Experimental measurement of local burning velocity within a rotating flow

The work presented in this paper details the implementation of a new technique for the measurement of local burning velocity using asynchronous particle image velocimetry. This technique uses the local flow velocity ahead of the flame front to measure the movement of the flame by the surrounding fluid. This information is then used to quantify the local burning velocity by taking into account the translation of the flame via convection. In this paper the developed technique is used to study the interaction between a flame front and a single toroidal vortex for the case of premixed stoichiometric methane and air combustion. This data is then used to assess the impact of vortex structure on flame propagation rates. The burning velocity data demonstrates that there is a significant enhancement to the rate of flame propagation where the flame directly interacts with the rotating vortex. The increases found were significantly higher than expected but are supported by burning velocities [22-24] found in turbulent flames of the same mixture composition. Away from this interaction with the main vortex core, the flame exhibits propagation rates around the value recorded in literature for unperturbed laminar combustion [18-21]

Optical diagnostics studies of air flow and powder fluidisation in Nexthaler®. Part II: Use of fluorescent imaging to characterise transient release of fines from a dry powder inhaler

© 2018 The fine particle fraction is a key indicator of therapeutic effectiveness of inhaled pharmaceutical aerosols. This paper presents a fluorescence imaging technique to visualise and characterise the emission of active pharmaceutical ingredient (API) fines in model formulations containing coarse lactose carrier and 1.5–2 μm diameter fluorescent microspheres (model API fines). A two-camera arrangement was used to acquire simultaneous images of spatial and temporal distribution of model API fines and fluidised powder formulation near the mouthpiece exit of a DPI. Digital image analysis showed that the model API fines were released along with the bulk of the powder dose. More rapidly accelerating airflows were found to cause earlier release of API fines. The fluorescence imaging technique analyses a substantial fraction of the aerosol plume and was found to provide effective time-resolved characterisation of the de-aggregation and release of API fines with consistent results across a wide range of model API concentrations. Future studies should demonstrate the usefulness of the fluorescence imaging technique across different formulations and DPI devices

Optical diagnostics study of air flow and powder fluidisation in Nexthaler (R)-Part I: Studies with lactose placebo formulation

Effective drug delivery to the lungs by a DPI device requires the air-stream through the device to have sufficient power to aerosolise the powder. Furthermore, sufficient turbulence must be induced, along with particle-wall and particle-particle collisions, in order to de-aggregate small drug particles from large carrier particles. As a result, the emitted and the fine particle doses produced by many commercially available DPI devices tend to be strongly affected by the natural inter-patient variability of the inhaled air flow. The Nexthaler® is a multi-dose breath-actuated dry-powder inhaler with minimum drug delivery-flow rate dependency and incorporating a dose protector. The actuation mechanism of the dose-protector ensures that the dose is only exposed to the inhaled air flow if the flow has sufficient power to cause complete aerosolisation. For this study, a proprietary lactose placebo powder blend was filled into “transparent “ Nexthalers® to allow application of high speed imaging and particle image velocimetry (PIV) techniques to successfully interrogate and reveal details of the powder entrainment and emission processes coupled with characterisation of the flow environment in the vicinity of the mouthpiece exit. The study showed that fluidisation of the bulk of the powder occurs very quickly (~20 ms) after withdrawal of the dose protector followed by powder emission from the device within ~50 ms thereafter. The bulk of the metered placebo dose was emitted within 100-200 ms. The visualisation study also revealed that a very small fraction of powder fines is emitted whilst the dose protector still covers the dosing cup as the flow rate through the device accelerates. The PIV results show that the flow exiting the device is highly turbulent with a rotating flow structure, which forces the particles to follow internal paths having a high probability of wall impacts, suggesting that the flow environment inside the Nexthaler® DPI will be very beneficial for carrier-drug de-aggregation

Large eddy simulation and PIV measurements of unsteady premixed flames accelerated by obstacles

