Numerical Simulation Of A Pulse Combustion Spray Drying Process

Pulsating spray drying technique makes use of the unstable hot gas stream generated by a pulse combustor to atomi/e and dry a liquid material. The unstable gas stream is characterized by oscillations with transient velocities of about +100 m/s and frequencies from 50-200H/. The enhanced mixing and transport processes lead to a highly efficient moisture evaporation rate during pulsating spray drying. The computational fluid dynamics (CFD) method was used for the analysis and investigation of flow,temperature and humidity fields in a pulsating flow spray-drying chamber.(1) The CFD model for the pulse combustion spray drying process.The Computational Fluid Dynamics (CFD) based on the two-phase flow theory was employed in this paper,which used the Standard k- e model and the Particle trajectory Model to simulate the gas-particle flow in the drying chamber. The momentum,heat and mass transfer regarding both gaseous and particulate phases during the spray drying inside the drying chamber was also revealed. The simulated profiles of flow field,temperature and humidity of the air phase,as well as particulate phase,in the drying chamber were showed. The simulation also showed that a large-scale vortex was observed in upper part of the drying chamber because of the unstable process of flow field and particle trajectories.(2) The explicit simulating process for the pulse combustion spray drying processIn this project,both the gas-phase equations and particle-phase equations were integrated in the computational cell using up-wild scheme to obtain the finite difference equations. The gas-phase equations are solved using the SIMPLER algorithm and multiple iterations have been made based on a two-way coupling (LEGAML algorithm).(3) Comparison of the experimental data with the simulation resultsA pulse combustion spray drying system was constructed and the spray drying of NaCl solution was carried out under a high oscillating flow field generated by the pulse combustor. The particle deposition which was observed in the simulation results and verified by the experiment and The comparison of the air experimental data with simulation data showed that the CFD model is a feasible way to simulate the spray drying process.(4) The influence of pulsation frequency on the drying processTwo special cases,in which the selected pulsation frequencies were 0 H/,and 83 H/ respectively,were simulated and their simulation results indicated that the pulsating frequency of gas stream could improve the intensities of the heat and mass transfer during a pulse combustion spray drying process.