Use of Computational Fluid Dynamics techniques to assess design alternatives for the plenum chamber of a small spray dryer

The inlet region of a pilot-scale, co-current spray dryer was simulated usi ng the proprietary Computational Fluid Dynamics (CFD) codes, CFX4 and CFX5. Several design alternatives were considered for correcting uneven inlet ai r distribution, which is known to influence spray dryer performance and air flow patterns. The simulations were used to assess each alternative prior t o construction, assuming isothermal and incompressible flow conditions. Exp erimental measurements were compared with the simulation results for the or iginal and one modified design. Drying air is supplied to this dryer via an overhead pipe feeding an annula r plenum chamber, of diameter 400 mm, surrounding the atomiser. A distribut or plate with two concentric rings of 50 holes, each of 5 mm diameter, form s the base of the plenum chamber. A three-dimensional grid was required to model each of the 100 holes separately and to consider the asymmetric flow behaviour. The resulting grid consisted of about 532,000 cells. The CFD sim ulations proved useful in predicting the trends in flow distributions in ea ch of the designs.