Response of thermal source in a transversely isotropic thermoelastic half-space with mass diffusion by finite element method

The two-dimensional problem of generalized thermoelastic diffusion material with thermal and diffusion relaxation times is investigated in the context of Lord-Shulman theory. As an application of the problem, a particular type of thermal source is considered and the problem is solved numerically by using a finite element method. The components of displacement, stress, temperature distribution, chemical potential, and mass concentration are obtained. The resulting quantities are depicted graphically for a special model. Appreciable effect of relaxation times is observed on various resulting quantities.     

Response of thermal source in a transversely isotropic thermoelastic half-space with mass diffusion by using a finite element method

The two-dimensional problem of generalized thermoelastic diffusion material with thermal and diffusion relaxation times is investigated in the context of the Lord-Shulman theory.As an application of the problem,a particular type of thermal source is considered and the problem is solved numerically by using a finite element method.The components of displacement,stress,temperature distribution,chemical potential,and mass concentration are obtained.The resulting quantities are depicted graphically for a special model.An appreciable effect of relaxation times is observed on various resulting quantities.     

Study of thermal conductivity and thermal rectification in exponential mass graded lattices

Concept of exponential mass variation of oscillators along the chain length of N oscillators is proposed in the present Letter. The temperature profile and thermal conductivity of one-dimensional (1D) exponential mass graded harmonic and anharmonic lattices are studied on the basis of Fermi-Pasta-Ulam (FPU) β model. Present findings conclude that the exponential mass graded chain provide higher conductivity than that of linear mass graded chain. The exponential mass graded anharmonic chain generates the thermal rectification of 70-75% which is better than linear mass graded materials, so far. Thus instead of using linear mass graded material, the use of exponential mass graded material will be a better and genuine choice for controlling the heat flow at nano-scale.     

Free convection on an inclined plate with variable viscosity and thermal diffusivity

The present numerical analysis addresses free convection flow of a viscous incompressible fluid along an inclined semi-infinite flat plate considering the variation of viscosity and thermal diffusivity with temperature. The governing equations are developed with the corresponding boundary conditions are transformed to non-dimensional form using the appropriate dimensionless quantities. Due to complexity in the transformed governing equations, analytical solution will fail to produce a solution. Hence, most efficient and unconditionally stable implicit finite difference method of Crank-Nicolson scheme has been used to solve the governing equations. Numerical results are obtained for different values of the viscosity, thermal conductivity, inclination angle, Grashof number, and Prandtl number. The overall investigation of the variation of velocity, temperature, shearing stress and Nusselt number are presented graphically. To examine the accuracy of the present approximate results, the present results are compared with the available results.     

Simultaneous measurements of thermal diffusivity, thermal conductivity and thermopower with application to copper and ceramic superconductors

A home made experimental set-up allows us to measure the thermal conductivity, the thermopower and the thermal diffusivity simultaneously in the temperature range (20-300 K). Therefore the specific heat can be deduced. The role of a radiation shield is shown to be relevant. Tests of the system are made on a 99.9% pure Cu sample and two polycrystalline cuprate ceramics for illustration. Without any complicated optimisation, the technique indicates much promise already due to its efficiency and rapidity. Received 9 November 1998 and Received in final form 12 July 1999     

Infrared thermography protocol for simple measurements of thermal diffusivity and conductivity

An accurate characterization of thermal properties requires the knowledge of both thermal diffusivity and conductivity. Most of the time, the thermal conductivity have to be measured with complicated setups. In this paper, we show that a combination of two experiments carried out with the same setup – stimulated infrared thermography – allows to estimate straightforwardly and quickly the absolute value of the thermal diffusivity and the thermal conductivity relatively to a reference material.     

Effects of variable thermal diffusivity on the structure of convection

The structure of multiscale convection in a thermally stratified plane horizontal fluid layer is investigated by means of numerical simulations. The thermal diffusivity is assumed to produce a thin boundary sublayer convectively much more unstable than the bulk of the layer. The simulated flow is a superposition of cellular structures with three different characteristic scales. In contrast to the largest convection cells, the smaller ones are localised in the upper portion of the layer. The smallest cells are advected by the larger-scale convective flows. The simulated flow pattern qualitatively resembles that observed on the Sun.     

