An introduction to endoreversible thermodynamics

Reversible thermodynamic processes are convenient abstractions of real processes, which are always irreversible. Approaching the reversible regime means to become more and more quasistatic, letting behind processes which achieve any kind of finite transformation rate for the quantities studied. On the other hand studying processes with finite transformation rates means to deal with irreversibilities 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. This material provides an introduction to the subject

Endoreversible Thermodynamics: A Tool for Simulating and Comparing Processes of Discrete Systems

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Endoreversible thermodynamics is concerned with reversible sub-systems that are in irreversible interaction with each other. Consequently, endoreversible thermodynamics represents the analogue for discrete systems to the local equilibrium hypothesis in continuum thermodynamics. Here a real cyclic 2-reservoir process is simulated by different endoreversible model processes. Simulation means that the simulating process has the same net heat exchanges, cycle time, power, entropy production, and efficiency as the original one. By introducing process-independent simulation parameters as constraints for the irreversible interaction, a family of comparative endoreversible processes is generated including the simulation of the original process. This procedure allows the process parameters of the family of comparative processes to be compared to those of the original one. The fraction “power of the real process over the maximal power inbetween the comparative family” is introduced as a parameter describing the process excellence

Die Entwicklung und Bewertung von managementunterstützenden Informationssystemen: Eine empirische Anwenderstudie

In dieser Arbeit werden der Entwicklungsprozeß und die damit verbundenen Bewertungen von managementunterstützenden Informationssystemen empirisch untersucht. Es zeigt sich, daß Kontextfaktoren, insbesondere die Initiatoren des Projektes, erheblichen Einfluß auf den Entwicklungsprozeß ausüben. Der Bewertungsprozeß wird in Hinblick auf die benutzten Kriterien, die eingesetzten Methoden und die Zufriedenheit mit der Bewertung analysiert. Dabei können theoretische Überlegungen und frühere empirische Ergebnisse weitgehend bestätigt werden, denen zufolge bei entscheidungsunterstützenden Systemen qualitativen Kriterien größere Bedeutung zukommt und nutzenorientierte Bewertungsmethoden besser geeignet sind.The paper describes the results of an empirical study on the development and evaluation of management support Systems in Germany. Contextual factors like the project initiator are found to have considerable influence on the development process. The evaluation of MSS is analyzed with respect to the criteria and methods employed and the level of satisfaction with the process. The results of previous studies are confirmed: in evaluating decision-oriented Systems, qualitative criteria are considered to be more important, and utility-oriented methods prove more suitable for this kind of evaluation

Drag on spheres in micropolar fluids with non-zero boundary conditions for microrotations

This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The Stokes formula for the resistance force exerted on a sphere moving with constant velocity in a fluid is extended to the case of micropolar fluids. A non-homogeneous boundary condition for the micro-rotation vector is used: the micro-rotation on the boundary of the sphere is assumed proportional to the rotation rate of the velocity field on the boundary.Peer Reviewe