Studying the limits of production rate and yield for the volume manufacturing of hollow core photonic band gap fibers.

Hollow core photonic band gap fibers have great potential in low latency data transmission and power delivery applications, but they are currently only fabricated in research scale fabrication facilities, with km-scale lengths. To drive cost reduction and volume manufacturing it is essential to be able to upscale the preform size, but before embarking on costly experimental attempts it is useful to apply fluid dynamics models to study how the fiber drawing dynamics would be affected by such a change. In this work we use a fluid dynamics model to virtually draw increasingly longer lengths of the same fiber from preforms of identical length but different diameters. Taking advantage of our fast numerical model we explore the physical dynamics of the draw process. We discover that the draw tension is the key thermodynamic parameter and that an upper length limit exists beyond which undesirable distortions in the microstructure become difficult to control. These mechanisms are identified and possible mitigation methods described which could allow the fabrication of over 200 km fiber from a single preform.

Whole cell quenched flow analysis.

This paper describes a microfluidic quenched flow platform for the investigation of ligand-mediated cell surface processes with unprecedented temporal resolution. A roll-slip behavior caused by cell-wall-fluid coupling was documented and acts to minimize the compression and shear stresses experienced by the cell. This feature enables high-velocity (100-400 mm/s) operation without impacting the integrity of the cell membrane. In addition, rotation generates localized convection paths. This cell-driven micromixing effect causes the cell to become rapidly enveloped with ligands to saturate the surface receptors. High-speed imaging of the transport of a Janus particle and fictitious domain numerical simulations were used to predict millisecond-scale biochemical switching times. Dispersion in the incubation channel was characterized by microparticle image velocimetry and minimized by using a horizontal Hele-Shaw velocity profile in combination with vertical hydrodynamic focusing to achieve highly reproducible incubation times (CV = 3.6%). Microfluidic quenched flow was used to investigate the pY1131 autophosphorylation transition in the type I insulin-like growth factor receptor (IGF-1R). This predimerized receptor undergoes autophosphorylation within 100 ms of stimulation. Beyond this demonstration, the extreme temporal resolution can be used to gain new insights into the mechanisms underpinning a tremendous variety of important cell surface events.

Perpetual sedimentation for the continuous delivery of particulate suspensions.

Particle sedimentation is deleterious to a tremendous variety of microfluidic applications. Using an open instrumentation approach we show that syringe rotation retains particles in a suspended state, providing a universal solution for the continuous delivery of particulate samples to microfluidic processors.

Experimental observations of dry powder inhaler dose fluidisation.

Dry powder inhalers (DPIs) are widely used to deliver respiratory medication as a fine powder. This study investigates the physical mechanism of DPI operation, assessing the effects of geometry, inhalation and powder type on dose fluidisation. Patient inhalation through an idealised DPI was simulated as a linearly increasing pressure drop across three powder dose reservoir geometries permitting an analysis of shear and normal forces on dose evacuation. Pressure drop gradients of 3.3, 10 and 30 kPa s(-1)were applied to four powder types (glass, aluminium, and lactose 6 and 16% fines) and high speed video of each powder dose fluidisation was recorded and quantitatively analysed. Two distinct mechanisms are identified, labelled 'fracture' and 'erosion'. 'Fracture' mode occurs when the initial evacuation occurs in several large agglomerates whilst 'erosion' mode occurs gradually, with successive layers being evacuated by the high speed gas flow at the bed/gas interface. The mechanism depends on the powder type, and is independent of the reservoir geometries or pressure drop gradients tested. Both lactose powders exhibit fracture characteristics, while aluminium and glass powders fluidise as an erosion. Further analysis of the four powder types by an annular shear cell showed that the fluidisation mechanism cannot be predicted using bulk powder properties.

Effect of expansion chamber geometry on atomization and spray dispersion characters of a flashing mixture containing inerts. Part II: High speed imaging measurements.

