Search

The article presents a review of works on mathematical modelling of biomass pyrolysis process. Models types, number of dimensions, captured phenomena, type and dimensions of the reactors and biomass particles as well as models validation methods were analysed. Particular attention was paid to descriptions of chemical reactions, which are the essence of biomass thermal decomposition simulation. The article briefly describes the most important issues related to biomass pyrolysis and provides a review of commonly used methods of modelling this process with emphasis on solutions "ready to employ" in CFD modelling. A summary of other review papers on this topic is also provided. The problem of mathematical modelling in the context of "model - an engineering tool" was also discussed. Mathematical model for an engineering applications must be prepared with consideration of necessary consensus between the calculations accuracy, calculation time, preparation efforts and analysis requirements. Therefore, in pyrolysis modelling context, the inclusion of chemical reactions and changes of heat transport conditions were considered as priority, while taking into account moisture evaporation and bed shrinkage should be conditioned by their actual contribution in the calculations accuracy and by their influence on the calculations time. • A review of research on mathematical modelling of biomass pyrolysis is presented. • Captured phenomena, kinetic models, properties change, reactor types are summarized. • Compromise between model precision and calculations costs is discussed. [ABSTRACT FROM AUTHOR]

This paper presents the computational fluid dynamics (CFD) model of small-scale a-type Stirling engine. The developed mathematical model comprises of unsteady Reynolds averaged Navier-Stokes set of equations, i.e., continuity, momentum, and energy equations; turbulence was modeled using standard Κ-ω model. Moreover, presented numerical model covers all modes of heat transfer inside the engine: conduction, convection, and radiation. The model was built in the framework of the commercial CFD software ANSYS FLUENT. Piston movements were modeled using dynamic mesh capability in ANSYS FLUENT; their movement kinematics was described based on the crankshaft geometry and it was implemented in the model using user-defined functions written in C programming language and compiled with a core of the ANSYS FLUENT software. The developed numerical model was used to assess the performance of the analyzed Stirling engine. For this purpose, different performance measures were defined, including coefficient of performance (COP), exergy efficiency, and irreversibility factor. The proposed measures were applied to evaluate the influence of different heating strategies of the small-scale α-type Stirling engine. [ABSTRACT FROM AUTHOR]

The paper presents numerical analysis of heat transfer in the human forearm and influence of its internal structure on the temperature distribution inside. For this purpose three geometrical models of a human forearm were developed: model containing continuous muscle tissue only, model in which muscle tissue and bones were considered and model which contained muscle tissue bones and main blood vessels. In those models heat transfer in the muscle tissues and bones were described by Pennes bioheat equation, while for blood flowing through main vessels (artery and vein) full set of governing equations were solved. Moreover, simplified one-dimensional description of skin was developed in order to reduce model complexity. Results obtained with all models were confronted against each other to reveal influence of the main blood vessels on the temperature distribution in a forearm. [ABSTRACT FROM AUTHOR]

In many engineering applications one can find periodically variable gas temperatures. Possible examples include the temperature inside the cylinders of Stirling Engines and other reciprocating machines. New methods are proposed and evaluated for the measurement of periodically varying temperature by thermocouples. A Computational Fluid Dynamics model is created to assess the method viability and efficacy in a realistic setting while avoiding measurement errors. The first method is based on matrix analysis, the two others on the particle filter algorithm used to estimate either the heat transfer coefficients with the additional use of other flow information, or to estimate the thermocouple constants without said information. It is shown that the matrix method is sufficient for cases with constant velocities. For variable velocities, the PF algorithm shows promising results as based on measurements generated from the numerical simulation. • Periodic gas temperature measurement is treated as an inverse heat transfer problem. • Two-thermocouple mechanistic solutions are generalized into an overdetermined system. • Application of 'Particle filter', utilizing other heat transfer information. • Methods are tested using CFD generated measurement data. • Particle Filter provides a high quality reconstruction of the actual temperature. [ABSTRACT FROM AUTHOR]

A 2D transient model of coupled heat and mass transfer phenomena occurring in a single coke chamber is developed. The interior of the chamber is partially filled by the coal charge, which is assumed to be a porous media. The standard equations of continuity, species transport, momentum and energy describing the flow of the single-phase fluid are applied. The model considers a range of aspects associated with the carbonization process, such as the evaporation and condensation of the water, the evolution of the volatile components, the change in the density and the flow resistance during the coking process. Conductive, convective and radiative types of heat transfer are included in the model. The model also provides for the creation of the lateral gap near the walls. Water evaporation and condensation are modeled with the modified Hertz–Knudsen equation linked to the sorption isotherm. The model of the specific process is implemented in the commercial CFD software ANSYS Fluent. Results of the CFD simulation are compared with thermocouple measurements performed at the Centre de Pyrolyse de Marienau test unit. Commonly known information regarding raw gas evolution and energy consumption are also used for validation purposes. The model agrees well with both experimental data and data from the literature. [ABSTRACT FROM AUTHOR]

• A zero dimensional model of an α type Stirling engine is created and explained. • Heat transfer models for internal convection in the engine are compared. • Those correlations are implemented in the model and the results are shown. • It is found the models produce starkly different results. In the paper the authors present a zero-dimensional model of an alpha type Stirling engine and special consideration is paid to the problems of the evaluation of internal heat transfer between the heat exchange surfaces and the working fluid. Furthermore, a thermodynamic model of the engine, developed by the authors is shown. The model can be classified as zero-dimensional. Energy and mass conservation equations are written in a differential form, and solved for finite time steps for control volumes, that is the expansion cylinder, the compression cylinder, the regenerator, the regenerator matrix and the engine as a whole, which allows to transform the differential equations into a solvable system of algebraic equations. Unlike most models shown in literature, the one created by the authors evaluates the gas properties based on a real gas model. The impl ementation of a real gas model further helps to evaluate parameters such as viscosity and thermal conductivity of the gas, which is necessary for calculating the heat transfer coefficients. Those are calculated for each volume from known correlations, for a given moment in time. That is, the gas parameters needed are not evaluated as an average for the stroke, rather, they are calculated from instantaneous gas parameters and implemented as variables in the energy equations. The engine working fluid is atmospheric air. The influence of different heat transfer models on the predicted engine performance is shown in the form of engine characteristics for different models, based on variables such as pressure, and rotational. It can be shown, that further research into in-cylinder heat transfer is necessary, as the established models, when implemented into the Stirling engine, predict starkly different engine performance. Furthermore, non-physical results based on those models are shown. [ABSTRACT FROM AUTHOR]