MEASUREMENTS OF SOLIDS CONCENTRATION AND AXIAL SOLIDS VELOCITY IN GAS-SOLID 2-PHASE FLOWS

Several techniques reported in the literature for measuring solids con centration and solids velocity in (dense) gas-solid two-phase flow hav e been briefly reviewed. An optical measuring system, based on detecti on of light reflected by the suspended particles, has been developed t o measure local solids concentration and local axial solids velocity i n dense gas-solid two phase flows. This system has been applied to stu dy hydrodynamics of a cold-flow circulating fluidized bed unit operate d in the dense flow regime (u degrees: 7.5-15 m s(-1) and G(s) = 100-4 00 kg m(-2) s(-1)). With increasing solids mass flux, at constant supe rficial gas velocity, lateral solids segregation became more pronounce d (i.e. extent of development of core-annulus structure) while the rad ial profiles of axial solids velocity hardly changed. A decrease in su perficial gas velocity, at constant solids mass flux, also augmented t he lateral solids segregation. The axial solids velocity decreased ove r the entire tube radius, although the shape of the profiles showed no strong dependence with respect to the superficial gas velocity. Avera ge solids mass fluxes calculated from the measured local values of sol ids concentration and solids velocity exceeded the imposed solids mass flux, a finding which could be explained by the downflow observed vis ually of solid particles close to the tube wall. In addition, cross-se ctional averaged solids concentrations obtained on the basis of the op tical measuring system and those obtained from the pressure gradient m easurements showed satisfactory agreement.