Laser sheet imaging

An individual isothermal surface can be traced with the help of laser tomography, also known as laser sheet imaging, where a laser sheet and oil droplets are combined to visualize the instantaneous flame surface in a plane. This technique is ideal when wrinkling of an isoline is of interest besides, typically it shows the area occupied by the combustion products if the instantaneous flame thickness is small, such as a black area in... 

Conceptual model of conventional Cl combustion characterized by a sequence of processes occurring in a fully developed reacting jet. (From Dec, A Conceptual Model of DI Diesel Combustion Based on Laser Sheet Imaging, SAE, 970873,1997. With permission.)... 

J. E. Dec. A conceptual model of DI diesel combustion based on laser-sheet imaging. SAE Paper 970873, 1997. 

Used laser-sheet imaging technique to study the jet penetration for 3[Pg.681]

The vast majority of work on pneumatic transport has been in pipes and ducts of much smaller diameter and higher HjD ratio than the riser reactors considered in this chapter. CFB research has usually only touched on such dilute conditions (generally Sgav < 1%) when necessary, e.g., in order to be able to obtain laser sheet images. Correlations and models developed for fast fluidization conditions are unlikely to give accurate predictions when pneumatic transport conditions prevail. 

At low solids concentration the laser sheet imaging shown in Fig. 40a is useful in observing fluidized beds. However, the original images on the light source... 

At higher solid fluxes, the core of the riser can be observed using a hood or an endoscope as shown in Fig. 40c,d. Examples of laser sheet images are shown in Fig. 40e. 

Figure 40 Laser sheet technique, image modification, and laser sheet picturing in dense suspension, (a) Scanning laser sheet imaging (Tsukada et al., 1997) (b) horizontal profiles of gray scales of the images before and after image modification (ro = 0.5 m, cellophane tape correction by interpolation) (Tsukada et al., 1997) (c) hood system of Kuroki and Horio (1994) (d) endoscopic system of Werther and Rudnick (1996, courtesy of Prof. Werther) (e) 3D image obtained from scanning laser sheet images (Horio and Ito, 1997)—upper turbulent bed ( o = 0.58 m/s = 0.045 kg/m s), and lower fast bed (wq = 1.1 m/s, Gs = 0.087 kg/m s).

Ito M, Tsukada M, Horio M. Three dimensional meso-scale structure of gas-solid suspensions in circulating fluidized beds, determined by the scanning laser sheet image analysis. Proc F Particle Technology Forum, Vol. 1, 1994, pp 428 33. 

Other measurements of Hanratty s p have been made or inferred from various techniques, including a hot film probe just under the water surface (Brumley and Jirka, 1987), particle image velocimetry in a vertical laser sheet leading up to the water surface with a florescent dye to indicate water surface location accurately (Law and Khoo, 2002) and PIV on the water surface (McKenna and McGillis, 2004 Orlins and Gulliver, 2002). The measurements of Law and Khoo (2002) are especially interesting because the following relationship was developed from experiments on both a jet-stirred tank and a wind-wave channel ... 

Figure 2 Diagram of a generalized 2D-PIV setup showing all major components flow channel with the particle seeded fluid flow, laser sheet pulses illuminating one plane in the fluid, a CCD camera imaging the particles in the laser-illuminated sheet in the area of interest, a computer with PIV software installed, a timing circuit communicating with the camera and computer and generating pulses to control the double-pulsed laser. The PIV software setups and controls the major components, and analyses the images to derive a vector representation of flow field (see Plate 4 in Color Plate Section at the end of this book).

In the gas-liquid two-phase flows illuminated by a laser sheet, for example, the intensity of light reflected from the gas-liquid interface (mostly the gas bubble s surface) not only saturate the CCD camera, but also overwhelm the intensity of light from the seeded tracer particles in its vicinity. Fluorescent particles are often used to realize the laser-induced fluorescence (LIF) technique together with PIV (e.g., Broder and Sommerfeld, 2002 Fujiwara et al., 2004a, b Kitagawa et al., 2005 Liu et al., 2005 Tokuhiro et al., 1998,1999), so that both images of gas-liquid interface (e.g., bubble s geometry) and velocity distribution in the liquid phase around the gas bubbles can be obtained. Issues on PIV measurement of gas-liquid two-phase flows will be further illustrated in the latter sections. 

As far as the sheet image scanner is concerned, another remaining issue is spatial resolution, which is currently 36 dpi. To improve the resolution we must reduce the size of both organic transistors and organic photo detectors. Reduction of device dimensions is not very difficult, but the bottleneck is the size of via interconnections. To reduce the diameter of via holes, we are currently working very hard to replace a CO2 laser with other short wavelength lasers, for example excimer lasers and/or YAG lasers. We believe that 600 dpi would be feasible in the near future. 

Further concerns regard other technical aspects. For example, out-of-plane motions of the particles caused by normal-to-laser-sheet velocity fluctuations, or the maximum parallax angle related to perspective distortions that grow from fhe confer to the edges of the images. 

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