An Aerosol Generator for High Concentrations of 0.5–5-μm Solid Particles of Practical Monodispersity

A continuous-flow, evaporation-condensation aerosol generator has been designed to produce particles of practical monodispersity of stearic acid in concentrations of over 1 g/m³ at flow rates > 6 L/min. Pure stearic acid containing a dissolved impurity is melt-sprayed and evaporated, producing a nuclei- vapor mixture. The mixture is recondensed and then quickly quenched into spherical, solid particles of a narrow size distribution. The condenser design is a straight, insulated glass tube of 5 cm in inner diameter and of 110 cm in length. A heating and flow straightening conditioning section previous to the condenser provides a relatively flat condensation front across the tube diameter, while the insulated condenser walls in free convection create a low radial temperature gradient, both of which enhance particle monodispersity with particle geometric standard deviations < 1.25. The dynamic condenser conditions for the suppression of homogeneous nucleation were investigated as a function of the ratio of the Grashof-Prandtl numbers product to the Reynolds number.     

Processing of Soot by Controlled Sulphuric Acid and Water Condensation—Mass and Mobility Relationship

The effects of atmospheric processing on soot particle morphology were studied in the laboratory using the Differential Mobility Analyzer-Aerosol Particle Mass Analyzer (DMA-APM) and the DMA-DMA (Tandem DMA) techniques. To simulate atmospheric processing, combustion soot agglomerates were altered by sulphuric acid vapor condensation, relative humidity (RH) cycling, and evaporation of the sulphuric acid and water by heating. Primary investigated properties were particle mobility size and mass. Secondary properties, derived from these, include effective density, fractal dimension, dynamic shape factor, and the mass fraction of condensed material. A transformation of the soot particles to more compact forms occurs as sulphuric acid and water condense onto fresh soot. The particle mass increases and initially the mobility diameter decreases, indicating restructuring of the soot core, likely due to surface tension forces. For a given soot source and condensing liquid, the degree of compaction depends strongly on the mass (or volume) fraction of condensed material. For water and sulphuric acid condensing on combustion soot, a mass increase of 2–3 times is needed for a transformation to spherical particles. In the limit of spherical particles without voids, the effective density then approaches the inherent material density, the fractal dimension approaches 3 and the dynamic shape factor approaches 1. Our results indicate that under typical atmospheric conditions, soot particles will be fully transformed to spherical droplets on a time scale of several hours. It is expected that the morphology changes and addition of soluble material to soot strongly affect the optical and hygroscopic properties of soot.     

Easyhaler® Multiple Dose Powder Inhaler—Practical and Effective Alternative to the Pressurized MDI

Due to the depletion of ozone layer linked to CFf propellants used in metered-dose inhalers (MDIs), alternative drug delivery systems for inhalation therapy of bronchial asthma is required. Dry powder inhalers have become a remarkable alternative to the MDIs. The research of powder delivery systems has strongly been focused on developing portable, preloaded multiple-dose powder inhalers, from which patients can reliably inhale several drug doses. Recently, a novel multiple-dose powder inhaler (Easyhaler®) has been developed. Easyhaler® is a suitable drug delivery system for various drugs already available or still under development. Optimum patient compliance is achieved by a design similar to the dose delivery system of the conventional MDI. In addition, the construction of the device allows high dose reproducibility and good in vitro and in vivo deposition of inhaled drug particles. Consequently, equal therapeutic efficacy, safety and tolerability with an MDI is documented in clinical trials. Thus the pharmaceutical, biopharmaceutical, and clinical features as well as the similar mode of use would facilitate a smooth transition from the freon based MDIs to the Easyhaler® multiple-dose powder inhaler.     

Comparative Study of the Kinetic Degradation of Differently Decrystallized Cotton Linters Using Nonisothermal DTA Curves

Cellulose samples of different degree of decrystallization were subjected to differential thermal analysis (DTA) technique under nonisothermal conditions. The samples were prepared by preswelling the cotton linters in 24-Baumé NaOH followed by the use of direct or indirect methods to dry the mercerized cotton. The thermal stabilities of the samples were estimated taking into account the values of initial decomposition temperature, maximum decomposition temperature, and activation energy. The activation energy preexponential constant, order of reaction, and other thermodynamic parameters (ΔH, ΔS, and ΔG) associated with each stage were derived by applying integrated peak areas (Satava and Skvara), the Borchart—Daniels general method, and the Prount—Tompkins equation. The results showed that the cellulose pyrolysis process cannot be described as having a single value of E _a over the entire pyrolysis range. Also, the decrystallization caused by destruction of the formed alkali cellulose complex with a isopropanol—water (WAN) system was found to be the most pronounced change in pyrolytic parameters (i.e., less thermal stability) compared with native and other decrystallized samples. The dependence of E _a on IR measurements is also discussed.     

Cyanoethylation of Hydroxyethyl Cellulose: Preparation and Characterization

Commercial hydroxyethyl cellulose (HEC) was cyanoethylated with acrylonitrile in nonaqueous medium in the presence of sodium hydroxide under a variety of conditions. Variables studied included the amount of acrylonitrile and the reaction temperature. The reaction was proved by NMR and its extent was measured by determining the nitrogen content. The physical properties of the obtained derivatives—i.e., the electric properties and the apparent viscosity at various rates of shear—were investigated. It was found that the extent of reaction was increased by increasing the amount of acrylonitrile as well as the reaction temperature. The products were water soluble and their apparent viscosity increased with increasing nitrogen content. The same holds true for the dielectric constant and dielectric loss.     

KINETICS OF WATER SORPTION IN OKARA AND ITS RELATIONSHIP TO THE GLASS TRANSITION TEMPERATURE

ABSTRACT

The water adsorption and desorption kinetics of okara were determined at different relative humidities (51·4- 83·6 %) at 30 °C. Initial rates of water sorption and the specific rate constants showed different responses to increased RH. Both the adsorption and desorption rate constants dropped significantly at RH 51-55 %; this behaviour is related to occurrence of glass transition phenomenon.     

An Idealized Child Throat that Mimics Average Pediatric Oropharyngeal Deposition

Copyright 2012 American Association for Aerosol Research     

Factors Affecting the Collision of Aerosol Particles with Small Water Drops

The factors influencing the collision of aerosol particles with small water drops at low collision efficiencies are examined. The gravitational force and velocity slip of air on the drop surface are found to affect the collision efficiency in the range of values of 10^?4–^?2. The efficacies of the different computational models are compared for ratios of particle radius to drop radius of less than 0.1. The accuracy of the numerical scheme in the trajectory model can be verified by comparing the efficiencies obtained for submicrometer particles with the convective-diffusion model.     

Dispersion of a Plume of Volatile Aerosol

A theoretical basis and numerical schemes are presented for simulating the dispersion of a plume of volatile aerosol. For special cases where analytical solutions are possible, excellent agreement is shown between analytical and numerical solutions. It is demonstrated that the error in the numerical simulation can be reduced to any desired level. Simulation results for volatile plume dispersion under realistic atmospheric conditions are also presented.