Assessment of the release of atomic Na from a burning black liquor droplet using quantitative PLIF

The quantitative measurement of atomic sodium (Na) release, at high concentration, from a burning black liquor droplet has been demonstrated using a planar laser-induced fluorescence (PLIF) technique, corrected for fluorescence trapping. The local temperature of the particle was measured to be approximately 1700 C, at a height of 10 mm above a flat flame burner. The PLIF technique was used to assess the temporal release of atomic Na from the combustion of black liquor and compare it with the Na concentration in the remaining smelt. A first-order model was made to provide insight using a simple Plug Flow Reactor model based on the independently measured concentration of residual Na in the smelt as a function of time. This model also required the dilution ratio of the combustion products in the flat flame entrained into the plume gas from the black liquor particle to be estimated. The key findings of these studies are: (i) the peak concentration of atomic Na from the combustion of the black liquor droplets is around 1.4 ppm; (ii) very little atomic Na is present during the drying, devolatilisation or char combustion stages; and (iii) the presence of atomic Na during smelt phase dominates over that from the other combustion stages

Insights from a new method providing single-shot, planar measurement of gas-phase temperature in particle-laden flows under high-flux radiation

Published online: 31 March 2021Two-colour laser-induced fluorescence (LIF) of toluene has been demonstrated to provide in situ, spatially resolved, planar measurements of the gas-phase temperature in a particle-laden flow with strong radiative heating at fluxes up to 42.8 MW/m². Toluene was seeded in trace quantities into the gas flow laden with particles of mean diameter 173 μm at a volumetric loading sufficiently high for particle–fluid and particle–particle interactions to be significant. The particle number density was also measured simultaneously using Mie scattering. The two-colour LIF method was found to resolve temperature with a pixelto- pixel standard deviation of 17.8 °C for unheated measurements in this system despite significant attenuation of the probe laser and signal trapping of the fluorescence emissions from the densely loaded particles. Following heating of the particles using high flux radiation, the increase in the gas-phase temperature from convection was found to be spatially non-uniform with highly localised regions of temperature spanning from ambient to 150 °C. This gas-phase heating continued well downstream from the limits of the region with radiative heating, with the time-averaged gas temperature increasing with distance at up to 2,200 °C/m on the jet centreline. The temperature of the flow was non-symmetrical in the direction of the heating beam, because the particles attenuate the radiation through absorption and scattering. The addition of radiation at fluxes up to 42.8 MW/m² did not significantly change the particle number density distribution within the region investigated here.Elliott W. Lewis, Timothy C. W. Lau, Zhiwei Sun, Zeyad T. Alwahabi, Graham J. Natha

A pressure drop correlation for low Reynolds number Newtonian flows through a rectangular orifice in a similarly shaped micro-channel

Current microfabrication methods mean that rectangular orifices in similarly shaped micro-channels are often found in microfluidic devices. The power required to overcome the pressure drop across such orifices is often of importance. In the contribution reported here, numerical results for low Reynolds number incompressible Newtonian fluid flow through rectangular orifice in similarly shaped micro-channel have been used to develop a correlation for pressure drop arising from the orifice. The correlation, which was motivated by theoretical developments, indicates that the pressure drop is proportional to the average velocity through the orifice, and a function of the orifice contraction ratio, length-to-width ratio and, most particularly, aspect ratio.V. Zivkovic, P. Zerna, Z.T. Alwahabi, M.J. Bigg

Diagnostics of Air Purification Plasma Device by Spatially Resolved Emission Spectroscopy

A non-thermal plasma, air purification device (PlasmaShield®, MD250, Keswick, SA, Australia), was investigated using spatially resolved optical emission spectroscopy. The emission spectra were measured with two spatial dimensions to analyze and identify the transition lines of excited NO–γ (A2Σ–X2Π), N2 (C3Π–B3Π), and N2 + (B2Σ–X2Σ) systems. The N2 emission band at 337 and 316 nm were used to determine the spatially resolved vibrational temperature of N2 molecules, T N2 vib. It was found that the average N2 vibrational temperatures in the x and y directions are almost the same. Two key operating parameters, supplied power and air flow, influence the N2 vibrational temperature. The results demonstrate that applying higher supplied power increases the vibrational temperature, while changes in air flow velocity do not affect the vibrational temperature values. The phenomenological plasma temperature (PPT) was also estimated from the N2 vibrational temperature. It was observed that PlasmaShield® generates excited N2 and NO only within a narrow region around the discharge electrode tip (with peak intensity below 100 µm from the tip). The study also shows no presence of excited OH*, O*, and other radicals.Wanxia Zhao and Zeyad T. Alwahab

Microwave assisted laser-induced breakdown spectroscopy at ambient conditions

Abstract not availableJan Viljanen, Zhiwei Sunb, Zeyad T. Alwahab

Contactless thermal diagnostics of acoustically levitated biomass under uniform high flux radiation

This study reports a contactless optical system developed for investigating the fast-thermal processes of biomass under high-flux radiation, particularly for understanding the synergy of renewable biomass and concentrated solar energy. A biomass tablet was successfully suspended using a home-built acoustic levitator in a well-controlled oxygen-lean atmosphere and was irradiated under uniform radiation with a high flux of approximately 1 MW/m2, i.e., ∼1000 suns. The biomass temperature profile was spatio and temporally recorded using an infrared thermographic camera. Several key thermal parameters of the biomass were determined, including the time-resolved heating rate and the ignition temperature. Three different thermal processes were identified from the temperature profiles. These are an initial fast-heating process, a following slow-heating process, and a final biomass ignition depending on the flux of radiation. At high flux, these three processes are merged, and only a steep linear increase in temperature was observed. The contactless apparatus provides the high-fidelity data of the heating rates of biomass and can benefit the understanding of the fast-thermal process associated with biomass under high flux concentrated solar radiation.Wanxia Zhao, Zhiwei Sun, Zeyad T. Alwahab

