Wave propagation and granular temperature in fluidized beds of nanoparticles



The speeds of motion of compression waves through a fluidized bed of 10 nm silica particles were determined by measuring the times of arrival of compression zones using a light probe. A correlation for the modulus of elasticity was determined as a function of void fraction. Using a kinetic theory type equation of state for particles, this experimentally determined modulus gives a value for the granular temperature for 10 nm particles of approximately one (meter per second) squared. This value is close to that obtained by assuming the motion of the 10 nm particles to be due to collision with air molecules with no energy dissipation. The values of the granular temperature were also determined in a two-dimensional (2-D) fluidized bed by measuring the volume fraction distributions of 10 nm silica particles. Granular temperatures were deduced from a one-dimensional particle momentum balance using an ideal equation of state for particles, which is similar to the barometric formula for gases. These granular temperatures agreed with the measurements obtained from wave propagation experiments. © 2007 American Institute of Chemical Engineers AIChE J, 2007