Abstract:In this paper we develop a theory for a rheometrical device for measuring the speed of shear waves into a region at rest. The device is a Couette apparatus with a narrow gap. The outer cylinder is moved impulsively and a time of transit is measured. The linearized theory governing this apparatus is reduced to a perturbation of Stokes’ first problem between parallel planes. A method for determining an effective shear modulus from measured values of the wave speed is discussed and various cases are analysed. An … Show more
“…(8). This was a special model obtained after generalization of Boltzmann's equation of linear viscoelasticity [58], and was inspired by the work done by Maxwell [59] and Boltzmann [60]. Differentiating Eq.…”
Please cite this article in press as: A. Singh, E.B. Tadmor, Thermal parameter identification for non-Fourier heat transfer from molecular dynamics, J. Comput. Phys. (2015), http://dx.
AbstractFourier's law leads to a diffusive model of heat transfer in which a thermal signal propagates infinitely fast and the only material parameter is the thermal conductivity. In micro-and nano-scale systems, non-Fourier effects involving coupled diffusion and wavelike propagation of heat can become important. An extension of Fourier's law to account for such effects leads to a Jeffreys-type model for heat transfer with two relaxation times. We propose a new Thermal Parameter Identification (TPI) method for obtaining the Jeffreys-type thermal parameters from molecular dynamics simulations. The TPI method makes use of a nonlinear regression-based approach for obtaining the coefficients in analytical expressions for cosine and sine-weighted averages of temperature and heat flux over the length of the system. The method is applied to argon nanobeams over a range of temperature and system sizes. The results for thermal conductivity are found to be in good agreement with standard Green-Kubo and direct method calculations. The TPI method is more efficient for systems with high diffusivity and has the advantage, that unlike the direct method, it is free from the influence of thermostats. In addition, the method provides the thermal relaxation times for argon. Using the determined parameters, the Jeffreys-type model is able to reproduce the molecular dynamics results for a short-duration heat pulse where wavelike propagation of heat is observed thereby confirming the existence of second sound in argon. An implementation of the TPI method in MATLAB is available as part of the online supplementary material.
“…(8). This was a special model obtained after generalization of Boltzmann's equation of linear viscoelasticity [58], and was inspired by the work done by Maxwell [59] and Boltzmann [60]. Differentiating Eq.…”
Please cite this article in press as: A. Singh, E.B. Tadmor, Thermal parameter identification for non-Fourier heat transfer from molecular dynamics, J. Comput. Phys. (2015), http://dx.
AbstractFourier's law leads to a diffusive model of heat transfer in which a thermal signal propagates infinitely fast and the only material parameter is the thermal conductivity. In micro-and nano-scale systems, non-Fourier effects involving coupled diffusion and wavelike propagation of heat can become important. An extension of Fourier's law to account for such effects leads to a Jeffreys-type model for heat transfer with two relaxation times. We propose a new Thermal Parameter Identification (TPI) method for obtaining the Jeffreys-type thermal parameters from molecular dynamics simulations. The TPI method makes use of a nonlinear regression-based approach for obtaining the coefficients in analytical expressions for cosine and sine-weighted averages of temperature and heat flux over the length of the system. The method is applied to argon nanobeams over a range of temperature and system sizes. The results for thermal conductivity are found to be in good agreement with standard Green-Kubo and direct method calculations. The TPI method is more efficient for systems with high diffusivity and has the advantage, that unlike the direct method, it is free from the influence of thermostats. In addition, the method provides the thermal relaxation times for argon. Using the determined parameters, the Jeffreys-type model is able to reproduce the molecular dynamics results for a short-duration heat pulse where wavelike propagation of heat is observed thereby confirming the existence of second sound in argon. An implementation of the TPI method in MATLAB is available as part of the online supplementary material.
“…The theory for the wave-speed meter is given in Joseph et al [19]. The apparatus and the measuring technique are described in Joseph et al [20] and in detail in Riccius [21].…”
Section: Wave Speeds Effective Rigidity and Effective Relaxation Timesmentioning
“…The concept of an effective modulus developed in [1] seems to be supported by measurements in [2], here and those of Fuller. Additional support for these ideas in a flow context come from recent measurements of delayed die swell [3].…”
Section: Introductionmentioning
confidence: 55%
“…In our earlier work we presented a theory [1] of effective wave-speeds for shear waves into regions at rest and developed the idea of an effective rigidity (shear modulus) and viscosity. A device, the wave-speed meter (U.S. patent 4,602,502), was described and used to measure wave speeds and effective rigidities in 51 liquids [2].…”
Section: Introductionmentioning
confidence: 99%
“…An effective-moduli theory for G (7, t -~) can be developed along exactly the same lines laid down in [1] and leads to effective rigidities Gc (i).…”
Abstract:Tables of values of shear-wave speeds, shear moduli and relaxation times for 18 new liquids are presented, supplementing the tables for 51 liquids given in Part 2. A brief discussion of errors and analysis of the oscilloscope traces is presented. The relation of the effective moduli measured on the wave-speed meter to independent measurements using phase-modulated birefringence and delayed die swell is discussed. A method of measuring wave speeds and rigidities for sheared media is proposed.
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