Showing papers on "Entropy (classical thermodynamics) published in 1969"

Untersuchungen über das Verhalten organischer Mischphasen 7. Mitteilung. Dampfdrücke, Dichten und thermodynamische Mischungsfunktionen des binären Systems Cyclohexan‐ Tetrahydrofuran bei 25°

Abstract: The total vapor pressures and the heats of mixing of the system cyclohexane-tetrahydrofuran were measured at 25°C. The density was used to determine concentrations for the total pressure measurements. The partial pressures, activity coefficients, excess free energies, entropy functions, and excess volumes were calculated.

Variational principles for parabolic equations

Abstract: New types of variational principles, each of them equivalent to the linear mixed problem for parabolic equation with initial and combined boundary conditions having been suggested by physicists, are discussed. Though the approach used here is purely mathematical so that it makes possible application to all mixed problems of mathematical physics with parabolic equations, only the example of heat conductions is used to show the physical interpretation. The principles under consideration are of two kinds. The first kind presents a variational characterization of the original problem, expressed in terms of a scalar function (temperature). The principles of the second kind characterize the same problem, formulated in terms of other variables, e.g. of a vector function (heat flux or entropy displacements).

On the evolution of a plasma interacting with radiation

Abstract: One of the basic problems in the theory of irreversible thermodynamics is the formulation of general evolution criteria. A universal criterion of this kind for macroscopic systems with time independent boundary conditions has been derived by Glansdorff and Prigogine. The derivation refers to transport processes in matter like diffusion, heat conduction and chemical reactions. Radiative transfer has not been included. In this investigation, we use statistical mechanics to extend the above evolution criterion and the principle of minimum entropy production to partially ionized, collision-dominated plasmas interacting with radiation. We consider a plasma with collisional—and radiative excitation—and ionization phenomena not restricted to local equilibrium. The entropy production, which is defined as the entropy change per unit time due to emission, absorption and scattering of radiation, is formulated with the use of statistical analogues to the fluxes and forces or irreversible thermodynamics. The time change of the entropy production is investigated for a homogeneous plasma and an isotropic radiation field.

Connections between the various forms of the second law of thermodynamics

Abstract: The forms of the second law due to Caratheodory, Kelvin and Clausius are examined The possible forms of thermodynamics which may be deduced from each of these statements are found before the connections between the separate forms of the law itself are examined It is found that the usual proof of the equivalence of the Kelvin and Clausius statements is invalidated at negative absolute temperatures However, it is shown that the Clausius statement is equivalent to the modified form of the Kelvin principle which is applicable for both positive and negative absolute temperatures

Engine Efficiencies and the Second Law of Thermodynamics.

Abstract: The second law of thermodynamics is stated in the form o∫ dS = o∫ dQ/T = 0 for a thermodynamic system undergoing a cyclic, reversible process. It is shown that this makes it possible to construct a T-S diagram. The Clausius and Kelvin-Planck statements, as well as the properties of the Carnot engine and general statements about engine and refrigerator efficiencies, are deduced from the properties of the T-S diagram.

Reversibility in the gas-phase decomposition of cyclopentene. The entropy of cyclopentadiene

Abstract: The entropy of cyclopentadiene has been determined from the unexpectedly reversible decomposition of cyclopentene.