any improper undertone of "uncontrolled approximation" or "necessary evil" which might arise, for example, in reducing a diffusion equation in configuration space to moment equations. In its widest sense, closure is associated with the search for self-contained levels of description on which time-evolution equations can be formulated in a closed, or autonomous, form. Proper closure requires the identification of the relevant structural variables participating in the dominant processes in a system of interest, and closure hence is synonymous with focusing on the essence of a problem and consequently with deep understanding.The derivation of closed equations may or may not be accompanied by the elimination of fast processes in favor of dissipation. As a general requirement, any closed set of evolution equations should be thermodynamically admissible. Thermodynamic admissibility comprises much more than the second law of thermodynamics, most notably, a clear separation of reversible and irreversible effects and a profound geometric structure of the reversible terms as a hallmark of reversibility.We discuss some implications of the intimate relationship between nonequilibrium thermodynamics and the principles of closure for rheology, and we illustrate the abstract ideas for the rod model of liquid crystal polymers, bead-spring models of dilute polymer solutions, and the reptation model of melts of entangled linear polymers.

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“…Then theory is needed to project the information acquired in simple experiments to the complex reality of the process. The need for robust theories is even more pressing when tackling more complex transport phenomena, like coupled flow and heat transfer [17][18][19][20][21][22] or mass transfer [23][24][25][26][27][28][29][30]; experimental evidence on such processes is still limited [31][32][33][34][35][36].…”

Section: Introductionmentioning

confidence: 99%

Theoretical modeling of microstructured liquids: a simple thermodynamic approach

Pasquali

Scriven

2004

Journal of Non-Newtonian Fluid Mechanics

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A new method is presented for accounting for microstructural features of flowing complex fluids at the level of mesoscopic, or coarse-grained, models by ensuring compatibility with macroscopic and continuum thermodynamics and classical transport phenomena. In this method, the microscopic state of the liquid is described by variables that are local expectation values of microscopic features. The hypothesis of local thermodynamic equilibrium is extended to include information on the microscopic state, i.e., the energy of the liquid is assumed to depend on the entropy, specific volume, and microscopic variables. For compatibility with classical transport phenomena, the microscopic variables are taken to be extensive variables (per unit mass or volume), which obey convection-diffusion-generation equations. Restrictions on the constitutive laws of the diffusive fluxes and generation terms are derived by separating dissipation by transport (caused by gradients in the derivatives of the energy with respect to the state variables) and by relaxation (caused by non-equilibrated microscopic processes like polymer chain stretching and orientation), and by applying isotropy. When applied to unentangled, isothermal, non-diffusing polymer solutions, the equations developed according to the new method recover those developed by the Generalized Bracket [J. Non-Newtonian Fluid Mech. 23 (1987) Rheol. 38 (1994) 769]. Minor differences with published results obtained by the Generalized Bracket are found in the equations describing flow coupled to heat and mass transfer in polymer solutions. The new method is applied to entangled polymer solutions and melts in the general case where the rate of generation of entanglements depends nonlinearly on the rate of strain. A link is drawn between the mesoscopic transport equations of entanglements and conformation and the microscopic equation describing the configurational distribution of polymer segment stretch and orientation. Constraints are derived on the generation terms in the transport equations of entanglements and conformation, and the formula for the elastic stress is generalized to account for reversible formation and destruction of entanglements. A simplified version of the transport equation of conformation is presented which includes many previously published constitutive models, separates flow-induced polymer stretching and orientation, yet is simple enough to be useful for developing large-scale computer codes for modeling coupled fluid flow and transport phenomena in two-and three-dimensional domains with complex shapes and free surfaces.

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Measuring anisotropic thermal conduction in polyisobutylene following step shear strains

Cited by 8 publications

References 18 publications

Measurements of Flow-Induced Anisotropic Thermal Conduction in a Polyisobutylene Melt Following Step Shear Flow

Measurements of Flow-Induced Anisotropic Thermal Conduction in a Polyisobutylene Melt Following Step Shear Flow

On the stupendous beauty of closure

Theoretical modeling of microstructured liquids: a simple thermodynamic approach

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