Calculate the velocity of water that would be required to fluidize spherical particles with $S G=1.6$ and a diameter of $1.5 \mathrm{~mm}$, in a tube with a diameter of $10 \mathrm{~mm}$. Also, determine the water velocity that would sweep the particles out of the tube. Use each of the two following methods, and compare the results:

(a) The bed starts as a packed bed and is fluidized when the pressure drop due to friction through the bed balances the weight of the bed.

(b) The bed is considered to be a "swarm" of particles, falling at the terminal velocity of the "swarm." (Assume $\varepsilon=0.45$.)

Comment on any uncertainties or limitations in your results.