Simulation of honeycomb-screen combinations for turbulence management in a subsonic wind tunnel

Honeycomb and screens, mainly used for turbulence reduction, are the key elements of a subsonic wind tunnel. In this paper, design aspects of these elements are addressed for an open-circuit wind tunnel, installed at Indian Institute of Technology Guwahati (IITG), India. The effectiveness of honeycomb and honeycomb-screen combinations, in reducing swirl and turbulence level in the test section, is studied by simulating the flowfield using commercial computational fluid dynamics (CFD) package ANSYS-CFX. RNG k−ε turbulence model, with scalable wall functions, is used for modeling turbulence. Results of these simulations for turbulence management, using honeycombs of different lengths, cell shapes and screens of different open area ratios, are found to be in good agreement with experimental and theoretical results available in open literature. These simulations have confirmed the methodology to be adopted for design of wind tunnel subsections. Thus validated design parameters have been used for fabricating the honeycomb and screens for the IITG wind tunnel.     

Influence of preparation conditions on nanoporous structure and optical transmission of sodium silicate based ambient pressure dried aerogels employing shaking

The experimental results on the “influence of preparation conditions on nanoporous structure and optical transmission of sodium silicate based ambient pressure dried aerogels employing shaking” are reported. Sol–gel derived gels shaked in the presence of ammonium fluoride (NH₄F) and organically modified with various silylating agents and aprotic solvents are useful in controlling the magnitude of capillary stress imposed on the gel. These parameters enormously affect the optical transmission and density of the aerogels. Therefore, in the present paper the influence of different concentrations of NH₄F, silylating agents and aprotic solvents on the physical properties of the aerogels were studied. The aerogels were characterized by measuring the bulk density, volume shrinkage (%), porosity (%) and thermal conductivity. The microstructural studies were carried out using transmission electron microscopy (TEM). The hydrophobicity is confirmed by measuring the contact angle of water on the surface of aerogel and Fourier Transform Infrared (FTIR) spectroscopy. The optical transmission of the aerogels is measured by the visible spectrophotometer. The thermal stability of the aerogels was checked by the thermo gravimetric and differential thermal analyses (TGA-DTA).     

Accelerometer-Based Force Balance for High Enthalpy Facilities

A single component accelerometer-based force balance is developed, calibrated, and used for high enthalpy applications. Functionality of this force balance, for such applications, is demonstrated for the first time during high enthalpy tests in a newly established free piston- driven shock tunnel, HST3, using a 60° apex angle blunt cone model at 0° angle of incidence. Usefulness of this force balance is also confirmed, for much complicated high enthalpy flow situations, during the drag reduction studies with counterflow supersonic jet from the stagnation point.     

A Comparative Study of Aqueous and Organic-Based Films and Coatings of PEGylated Rosin Derivative

Rosin was partially esterified with polyethylene glycol 400 and reacted with maleic-anhydride to form an ester-adduct derivative. Derivative and native rosin were characterized for physicochemical properties. Aqueous coating system of derivative was developed by ammonia neutralization method. Organic-based films were produced using acetone. Aqueous and organic-based films were comparatively evaluated. Derivative exhibited an excellent coat-forming ability on spherical-units. Aqueous-based film exhibited very high water vapor transmission rate, wettability, water uptake, and leaching at pH 6.8. A 20% w/w aqueous-based coat could sustain diclofenac sodium release for 8 h, whereas, 20% w/w organic-based coat released 20.11% of drug in 8 h. In conclusion, aqueous coating system of synthesized rosin derivative can be developed; however, aqueous-coats are less efficient to retard the drug release rate. Instead, the organic-based coatings can efficiently be used for sustained drug delivery.     

Relation between hydrodynamics and drop size distributions in pump–mix mixer

In the present work, experiments have been carried out to measure the drop size distributions in a pump–mix mixer over a wide range of geometry and operating conditions. The effects of impeller type, (single and multiple impellers), impeller speed, location, phase flow rates, and interfacial tension have been investigated. Computational fluid dynamics model has been developed to predict the hydrodynamic characteristics of pump–mix mixers. Population balance modeling has been carried out to predict the drop size distributions. The hydrodynamic characteristics predicted through CFD simulations have been related to the drop size distributions. The role of convection and energy dissipation in influencing the drop size distributions has been elucidated.     

