Mixtures of Ideal Gases

This paper is Part I of a study concerned with developing a formal framework for modelling air-cooled gas turbine cycles and deals with basic thermodynamic issues. Such cycles involve gas mixtures with varying composition which must be modelled realistically. A possible approach is to define just two components, air and gas, the latter being the products of stoichiometric combustion of the fuel with air. If these components can be represented as ideal gases, the entropy increase due to compositional mixing, although a true exergy loss, can be ignored for the purpose of performance prediction. This provides considerable simplification. Consideration of three idealised simple cycles shows that the introduction of cooling with an associated thermal mixing loss does not necessarily result in a loss of cycle efficiency. This is no longer true when real gas properties and turbomachinery losses are included. The analysis clarifies the role of the cooling losses and shows the importance of assessing performance in the context of the complete cycle. There is a strong case for representing the cooling losses in terms of irreversible entropy production as this provides a formalised framework, clarifies the modelling difficulties and aids physical interpretation. Results are presented which show the effects on performance of varying cooling flowrates and cooling losses. A comparison between simple and reheat cycles highlights the rôle of the thermal mixing loss. Detailed modelling of the heat transfer and cooling losses is discussed in Part II of this paper.

Download Full-text

Development and Application of a Simulation Tool for Biomass Gasification Based Processes

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.1769 ◽

2008 ◽

Vol 6 (1) ◽

Cited By ~ 19

Author(s):

Tobias Pröll ◽

Hermann Hofbauer

Keyword(s):

Background Information ◽

Simulation Tool ◽

Water Steam ◽

Organic Mixtures ◽

Ideal Gases ◽

Dual Fluidized Bed ◽

Modelling Environment ◽

Model Equations ◽

Key Aspects ◽

Energy Balances

A simulation tool for gasification based processes is presented for an equation-oriented, steady state modelling environment. The approach aims at an adequate description of phenomena linked to gasification. Background information is provided regarding the structure of the framework, thermodynamic data processing, and on the formulation of the model equations. The implemented substance streams are water/steam, ideal gases, inorganic solids, and organic mixtures. The models are based upon mass and energy balances and feature thermodynamic considerations. The addition of correlations for fluid dynamics or chemical kinetics is generally possible but not within the focus of this paper. The key-aspects of the typical unit-models, like pumps, turbines, heat exchangers, separators and chemical reactors are highlighted. The model of a dual-fluidized bed biomass gasifier is presented in detail. In a final case study, the suitability of the simulation tool is demonstrated for the description of the gasification-based biomass combined heat and power plant in Güssing/Austria.

Download Full-text

Continuum Thermodynamics of Constrained Reactive Mixtures

Journal of Biomechanical Engineering ◽

10.1115/1.4053084 ◽

2021 ◽

Author(s):

Gerard A. Ateshian ◽

Brandon Zimmerman

Keyword(s):

Heat Supply ◽

Damage Mechanics ◽

Reactive Power ◽

Mixture Theory ◽

Biological Tissues ◽

Heat Of Reaction ◽

Chemical Potentials ◽

Ideal Gases ◽

Reactive Processes ◽

Energy Of Formation

Abstract Mixture theory models continua consisting of multiple constituents with independent motions. In constrained mixtures all constituents share the same velocity but they may have different reference configurations. The theory of constrained reactive mixtures was formulated to analyze growth and remodeling in living biological tissues. It can also reproduce and extend classical frameworks of damage mechanics and viscoelasticity under isothermal conditions, when modeling bonds that can break and reform. This study focuses on establishing the thermodynamic foundations of constrained reactive mixtures under more general conditions, for arbitrary reactive processes where temperature varies in time and space. By incorporating general expressions for reaction kinetics, it is shown that the residual dissipation statement of the Clausius-Duhem inequality must include a reactive power density, while the axiom of energy balance must include a reactive heat supply density. Both of these functions are proportional to the molar production rate of a reaction, and they depend on the chemical potentials of the mixture constituents. We present novel formulas for the classical thermodynamic concepts of energy of formation and heat of reaction, making it possible to evaluate the heat supply generated by reactive processes from the knowledge of the specific free energy of mixture constituents as well as the reaction rate. We illustrate these novel concepts with mixtures of ideal gases, and isothermal reactive damage mechanics and viscoelasticity, as well as reactive thermoelasticity. This framework facilitates the analysis of reactive tissue biomechanics and physiological and biomedical engineering processes where temperature variations cannot be neglected.

Download Full-text