The pressure drop in a venturi meter (Fig. P3.128) varies onlywith the fluid density, pipe approach velocity, and diameterratio of the meter. A model venturi meter tested in water at20°C

shows a 5-kPa drop when the approach velocity is 4 m/s.A geometrically similar prototype meter is used to measuregasoline at 20°C and a flow rate of 9 m'/min. If the prototypepressure gage is most accurate at 15 kPa, what should theupstream pipe diameter be?