Modeling of laboratory and commercial scale hydro-processing reactors using CFD

Trickle bed reactors (TBRs) are commonly used in chemical industries. Scale-up of TBR is difficult and simple scaling rules often lead to poor design. Flow mal-distribution, channeling, wetting of catalyst and local temperature variation are some of the important parameters which controls the overall performance of the TBRs. Fluid dynamics of the TBRs is complex and very sensitive to the scale of the reactors. Conventional modeling techniques are unable to account these key design issues. Recent advances in computational fluid dynamics (CFD) show promising results in understanding fluid dynamics and its interactions with chemical reactions. In this study we have developed a CFD model for simulating flow and reactions in the laboratory scale and commercial scale reactors. A case of hydro-processing reactions was considered. The CFD models were first evaluated by comparing the model predictions with the published experimental data. The models were then used to understand the influence of porosity distribution, particle characteristics and reactor scale on overall performance. Validated model was used to predict the performance of the commercial scale reactor. Various critical issues of scaling of TBR and how CFD modeling can help in reducing uncertainties associated with it are discussed in details. The approach, model and results presented here will be useful for understanding the complex hydrodynamics, its interaction with chemical reactions and influence of different reactor scales on performance of the TBRs

Computational study of a single-phase flow in packed beds of spheres

Packed-bed reactors are widely used in petrochemical, fine chemical, and pharmaceutical industries. Detailed knowledge of interstitial flow in the void space of such packed-bed reactors is essential for understanding the heat and mass transfer characteristics. In this paper, fluid flow through the array of spheres was studied using the unit-cell approach, in which different periodically repeating arrangements of particles such as simple cubical, 1-D rhombohedral, 3-D rhombohedral, and face-centered cubical geometries were considered. Single-phase flow through these geometries was simulated using computational fluid dynamics (CFD). The model was first validated by comparing predicted results with published experimental and computational results. The validated model was further used to study the effect of particle arrangement/orientation on velocity distribution and heat transfer characteristics. The simulated results were also used to understand and to quantify relative contributions of surface drag and form drag in overall resistance to the flow through packed-bed reactors. The model and the results presented here would be useful in elucidating the role of microscopic flow structure on mixing and other transport processes occurring in packed-bed reactors

Dynamics of drop impact on solid surface: experiments and VOF simulations

The process of spreading/recoiling of a liquid drop after collision with a flat solid surface was experimentally and computationally studied to identify the key issues in spreading of a liquid drop on a solid surface. The long-term objective of this study is to gain an insight in the phenomenon of wetting of solid particles in the trickle-bed reactors. Interaction of a falling liquid drop with a solid surface (impact, spreading, recoiling, and bouncing) was studied using a high-speed digital camera. Experimental data on dynamics of a drop impact on flat surfaces (glass and Teflon) are reported over a range of Reynolds numbers (550-2500) and Weber numbers (2-20). A computational fluid dynamics (CFD) model, based on the volume of fluid (VOF) approach, was used to simulate drop dynamics on the flat surfaces. The experimental results were compared with the CFD simulations. Simulations showed reasonably good agreement with the experimental data. A VOF-based computational model was able to capture key features of the interaction of a liquid drop with solid surfaces. The CFD simulations provide information about finer details of drop interaction with the solid surface. Information about gas-liquid and liquid-solid drag obtained from VOF simulations would be useful for CFD modeling of trickle-bed reactors

Suture fixation of migrated septal occluder device to prevent further migration: a simple surgical technique

<p>Abstract</p> <p>As the use of percutaneous intervention is increasing for the closure of the atrial septal defect, the procedure related complications are also on rise, migration of the device being most common. The migrated devices with failed percutaneous retrieval must be removed surgically under cardiopulmonary bypass. During establishment of cardiopulmonary bypass, the handling of heart may cause further migration of the device into other chambers of heart which leads to difficulty in finding and retrieval of the device. The authors propose a simple and unique technique to prevent further migration of the septal occluder device.</p