A thermoelastic method to accurately measure the grüneisen parameter and thermal diffusivity

A homogeneous thermoelastic heat source is fed, in a cylindrical sample, by compression; the amount of generated heat is controlled by the Grüneisen parameter. The heating process is followed by a thermal relaxation controlled by the thermal diffusivity. The temperature transient is detected by a miniature temperature sensor mounted on the lateral surface of the sample. The value obtained for the Grüneisen parameter of a technological steel is 1.14±0.03, the thermal diffusivity turning out to be (6.1±0.1)·10⁻⁶ m² s⁻¹.     

Differential temperature sensors method for simultaneous determination of thermal conductivity and diffusivity

An attempt has been made to minimize the sources of error involved in the transient probe method for thermal conductivity determination. Two sensors (thermocouples) are mounted parallel to the needle probe at known distances. This modification makes it a device for simultaneous conductivity and diffusivity determination. Thermal conductivity and diffusivity for glycerine, dune sand and mustard seed are determined by this method. Results obtained are compared with those obtained by a calibrated transient probe for conductivity and by a parallel wire method for diffusivity. Analysis of the results prove it to be a better instrument over the traditional ones. The technique can also be used as a direct reading device for conductivity and diffusivity measurements.     

Three-dimensional mixed convection flow with variable thermal conductivity and frictional heating

In this article,three-dimensional mixed convection flow over an exponentially stretching sheet is investigated.Energy equation is modelled in the presence of viscous dissipation and variable thermal conductivity.Temperature of the sheet is varying exponentially and is chosen in a form that facilitates the similarity transformations to obtain self-similar equations.Resulting nonlinear ordinary differential equations are solved numerically employing the Runge-Kutta shooting method.In order to check the accuracy of the method,these equations are also solved using bvp4c built-in routine in Matlab.Both solutions are in excellent agreement.The effects of physical parameters on the dimensionless velocity field and temperature are demonstrated through various graphs.The novelty of this analysis is the self-similar solution of the threedimensional boundary layer flow in the presence of mixed convection,viscous dissipation and variable thermal conductivity.     

Simultaneous measurement of thermal diffusivity,thermal conductivity and specific heat by impulse-response photopyroelectric spectrometry

A novel photothermal technique is developed, which enables the simultaneous measurement of the thermal diffusivity , thermal conductivity , and the specific heat C of a sample. The technique is based on frequency-modulated time-delay photopyroelectric spectrometry (FM-TDPS), which consists of chirped laser excitation of the sample and detection of the thermal impulse response by a thin-film pyroelectric detector. No calibration is required for the measurements; absolute values for , , and C may be obtained without having to employ a reference sample. Results on superconducting YBa₂Cu₃O_7–x are reported for the temperature range 50–300 K; the values obtained compare favorably with reported measurements of , , and C for YBa₂Cu₃O_7–x , which previously required separate experiments for their determination.     

Thermal conductivity and thermal diffusivity of the R134a refrigerant in the liquid state

Thermal conductivity and thermal diffusivity of “ozone-safe” refrigerant R134a in liquid state within the range of temperatures 295.9–354.9 K and pressures from the liquid — vapor equilibrium line up to 4.08 MPa have been studied by high-frequency thermal-wave method. The experimental uncertainties of the temperature, pressure, thermal conductivity and thermal diffusivity measurement errors were estimated to be 0.1 K, 3 kPa, 1.5 and 2.5 %, respectively. Values of thermal conductivity and thermal diffusivity of liquid R134a on saturated line have been calculated. Approximation dependences for thermal conductivity and thermal diffusivity within the whole studied range of temperatures and pressures as well as on the saturated line have been obtained. The work was financially supported by the Russian Foundation for Basic Research (grant No. 07-08-00295-a).     

