Date of Award

Spring 1981

Project Type

Dissertation

Program or Major

Engineering (Theoretical and Applied Mechanics)

Degree Name

Doctor of Philosophy

Abstract

Thermodynamic analysis of various physical phenomena, chemical processes, and industrial installation has become a very important part of engineering work. The evergrowing sophistication of the contemporary technical world has brought about the necessity of extensive developments and applications in the field of Irreversible Thermodynamics which enables one to efficiently treat phenomena that are spatially and temporally non-equilibrium ones, and therefore thermodynamically irreversible. The unavoidable facts that all industrial processes experience randomly distributed external and internal excitations, and also that their variables, being automatically controlled, fluctuate in space in time, require a systematic improvements of the adopted methods of Irreversible Thermodynamic analyses and evaluations, and continuous developments of new ones, evermore accurate and consistent.

The purpose of this project was to systematically present the existent methods, and to develop some alternative ones, of analysis and evaluations of the main irreversible phenomena that occur in thermoviscoelastic solids and fluids, namely, the absorption and propagation of the sound waves and the influence of thermal energy conduction and dissipation within the said media upon the phenomena is discussion.

The theoretical methods of such analysis, specifically those of evaluation of the spatial attenuations of the sound wave propagating through a thermoviscoelastic media (solid or fluid) contain a substantially incomplete and very restricted in its validity procedure which is based upon a dimensional modification of the temporal attenuations. Specifically, the sound absorption coefficient, (gamma), defined as the ratio of the mean value of the mechanical energy dissipation to twice the mean energy flux of the wave, is dimensionally modified by dividing it by the transverse or longitudinal velocities of sound in a given media, which procedure formally permits to obtain a dimensionally consistent result. However, it does not reflect the physical nature of the phenomenon and therefore may not, in general, provide for sound and meaningful engineering results.

An alternative method for evaluation of spatial attenuations has been introduced, which employs newly proposed energy partition and spectral theorems. The results obtained from evaluation of the temporal attenuations by means of the proposed methods agree with those well-known ones, and new results have been obtained from evaluation of the spatial attenuations by the same means, which agree with some partial results been previously published, but render a more generalized and applicable approach.

One field where until recently no interest with regards to the methods of Irreversible Thermodynamics has been displayed is the Thermodynamics of Power and Refrigeration Cycles. However, at the present time, particularly when Automatic Control systems have become an integral part of this type of industrial installations, the state variables and characteristic parameters of the working regimes experience temporal fluctuations, which, if the system has been designed without proper consideration of the stated facts, introduce additional irreversibilities that must be accounted for. The most important part of such analysis is the evaluation of the timely rate of entropy production. For this purpose, a mathematical model of a Refrigeration Machine has been developed and presented, which interconnects the dynamics of the temporal changes of the variables and of the temporal energy fluctuations with the randomly distributed changes in entropy production due to performance of an Automatic Control System.

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