Session T11: Experimental Techniques: Multiphase Flow (8:00am - 8:45am CST)

Internal Phase Change Measurement Using Novel Luminescent Sensor

Numerous measurement techniques exist for measuring surface and bulk properties, but there are virtually no tools for spatially resolved internal measurements for a solid. A novel measurement technique was developed using the same luminophore technology used in temperature sensitive paints (TSPs). Particles of Acid Rhodamine B, a pH-sensitive luminophore, were embedded within an ice block and excited with UV light. Calibration tests demonstrated the luminescent peak and intensity of Acid Rhodamine B are functions of the phase, solid or liquid, of the water in which it is dissolved. Measurements of this luminescence provides a way to visualize fracture patterns and collect phase change information within ice. A high-speed camera was used to collect spatially and temporally resolved measurements of the internal properties of an ice block during melting. Additionally, tests were conducted to measure fracture behavior and phase changes produced by impacting an ice block at low speeds.   

Ultra Small Angle X-ray Scattering Measurements in Pharmaceutical Aerosols

Pressurised metered dose medical inhalers (PMDIs) contain a hydrofluorocarbon propellant and an active drug which is dissolved in a cosolvent where solubility in the propellant is poor. As the propellant is more volatile than the cosolvent, the composition of the liquid changes considerably as it flows through the device's nozzle and forms the inhaled aerosol. The initial droplet composition affects precipitation of the inhaled drug particles, but remains elusive. The propellant is too volatile for single-particle optical or acoustic trap measurements, and it is difficult to measure in situ due to multiple scattering and beam steering. We circumvented these problems through a novel application of Ultra-Small Angle X-ray Scattering (USAXS). We considered a PMDI solution of 3.38 $\mu$g/$\mu$L ipratropium bromide, 85\% $^v/_v$ R-134a propellant and 15\% ethanol. The experiments were conducted at the 9-ID \& 7-BM beamlines of the Advanced Photon Source at Argonne National Laboratory. USAXS exploits the high electron density of R-134a relative to the cosolvent. Combining USAXS with X-ray radiography and laser diffraction measurements, the ensemble average droplet composition can be determined for the first time.   

Herder-Induced Contraction and Fragmentation of Floating Crude Oil Slicks.

Crude oil spills often form harmful oil slicks on the sea surface. Chemical herders may be used to contract slicks for subsequent burning or collection and are an important oil spill treatment tool, especially in cold and remote ice-infested waters in the Arctic. However, the fluid mechanics of oil slick contraction and fragmentation in the presence of obstacles (e.g. floating ice) is not well understood. Here we present controlled laboratory experiments investigating the contraction of Alaska North Slope crude oil slicks under the influence of the chemical herder OP-40 (Siltech). A 100 \textmu m thick oil slick is created in a basin (92\texttimes 42\texttimes 20 cm) of chilled water (\textasciitilde 5\textdegree C) within a fume hood and is subjected to the controlled release of herder from a rectangular ring pneumatically lifted from the water surface at one edge of the basin. The resulting oil slick contraction across the basin is visualized using a high speed camera, and slick contraction speed, area, and thickness are calculated over time. Oil slick fragmentation and retention by obstacles simulating sea ice also are tested by placing 3D-printed objects of various shapes and sizes in the basin. Maximum oil slick edge contraction speeds sharply decrease from \textasciitilde 0.2 m/s over 1 min as the slick thickness increases up to \textasciitilde 1 mm.   

Particle and fluid velocity measurement technique in suspended sediment sheet flow

Particle-turbulence interaction within the suspension layer of oscillatory sheet flow is complicated and remains an open question in the literature. Existing experimental measurements in this region usually lack the resolution required to resolve the coupled behavior between the fluid and sediment phase, due to the strong light scattering that occurs from the mobile bed and the large difference in size between the sediment and fluid tracer particles. A multi-camera imaging method in combination with fluorescent tracer particles has been developed using an apertured spectral filter to provide a balanced image of both the tracer and sediment particles. This enables whole field, temporally-resolved particle-scale concurrent measurement of both phases within the suspended region, up to sediment volumetric fractions of close to 0.01. The proposed technique is validated with composite/synthetic two-phase flow. The dispersed phase motion is generated by translating, with prescribed motion, a gel box that contains layers of sediment particles with known concentrations, mimicking the sediment distribution and motion encountered in an actual sheet flow. The uncertainties in the measured kinematics of both phases are quantified.   

Small and Large-Scale Mixing Measurements in a Shock-Driven Multiphase Instability.

New experimental techniques and methodologies are applied for the investigation of the physical phenomena induced by the impulsive acceleration of a heterogeneous multiphase flow-field within a shock tube system. New equipment was designed to create and a cylindrical interface comprising of nitrogen gas, seeded with micron-sized acetone droplets, generated within the shock tube's test section. The nitrogen gas itself was saturated with acetone vapor tracer and mixed into the interface to prevent premature droplet evaporation. The interface is then impulsively accelerated by a planar shock wave. The development of both the dispersed and carrier phases was captured through a series of Planar Laser Mie Scattering and Planar Laser-Induced Fluorescence images, respectively. Results of these experiments were compared against evaporation measurements with models like the D-Square-Law and simulations. This experimental investigation has a multitude of applications in a variety of scientific and engineering systems; with relevance to systems that involve high-speed or shock-induced multiphase combustion.   

Effective properties and flow transitions in an annular Couette rheometer for liquid-particle suspensions and gas fluidized beds

Effective properties are extremely important in modeling and simulating multiphase flows. For example, the Krieger-Dougherty (KD) model of effective viscosity is commonly applied to study flows of neutrally buoyant suspensions at low Reynolds numbers. In this work, a coaxial rheometer is used to measure the shear stress of a variety of particulate compositions, including density matched particle suspensions, density mismatched particle suspensions, and gaseous-fluidized particles. We apply KD effective viscosity to the rheological results of the particle suspensions to show that at high shear rates, particle suspensions undergo a similar transition as observed in pure fluids from a circular Couette flow to a flow with toroidal vortices. Similar measurements on gaseous-fluidized particles show that at low shear rates, the shear stress of particles fluidized beyond incipient fluidization evolves as a Bingham pseudoplastic. At higher shear rates, the shear stress increases at a rate comparable to a Newtonian fluid in Taylor vortex flow.~These results demonstrate that past critical rates of shear, particle suspensions and gaseous-fluidized particles alike demonstrate rheological behavior similar to that of pure liquids in Taylor vortex flow.   

A High-Speed Limited Angle X-ray Tomography System for Optically Opaque Multi-Phase Flows

Diagnostics of optically opaque flows can aid in the understanding of underlying flow physics and also help advance numerical simulations by providing datasets for validation. In this study, we present the development of a true 3D (initially 4-plane) scanning electron beam X-ray tomography to image and measure void fraction distributions of optically opaque flows. The configuration consists of stationary high speed detector array located concentric around a pipe of circular cross-section. Source position is varied using a 20 kW electron beam that can be rapidly focused and deflected. This results in the ability of the system to generate limited-angle projection data of an object of interest at O(kHz) rates. A statistical reconstruction algorithm capable of reconstructing limited-angle projection data with reduced artefacts is used to produce cross-sectional images of flows. System performance is evaluated by reconstructing measured data of a static and a dynamic phantom emulating bubbly flow. Preliminary results for a bubbly flow are also presented.