Current views on thermal conductivity and diffusivity measurements of oxide melts at high temperature

There have been various attempts to measure thermal conductivity of relatively low conductive materials such as oxides and nitrides, at high temperature. However, their accuracy was not sufficient to allow quantitative discussion mainly because of experimental difficulties, particularly at sample temperature above 1000 K, for several reasons. For example, the radiative heat flow is known to play a significant role at higher temperature, but the separation of such a component from the measured heat flows has only been established recently. An attempt will be made in this paper to review current information on thermal conductivity measurement of oxide melts at high temperature above 1000 K. Thus, this review is primarily concerned with the several methods for determining thermal conductivity of high temperature melts including their respective merits and demerits. A new laser-flash method proposed in the early 1960's has received much attention for determining thermal conductivity of high temperature melts and is an even better technique than the conventional techniques such as the hot-wire method. Although some advantages of the laser-flash method are readily apparent, major progress has been obtained only in the last few years and new information is now available. Therefore, it will be the authors' intention to provide the principle and the new data processing for the laser-flash method, including some selected examples of its application to determining thermal conductivity of oxide melts at high temperature. The relevant significant quantities such as the radiative heat transfer coefficient are also discussed, in order to facilitate the understanding of the present status of fundamentals and the powerful link between physical constants such as the reflective index of sample material and the required formulae for determining thermal conductivity of high temperature melts by the laser-flash method.     

Temperature dependence of effective thermal conductivity and effective thermal diffusivity of Se90In10 bulk chalcogenide glass

Measurement of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) of twin pellets of Se₉₀In₁₀ bulk chalcogenide glass has been carried out in the temperature range from 303 to 323 K and cooling from 323 to 303 K using transient plane source (TPS) technique. In the heating process variation of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) is observed. Both quantities are found to be maximum at 313 K, which lies in the vicinity of glass transition temperature (T_g). During the cooling process λ_e and χ_e remain same at all temperatures. Such type of behavior shows thermal hysteresis in this sample, which can be explained on the basis of structural change of the Se₉₀In₁₀ bulk chalcogenide glass.     

Simultaneous determination of specific heat,thermal conductivity and thermal diffusivity at low temperature via the photopyroelectric technique

The photopyroelectric effect has been used to measure simultaneously specific heat (c), thermal conductivity (k) and thermal diffusivity () at low temperatures. A calibration procedure which allows the use of a pyroelectric transducer at low temperatures is described. Simultaneous measurements of c, k, and over a high T _c superconducting phase transition are reported.     

Specific heat,thermal diffusivity and thermal conductivity of Ca doped NaNO3 crystals near the transition point

Thermal characteristics of calcium doped NaNO₃ crystals near the transition point were investigated. Their values near the transition point decrease proportionally to the increasing calcium concentration in crystal. In the same way decreases the critical temperature. Thermal conductivity changes can be explained by the presence of an order-disorder scattering mechanism.Dúbravská cesta, Bratislava, Czechoslovakia.     

Cosmology with a variable generalized Chaplygin gas

We investigate observational constraint on the variable generalized Chaplygin gas (VGCG) model as the unification of dark matter and dark energy by using the Union supernovae sample and the baryon acoustic oscillations data. Based on the best fit parameters for VGCG model it is shown that the current value of equation of state for dark energy is w_0de=−1.08<−1, and the universe will not end up with big rip in the future. In addition, we also discuss the evolution of several quantities in VGCG cosmology such as deceleration parameter, fractional density parameters, growth index and sound speed. Finally, the statefinder diagnostic is performed to discriminate the VGCG with other models.     

Thermal radiation effects on MHD flow of a micropolar fluid over a stretching surface with variable thermal conductivity

In this paper, the effects of variable thermal conductivity and radiation on the flow and heat transfer of an electrically conducting micropolar fluid over a continuously stretching surface with varying temperature in the presence of a magnetic field are considered. The surface temperature is assumed to vary as a power-law temperature. The governing conservation equations of mass, momentum, angular momentum and energy are converted into a system of non-linear ordinary differential equations by means of similarity transformation. The resulting system of coupled non-linear ordinary differential equations is solved numerically. The numerical results show that the thermal boundary thickness increases as the thermal conductivity parameter S$S$ increases, while it decreases as the radiation parameter F$F$ increases. Also, it was found that the Nusselt number increases as F$F$ increases and decreases as S$S$ increases.