Gas velocity measurements

The second method to calculate of void fraction is based on gas velocity measurement. A high-speed motion analyzer was employed by Zhao and Bi (2001b) to visualize bubble behavior in the test sections. 

Huffaker, R. M., 1970. Laser Doppler detection system for gas velocity measurement, Appl. Opt., 9, 1026-1039. 

The particles in a pressurized gas jet do not necessarily move at the gas velocity. Measurement of gas entrained particle velocities is difficult. Therefore, another test method, involving moving the specimen through a suspended column of particles can also be used. The specimen or specimens are mounted on a rotating arm or wheel with set approach angles and rotated through a stream of particles dropped in their path or suspended in a fluidized bed. There is no ASTM standard for this however, recommended practice does exist for liquid particle impingement (see below). 

Horio et al. (1992a) O3 Optical fiber probe applied to measure particle and gas velocities simultaneously ozone injection upstream of two optieal probes, tracer gas velocity measured using UV light, optical fiber and photomultiplier... 

Temperature compensated anemometry was used for the gas velocity measurements. By sensing the changes in heat transfer from a heated sensor exposed to the fluid motion, thermaJ anemometers measure fluid velocity in terms of voltage. Measurement at conditions should be such that fluid temperature and composition are constant. The system consists of a sensor and a control box which supplies current to keep the temperature constant around the sensing... 

Fig. 4.4.3. The tangential gas velocity measured with LDA at a series of axial stations in a cyhndrical swirl tube. The highest station is just under the vortex finder. The darker the points the lower the station...

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