A practical CFD modeling approach to estimate outlet boundary conditions of industrial multistage spray dryers: Inert particle flow field investigation

Abstract

Industrial multistage spray drying systems often have limited in situ process measurements to provide sufficient information for computational fluid dynamics (CFD) simulations of the primary drying chamber. In this case study on the spray dryer at Davis Dairy Plant (South Dakota State University), uncertainties were encountered in specifying the outlet boundary conditions of the spray drying chamber with two outlets: the side outlet and the bottom outlet leading to the second stage external vibrating bed. Using the available data on the vacuum pressure of the chamber, a numerical framework was introduced to approximate suitable outlet boundary conditions for the drying chamber. The procedure involved analyzing the ratio of the airflow rate between the two outlets and using a pseudo-tracer inert particle injection analysis. The goal of this approach was to determine a suitable range of outlet vacuum pressure that will lead to realistic particle movement behaviors during the actual plant operation. The protocol developed here will be a useful tool for CFD modeling of large scale multistage spray drying systems.

Implementation of P-Controller in Computational Fluid Dynamics (CFD) Simulation of a Pilot Scale Outlet Temperature Controlled Spray Dryer

“…[7]. The details of mesh dependency is described in [6]. Boundary condition for air inlet was mass flow inlet that was entered according to the manufacturer's blower air flow specifications (mass flow rate=1.1 kg/s).…”

“…This approach allowed numerical capturing of the negative pressure within the drying chamber. The pseudo tracer analysis and how to predict the bottom outlet pressure is explained in [6]. Convergence criteria was 1x10 -3 for all scaled residuals.…”

“…The bottom outlet pressure was unknown. Simulation of airflow and particles trajectories ratios between two outlets revealed that the -250 Pa pressure would be a reliable prediction for the bottom outlet [6].…”

Numerical Study on Spray Drying Process: Effect of Nonuniform Temperature Field and Interaction between Droplets on Evaporation Rates of Individual Droplets

“…20) In addition, the effect of drying condition and the drying tower geometry on the fluid behavior and droplet trajectory have been investigated. [21][22][23][24][25] Recently, the CFD studies that considered the collision between droplets (or particles) and deposition on a spray dryer wall have increased, and the importance of the boundary condition between a particle and wall has been discussed. [26][27][28][29][30] Previous studies have primarily focused on a single droplet drying or the overall fluid and droplet drying behaviors inside a spray dryer.…”