A standpipe operates in the packed bed flow regime when

Question $9$Select one:

a$.$

The superficial velocity of the gas is less than the relative velocity between gas and solids at incipient fluidization

b$.$

The relative velocity of the gas is less than the relative velocity between gas and solids at incipient fluidization

c$.$

The actual velocity of the gas is less than the relative velocity between gas and solids at incipient fluidization

d$.$

The actual velocity of the solids is less than the relative velocity between gas and solids at incipient fluidization