Magnitude Of Relaxation Time Research Articles

Mathematical modelling of heat transfer effects on swallowing dynamics of viscoelastic food bolus through the human oesophagus

The present paper describes a mathematical study on peristaltic flow of viscoelastic fluids (with the robust Jeffrey model) through a finite length channel under the influence of heat transfer. The study is motivated by the need to further elucidate the mechanisms inherent in swallowing of diverse food bolus types (bread, fruit jam and almost all edible semi-solids) through the oesophagus, by taking account of the viscous and elastic effects. The expressions for temperature field, axial velocity, transverse velocity, volume flow rate, pressure gradient, local wall shear stress, mechanical efficiency, stream function, and reflux limit are obtained, when the Reynolds number is small and the wavelength is large, by using appropriate analytical and numerical methods. The computational results are presented in graphical form. The influence of thermophysical (heat transfer), relaxation time and retardation time parameters on pressure distribution, local wall shear stress profiles, temperature profiles and velocity profiles are studied in detail. Furthermore we investigate the effects of these parameters on two inherent phenomena (reflux and trapping) characterizing peristaltic flow using streamline plots. The present study emphasizes an important observation, namely that pressure along the entire length of the channel reduces when the magnitude of relaxation time (retardation time is fixed) or Grashof number or indeed thermal conductivity increase, whereas pressure is enhanced by increasing the magnitude of retardation time (relaxation time is fixed).

Lattice thermal conductivity of skutterudite compounds

A generalized expression is used on the basis of relaxation time approximation to facilitate calculation of lattice thermal conductivity of dielectric materials as well as skutterudite family consists of compounds of the form AB3. It is assumed that phonon scattering processes are independent and is represented by frequency dependent relaxation times. The contributions of normal three phonon scattering processes are included explicitly as redistribution of phonon momentum between two oscillation branches is considered. Magnitudes of relaxation times are estimated from the experimental data. The result for CoSb3 is in reasonably good agreement with the experimental result in the temperature range 1–1000°K. It is observed that redistribution of phonon momentum between two oscillation branches leads to a significant suppression of thermal conductivity maximum and it is observed that for unfilled skutterudite the main dominant mechanism at the thermal conductivity maximum is three phonon normal scattering process.

Effect of Critical State Model on Magnetic Relaxation in Type-II Superconductors

Based on the theoretical model in which magnetic relaxation was considered, exact equations are derived for the relaxation rate, normalized relaxation rate and relaxation time. The relations between the theory on relaxation rate and experimental data are compared, as well as the relaxation time. The valid ranges of several models are specified and the magnitude of relaxation time is estimated. The results indicate that different models are suitable for different temperature regions and the effect of relaxation time on the experimental measurements could not be neglected.

Compensation effect in grain boundary internal friction

Experimental evidence is provided for the occurrence of the compensation effect, i.e., a linear relationship between the activation enthalpy and the logarithm of the pre-exponential factor, for grain boundary internal friction. The results of internal friction measurements in bicrystals of high purity Al with structurally different grain boundaries were analyzed. The extracted compensation temperature was found to be the same as for grain boundary migration and diffusion of solutes along grain boundaries in Al bicrystals. This temperature divides the investigated temperature range of the internal friction peak into two regimes, with different relations between the magnitude of relaxation time and enthalpy of activation.