Simultaneous planar measurements of gas and particle velocities in particle-laden flows: proof-of-concept

A laser-based technique is reported, employing simultaneous laser-induced fluorescence (LIF) and phosphorescence (LIP) to respectively mark the gas- and particle- phases and allow their simultaneous velocity measurement in a particle-laden flow. The technique discriminates the phases by optically separating the fluorescent and phosphorescent signals from each other and also from the scattering signals, thorough the novel use of optical filters and temporal separation. A proof-of-concept demonstration was conducted with using 250 μm PMMA spherical particles and 4 μm BAM:Eu²⁺ phosphorescent tracers, suspended in a water cuvette. Under 355 nm excitation (3rd harmonic of the Nd:YAG laser), both PMMA fluorescent and BAM:Eu²⁺ phosphorescent signals are shown to be sufficiently strong for imaging with CCD cameras, and sufficiently separable with using spectral filters and temporal profiles.Xiaopeng Bi, Zhiwei Sun, Timothy Lau, Zeyad Alwahabi and Graham Natha

Non-intrusive temperature measurement of particles in a fluidised bed heated by well-characterised radiation

Abstract not availableKimberley C.Y. Kueh, Timothy C.W. Lau, Graham J. Nathan, Zeyad T. Alwahab

Gas-phase temperature measurement of particle-laden jets

Planar laser-induced fluorescence (PLIF) has been applied as to measure the temperature in particle-laden jet flows. A turbulent pipe jet flow was investigated at temperatures from 20-140oC, at particle volume loadings from 0-1x10⁻³. 2D temperature distributions were measured at the jet exit through the centerline of the pipe. Toluene was used as the flow tracer due to a strong signal temperature sensitivity in the measurement range. Two-color PLIF thermometry collects the fluorescent signal in two spectral regions, utilizing the red shift of the fluorescent emission spectrum of toluene with increasing temperature. Nitrogen was used as the carrier gas to minimize quenching of the fluorescence signal by oxygen. The elastic scattering from particles is much stronger than the fluorescence signal and the signals were separated using optical filters. The PLIF method was found to be accurate to within 2% for all temperatures in the range measured, for particle volume loadings less than 1x10⁻⁴.Elliott Lewis, Timothy Lau, Zhiwei Sun, Graham Nathan, and Zeyad Alwahab

Single-shot planar temperature imaging of radiatively heated fluidized particles

A single-shot, non-intrusive planar technique for measuring the temperature of radiatively heated particles with good spatial resolution has been demonstrated. This technique has been applied to particles with diameters between 10µm and 50µm, suspended in a highly unsteady flow within a fluidized bed. The particles were heated with a high-flux radiation source to provide high and well-characterized heat fluxes ranging from 2.4 MW/m2 ≤ Ф ≤ 21.1 MW/m2. Each measurement is derived from two images with an area of 15mm × 10.8mm using an image splitter and a single ICCD camera. An average of 30 particles were recorded in each image with a spatial resolution of 51 pixels/mm. A maximum temperature rise of 350°C was recorded with a heat flux of 21.1 MW/m2, with a corresponding heating rate of up to 23,000°C/s, given the maximum residence time of the particles in the heating region of 0.05s. The normalized temperature distribution within an individual particle agglomerate was found to be up to ± 4%, which is attributable to ICCD noise so that the mean temperature is well resolved.Kimberley C.Y. Kueh, Timothy C.W. Lau, Graham J. Nathan and Zeyad T. Alwahab

Temperature measurements by laser-induced phosphorescence: Effect of laser flux variation

Laser-induced Phosphorescence technique (LIP) was applied to non-intrusive temperature measurements of a hot plate coated with ZnO:Zn. The dependence of the emission intensity ratio of two wavelength ranges on the temperature was evaluated. A non-linear relationship at temperatures below 600K was found. The effect of the laser flux on the accuracy of the LIP temperature measurement was investigated. It was found that a 10% increase of laser flux, in the range of 2-14 mJcm-2, results in a 2% change in the computed temperature, centred around 600K.K. C. Y. Kueh, ., T. Lau, G.J. Nathan, Z.T. Alwahab

