Papers by Keyword: Irreversibility

Abstract: The minimization of the entropy generation is fundamental for the thermodynamic design. Based on theoretical relations contained in the references [1,2,3,4], a numerical simulation program of the entropy flow generated at the flow with friction and heat exchange was developed, whose results are included herein. From their analysis it is clear that between irreversibility and design parameters there isn’t a monotonous dependence, and that, by the mere intuition, without a directed concern, we cannot predict the effect of a design change on the global configuration of irreversibility.

Abstract: Generating entropy is a measure of the irreversibility of a system or of its component. Any measure for minimizing the generation rate of entropy in a component of a system leads to reducing the irreversibility of the system’s assembly. We are interested into the entropy generation minimization procedure, which is the basis of the thermodynamic design.

Abstract: Modern internal combustion (IC) engines employ a variety of injection techniques for preparing a combustible mixture of fuel and air. In a fuel injection-based system, the vaporization of the atomized hydrocarbon fuel droplets has significant influence on engine performance and emissions. The entropy generation associated with droplet vaporization is particularly important as it is directly related to the destruction of exergy i.e. the potential to produce useful work. Since a fuel spray could involve millions of droplets, solving the entire set of governing equations for individual droplets in a spatiotemporally discretized domain is impractical. The present work explores the utility of a simple phenomenological model in predicting the entropy generation history. The results indicate that this model ensures computational efficiency without much sacrifice in accuracy.

Abstract: In this paper, a generalized irreversible heat pump driven by steam turbine cycle model was established by taking account of the heat resistances, heat leak and irreversibility due to the internal dissipation of the working substance. The heat transfer between the heat reservoir and the working substance is assumed to obey the linear (Newtonian) heat transfer law, and the overall heat transfer surface area of the assumed to be constant. The fundamental optimal relations between the heat load, the thermal coefficient of the system and the temperature difference of the evaporator are obtained. Moreover, the effects of the cycle parameters on the characteristics of the cycle are studied by numerical example. The results obtained herein have realistic significance and may provide some theoretical guidance for the performance improvements and optimizations of heat pumps driven by steam turbine.

Abstract: The general cycle model of a class of external combustion engines is established in which the influence of the multi-irreversibilities mainly resulting from the linear heat-loss model between the high and low heat reservoir, and the irreversible adiabatic processes. Some important parameters such as the power output, efficiency and the temperatures of the working substance are calculated and some important characteristic curves are given. The results obtained in this paper may provide some theoretical guidance for the optimal design of the Carnot, Brayton, Braysson and some new heat engines.

Abstract: In this paper, symbolic relative entropy was used to analyze the average energy dissipation of epilepsy electroencephalagram (EEG) signals and normal electroencephalagram signals. Hypothesis testing showed that the average energy dissipation of epilepsy electroencephalagram signals was distinctly higher than that of normal electroencephalagram signals. It discoved that symbolic relative entropy can be used to analyze the irreversibility of time series and to assess the health state of human brain. It can be used to assisted clinical diagnosis.

Abstract: Analysis of the flow loss is important in the turbomachinery, the current analysis methods based on the cumulative loss such as the total pressure loss coefficient and the adiabatic efficiency, and the local loss method reflect the loss, can’ t quickly reflect the physical principles that leads the loss and its’ development. To solve this problem, the paper based on the first and second laws of thermodynamics, a local losses model about the compressor internal flow was estimated using the entropy gradient, give a dimensionless loss function parameter I , and was verified in a three-dimensional numerical simulation about Rotor67. The numerical results show that: the model can quickly capture the magnitude and location of loss, it also can reflect the loss source, when the dimensionless parameter , the area is considered as an high loss area, the local loss is expressed as I. If the parameter near the wall for negative value indicates that reflux occurred.

Abstract: The objective of this work is to present an exergy analysis of a novel absorption configuration using water-ammonia as working fluid. The proposed configuration operates at three pressure levels. The absorber is at an intermediate pressure (Pint). A thermodynamic model based on the mass energy and exergy balances is developed for this purpose. The parameters analyzed are the refrigeration systems performance (COP), the exergy efficiency, the global exergy destruction in the system, the exergy destruction and the irreversibility in different components. The effects of generator, absorber, condenser and evaporator on the performance of the system are examined. Numerical results highlight the great importance of the intermediate pressure on the performance of the system and specially on reducing the operating generator temperature. Consequently, the intermediate pressure is directly responsible on the adaptability of the proposed cooling absorption cycle to low enthalpy sources.

Abstract: Self-formation concept as a generalization of the huge number of technologies in microelectronics was defined. Self-formation as irreversible evolution, causing self-increasing of an object complexity, is presented. Differential equation method allows description of evolution of any figures contour. Numerical model of self-formation in essence is a cellular automata of the second kind. Neither analytical nor numerical models did not involve causes of contour evolution. However causes of evolution are hidden in interactions of parameters which approximate an object and ambient materials. On the basis of above-mentioned factors, the right-dimensional topological space was created. It is the Cartesian product of the eight sets, including three Euclidean space axes, four parameter axes (defining parameters of the Euclidean points and interaction matrix) and time axis. Self-formation is a result of non-homogeneous mapping sequence in time. On the other hand non-homeomorpheous mapping indicates irreversibility of an evolution. Evolution is irreversible in time if only the object either contains the peculiar points or they arise under evolution. Therefore an interaction, defining the figure evolution out-side, does not return the object to initial state after its diversion inside and can implicate the complexity increasing. The new self-formation technologies for electron devices and integrated circuits manufacturing were carried out. Topological approach allows analysis and synthesis of real world structures, known in the areas of microelectronics, nanotechnology, photovoltaics and fuel cell technology, possibly in living world (genes, cells, organs, organism) as well. Problems remaining to be investigated are presented.