Superficial velocity is a term that describes the velocity of a fluid in a packed column. In chemical engineering, it is important to control the superficial velocity to achieve proper fluidization and contact between reactants. Some synonyms for superficial velocity include superficial flow rate, superficial gas velocity, and superficial liquid velocity. The term superficial refers to the flow rate of the fluid as if the column was completely filled with fluid, whereas the actual fluid flow rate is a fraction of the superficial velocity due to the presence of packed bed material. The term is often used interchangeably with bed velocity, which is the velocity of fluid within the interstices of the packed bed.