Heat transfer in a radiatively heated particle-laden laminar jet flow

An investigation on the heat transfer within a radiatively heated laminar particle-laden flow was performed using the spatially and temporally-resolved laser-induced phosphorescence (LIP) technique. It was found that particle concentration is higher near the edge of the jet ( / ≈0.5) as compared to the jet axis. This non-uniform particle concentration distribution was found to have a direct impact on particle temperatures, Tp, likely due to the effects of inter-particle re-radiation. Additionally, it was found that the radiative heating of the particles induces complex phenomenon such as buoyancy, re-radiation, and clustering, even for this simple laminar flow field. These results are internally consistent and extremely repeatable, justifying the need for further investigation.K.C.Y. Kueh, T.C.W. Lau, Z. Alwahabi and G.J. Natha

Interference modes in laser induced fluorescence thermometry applied to particle-laden flows

The influence of interference from solid particles on gas-phase temperature measurements using two-colour laser induced fluorescence (LIF) thermometry was analysed for two different particle types, PMMA and ZnO:Zn. The signal from interactions of the particles with the incident laser sheet (from Mie scattering, fluorescence and phosphorescence) was measured in the collection wavelength bands for two-colour toluene LIF thermometry. The intensity of the signal from the PMMA particles was significantly stronger than from the ZnO:Zn particles, due to particle fluorescence in the two-colour wavelength bands. The intensity from both particle types was also stronger relative to the toluene fluorescent emission intensity in the wavelength of 315±10 nm than 285±5 nm.E.W. Lewis, T.C.W. Lau, Z.W. Sun, Z.T. Alwahabi, and G.J. Natha

Particle temperature measurements in a flow using laser-induced phosphorescence

Paper No. HTFF 137 - Multiphase flow and heat transferThe temperature of particles, heated by radiation, has been investigated using laser-induced phosphorescence. The particles were fluidised using an optically-accessible fluidised bed system, while the radiation was supplied by a solid state solar thermal simulator operated at ~915 nm. When the flux and the irradiation time was set at 19.7MW/m2, the maximum particle’s temperature and the average particle’s temperature over 250s were 650°C and 123°C respectively.Kimberley C. Y. Kueh, Timothy C. W. Lau, Graham J. Nathan, Zeyad T. Alwahab

In-situ, well-resolved planar temperature measurement of radiatively-heated particles

DAY 3 Plenary Session - Concentrating Solar Thermal - Minerals Processing. Stream – Concentrating Solar Power - Kueh, K. paper.A direct, single-shot, non-intrusive planar temperature measurement of micron-sized particles in an unsteady flow has been demonstrated. Particles of diameters between 10µm and 50µm were fluidised using an optically-accessible fluidised bed system. The particle temperature was measured with a single ICCD camera fitted with an image splitter and filters to simultaneously record two images over a 7.5mm × 10.8mm area. This resulted in particle temperature maps of 51 pixels/mm, with an average of 15 particles in the measurement region at any given time. The particles were heated to temperatures up to 350°C with solid-state solar thermal simulator to generate a highly uniform heating region at fluxes of up to 21.1 MW/m². These fluxes exceed the range typically found in the particle receivers in Concentrated Solar Thermal (CST) systems, demonstrating that the method is more suitable for investigating heat transfer in them.Kimberley C.Y. Kueh, Timothy C.W. Lau, Graham J. Nathan, Zeyad T. Alwahab

Effect of particle loading on interference in planar laser induced fluorescence thermometry

Planar laser-induced fluorescence (PLIF) of toluene has been applied to measure the gas-phase temperature in a particle-laden jet heated to controlled gas temperatures between 20°C ≤T≤ 120°C. This method utilises the dependence on temperature of the spectral emission of toluene vapour when excited at a wavelength of 266 nm. Single-shot, planar imaging of temperature was achieved with a high signal-to-noise ratio from the ratio of the fluorescent emissions at two wavelength bands that are recorded simultaneously with two intensified CCD cameras, after first correcting for spatial variations in camera efficiency. The effects of interference from particles and laser sheet attenuation on the accuracy of the PLIF thermometry method was investigated for 40 μm PMMA particles, with the volume loading varied in the two-way coupling regime. Reliable measurements were achieved into the two-way coupling regime.E. W. Lewis, T. C. W. Lau, Z. W. Sun, G. J. Nathan and Z. T. Alwahab