**6. Conclusion**

The LES and DNS methods are more and more important recently. There are many SGS turbulent combustion models for LES. The algebraic sub-grid scale turbulent combustion is quite simple in expression, while it is successfully applied in partly diffusion jet flame and premixed after bluff body flame. The predicted temperature, species, velocity and RMS values are all close to the experimental data in the most regions.

**11**

*Germany* 

**Numerical Simulation of Dense**

Matthias Schreiber and Hans Joachim Krautz *Brandenburg University of Technology Cottbus* 

Teklay Weldeabzgi Asegehegn,

**Gas-Solid Multiphase Flows Using Eulerian-Eulerian Two-Fluid Model** 

Gas-solid fluidized beds are widely applied in chemical processes such as drying, combustion, synthesis of fuels, granulation, polymerization etc. They have several advantageous properties including; excellent heat and mass transfer, nearly isothermal conditions due to intense gas-solid mixing, large gas-solid surface area, smooth transport of solids, uniform solid product in batch processes, and possibility of continuous and largescale operations. On the other hand, these reactors have several drawbacks that provide a strong motivation for further studies and developments. These include; difficulty in scalingup and design, erosion of vessel and internals, formation of agglomerates, non-uniform products due to non-uniform solids residence time during continuous operation, and high particle entrainment. These drawbacks are bottlenecks for practitioners to reliably design and scale-up commercial fluidized bed reactors. The main reason for this is that the gassolid multiphase flow dynamics coupled with heat and mass transfer and chemical reactions

In bubbling gas-solid fluidized beds, bubble characteristics such as size, shape, velocity, distribution have a vital influence on the hydrodynamics of bed and hence on its performance as a chemical reactor and/or a heat exchange unit. The extent of gas-solid mixing and segregation, heat and mass transfer as well as reaction conversion are governed by the number, size and motion of bubbles passing through the bed (Kunii & Levenspiel, 1991). Therefore, fundamental understanding of the hydrodynamics of fluidized beds thereafter their heat and mass transfer as well as chemical conversion come only after a sound understanding of bubbling behaviour is achieved. However, prediction of bubble characteristics is extremely complex as bubbles can grow, coalesce, split or even disappear as they move from the distributor where they are formed to the top of the bed where they finally erupt. Moreover, bubble characteristics vary with geometric construction of the bed and operating conditions. In many applications, heat exchanger tubes are inserted to enhance the rate of heat and mass transfer and chemical conversion, control the operating temperature, promote good mixing and reduce gulf circulation of solids. In these systems, the bubbling behaviour is also strongly influenced by the geometry and arrangement of the internals (Yates et al., 1990; Hull et al., 1999; Asegehegn et al., 2011a). Therefore,

that occur in these systems are very complex and not yet fully understood.

**1. Introduction** 

A spectral method DNS is carried in a channel reaction flow. The results are used for turbulent model research. It is shown that the ASSCM SGS model value is close to the exact value mainly, so ASSOM model is reasonable again.

The ASOM RANS turbulent combustion model is tested by LES and DNS results. Though this model is simple, its value has same trend with the exact value and quite close to the exact value sometimes. It can give quick and roughly prediction for average parameters but not RMS value.

The correlations in turbulent combustion model are studied in DNS, the temperature fluctuation is very important. The RANS equations were modelled. The near wall damping modification can improve the prediction ability of SGS model.
