Abstract The Supercritical Antisolvent (SAS) technique allows for the precipitation of drugs and biopolymers in nanometer size in a wide range of industrial applications, while guaranteeing the physical and chemical integrity of such materials. However, a suitable combination of operating parameters is needed for each type of solute. The knowledge of fluid dynamics behavior plays a key role in the search for such parameter combinations. This work presents a numerical study concerning the impact of operating temperature and pressure upon the physical properties and mixture dynamics within the SAS process, because in supercritical conditions the radius of the droplets formed exhibits great sensitivity to these variables. For the conditions analyzed, to account for the heat of mixture in the energy balance, subtle variations in the temperature fields were observed, with almost negligible pressure drop. From analyses of the intensity of segregation, there is an enhancement of the mixture on the molecular scale when the system is operated at higher pressure. This corroborates experimental observations from the literature, related to smaller diameters of particles under higher pressures. Hence, the model resulted in a versatile tool for selecting conditions that may promote a better control over the performance of the SAS process.

This work deals with experimental and numerical studies of a 3-D transient free-surface two-phase flow in a bench-scale channel flow. The aim was to determine how well the homogeneous model can predict the fluid dynamics behavior and to validate the model. The model was validated with experimental data acquired for two hydrodynamic situations. The mathematical model was based on the mass conservation equations for liquid and gas phases and on the momentum conservation equation for the mixture, assuming interpenetrating, continuum and homogeneous hypotheses. Turbulence has been considered for the mixture through the standard k-ε model. The numerical methods were the finite volume method with pressure-velocity coupling and a numerical grid on a generalized Cartesian coordinate system. Good qualitative and quantitative agreements were found for both cases, making the prediction of the fluid dynamics behavior quite robust.

Usually, heat and/or mass transfer models with time dependence, in a fixed, moving or cross-flow beds, are solved analytically by the use of the Laplace transform method. When the determination of the character of the poles is not on easy problem, this method presents the transform inversion using the residue theorem as the major application difficulty. In this work, an alternative method is discussed which casts the system of equations into a matrix problem of the Sturm-Liouville type. As an example, the solution of a heat transfer model in a moving bed is presented. The advantage this approach is a direct solution of the temperature profiles in the particle and in the bulk fluid near the solid-fluid interface by using a spectral expansion in terms of the self-adjoint matrix operator involved, with guaranteed convergency, and it can be used easily as an interpolation scheme to solve numerically advection/diffusion problems.

In this work a new mechanical device to improve the gas flow in cyclones by pressure drop reduction is presented and discussed. This behavior occurs due to the effects of introducing swirling breakdown phenomenon at the inlet of the vortex finder tube. The device consists of a tube with two gas inlets in an appositive spiral flux that produces a sudden reduction in the tangential velocity peak responsible for practically 80 % of the pressure drop in cyclones. In turn, peak reduction causes a decrease in pressure drop by a breakdown of the swirling, and because of this the solid particles tend to move faster toward the wall , increasing collection efficiency. As a result of this phenomenon the overall performance of cyclones is improved. Numerical simulations with 3-D, transient, asymmetric and anisotropic turbulence closure by differential Reynolds stress for Lapple and Stairmand standard geometries of 0.3 m in diameter, show a reduction in pressure drop of 20 % and a shift of the tangential velocity peak toward the wall. All numerical experiments were carried out with a commercial CFD code showing numerical stability and good convergence rates with high-order interpolation schemes, SIMPLEC pressure-velocity coupling and other numerical features.