This paper presents results of an experimental investigation of a single drop impact onto a dry, partially wettable substrate and its numerical simulation Particularly, the drop spreading diameter and the dynamic contact angle are measured at different time instants after impact Two surfaces, wax (low wettability) and glass (high wettability), are used to study the effect of surface wettability (static contact angle) on the impact dynamics It is shown that existing empirical models for the dynamic contact angle (eg, Hoffman–Voinov–Tanner law) do not predict well the change of the dynamic contact angle, especially at high capillary numbers In addition to the experimental investigations, the drop impact was studied numerically, focusing primarily on the contact angle treatment The singularity in the neighborhood of the moving contact line is removed from the computational domain and replaced by a local force with some dependence on the instantaneous advancing/receding contact-line velocity The predicted time dependence of the drop spreading diameter and of the dynamic contact angle agrees well with the experimental data for both the advancing and receding phases of the impact process

Dynamic contact angle of spreading droplets: Experiments and simulations

To discover new rheumatoid arthritis (RA) risk loci, we systematically examined 370 SNPs from 179 independent loci with P < 0.001 in a published meta-analysis of RA genome-wide association studies (GWAS) of 3,393 cases and 12,462 controls. We used Gene Relationships Across Implicated Loci (GRAIL), a computational method that applies statistical text mining to PubMed abstracts, to score these 179 loci for functional relationships to genes in 16 established RA disease loci. We identified 22 loci with a significant degree of functional connectivity. We genotyped 22 representative SNPs in an independent set of 7,957 cases and 11,958 matched controls. Three were convincingly validated: CD2-CD58 (rs11586238, P = 1 x 10(-6) replication, P = 1 x 10(-9) overall), CD28 (rs1980422, P = 5 x 10(-6) replication, P = 1 x 10(-9) overall) and PRDM1 (rs548234, P = 1 x 10(-5) replication, P = 2 x 10(-8) overall). An additional four were replicated (P < 0.0023): TAGAP (rs394581, P = 0.0002 replication, P = 4 x 10(-7) overall), PTPRC (rs10919563, P = 0.0003 replication, P = 7 x 10(-7) overall), TRAF6-RAG1 (rs540386, P = 0.0008 replication, P = 4 x 10(-6) overall) and FCGR2A (rs12746613, P = 0.0022 replication, P = 2 x 10(-5) overall). Many of these loci are also associated to other immunologic diseases.

Genetic variants at CD28, PRDM1, and CD2/CD58 are associated with rheumatoid arthritis risk

Droplet impact on superhydrophobic surfaces: A review of recent developments

Lattice-Boltzmann simulation of fluid flow through packed beds of uniform spheres: Effect of porosity

Computational study of forced convective heat transfer in structured packed beds with spherical or ellipsoidal particles

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.

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

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.

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

Hydrodynamics of trickle-bed reactors involve complex interactions of gas and liquid phases with packed solids. Such complex interactions manifest in different flow regimes occurring in trickle-bed reactors. Knowledge of prevailing flow regime, pressure drop, and liquid holdup is essential for design and performance evaluation of the reactor. Detailed knowledge of fluid dynamics is essential for “a priory” predictions as well as for interpretation of available data. In this study, we have used wall pressure fluctuation measurements to identify prevailing flow regime in trickle beds. Experiments were carried out on two scales of columns (of diameter 10 cm and 20 cm) with two sets of particles (3 mm and 6 mm diameter spherical particles). Effects of prewetted and unwetted bed conditions on pressure drop and liquid holdup were reported for a range of operating conditions (VG = 0.22−0.44 kg/m2s, VL = 2−24 kg/m2s). A comprehensive CFD model was developed to predict measured hydrodynamic parameters. The model w...

Hydrodynamics of Trickle-Bed Reactors: Experiments and CFD Modeling

Hydrodynamics and mixing in trickle bed reactors (TBR) are governed by bed porosity, capillary forces, wetting and non-uniform distribution at the inlet. In this work, experiments were carried out to study pressure drop, liquid hold-up and residence time distribution for pre-wetted and non-wetted bed. CFD models were developed, in which bed heterogeneity and capillary models were incorporated. Mixing and RTD were simulated using the CFD model. This study was further extended to study the flow mal-distribution in TBR. Based on these results, current capabilities and limitations of the CFD model were discussed. The model and the results discussed here would be useful to extend application of CFD models for simulating mixing in TBR.

Prashant R. Gunjal

Papers

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

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

Hydrodynamics of Trickle-Bed Reactors: Experiments and CFD Modeling

Liquid Distribution and RTD in Trickle Bed Reactors: Experiments and CFD Simulations

Experimental and computational study of liquid drop over flat and spherical surfaces