Volume 28, Issue 3

The problem of flame propagation over premixed gas mixtures is analyzed using the principle of minimal entropy production. The flame propagation velocity predicted by a general approach based on the integral mass balance is considered as an exact physical solution corresponding to the actual stationary regime of flame propagation. The difference between the actual stationary state of the system and the state with minimal entropy production has been estimated. An adequate physical description of the flame propagation phenomenon by the approach, assuming that the stationary state is characterized by minimal entropy production, has been obtained for a variety of physical and kinetic parameters.

The process of heat conduction, with allowance made for the lag effect, is considered. A postulate of extended irreversible thermodynamics is suggested, according to which the entropy is a function of the internal energy and its time derivatives (up to the third derivative, inclusive). On the basis of the developed thermodynamic formalism, a third-order heat conduction equation is derived, generalizing the known dual-phase-lag model equation. A mathematical model of heat conduction in a package of heat-conducting plates is built, leading to the considered third-order equation. By numerical modeling it is shown that this equation describes heat wave propagation.

The Ericsson refrigeration cycle working with an ideal Bose gas is called the Bose Ericsson refrigeration cycle. The effect of quantum degeneracy on the performance of the cycle is investigated, based on the thermodynamic properties of an ideal Bose gas. The inherent regenerative losses of the cycle are analyzed, and the coefficient of performance and the refrigeration load of the cycle are calculated. The results obtained here are compared with those derived from the classical Ericsson refrigeration cycle using an ideal gas as the working substance. General performance characteristics of the Bose Ericsson refrigeration cycle are revealed.

All energy transformation processes occurring in reality are irreversible and in many cases these irreversibilities must be included in a realistic description of such processes. Endoreversible thermodynamics is a non-equilibrium approach in this direction by viewing a system as a network of internally reversible (endoreversible) subsystems exchanging energy in an irreversible fashion. All irreversibilities are confined to the interaction between the subsystems. This review is dedicated to the dynamical investigation of such endoreversible systems. First the general framework for the endoreversible description of a system is briefly introduced, and then the necessary mathematical tools to determine optimal process paths for such systems are presented. These are complemented by simple examples for the application of the different methods. Then the optimal paths for endoreversible processes of increasing complexity are discussed: first the processes between given equilibrium states, and then cyclic processes. These are followed by a review of internal combustion engines and by a number of further selected applications. We conclude with an outlook to other areas of irreversible thermodynamics where path optimization methods have been successfully used.

We derive an equation for the Second Law efficiency of an osmotic membrane. This expression of efficiency depends on the ratio between the solvent and solute flux, but remains independent of the actual values of the fluxes and of any transport model. The equation can be used to find the magnitude of solute leakage that can be accepted for optimally performing osmotic membranes. Special emphasis is given to osmotic power generation systems. We additionally compare the fraction of total power destruction that occurs inside the selective layer of the membrane, and the fraction that occurs inside the support material of the membrane.

Three types of equations linking the diffusion equation and the wave equation are studied: the time fractional diffusion equation, the space fractional diffusion equation and the telegrapher's equation. For each type, the entropy production is calculated and compared. It is found that the two fractional diffusions, considered as linking bridges between reversible and irreversible processes, possess counter-intuitive properties: as the equation becomes more reversible, the entropy production increases. The telegrapher's equation does not have the same counter-intuitive behavior. It is suggested that the different behaviors of these equations might be related to the velocities of the corresponding random walkers.