Band 29, Heft 1

In this case study a complex Otto engine simulation provides data including, but not limited to, effects from losses due to heat conduction, exhaust losses and frictional losses. This data is used as a benchmark to test whether the Novikov engine with heat leak, a simple endoreversible model, can reproduce the complex engine behavior quantitatively by an appropriate choice of model parameters. The reproduction obtained proves to be of high quality.

Computations using orientation-free discrete velocity models for the dispersion relationship of ultrasound propagation in monatomic hard-sphere gases (or gases composed of systems of vortices) are presented. Comparisons with previous verified fixed-orientation results for the propagation of the sound mode of ultrasound in rarefied gases show that if collective excitations are considered, orientation-free discrete velocity models can provide more physical insight. We also address the symmetry and limits of these models.

The main goal of the paper is to establish possible thermodynamic conditions at a phase boundary to describe a propagation of phase-transition fronts in crystalline solids. Classical equilibrium conditions are not valid in the case of fast propagation of sharp phase interfaces through the material during a stress-induced martensitic phase transformation. We propose to extend the equilibrium conditions to the non-equilibrium case in the framework of the thermodynamics of discrete systems. To provide the description of non-equilibrium states, the thermodynamic state space includes so-called contact quantities in addition to usual local equilibrium variables.

A system of uniform temperature in contact with a thermal bath must be heated in a fixed time interval between given initial and final temperatures. Several ways of defining the lost work associated with the heating process are presented. The minimum entropy generation is generally not equivalent to the minimum lost available work. Two optimal control problems are defined and solved for various heat transfer mechanisms, among them Newtonian heat convection and radiative heat transfer. The optimal paths are obtained for both objective functions (i.e., entropy generation and lost available work). The results of the optimal strategies are different from those associated with the usual industrial heating strategy that keeps a constant heat reservoir temperature. Much better results are obtained by using another simple heating procedure, namely the constant heat flux strategy. The difference between various heating strategies is higher in the case of Newtonian convection than in the case of radiative heat transfer and increases by increasing the final temperature of the heating process. The analytical expressions of the optimal paths are presented in dimensionless form, allowing easy implementation.

Liquid crystals of uniaxial and biaxial molecules are considered in the framework of the mesoscopic description which is a general tool of continuum theory. A mesoscopic theory introduces the fields beyond hydrodynamics as additional variables of a configuration space, called mesoscopic space, on which the fields appearing in balances are defined. Besides the mesoscopic space, a mesoscopic distribution function is introduced which describes the distribution of the additional variables at each time and position. It is demonstrated, how the mesoscopic theory can be applied to liquid crystals, and how the Ericksen-Leslie theory and the alignment tensor theory of liquid crystals fit into the mesoscopic framework.