(740f) On the Effect of Sample Area in Particle Velocity Measurements in Circulating Fluidized Bed Risers

Gas‐particle flow fields with high particle concentrations are ubiquitous in many industries.  Yet these flow fields are often not well understood because the erosive and opaque nature of the high concentration particle flows makes it difficult, if not impossible, to measure flow properties such as particle velocity and concentration.  This has led to the development of a number of novel measurement techniques that are customized for high concentration particle flows.  The data from many of the novel techniques is used for evaluation and improvement of CFD models.  This work shows that the definition of the particle velocity measured with different novel techniques can vary from technique to technique.  Also, the definition of the measured particle velocity may not necessarily be the same as the particle velocity in CFD models.  This can be an important issue when evaluating CFD models with novel measurement techniques. 

In this work high speed PIV was utilized to measure velocities of individual particles in gas‐particle flow fields at the walls of a 0.305 m diameter circulating fluidized bed (CFB) riser, at the National Energy Technology Laboratory (NETL) and a 0.203 m diameter CFB riser at Particulate Solid Research Inc (PSRI), Chicago.  The NETL riser, with High Density Poly Ethylene particles of a mean diameter of 800 micron, was operated in the core‐annulus regime while the PSRI riser with 80 micron mean diameter FCC particles was operated in the dense upflow regime. The HSPIV measurement technique, developed by NETL, has the ability to simultaneously recognize and track thousands of individual particles in flows of high particle concentration. In this study, particle motion was measured over a large sample area with dimensions on the order of 100 particle diameters.  To determine the effect of the size of the sample area, the sample area was divided into smaller sample areas and Lagrangian and Eulerian particle velocities were calculated. The probability density function (PDF) of Lagrangian particle velocity  was compared with the PDF of Eulerian for different domain sizes over a range of flow conditions. The mean shear rate of Eulerian particle velocity, concentration and the granular temperature was examined as a function of the sample area. Finally, the relationship between the Lagrangian and the Eulerian autocorrelation timescale was calculated. This will allow highly accurate measurements of particle dispersion coefficients in CFB risers.