Hamid Reza Norouzi

Continuous crystallization of lovastatin from a lovastatin-methanol solution and water as the anti-solvent in an impinging jet crystallizer is investigated using a computational fluid dynamics model. To capture the important phenomena, the model is coupled with micro-mixing, population balance, and related energy balance equations. It is implemented in OpenFOAM and validated against experimental data, where a fairly good agreement is found. The effects of key process parameters on the crystallization performance are also studied using the validated model. The results show that increasing the inlet jet velocity from 1 to 4 m/s yields a much narrower size distribution and 70% reduction in the mean crystal size. The four-fold increase in the inlet jet velocity also reduces the crystal production rate by one order of magnitude. Also, it is found that increasing the inlet supersaturation ratio from 6.8 to 8.8 nearly doubles the mean crystal size. Moreover, it results in a wider size distribution and a six-fold increase in the crystal production rate. The simulations also confirm that lower solution to anti-solvent mass flow ratios yield a wider size distribution, a larger mean crystal size and a higher crystal production rate. Increasing this ratio from 0.5 to 2 reduces the production rate by two orders of magnitude.

The motion of non-spherical particles with sharp edges, as they are commonly involved in practice, was characterized by residence time distribution (RTD) measurement in a continuous drum. Particles with two sizes, 6 and 10 mm, and two densities, 750 and 2085 kg/m³, were used in the experiments. The effects of rotation speed (3–11 rpm), incline angle (2–4°), feed rate, and mixture composition were investigated and compared to the results of other researchers on particles without sharp edges. We also fitted the RTD with an axial dispersion model to obtain a better insight into the flow behavior. MRT of non-spherical particles with sharp edges depends on ω^−α similar to other shapes, while the value of alpha is higher for particles with sharp edges (0.9 < α < 1.24), especially at high incline angles. The MRT depends on incline angle, β^−b, where b varies between 0.81 (at low ω) and 1.34 (at high ω), while it is close to 1 for other shapes. Feed rate has a slight effect on the MRT of particles with sharp edges and the effect of particle size diminishes when rotation speed increases. The MRT linearly increases with volume fraction of light particles in a mixture of light and heavy particles (from pure heavy to pure light particles).

Drag force models are one of the most important factors that can affect TFM and CFD-DEM simulation results of two-phase systems. This article investigates the accuracies, implementation issues and limitations of the majority of the drag models for spherical, non-spherical and systems with size distribution and evaluates their performance in various simulations. Around 1888 data points were collected from 19 different sources to evaluate the drag force closures on mono-dispersed spherical particles. The Reynolds number and fluid volume fraction ranges were between 0.01 and 10,000 and between 0.33 and 1, respectively. In addition, 776 data points were collected from seven different sources to evaluate the drag force closures on poly-dispersed spherical particles. The Reynolds numbers were between 0.01 and 500, fluid volume fractions between 0.33 and 0.9, and diameter ratios up to 10. A comprehensive discussion on the accuracy and application of these models is given in the article.