Combustion fluid mechanical models

Appendix B consists of a systematic classification and review of conceptual models (physical models) in the context of PBC technology and the three-step model. The overall aim is to present a systematic overview of the complex and the interdisciplinary physical models in the field of PBC. A second objective is to point out the practicability of developing an all-round bed model or CFSD (computational fluid-solid dynamics) code that can simulate thermochemical conversion process of an arbitrary conversion system. The idea of a CFSD code is analogue to the user-friendly CFD (computational fluid dynamics) codes on the market, which are very all-round and successful in simulating different kinds of fluid mechanic processes. A third objective of this appendix is to present interesting research topics in the field of packed-bed combustion in general and thermochemical conversion of biofuels in particular. 

Smirnov, N.N., V. F. Nikitin, J. Klammer, R. Klemens, P. Wolanski, and J. C. Legros. 1997. Turbulent combustion of air-dispersed mixtures Experimental and theoretical modeling. Experimental Heat Transfer, Fluid Mechanics Thermodynamics 4 2517-24. 

Typically, a fire growth model is evaluated by comparing its calculations (predictions) of large-scale behavior to experimental HRR measurements, thermocouple temperatures, or pyrolysis front position. The overall predictive capabilities of fire growth models depend on the pyrolysis model, treatment of gas-phase fluid mechanics, turbulence, combustion chemistry, and convective/radiative heat transfer. Unless simulations are truly blind, some model calibration (adjusting various input parameters to improve agreement between model calculations and experimental data) is usually inherent in published results, so model calculations may not truly be predictions. 

FIGURE 20.6 Comparison of measured and modeled HRR in room/corner test on plywood. From Moghaddam et al. [96] for ethanol reaction case. (Adapted from Moghaddam, A.Z. et al., Fire behavior studies of combustible wall linings applying fire dynamics simulator, in Proceedings of the 15th Australasian Fluid Mechanics Conference, Sydney, Australia, 2004.)... 

For the first two cases Da << 1 (slow reactions) and Da >> 1 (very fast reactions) adequate closure models are available in many commercial CFD codes. For the third case, where the time scale for chemical conversion approximately equals the time scale for turbulent micromixing, moment methods are inappropriate and other methods should be used. In this situation the reactor performance may be significantly affected by mixing efficiency. Here the engineer is faced with the difficult problem of predicting the overall conversion and/or selectivity of the chemical process. In the last three decades this problem has received considerable attention in three scientific areas, namely, chemical reaction engineering, fluid mechanics and combustion, and various approaches have been followed. 

Guido Troiani, PhD, is a researcher in combustion and fluid-mechanics at ENEA (Rome, Italy) where he has been since 2006 as a postdoctorate. He received his degree in fluid mechanics from the Faculty of Engineering of the University of Rome "La Sapienza" (2004). He began his postdoctoral research at the University of Rome "La Sapienza" in cooperation with the Italian Ship Model Basin (INSEAN), performing experiments and theoretical analysis on free-surface turbulence and on the transition to turbulence of laminar flows. Successively he was employed as postdoctorate at the ENEA research center in the field of turbulent combustion. His main topics... 

Volume B1 Fundamentals of Chemical Engineering contains chapters on mathematical and numerical methods, modelling, transport phenomena, fluid mechanics, the estimation of physical properties, combustion. 

Wamatz J, Allendorf MD, Kee RJ, Coltrin ME A model of elementary chemistry and fluid-mechanics in the combustion of hydrogen on a platinum surfaces. Combust Flame 96 393-406, 1994a. 

Today, CAD/CAM simulations as a tool to estimate performanee of various systems, reduce costs and testing time is taken into consideration. In this study speeified engine and its components have been simulated by GT-POWER software carefully. Modeling of software is based on fluid mechanics laws, thermodynamic laws, mass conservation law, equilibrium reactions, and chemical kinetics. In particular, combustion simulation of this software is based on one... 

Using these methods, the elementary reaction steps that define a fuel s overall combustion can be compiled, generating an overall combustion mechanism. Combustion simulation software, like CHEMKIN, takes as input a fuel s combustion mechanism and other system parameters, along with a reactor model, and simulates a complex combustion environment (Fig. 4). For instance, one of CHEMKIN s applications can simulate the behavior of a flame in a given fuel, providing a wealth of information about flame speed, key intermediates, and dominant reactions. Computational fluid dynamics can be combined with detailed chemical kinetic models to also be able to simulate turbulent flames and macroscopic combustion environments. 

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