Modelling and numerical computation of droplet behaviour in spray drying equipment
Modelling and numerical computation of droplet behaviour in spray drying equipment
The numerical computation of spray dryers shall be performed with the Euler/Lagrange approach using turbulence modelling based on RANS (or URANS) or LES. One option would be to use the in house code FASTEST/Lag3D which incorporates the most advanced Lagrangian approach for simulating the particle phase. The models available in the Lagrangian calculation are:
- Turbulent dispersion models (isotropic and un-isotropic)
- LES sub-grid dispersion model
- All relevant forces, e.g. drag transverse lift, added mass and pressure term (Sommerfeld et al. 2008)
- particle-wall collision modelling with wall roughness (not for droplets), see Sommerfeld and Huber (1999)
- stochastic inter-particle collision model (Sommerfeld 2001)
- Different types of agglomeration models (volume equivalent sphere model and structure model, see Stübing et al. 2011)
However, FASTEST is a block-structured finite volume code which often runs into problems if complex geometries are considered. Alternatively the open source code OpenFoam may be used for the project. This however would imply the implementation of all relevant Lagrangian models in OpenFoam.
The main emphasis of the present project is related to the consideration of a reliable model for describing the evaporation of suspension or solution droplets under conditions relevant for spray dryers. Different models available in literature shall be tested and validated. Most relevant are the models of Farid (2003), Nesic and Vodnik (1991) and Sano and Keey (1982). Other more recent models may be also considered. For validating the models, a laboratory-scale simplified spray dryer is available, allowing air temperatures up to about 100°C. Measurements can be conducted by Phase-Doppler anemometry as well as high-resolution imaging methods.
In a later stage also droplet collision and coalescence models shall be implemented, based on micro-scale measurements performed at the institute presently (Kröner and Sommerfeld 2010). The basis of collision modelling shall be the stochastic approach of Sommerfeld (2001). Experimental data for validation can be also obtained with the laboratory spray dryer.
References
Farid, M.: A new approach to modelling of single droplet drying. Chemical Engineering Science Vol. 58, 2985-2993(2003)
Kröner, M. and Sommerfeld, M.: Experimental investigation of droplet collisions with higher viscosity. CD-ROM Proceedings ILASS – Europe 2010, 23rd Annual Conference on Liquid Atomization and Spray Systems, Brno, Czech Republic, September 2010
Nesic, S. and Vodnik, J.: Kinetics of droplet evaporation. Chemical Engineering Science, Vol. 46, 527-537 (1991)
Sano, Y. and Keey, R.B.: The drying of a spherical particle containing colloidal material into a hollow sphere. Chemical Engineering Science, Vol. 37, 881-889 (1982)
Sommerfeld, M. and Huber, N.: Experimental analysis and modelling of particle-wall collisions. International Journal of Multiphase Flow, Vol. 25, 1457-1489 (1999)
Sommerfeld, M.: Validation of a stochastic Lagrangian modelling approach for inter-particle collisions in homogeneous isotropic turbulence. International Journal of Multiphase Flows, Vol. 27, 1828-1858 (2001)
Sommerfeld, M., van Wachem, B. and Oliemans, R.: Best Practice Guidelines for Computational Fluid Dynamics of Dispersed Multiphase Flows. ERCOFTAC (European Research Community on Flow, Turbulence and Combustion, ISBN 978-91-633-3564-8 (2008)
Stübing, S., Dietzel, M. and Sommerfeld, M.: Modelling agglomeration and the fluid dynamic behaviour of agglomerates. Proceedings of ASME-JSME-KSME Joint Fluid Engineering Conference 2011
(AJK2011-FED) July 2011, Hamamatsu, Shizuoka, Japan, Paper No. AJK2011-12025.