Question

A bed of spherical glass beads (density 3000 kg/m³, diameter 1 mm, bed porosity 0.5) is to be fluidized by a liquid of density 1000 kg/m³ and viscosity 0.1 Pa.s. Assume that the Reynolds number based on particle diameter is very small compared to one. If g=10 m/s², then the minimum velocity (in m/s) required to fluidize the bed is

Accepted Answer

The correct answer is (A) 3.33×10⁻⁴. At incipient fluidization, the pressure drop balances the buoyant weight of the bed: 150(1−ε)²μUmf/(ε³dp²)=(1−ε)(ρs−ρf)g. Solving: Umf=(ρs−ρf)g·dp²·ε³/[150(1−ε)μ]=(2000)(10)(0.001)²(0.5)³/[150(0.5)(0.1)]=2.5×10⁻³/7.5≈3.33×10⁻⁴ m/s.

Explanation