Space-Charge Distribution across Internal Interfaces in Electroceramics Using Electron Holography: II, Doped Grain Boundaries

Transmission high-energy electron holography has been utilized to quantitatively determine the magnitude, sign, and spatial extent of the electrical potential, electric field, as well as the charge and stress field distributions across electrically active grain boundaries (GBs) in polycrystalline SrTiO₃. The polycrystalline compacts utilized were bulk-doped with Fe and GB-doped with Mn, which is diffused into them under a nonequilibrium situation. The holography results reveal negatively charged GBs with associated positive space-charge, indicating that Mn resides as an acceptor dopant on the Ti site, creating a negative bound charge at the GBs. A large heterogeneity in the electrical activity is observed among various GBs; while some GBs show high Schottky barriers, others have very small barriers. The distribution of the bound charge and the compensating free charge, which together contribute to the formation of GB charge and space-charge, has been estimated. The bound charge experiences an outward stress field due to the force of the electric field on either side of the GB. The height of the double Schottky barrier, the Debye length, as well as the spatial extent of the bound charge and space-charge at the GB are derived from these holography results. The results also provide a quantitative measure of the defect densities as well as of the contribution of the electrostatic stress field to the lattice relaxation at the GBs and yield a point defect model for the GB.     

A novel approach to determine wet restitution coefficients through a unified correlation and energy analysis

Wet particle interactions are observed in many applications, for example, pharmaceutical, food, agricultural, polymerization, agglomeration, and coating, in which an accurate evaluation of the wet restitution coefficient (e_wet) is crucial to understand the particle flowability, operating conditions and product size distribution. Experiments were performed to measure the wet restitution coefficient by impacting a spherical particle on a stationary plate covered with a thin liquid layer of water or glycerol solution in this work. Furthermore, novel approaches for estimation of e_wet were developed using dimensional analysis (using the Buckingham π theorem and regression analysis) in combination with energy budget analysis. In the correlation development, the dominant physical properties of solid and liquid, particle impact velocity and liquid layer thickness are grouped into well‐known dimensionless numbers viz. Reynolds, Weber and Stokes. Whereas in the energy analysis, the energy dissipation rates were determined for five distinct collision phases, that is, dipping, dry collision, undipping, formation and breakage of the liquid bridge, and added mass. The efficacy of the developed approaches was analyzed by comparing obtained results with experiments and an elastohydrodynamic model, and a modified elastohydrodynamic model. © 2014 American Institute of Chemical Engineers AIChE J, 61: 769–779, 2015     

Crack-Interface Interactions in a Tungsten-Yttria-Stabilized-Zirconia Directionally Solidified Eutectic

A directionally solidified eutectic (DSE) of W-ZrO₂(Y₂O₃) consists of faceted fibers of tungsten embedded in yttriastabilized cubic zirconia. The W-ZrO₂ interfaces in this system are devoid of any impurity phases or a reaction product. Microindentation-induced cracks and their interactions with interphase interfaces are investigated using scanning and transmission electron microscopy. Crack-interface interactions are found to fall into one of four categories: propagation along the metal-ceramic interface, deflection away from the interface, crack-interface bridging, and shearing of tungsten fibers. Further crack propagation is investigated in situ in a TEM with a propagation induced by local electron beam heating. These crack path selections are analyzed within the framework of phenoin-enological understanding of crack-interface interactions in composites.     

Development of An Oral Sustained-Release Antibiotic Matrix Tablet Using In-Vitro/In-Vivo Correlations

A sustained release (SR) cephalexin tablet formulation containing xanthan gum and sodium alginate as matrix formers was evaluated in human volunteers. The formulation was optimized based on response surface analysis and computer simulation of cephalexin plasma levels versus time curves. The optimized formulation was tested in-vivo in human volunteers along with a fast release (FR) capsule formulation. The SR matrix formulation prolonged the cephalexin blood levels up to 8 hours in humans. The matrix formulation reduced variations in cephalexin plasma levels in individual subjects without any dose dumping as compared to the FR formulation. The plasma levels predicted by the computer program using in-vitro release data and the drug's pharmacokinetic parameters showed excellent correlation with in-vivo data. Using the Wagner-Nelson method, there was good correlation between in-vitro dissolution and in-vivo absorption in individual subjects. The relative bioavailability of cephalexin was reduced by about thirty percent. Very little absorption was seen after six to eight hours. The SR matrix formulation is an alternative delivery method to produce prolonged concentrations.