Emissivity and absorption function measurements of Al(2)O(3) and SiC particles at elevated temperature for the utilization in concentrated solar receivers

Solar thermal receivers collect and can store concentrated solar radiation using solid particles. Solid ceramic particles have shown to be a practical and efficient heat transfer media in solar-particle receivers, however, their emissivity and absorptivity at high temperatures are scarcely reported. This gap has led to large uncertainties in the assessment of solar thermal receivers’ efficiency. In this work, an experimental method was developed to measure the emissivity and absorption function of solar particles at elevated temperatures up to 1200 K. Two types of solar particles, aluminum oxide (Al₂O₃, ∼95% purity) and silica carbide (SiC, ∼99% purity), were studied, particularly aiming to understand the dependence of emissivity and absorption function on temperature. Using a heat transfer model, the emissivity of particles was evaluated based on the fitting of the cooling rate, while the particle absorption function was obtained by fitting of the heating rate, following a well-controlled heating radiation at 910 nm. It was found that the emissivity values of the two particles are independent of temperature, showing constant values of 0.75 ± 0.015 and 0.92 ± 0.012 for Al2O3 and SiC respectively, in the temperature from 300 to 1200 K. The absorption function was found to be increased nonlinearly with temperature for Al₂O₃, while that of SiC dropped slightly. These absorption functions are specified for 910 nm. Using the evaluated experimental values of emissivity and absorption function, the maximum temperature and the temperature rise time of micro-sized particles (hundreds of micrometers) under different radiation fluxes were simulated taking into account the effect of particle diameter.Wanxia Zhao, Zhiwei Sun, Zeyad T. Alwahab

Temperature imaging of mobile BaMgAl10O17:Eu phosphor aggregates under high radiation flux

Planar laser-induced phosphorescence (PLIP) has been used for the temperature measurement of suspended phosphor aggregates. Two-dimensional surface temperature of fluidized phosphor aggregates was measured through a pair of spatial and wavelength resolved images in an environment where phosphors are heated by high-flux radiation. The heating was supplied by a multi-diode laser system which provides a well-characterized high-flux radiation up to 28.87 MW/m2. Phosphors made of BaMgAl10O17:Eu (BAM) were selected as the material and suspended in a fluidized bed. Single-shot temperature imaging of BAM aggregates were inferred and compared at several heat fluxes. With the increasing heat flux up to 28.87 MW/m2, the BAM aggregates were found to exhibit a wider range of temperature distribution, and the maximum average aggregate temperature achieved 723 K, while the maximum temperature of a single aggregate could reach up to 1063 K. The wider temperature distributions that observed under higher radiation fluxes were caused by the elevated temperature of cooling air and the non-uniform aggregate surfaces. This non-intrusive method of measuring temperature offers advantages over other available methods in the study of heat transfer processes involving high-temperature reactions.Wanxia Zhao, Kimberley C.Y.Kueh, Graham J.Nathan, Zeyad T.Alwahab

Optical properties and scattering distribution of thermographic phosphors

The optical properties and scattering distribution of thermographic phosphors have been demonstrated using a combined experimental and numerical method. ZnO:Zn and BaMgAl₁₀O₁₇:Eu²⁺ (BAM) are two types of widely used phosphors due to their stable physical properties and high-temperature sensitivities. To study their inter-phosphor light transfer, the angular scattering distribution and light propagation of these two phosphor suspensions was measured using a spectro-goniometric system. A collision-based Monte Carlo ray-tracing model was developed to extract their optical properties, including extinction coefficient, scattering albedo, asymmetry factors, and scattering fraction. With the void fraction around 0.98, the extinction coefficient of ZnO:Zn was determined to be 4.719, while that of F grade BAM and N grade BAM were 11.584 and 9.777, respectively. In addition, BAM had a higher scattering fraction (α = 0.99) than ZnO:Zn (α = 0.88). Due to the higher values of extinction coefficient and scattering fraction, BAM demonstrated more significant scattering than ZnO:Zn. Light transmission through phosphor suspensions was predicted along the direction of the light path. For ZnO:Zn, 70% of flux was scattered when the distance increases to 0.5, while for BAM, the distance was 0.15. Furthermore, with the same mass loading, smaller particle sizes can promote scattering and reduce the amount of light transmitted through phosphor suspensions.Wanxia Zhao, Jan Marti, Aldo Steinfeld, Zeyad T. Alwahab

The effect of particle size and volumetric loading on the gas temperature distributions in a particle-laden flow heated with high-flux radiation

The instantaneous, spatially resolved gas-phase temperature distribution within a particle-laden flow heated using high-flux radiation has been measured for a series of heating fluxes, particle volumetric loadings and particle diameters using two-colour laser induced fluorescence of toluene. The temperature of the gas downstream from the start of the heating region was found to increase with an increase in heat flux, an increase in particle loading and a decrease in particle diameter. Coherent regions of high and low temperature in the instantaneous flow associated with spatial variations in the particle distribution were identified for all particle diameters investigated. The time-averaged gas-phase temperature on the jet axis was found to increase approximately linearly with distance in the region downstream from the heating beam to the edge of the measurement region investigated, indicating near-constant convective heat transfer due to the large temperature difference between the gas and radiatively heated particles throughout this region. The axial gradient of gas-phase temperature with distance was also calculated using a simplified, one-dimensional heat transfer model. The difference between the model and measurements was, on average, less than 20%, with the magnitude of this difference found to increase with a decrease in particle diameter and an increase in particle loading.Elliott W. Lewis, Timothy C.W. Laua, Zhiwei Suna, Zeyad T. Alwahabi, Graham J. Natha