An API (American Petroleum Institute) separator is designed using Stokes' Law to determine the residence time required for particle rise. API recommends that turbulence should be controlled and that the horizontal flow velocity should not exceed 3 ft/s. It recommends a channel depth of 3 to 8 ft and a channel width of 6 to 20 ft with a depth to width ratio of 0.3 to 0.5. API also recommends a minimum channel length of 5 times the width. Based on API's recommendations, the minimum design Reynolds number for flow through the separator is in the range of 400 000. This is 40 times the transition to fully turbulent flow through a tube.