József Verhás

Deviation from the Fourier law in room-temperature heat pulse experiments

Abstract We report heat pulse experiments at room temperature that cannot be described by Fouriers law. The experimental data are modeled properly by the Guyer–Krumhansl equation, in its over-diffusion regime. The phenomenon may be due to conduction channels with differing conductivities and parallel to the direction of the heat flux.

On the representation of dynamic degrees of Freedom

The different possibilities for choosing dynamic state variables are analyzed, with the dielectric polarization in an isothermic electric conductor being taken as an example. The advantage of a canonical choice for the dynamic variables is shown. Several questions involving non-linear theories are also discussed.

A Thermodynamic Theory for Heat Radiation Through the Atmosphere

Basing on the conclusions of a previous work [1], a simple thermodynamic model is established for radiating heat transfer through the air. The model is applied to the temperature distribution of the atmosphere and the radiating heat loss of the Earth.

A Thermodynamic Theory for Radiating Heat Transfer

In a previous paper [1] we investigated what influence the scalar dynamic variables had on heat propagation. In this paper we study that of vectorial dynamic degrees of freedom. We point out that the phenomena described this way are heat propagation by electromagnetic radiation and/or acoustic waves and/or electron waves

On the Nonlinear Generalizations of Onsager’s Reciprocal Relations

In a nonlinear thermodynamic theory, a nonlinear generalization of Onsagers reciprocal relations is expected. In the literature of modern thermodynamics, there are propositions for them. In the special case of isomerization reaction we have confronted two of them with the Guldberg-Waage equations of the chemical reaction kinetics, which are well verified both experimentally and theoretically. We found that the only nonlinear generalization compatible with the Guldberg Waage equations is that given by Hurley and Garrod and later by Verhas. The Gyarmati-Li reciprocal relations can not be fitted to the reaction kinetics but in linear order. Nevertheless, the Principle of Macroscopic Reversibility proposed by Meixner gives a good insight to the structure of the Onsager-Casimir reciprocal relations, demanding its validity to higher order leads to conflict with the rules of the rate of chemical reactions.

Fundamental problems of variational principles: Objectivity, symmetries and construction

Abstract Some aspects of the relation of governing equations, spacetime symmetries and fundamental balances in nonrelativistic field theories are investigated. Special emphasis is given to variational principle construction methods for a given differential equation.

Thermodynamic theory for wave guides

Abstract The mechanical waves of an earthquake travelling in the crust of the Earth show that the material is not perfectly elastic. To study the propagation in a viscoelastic material needs a model, the parameters of which which can be fitted to the measurements. To survey the possible choices, we assume the thermodynamic theory of viscoelasticity. To get experience in the thermodynamic theory of wave propagation, the electromagnetic waves in a wave guide have been studied. The most simple model based on the hypothesis of local equilibrium turned out to be oversimplified, while extended thermodynamics and Gyarmatis wave approach of thermodynamics gave equivalent results, which can be simplified to the usual model of a wave guide without losses. Introducing several kinds of dynamic degrees of freedom, a hierarchy of models for wave guides with losses has been obtained.

On thermal waves and radiating heat transfer

Splitting up the heat flow into several parts and applying the basic ideas of Gyarmati’s wave approach of thermodynamics, a systematic thermodynamical analysis is given for radiating heat transfer. The possible transformations make clear that the above splitting can be done so that the different parts of the radiating heat transfer are independent of each other. The different parts of the heat flow are dynamic state variables and the whole treatment based on variables witha priori physical meaning is a bit more complicated than that based on abstract dynamic variables while the result is the same [1].