On the effect of turbulence models on CFD simulations of a counter-current spray drying process

Abstract

Accurate modeling of the flow field by means of capturing turbulence is crucial in CFD simulations. However, choosing the appropriate turbulence model remains quite challenging for simulating spray drying applications. Only a few studies have touched on this issue, although experimentally validated comparisons throughout the dryer are rare. This work aims to provide an assessment of five different turbulence models (RNG k−ε, standard, BSL and SST k−ω as well as transition SST) in terms of the predicted flow field throughout a lab-scale counter-current spray dryer. None of the tested models could initially provide a satisfactory match with locally measured temperatures within the chamber. The popular choice RNG k−ε model led to highest discrepancies, while the k−ω variants performed only slightly better. All these models under-predicted the dissipation of the central hot air jet. Modification to the k−ω variant’s characteristic constant to allow increased production of turbulence led to satisfactory agreement between the measurements and simulation results. Extended analysis revealed that different turbulence models produced significantly different drying histories. Only the k−ω SST variant with modified constant could provide predictions close to measured outlet particle moisture content and air conditions. The RNG model proved unsuitable due to unrealistic results with particle injection as well. The differences in predictions with injection among the models were attributed to different transient self-sustained air fluctuation behavior predicted within the chamber. This work will be useful in the selection of turbulence models which is fundamental to accurate CFD modeling of spray dryers.