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Mohsin October 25, 2011 05:34

Drying of particles
I am simulating a 3D spray dryer in FLUENT 13 using DPM model (Euler-Lagrangian Approach). Hot N2 enters the dryer in order to dry the solution and to provide swirl motion for proper mixing and heating of the solution (dissolved solution of N-Methyl-2-pyrrolidone (C5H9NO) and Coal). After the initial flow field of N2 is established and simulated, the solution needs to be sprayed into the dryer from the nozzle. The aim of the work is to simulate the drying kinetics of the droplet. Somewhat similar to the drying of milk powder in spray dryers.

After being injected into the dryer, the solution heats up due to the surrounding N2. The liquid N-Methyl-2-pyrrolidone (C5H9NO) evaporates from the solution leaving behind solid coal particles (which will be collected at the bottom of the dryer) whereas the N-Methyl-2-pyrrolidone (C5H9NO)vapors will leave the domain from the dryer’s outlet.

Could you please put some light on the following issues encountered by me on this problem?

1. In “species transport" or "materials" panel, how to define the mixture material (solution of N-Methyl-2-pyrrolidone (C5H9NO) and Coal)? As mentioned earlier, the domain also has N2 which has the largest mass fraction.

2. The problem seems to be complicated (dissolved single phase solution will enter into the domain and it will be converted into solids and vapor during drying). I may need to write a UDF to solve this (for the formation of solids during drying and evaporation of N-Methyl-2-pyrrolidone(C5H9NO) from the dissolved solution). However, to make it simpler, at first; I may consider the coal particles as a suspension not a solution. For suspension, I need to inject 2 phases (solid suspension in liquid) in the domain rather than 1 phase (solution-containing dissolved coal). In this method, the liquid will evaporate from the surface of the solid particle (suspension) leaving behind only the solid particles. For this problem, would FLUENT’s in built evaporation model help me or I'd still need to write a UDF to solve this issue.

Mohsin Mukhtar

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