The flow induced instability in the flow past a soft material is studied in the limit of low Reynolds number where inertial effects are insignificant. A transition from laminar flow to a more complicated flow profile is observed when the strain rate of the base flow increases beyond a critical value; the transition is found to be reproducible. The experimental results are compared with theoretical predictions and quantitative agreement is found with no adjustable parameters.

The viscous instability in the flow past a soft material is experimentally studied. The experiment is carried out using the parallel plate geometry of a rheometer, and a sheet of polyacrylamide gel of thickness about 4.5 mm is placed on the bottom plate. The fluid, silicone oil, is placed on the surface of the gel and the top plate is lowered till a preset gap of thickness between 300 and 1000 μm is attained. The rheometer is operated in the stress controlled mode, where the stress is increased at a constant rate, and the strain rate and apparent viscosity (assuming the flow in the gap is laminar) are recorded. Care is taken to ensure the Reynolds number is less than 1, so that inertial effects are negligible. The experimental results show that there is an anomalous increase in the apparent viscosity, determined assuming the flow is laminar, at a certain strain rate. This indicates that the flow becomes unstable and undergoes a transition from a laminar flow to a more complicated flow profile. This transition is repeatable if the experiment is stopped before there is irreversible damage to the gel surface. The experimental results are compared with theoretical predictions, and quantitative agreement is found with no adjustable parameters for a range of gap thicknesses and gel moduli.

The present paper concerns the development and validation of an Eulerian multiphase boiling model to predict boiling and critical heat flux within the general-purpose computational fluid dynamics (CFD) solver FLUENT. The governing equations solved are generalized phase continuity, momentum and energy equations. Turbulence effects are accounted for using mixture, dispersed or per-phase multiphase turbulence models. Wall boiling phenomena are modeled using the baseline mechanistic nucleate boiling model, developed in Rensselaer Polytechnic Institute (RPI). Modifications have been introduced to the quenching heat flux model to achieve mesh-independent solutions. The influences of boiling model parameters have also been systematically investigated. To model non-equilibrium boiling and critical heat flux, the PRI model is extended to the departure from nucleate boiling (DNB) by partitioning wall heat flux to both liquid and vapor phases and considering the existence of thin liquid wall film. Topological functions are introduced to consider the wall boiling regime transition from the nucleate boiling to critical heat flux (CHF), and the corresponding flow regime change from bubbly flows to mist flows. A range of sub-models are implemented to model the interfacial momentum, mass and heat transfer and turbulence-bubble interactions. To validate the Eulerian multiphase boiling model, it has been used to predict nucleating boiling and critical heat flux in a range of 2D and 3D boiling flows. The examples presented in the paper include: (1). Nucleate boiling of sub-cooled water in an upward heated pipe; (2) R113 liquid flows through a vertical annulus with internal heated walls; (3). 3D boiling flows in a rectangular-sectioned duct; and (4). Critical heat flux and post dryout in vertical pipes. The results demonstrate that the model is able to predict reasonably well the distributions of wall temperature, the bulk fluid sub-cooling temperature and cross-sectional averaged vapor volume fraction in the vertical pipe. The computed profiles of the vapor volume fraction, liquid temperature, and the liquid and vapor velocity profiles are generally in good agreement with available experiments in the 2D annular case. In the 3D rectangular duct, the cross-sectional averaged vapor volume fractions are well captured in all the ten cases under investigation. In the case of critical heat flux and post dryout, the model is also able to predict reasonably well the location and the temperature rise under critical heat flux conditions. The computed wall temperature distributions along the pipes are in overall good agreement with available experiments.

PurposeA computational fluid dynamics (CFD) study examined the impact of particle size on dissolution rate and residence of intravitreal suspension depots of Triamcinolone Acetonide (TAC).MethodsA model for the rabbit eye was constructed using insights from high-resolution NMR imaging studies (Sawada 2002). The current model was compared to other published simulations in its ability to predict clearance of various intravitreally injected materials. Suspension depots were constructed explicitly rendering individual particles in various configurations: 4 or 16 mg drug confined to a 100 μL spherical depot, or 4 mg exploded to fill the entire vitreous. Particle size was reduced systematically in each configuration. The convective diffusion/dissolution process was simulated using a multiphase model.ResultsRelease rate became independent of particle diameter below a certain value. The size-independent limits occurred for particle diameters ranging from 77 to 428 μM depending upon the depot configuration. Residence time predicted for the spherical depots in the size-independent limit was comparable to that observed in vivo.ConclusionsSince the size-independent limit was several-fold greater than the particle size of commercially available pharmaceutical TAC suspensions, differences in particle size amongst such products are predicted to be immaterial to their duration or performance.

The present research examines the remediation of three different reactive dyes namely Reactive Orange 16 (RO16), Reactive Black 5 (RB5) Reactive Blue 19 (RB19) using biochar derived from coconut shell in an aqueous solution. The batch study showed that the pH of 2, temperature of 35 °C and biochar dosage of 1 g/L is the optimum condition for the maximum adsorption of reactive dyes. The adsorption isotherms demonstrated the highest uptake of 73.03 mg/g, 56.92 mg/g and 57.06 mg/g for RO16, RB5 and RB19 respectively. Isotherm studies predicted that the Toth model is the best fit model with a correlation coefficient greater than 0.9837. The kinetic study was carried out and results indicated that 120 minutes as an equilibrium time, the pseudo‐first‐order kinetic model and pseudo‐second‐order kinetic model were used to fit the experimental data. Finally, the reusability of the biochar was studied by using different elutants, sorbent to liquid ratio and regeneration cycles.

Adsorption behavior of Reactive Red 120 from aqueous solutions onto rice husk-derived biochar was examined in batch mode of operation. To obtain the optimized conditions, various adsorption variables including temperature, initial dye concentration, biochar dosage, pH, and contact time were studied for effective remediation of the dye. The results showed that biochar uptake capacity varied linearly with biochar dosage and pH, but varied nonlinearly with temperature. The optimum value of pH, temperature, and a dosage of biochar was obtained as 2.0, 35°C, and 1 g/L, respectively, for reactive red 120 adsorption. TG analysis, FTIR, and SEM were used to investigate biochar characterization, and the results revealed that dye sorption onto biochar caused biochar variation. The possibility of reusing the biochar was examined from desorption studies, and they are conducted by studying different elutants and by altering the ratio of solid to liquid. From the results of experiments, the rice husk-derived biochar was reported to remediate reactive red 120 with the maximum removal efficiency of 75%.

Today, the use of Computational Fluid Dynamics (CFD) software in academia occurs primarily in the context of student projects or research. The potential of CFD as a tool to enhance teaching is largely untapped, despite growing interest in computer tools to assist learning. FlowLab (http://flowlab.fluent.com) is a CFD-based educational software package that will allow students to solve fluid dynamics problems without the long learning curve required by today's commercial CFD packages.

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