A Global Second Law Approach to the Evaluation of Energy Conversion Systems Taking into Account Economic and Environmental Factors

In the design and/or performance analysis of an energy conversion system, there are two factors other than the thermodynamic operation of the system which play an important role. They are the economis of the capital equipment used in the cycle and the past effects of the cycle (i.e., the construction of the capital equipment) and present and future effects of the cycle (i.e., its operation and the recycling of any used-up capital equipment) on the environment. All three factors - the thermodynamics, the economics and the environmental effects - are presently taken into account to some degree or another at different stages in the analysis of such a system. However, they are only considered separately or in some limited combination or not at all, since a consistent methodoligy which combines all of them into a single entity or tool is lacking. The purpose of our proposal is to develop such a methodology, providing a framework simple enough to be practical yet sufficiently consistent with good engineering practice and the complexities involved in this type of modelling. As a base, we will use some of the extensive work which has already been done in the literature by the authors themselves and others

Analyse exergétique théorique et expérimentale du corps humain.

Human body is the place of irreversibilities related to entropy increase, due to internal operations which is always positive according to the second principle of thermodynamics. Exergy analysis, based on first and second principles, quantifies these irreversibilities and enlightens differently the biological processes. Exergy computation requires the knowledge of body composition, which has been obtained by Magnetic Resonance Imaging. Direct and indirect calorimetric measurements enable to determine the energy transfers between the body and its surroundings, as well as the metabolism. A model of the human body at rest, whith thirteen components and three temperature levels has been developed. Results show that energy losses (convection, sweating) are high when the corresponding exergy contributions are zero or very small. Moreover the values of the exergetic and energetic metabolisms are very close. Finally the exergy yield of a man at rest is zero

The Performance Optimization of a Gas Turbine Cogeneration / Heat Pump Facility with Thermal Storage

With the push for greater energy conservation, the need for heating and/or power production is being filled by cogeneration facilities. Thus, the search for the best performance at the least cost for such multipurpose plants is made much more difficult by the fact that such facilities must meet differing goals or demands. Such a facility exists at the Ecole Polytechnique Fédérale de Lausanne (EPFL) and has been studied in order to find the optimum modes of operation as a function of time for variations in both the heating and electrical demands this facility must meet. The results of this study are presented here. The plant itself provides heat and electricity for both the EPFL and the University of Lausanne and is projected to supply electricity to the exterior utility grid provided it can be shown to be economically viable. The plant’s primary components include two gas turbines, a heat recovery system, two heat pumps, a set of heat storage tanks, and both medium and low-temperature district heating networks. In order to find the optimum mode of operation, a mixed-integer linear programming approach was used, which balances the competing costs of operation and minimizes these costs subject to the operational constraints placed on the system. The effects of both the cost of the fuel and the costs of electricity sold and bought on the best performance of the system are evaluated. In addition, the important features of the modeling process are discussed, in particular the heat storage tanks, which complicate the optimization of the series of steady-state models used to model the overall quasi-steady-state behavior of the system

Analyse exergétique théorique et expérimentale du corps humain

Human body is the place of irreversibilities related to entropy increase, due to internal operations which is always positive according to the second principle of thermodynamics. Exergy analysis, based on first and second principles, quantifies these irreversibilities and enlightens differently the biological processes. Exergy computation requires the knowledge of body composition, which has been obtained by Magnetic Resonance Imaging. Direct and indirect calorimetric measurements enable to determine the energy transfers between the body and its surroundings, as well as the metabolism. A model of the human body at rest, whith thirteen components and three temperature levels has been developed. Results show that energy losses (convection, sweating) are high when the corresponding exergy contributions are zero or very small. Moreover the values of the exergetic and energetic metabolisms are very close. Finally the exergy yield of a man at rest is zero