Granular temperature distribution in a gas fluidized bed of hollow microparticles prior to onset of bubbling

Abstract

It has been unclear whether bubbles are required to induce particle velocity fluctuations in gas fluidized beds (FBs). We show that bubbles are not necessary by applying diffusing-wave spectroscopy to particles whose minimum bubbling velocity is approximately 5 times that of the minimum fluidization velocity. Fluctuations are first observed at or just above fluidization and increase in magnitude with superficial velocity. The distribution of velocity fluctuations in the bed is also presented: they are symmetrical about the centreline where they are maximal and increase with height above the distributor.

Granular temperature in a liquid fluidized bed as revealed by diffusing wave spectroscopy

“…9 shows variation of height-averaged velocity fluctuations with superficial velocity. The velocity fluctuations are the same order of magnitude as the driving velocity as observed in the other FB systems considered by us to date (Xie et al, 2006;Biggs et al, 2008a,b;Zivkovic et al, 2008), and increase with superficial velocity up to a maximum at U 0 = 7.5 mm/s. Batchelor (1988) hypothesized that for a uniform FB, the particle velocity fluctuations can be related to the mean particle velocity averaged over the FB cross-section, v, by where H() is a function of the solid fraction only.…”

“…DWS (Weitz and Pine, 1993), which has now been applied extensively in the study of particle dynamics in various dense granular systems (Menon and Durian, 1997a,b;Xie et al, 2006;Biggs et al, 2008a,b;Zivkovic et al, 2008) was used here in the transmission mode as illustrated in Fig. 1b.…”

“…The scaling factor, , was set to unity in line with common practice (Weitz and Pine, 1993;Xie et al, 2006).…”

Properties of stationary (bubbling) fluidised beds relevant to combustion and gasification systems

“…Menon and Durian, 1997). Diffusing wave spectroscopy (DWS) has demonstrated that spatial variations in the granular temperature in a two-dimensional gas-fl uidised bed are signifi cant and cannot be ignored (Xie et al, 2006). Positron emission particle tracking (PEPT) has been used to track the velocity and fl uctuations of a single radioactive tracer particle in a dense, three-dimensional system (Wildman et al, 2001).…”

Simulations of flow behavior of gas and particles in a spouted bed using a second-order moment method-frictional stresses model

“…They found that the granular temperature in the axial direction is larger than that in the lateral direction. Xie et al (2006) used a diffusing wave spectroscopy (DWS) to measure the displacement of glass beads in a fluidized bed, and demonstrated that the spatial variations in the granular temperature are significant in a fluidized bed. Holland et al (2008) and Muller et al (2008) measured particle motion in the bubbling fluidized bed by a magnetic resonance technique (MR).…”