In gas explosions, the unsteady coupling of the propagating flame and the flow field induced by the presence of blockages along the flame path produces vortices of different scales ahead of the flame front. The resulting flame/vortex interaction intensifies the rate of flame propagation and the pressure rise. In this paper, a joint numerical and experimental study of unsteady premixed flame propagation around three sequential obstacles in a small scale vented explosion chamber is presented. The modelling work is carried out utilising Large Eddy Simulation (LES). In the experimental work, previous results [Patel, S.N.D.H., Jarvis, S., Ibrahim, S.S., Hargrave, G.K., Proceedings of the Combustion Institute 29, 1849-1854 (2002)] are extended to include simultaneous flame and Particle Image Velocimetry (PIV) measurements of the flow field within the wake of each obstacle. Comparisons between LES predictions and experimental data show a satisfactory agreement in terms of shape of the propagating flame, flame arrival times, spatial profile of the flame speed, pressure time history and velocity vector fields. Computations through the validated model are also performed to evaluate the effects of both large scale and sub-grid scale (sgs) vortices on the flame propagation. The results obtained demonstrate that the large vortical structures dictate the evolution of the flame in qualitative terms (shape and structure of the flame, succession of the combustion regimes along the path, acceleration-deceleration step around each obstacle, pressure time trend). Conversely, the sgs vortices do not affect the qualitative trends. However, it is essential to model their effects on the combustion rate to achieve quantitative predictions for the flame speed and the pressure peak

The dynamics of droplet impact on a heated porous surface

In this paper, droplet impact on a porous surface is experimentally investigated over a wide range of Weber numbers and surface temperatures. Regime transition criteria have been deduced to determine droplet post-impingement behaviour as a function of the Weber number and surface temperature for which a droplet impacting on a porous surface. Based on the energy balance, an analytical model with improved boundary layer description is proposed to predict maximum spreading of droplet following impact on porous surfaces when the effect of heat transfer is negligible. The results of the model indicate that the spreading process after droplet impact on porous surfaces is governed by the viscous dissipation and matric potential. The maximum-spread model predictions agreed well with experimental measurements reported in this paper and the literature over a large range of Weber numbers and different porous surfaces

The effect of active pharmaceutical ingredients on aerosol electrostatic charges from pressurized metered dose inhalers

Purpose. This study investigated the effect of different active pharmaceutical ingredients (API) on aerosol electrostatic charges and aerosol performances for pressurized metered dose inhalers (pMDIs), using both insulating and conducting actuators. Methods. Five solution-based pMDIs containing different API ingredients including: beclomethasone dipropionate (BDP), budesonide (BUD), flunisolide (FS), salbutamol base (SB) and ipratropium bromide (IPBr) were prepared using pressure filling technique. Actuator blocks made from nylon, polytetrafluoroethylene (PTFE) and aluminium were manufactured with 0.3 mm nominal orifice diameter and cone nozzle shape. Aerosol electrostatics for each pMDI formulation and actuator were evaluated using the electrical low-pressure impactor (ELPI) and drug depositions were analysed using high performance liquid chromatography (HPLC). Results. All three actuator materials showed the same net charge trend across the five active drug ingredients, with BDP, BUD and FS showing positive net charges for both nylon and PTFE actuators, respectively. While SB and IPBr had significantly negative net charges across the three different actuators, which correlates to the ionic functional groups present on the drug molecule structures. Conclusions. The API present in a pMDI has a dominant effect on the electrostatic properties of the formulation, overcoming the charge effect arising from the actuator materials. Results have shown that the electrostatic charges for a solution-based pMDI could be related to the interactions of the chemical ingredients and change in the work function for the overall formulation

High-speed laser image analysis of plume angles for pressurised metered dose inhalers: the effect of nozzle geometry

