Laser Doppler flow probe, measurement

To study the effect of PGDN on cerebral blood flow, Godin et al. (1995) injected male Sprague-Dawley rats (through a jugular vein cannula) with PGDN at 0.1 to 30 mg/ kg and measured cerebral blood flow with a fiberoptic laser-Doppler flow probe in contact with the brain. Following a small initial drop in cerebral perfusion that lasted 1 min, blood flow rapidly increased and reached a maximum 2 min after injection. The increase in perfusion was correlated with dose, but due to the small number of animals and individual variability, a clear dose-response relationship was not obtained. 

Nonintrusive Instrumentation. Essential to quantitatively enlarging fundamental descriptions of flow patterns and flow regimes are localized nonintmsive measurements. Early investigators used time-averaged pressure traverses for holdups, and pilot tubes for velocity measurements. In the 1990s investigators use laser-Doppler and hot film anemometers, conductivity probes, and optical fibers to capture time-averaged turbulent fluctuations (39). 

Cerebral blood flow (CBF) was monitored in the cerebral cortex of the ischemic hemisphere corresponding to the supply territory of the middle cerebral artery by laser-doppler flowmetry (DRT4, Moor Instruments, Devon, UK). To this aim, a rectangular bent laser-doppler probe was glued onto the parietal bone (2 mm posterior and 5 mm lateral from bregma) and local CBF was continuously measured from 20 min before the onset of ischemia until 10 min after reperfusion, keeping the animal under isoflurane anaesthesia. Flow values were collected every 5 min before MCAo and after reperfusion whereas data were collected at 10 min intervals during occlusion. 

In measurement and visualization of gas-solid flow in fast fluidization, various techniques have been developed and used, such as pressure gradient, pressure fluctuation, capacitance probe, optical fiber probe, momentum probe, laser Doppler velocimeter, night-television, and video camera. The resulting data on local gas and solid velocity, solids concentration and its... 

Droplet size may be determined with the use of a laser interferometer. This technique is an extension of the laser Doppler anemometry (LDA) technique commonly used to measure velocities of small particles in a flowing stream. Two equal-intensity Gaussian beams are made to intersect at their focal waists to form a standing electromagnetic wave distribution in the intersection (probe) volume. This standing wave can be visualized conceptually as a set of planar fringes perpendicular to the... 

Groen et al [48] measured the local and time-dependent behavior of the two-phase flow in a bubble column. Measurements with Laser Doppler Anemometry (LDA) and with glass fibre probes were performed in two air/water bubble columns of inner diameter 15 and 23 (cm), respectively. These measurements showed that the time averaged axi-symmetric liquid velocity profiles are a result of the passage of coherent structures (bubble swarms). It was concluded that considering the flow in a bubble column as stationary by far oversimplifies the actual phenomena present. 

The chapter begins with the fundamental measurements of resistance, capacitance, charge, and particle force. We proceed with flow measurements with various probes followed by a listing of some commercial electrostatic instruments. Nonelectrosatic measurements in multiphase flow such as the laser-Doppler anemometer, radioactive tracers, and stroboscopic techniques (Polaskowski, et. al, 1995 Soo, 1982) have not been discussed unless in relation to an electrostatic effect. 

Lehner P, Richtberg M, Wirth KE. Measurement of solids velocities in a co-current gas/solids flow with a laser Doppler anemometer and a capacitance probe system. Werther J, ed. Proc 6 Conf CFB. Wurzburg, Germany, 1999, pp 843-848. 

The experimental apparatus has been described in Sect. 3.2.2. The electroresistivity probe was removed and a two-channel laser Doppler velocimeter was set up to measure the three velocity components of water flow in the bath. The origin of the cylindrical coordinates (z, r, 9) was placed at the center of the bath, as shown in Fig. 3.3. The velocity components were designated by u, v, and w, respectively. The components, u and v, were measured in the z — r plane including the centerline of the bath and the center of the nozzle exit [21,23]. Digitized velocity data were decomposed into the mean velocity and turbulence components as follows ... 

The bubble characteristics, represented by the bubble frequency /b, gas holdup a, mean bubble rising velocity b, and mean bubble chord length Lb, were measured mainly on the y—z plane with a two-needle electroresistivity probe. Water velocity was measured with a two-channel laser Doppler velocimeter [25], The locations at which measurements were made were chosen by reference to the results for the bubble characteristics. The characteristics of water flow were represented by the vertical mean velocity u, the root-mean-square value of the vertical turbulence component w rms, and the skewness and flatness factors of the vertical turbulence component, and F . Data aquisition time was 600 s for each position. 

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