1) Explain what you understand of the concept of "stability of the homogeneously expanded
state". Using excel, plot the kinematic and dynamic wave velocities for a fluidized
system having the characteristics below and apply the Wallis stability criterion to
determine the voidage at minimum bubbling, emb.
dp = particle diameter = 48 μm
rp = particle density = 1420 kg/m3
rf = fluid density = 1.2 kg/m3
μ = fluid viscosity = 1.75x10-5 kg/m s
2) Calculate the heat transfer coefficient h on an horizontal tube bandle with wall
temperature T=80°C immersed in a 110°C bed of 82μm sand particles and fluidized by air at
various velocities. Ignore transfer by convection when gas bubbles contact the surface, i.e.
hg.
Data:
Solids: dp = 82 μm
rs = 2700 kg/m3
ks = 1.2 W/m K
Cps = 756 J/kg K
Gas: kg = 0.033 W/m K
Bed: umf = 0.0075 m/s
emf = 0.476
deq = 0.13 m (equivalent diameter of bubbles in the fluid bed)
The bubble frequency at various gas flow rates is as follows:
u (m/s) = 0.05; 0.2; 0.4;
nw (s-1) = 0.5; 1.4; 2.4;
Please