space velocity refers to the quotient of the entering volumetric flow rate of the reactants divided by the reactor volume (or the catalyst bed volume) which indicates how many reactor volumes of feed can be treated in a unit time (for instance, a reactor with a space velocity of 7 h−1 is able to process feed equivalent to seven times the reactor volume each hour). It is commonly regarded as the reciprocal of the reactor space time. In industry, space velocity can be further defined by the phase of the reactants at given conditions. Special values for this measurement exist for liquids and gases, and for systems that use solid catalysts.[1]