Timothy C. W. Lau

Experimental and numerical investigation of the iso-thermal flow characteristics within a cylindrical chamber with multiple planar-symmetric impinging jets

We present a joint experimental and numerical study of the flow structure within a cylindrical chamber generated by planar-symmetric isothermal jets, under conditions of relevance to a wide range of practical applications, including the Hybrid Solar Receiver Combustor (HSRC) technology. The HSRC features a cavity with a coverable aperture to allow it to be operated as either a combustion chamber or a solar receiver, with multiple burners to direct a flame into the chamber and a heat exchanger that absorbs the heat from both energy sources. In this study, we assess the cases of two or four inlet jets (simulating the burners), configured in a planar-symmetric arrangement and aligned at an angle to the axis (αj) over the range of 0°–90°, at a constant inlet Reynolds number of ReD = 10 500. The jets were positioned in the same axial plane near the throat and interact with each other and the cavity walls. Measurements obtained with particle image velocimetry were used together with numerical modeling employing...

Laser Attenuation Correction for Planar Nephelometry Concentration Measurements

Planar imaging of optically dense media using laser diagnostics is subject to measurement errors due to the occurrence of laser attenuation. Laser attenuation effects are particularly significant in Planar Nephelometry, a technique which infers particle concentration from the intensity of light scattered from particles. The current study presents an iterative correction method for Planar Nephelometry concentration measurements to account for errors due to laser attenuation. This method minimizes the influence of laser attenuation by applying the corrections directly on instantaneous planar images of the medium investigated. As instantaneous images are used, the method is suitable for measurements of highly turbulent flows that require instantaneous planar information. The proposed correctionmethod is validated experimentally using Planar Nephelometry concentration measurements. Experiments conducted used neutrally buoyant spherical particles suspended in water at various known concentrations. Results indicate that corrections can be used to improve the accuracy of concentration measurements from 65% to approximately 90%.

Iso-thermal flow characteristics of rotationally symmetric jets generating a swirl within a cylindrical chamber

We present a systematic experimental study of the interaction between four rotationally symmetric jets within a cylindrical chamber, under conditions relevant to a wide range of engineering applications, including the technology of a Hybrid Solar Receiver Combustor (HSRC). The HSRC geometry is simplified here to a cylindrical cavity with four inlet jets (representing four burners) which are configured in an annular arrangement and aligned at an inclination angle to the axis with a tangential component (azimuthal angle) to generate a swirl in the chamber. In this study, the jet inclination angle (αj) was varied over the range of 25°–45°, while the jet azimuthal angle (θj) was varied from 5° to 15°. The inlet Reynolds number for each injected jet and the number of jets were fixed at ReD = 10 500 and 4, respectively. Measurements obtained with Particle Image Velocimetry were used to characterise the large-scale flow field within selected configurations. The results reveal a significant dependence of the mean and root-mean-square flow-fields on the jet azimuthal angle (θj) and the jet inclination angle (αj). Three different flow regimes with distinctive flow characteristics were identified within the configurations investigated here. It was also found that θj can significantly influence (a) the position and strength of an external recirculation zone and a central recirculation zone, (b) the extent of turbulence fluctuation, and (c) the flow unsteadiness. Importantly, the effect of αj on the flow characteristics was found to depend strongly on the value of θj.We present a systematic experimental study of the interaction between four rotationally symmetric jets within a cylindrical chamber, under conditions relevant to a wide range of engineering applications, including the technology of a Hybrid Solar Receiver Combustor (HSRC). The HSRC geometry is simplified here to a cylindrical cavity with four inlet jets (representing four burners) which are configured in an annular arrangement and aligned at an inclination angle to the axis with a tangential component (azimuthal angle) to generate a swirl in the chamber. In this study, the jet inclination angle (αj) was varied over the range of 25°–45°, while the jet azimuthal angle (θj) was varied from 5° to 15°. The inlet Reynolds number for each injected jet and the number of jets were fixed at ReD = 10 500 and 4, respectively. Measurements obtained with Particle Image Velocimetry were used to characterise the large-scale flow field within selected configurations. The results reveal a significant dependence of the mean...

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.

Optics and Photonics in Solar Thermal Energy Technologies

The complex optical diagnostics employed in the development and application of solar thermal and wind energy technologies are reviewed, with application in particle receivers, solar reactors, solar-hybrids, heliostat aerodynamics and wind turbines.