What is space velocity and space time?

Space velocity (SV) is the ratio of volumetric flow rate to reactor volume: SV = v0/V, with units of inverse time (h-1). It indicates how many reactor volumes of feed are processed per unit time. Space time (tau) is the inverse: tau = V/v0, representing the time to process one reactor volume of feed. For continuous reactors, space time relates to residence time. Common terms: GHSV (gas hourly space velocity), LHSV (liquid hourly space velocity), WHSV (weight hourly space velocity based on catalyst weight).