$55.$ Investigate the design and operation of trickle bed reactors, emphasizing their role in multiphase reaction processes.

a$.$ Explain the fluid dynamics and mass transfer mechanisms that occur in trickle bed reactors, including the impact of liquid flow rate and gas$-$liquid distribution on reactor performance.

b$.$ Detail the considerations involved in selecting packing materials and designing the bed structure to optimize contact efficiency between the phases.

c$.$ Provide an analysis of the common operational issues encountered in trickle bed reactors, such as channeling and flooding, and the strategies employed to mitigate these issues.