A breath activated, pressurized metered dose inhaler (pMDI) device (Oxette(®)) has been developed to replace the traditional cigarette. In this paper, internal and external spray characters are measured by high speed imaging along with sizing the residual droplets at the distance from the discharge orifice where the human oropharynx locates. Two different formulations with 95% and 98% mass fraction of HFA 134a and two prototype cigarette alternatives with different expansion chamber volumes have been analyzed. The internal and external flows issuing from early stage prototype Oxette(®) are discussed along with boiling and evaporation phenomena. The expansion and entrainment regions of the jet are observed and discussed with comparison to the turbulent round jet of a single phase. From the visualizations of internal flows in the earlier design, a small expansion chamber can hardly generate small bubbles, which is difficult to produce fine sprays. The larger the expansion chamber volume, the more room for the propellant evaporation, recirculation, bubble generation and growth, all of which produces finer sprays. Therefore the later prototype of Oxette(®) 2 made a significant improvement to produce fine sprays and facilitated development of the cigarette alternative. Furthermore, the characters of the spray generated by Oxette(®) are compared to that issuing from a pMDI by previous researchers, where the residual MMD is larger than that of a pMDI, because the Oxette(®) has a smaller expansion chamber and the geometry provides less opportunity for the recirculation due to restrictions of the design space. Although the formulation with higher mass fraction of HFA 134a can generate smaller droplets, it cannot produce steady puffs with relatively low mass flow rate.

Effect of expansion chamber geometry on atomization and spray dispersion characters of a flashing mixture containing inerts. Part I. Numerical predictions and dual laser measurements.

A cigarette alternative is designed to deliver a dose of medicinal nicotine within a timeframe comparable to that of a cigarette, and gives much of what smokers expect from a cigarette without the risks of smoking tobacco. The design concept is the same as a pressurized metered dose inhaler (pMDI), but is a breath actuated device (Oxette(®)). This work predicts the residual mass median diameter (MMD) of the spray issuing from early stage Oxette(®) prototypes by using an evaporation model of multi-component liquid droplets with the help of a numerical multi-component two-phase actuation model (developed by the authors) to quantify the sprays. Two different formulations with 95% and 98% mass fraction of HFA 134a, and two prototypes of cigarette alternatives with different expansion chamber volumes have been analyzed by the numerical model and compared with laser based measurements. The later designed device provides a larger expansion chamber volume to enhance the propellant evaporation, recirculation, bubble generation and growth inside the chamber, and it makes a significant improvement to produce finer sprays than the earlier design. The mass fraction of the formulation does not affect significantly on the initial MMD of the droplets near the discharge orifice. However, it influences the residual MMD at x=100mm from the discharge orifice, where the ratio of the predicted residual MMDs of the droplets generated by the formulations with 98% and 95% of HFA 134a is 0.73. Although the formulation with 98% of HFA 134a can generate smaller droplets, the formulation with 95% of HFA 134a produces more steady puffs with relatively low mass flow rate.

The effect of reduction of propellant mass fraction on the injection profile of metered dose inhalers.

In order to provide an improved understanding of the flow in pressurized-metered dose inhalers (pMDIs), especially monitoring the output temperature and mass flow rate to obtain maximum atomization efficiency from the available energy, a numerical model for a two phases, multi-component compressible flow in a pressurized-metered dose inhaler is presented and validated. It is suitable for testing with various formulations and different geometries for a range of pMDI devices. We validated the model against available data in the literature for a single component HFA 134a propellant, and then investigated the response of the model to other formulations containing non-volatile components. Further validation is obtained by an experiment using the dual beam method which acquired the actuation flow properties such as spray velocity and duration. The deviation of the numerical predictions for the peak exit velocity against the experimental results is 5.3% and that for effective spray duration 5.0%. From the numerical and experimental results, it is found that for the formulations with the mass fraction of HFA 134a>80%, the effective spray duration of the pMDI is around 0.1s. Furthermore the droplet peak exit velocity at the axial station x=25 mm from the actuation nozzle decreases from 20 to 15m/s with the reduction of the propellant (HFA 134a) from 95%. Formulations with the mass fraction of HFA 134a below 80% produce poor quality spray which is indicated from the unsteady peak exit velocity, changeable spray number density in each experimental test, and numerical simulations also confirmed the non-viability of this condition.