High Speed Particle Beam Generation: A Dynamic Focusing Mechanism for Selecting Ultrafine Particles

RSMS-II is a unique characterization technique for analyzing the chemical content of individual airborne ultrafine particles in real time. Although based on earlier versions, the newest implementation offers crucial enhancements including a smart data acquisition system and a completely redesigned particle inlet. The particle inlet is based on a dynamic focusing mechanism that selectively transmits a narrow particle size range in the form of a high speed particle beam. The mean particle size that is optimally transmitted is dynamically altered by changing the nozzle source pressure, thus particles over a wide size range may be selected. Inherent in the design of dynamic focusing mechanisms is the ability to size-select particles based on their aerodynamic characteristics, thus obviating the need for additional sizing components. The principle, design, and calibration of a variable pressure inlet is presented in the current work. Characteristics are estimated employing a theoretical approach based on the Stokes number definition and supported with numerical simulations using CFD tools. Results from a preliminary effort in calibrating the inlet using monodisperse aerosol are presented. Results indicate that the size resolving capability of the inlet may be enhanced at the expense of lowered transmission rates. Finally, the capability of RSMS-II as a characterization technique is demonstrated by analyzing ultrafine atmospheric particles from a moderately polluted episode.     

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.     

An Investigation into the Powder Release Behavior from Capsule-Based Dry Powder Inhalers

A methodology for studying the deagglomeration performance and emptying behavior of micronized mannitol powder from two commercial capsule-based dry powder inhalers (DPIs), the low- and high-resistance RS01®, is presented. Mathematical modeling played a key role in the interpretation of the powder release behavior from these two DPI systems. Non-linear regression models, which were characterized from the aerosol obscuration versus time profiles obtained from laser diffraction particle sizing data, were used to estimate rate constants for emptying of mannitol powder. The effects of device resistance and associated pressure drops, sampling flow rate, rates of powder emptying, and the presence of capsule on the dispersion characteristics were studied. The presence of a capsule significantly improved the aerosolization performance of mannitol powder from both inhalers, which may be due to the extended powder–air–device interactions within the device. It is important to consider the stochastic nature of movement and physical state of the capsule when assessing the aerosolization mechanisms and dispersion performance from these complex delivery systems. The methodology set out in this study has the capacity to provide a greater level of detail in the study of aerosol plume characteristics from capsule-based DPIs.

Copyright 2015 American Association for Aerosol Research     

Effective Moisture Diffusivity Estimation from Drying Data. A Comparison Between Various Methods of Analysis

ABSTRACT

Moisture diffusivity is the most crucial property in drying calculations. Literature data are scarce due to the variation of both experimental measurement techniques and methods of analysis. The effect of using different methods of analysis on the same experimental drying data is examined in this work. Detailed and simplified mathematical models, incorporating moisture diffusivity as model parameter, are applied. It is proved, that significant differences in the calculated values of moisture diffusivity result when different models are used, and probably these differences explain the variation in literature data. Thus, the adoption of a standardised methodology will be of great importance in moisture diffusivity evaluation.

The above findings resulted from the application of four alternative models on the drying data of three common food materials, potato, carrot and apple. A typical pilot plant scale dryer with controlled drying air conditions was used for the experiments. The moisture content dependence of the diffusion coefficient was proved significant at the last drying stage, while the temperature dependence followed the well known Arrhenius relation. The effects of considering external mass transfer and volume shrinkage during drying, were also investigated.     

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.     

Detection Efficiency of a Water-Based TSI Condensation Particle Counter 3785

In this article we present observations on the detection efficiency of a recently developed TSI 3785 Water Condensation Particle Counter (WCPC). The instrument relies on activation of sampled particles by water condensation. The supersaturation is generated by directing a saturated airflow into a “growth tube,” in which the mass transfer of water vapor is faster than heat transfer. This results in supersaturated conditions with respect to water vapor in the centerline of a “growth tube.” In this study, the cut-off diameter, that is, the size, where 50% of the sampled particles are successfully activated, varied from 4 to 14 nm for silver particles as a function of temperature difference between the saturator and the growth tube. The solubility of the sampled particles to water played an important role in the detection efficiency. Cut-off diameters for ammonium sulphate and sodium chloride particles were 5.1 and 3.6–3.8 nm, respectively at nominal operation conditions. Corresponding cut-off diameter for hydrophobic silver particles was 5.8 nm.     

High Temperature Interactions Between Residual Oil Ash and Dispersed Kaolinite Powders

The potential use of sorbents to manage ultrafine ash aerosol emissions from residual oil combustion was investigated using a downfired 82 kW laboratory-scale refractory-lined combustor. The major constituents were vanadium (V), nickel (Ni), iron (Fe), and zinc (Zn). The overall ash content of residual oil is very low, resulting in total ash vaporization at 1725 K with appreciable vaporization occurring at temperatures as low as 1400 K. Therefore, the possibility of interactions between ash vapor and sorbent substrates exists. Kaolinite powder was injected at various locations in the combustor. Ash scavenging was determined from particle size distributions (PSDs) measured by a Scanning Mobility Particle Sizer. Impactor samples and X-ray fluorescence (XRF) analyses supported these data. Injection of kaolinite sorbent was able to capture up to 60% of all the ash in the residual fuel oil. However, captures of ～ 30% were more common when sorbent injection occurred downstream of the combustion zone, rather than with the combustion air into the main flame. Without sorbent addition, baseline measurements of the fly ash PSD and chemical composition indicate that under the practical combustion conditions examined here, essentially all of the metals contained in the residual oil form ultrafine particles (～0.1 μ m diameter). Theoretical calculations showed that coagulation between the oil ash nuclei and the kaolinite sorbent could account for, at most, 17% of the metal capture which was always less than that measured. The data suggest that kaolinite powders reactively capture a portion of the vapor phase metals. Mechanisms and rates still remain to be quantified.