Computational fluid dynamics boundary condition

Takeuchi et al. 7 reported a membrane reactor as a reaction system that provides higher productivity and lower separation cost in chemical reaction processes. In this paper, packed bed catalytic membrane reactor with palladium membrane for SMR reaction has been discussed. The numerical model consists of a full set of partial differential equations derived from conservation of mass, momentum, heat, and chemical species, respectively, with chemical kinetics and appropriate boundary conditions for the problem. The solution of this system was obtained by computational fluid dynamics (CFD). To perform CFD calculations, a commercial solver FLUENT has been used, and the selective permeation through the membrane has been modeled by user-defined functions. The CFD simulation results exhibited the flow distribution in the reactor by inserting a membrane protection tube, in addition to the temperature and concentration distribution in the axial and radial directions in the reactor, as reported in the membrane reactor numerical simulation. On the basis of the simulation results, effects of the flow distribution, concentration polarization, and mass transfer in the packed bed have been evaluated to design a membrane reactor system. 

Fortunately, numerical modeling despite its many limitations associated with grid resolution, choice of turbulence model, or assignment of boundary conditions is not intrinsically limited by similitude or scale constraints. Thus, in principle, it should be possible to numerically simulate all aspects of fires within canopies for which realistic models exist for combustion, radiation, fluid properties, ignition sources, pyrolysis, etc. In addition it should be possible to examine all interactions of fire properties individually, sequentially and combined to evaluate nonlinear effects. Thus, computational fluid dynamics may well provide a greater understanding of the behavior of small, medium, and mass fires in the future. 

Computational fluid dynamics (CFD) is essentially a computer-based numerical analysis approach for fluid flow, heat transfer and related phenomena. CFD techniques typically consist of the following five subprocesses geometrical modelling, geometry discretisation, boundary condition definition, CFD-based problem solving, and post-processing for solution visualisation. 

The use of computer generated solutions to problems and computational fluid dynamics is also another approach of comparing impellers and process results. There are software packages available. It is very helpful to have data obtained from a laser velocity meter on the fluid mechanics of the impeller flow and other characteristics to put in the boundary conditions for these computer programs. 

Fig. 10.8 Effect of interfacial boundary conditions on the predicted flow from a two-dimensional computational fluid dynamics ° model with a profiled tool, (a, b) Velocity vectors and the boundary at which the effective strain rate is 2 s b (c, d)...

This partial differential equation is deterministic by nature. In practice, however, many hydrodynamic phenomena (e.g., transition from laminar to turbulent flow) have chaotic features (deterministic chaos [Stewart 1993]). The reason for this is that the Navier-Stokes equation assumes a homogeneous ideal fluid, whereas a real fluid consists of atoms and molecules. Today highly developed numerical flow simulators (computational fluid dynamics, CFD) are available for solving the Navier-Stokes equation under certain boundary conditions (e.g.. Fluent Deutschland GmbH). These even allow complex flow conditions, including particle, droplet, bubble, plug, and free surface flow, as well as multiphase flow such as that foundin fluidized-bed reactors and bubble columns, to be treated numerically [Fluent 1998]. 

Measurements have been made of turbulence structure by a number of workers using laser-Doppler methods and using hot-film anemometry Application of computational fluid dynamics to turbulent flow in stirred tanks is developing rapidly and involves using assumptions inherent in Kolmogoroff s theory and turbulence measurements to supply boundary conditions. 

Hauptmanns U (2012) Do we really want to calculate the wrong jnoblem as exactly as possible The relevance of initial and boundary conditions in treating the consequences of accidents. In Schmidt J (ed) Safety technology—applying computational fluid dynamics. Wiley-VCH, Weinheim... 

The immersed boundary method is a numerical method in computational fluid dynamics where the flow boundary, e.g., the surface of a solid body in contact with the fluid or the interface between two immiscible fluids, is immersed in the mesh that does not conform with the boundary. In the immersed boundary method, special treatment has to be taken at the boundary to incorporate the boundary conditions. 

The same authors developed this model further by transforming the volumetric catalyst layer source terms into interfacial boundary conditions for a full three-dimensional fuel-cell model [23]. The catalyst surface is represented as a two-dimensional plane, which is coupled to computational fluid dynamics (CFD) code. The modeling domain includes a channel pair with ribs and MEA. 

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