(220d) Counter-Intuitive and/or Unique Occurrences in Gas-Solids Flow

There are several instances in gas-solids flow systems when what occurs is counter-intuitive and/or unique. A list of questions describing these instances in gas-solids flow systems are:

1. Why does the pressure drop across a cyclone decrease with increasing solids flow rate into the cyclone when adding solids to a pneumatic conveying line causes the pressure drop to increase across it?
2. How can a cyclone dipleg immersed in a fluidized bed operate with no dense-phase section in the dipleg?
3. How can an L-valve feeding into a fluidized bed operate with no solids flow through it and still prevent gas from the fluidized bed from flowing up the standpipe above it?
4. Why does the solids flow rate from a hopper increase when a pipe is added to the outlet of the hopper?
5. Why does a pressure reversal zone exist immediately above the solids flow control valve in an underflow, fluidized-bed standpipe (operating with Group A solids) used in many catalytic regenerator/reactor types of processes?

These counter-intuitive and unique instances occurring in gas solids flow systems will be described and explained.