The aim of this study is to investigate aerosol plume geometries of pressurised metered dose inhalers (pMDIs) using a high-speed laser image system with different actuator nozzle materials and designs. Actuators made from aluminium, PET and PTFE were manufactured with four different nozzle designs: cone, flat, curved cone and curved flat. Plume angles and spans generated using the designed actuator nozzles with four solution-based pMDI formulations were imaged using Oxford Lasers EnVision system and analysed using EnVision Patternate software. Reduced plume angles for all actuator materials and nozzle designs were observed with pMDI formulations containing drug with high co-solvent concentration (ethanol) due to the reduced vapour pressure. Significantly higher plume angles were observed with the PTFE flat nozzle across all formulations, which could be a result of the nozzle geometry and material’s hydrophobicity. The plume geometry of pMDI aerosols can be influenced by the vapour pressure of the formulation, nozzle geometries and actuator material physiochemical properties

The effect of actuator nozzle designs on the electrostatic charge generated in pressurised metered dose inhaler aerosols

Purpose To investigate the influence of different actuator nozzle designs on aerosol electrostatic charges and aerosol performances for pressurised metered dose inhalers (pMDIs). Methods Four actuator nozzle designs (flat, curved flat, cone and curved cone) were manufactured using insulating thermoplastics (PET and PTFE) and conducting metal (aluminium) materials. Aerosol electrostatic profiles of solution pMDI formulations containing propellant HFA 134a with different ethanol concentration and/or model drug beclomethasone dipropionate (BDP) were studied using a modified electrical low-pressure impactor (ELPI) for all actuator designs and materials. The mass of the deposited drug was analysed using high performance liquid chromatography (HPLC). Results Both curved nozzle designs for insulating PET and PTFE actuators significantly influenced aerosol electrostatics and aerosol performance compared with conducting aluminium actuator, where reversed charge polarity and higher throat deposition were observed with pMDI formulation containing BDP. Results are likely due to the changes in plume geometry caused by the curved edge nozzle designs and the bipolar charging nature of insulating materials. Conclusions This study demonstrated that actuator nozzle designs could significantly influence the electrostatic charges profiles and aerosol drug deposition pattern of pMDI aerosols, especially when using insulating thermoplastic materials where bipolar charging is more dominant

Time-Resolved Particle Image Velocimetry of dynamic interactions between hydrogen-enriched methane/air premixed flames and toroidal vortex structures

Time-Resolved Particle Image Velocimetry was used to study transient interactions between hydrogen-enriched methane/air premixed flames and toroidal vortex structures. Lean and stoichiometric mixtures with hydrogen mole fraction in the fuel (hydrogen plus methane), xH2xH2, varying in the range of 0–0.5 were investigated. Results have shown that the hydrogen presence affects the flow field both quantitatively (increase of the velocity of the main toroidal vortex) and qualitatively (generation of different sub-vortices within the main vortex), enhancing the intensity of the interaction. Regardless of the mixture stoichiometry, the hydrogen substitution to methane leads to a transition from a regime in which the vortex only wrinkles the flame front (xH20.2xH2>0.2). This transition was characterised in terms of time histories of flame surface area and burning rate

A long nozzle for intra-nasal drug delivery by pMDI: prediction of spray velocity and droplet size

Intra-nasal drug delivery via nasal pressurized metered-dose inhalers (nasal-pMDI) is very successful in delivering treatment of conditions of the anterior regions of the human nasal cavity, such as rhinitis and sinusitis [1]. Intranasal drug delivery has also been postulated as a potential technique to treat central nervous system (CNS) diseases by delivering CNS-active drugs to the olfactory region – positioned at the upper region of the nasal cavity [1]. Our in-house in-vitro data suggest that the olfactory region can be targeted more accurately by extending the nasal pMDI nozzle length. Such nozzle length extension can potentially impact spray characteristics such as velocity, which directly determines the deposition efficiency [2]. In this work we report the development of a modeling tool validated by particle image velocimetry (PIV) and laser diffraction (LD) measurements, to predict the velocity and droplet size delivered from a long nozzle solution pMDI.</p