UNCHOKING PRESSURE RATIO FOR CRITICAL FLOW VENTURIS

摘要

The choking pressure ratio (CPR) for a Critical FlowVenturi (CFV) is defined as the ratio of the maximumpermissible exit pressure to the inlet pressure that can existacross the venturi and still maintain sonic velocity at the throat.Experimental data is presented for a series of small critical flowventuris with throat diameters from 0.79mm (0.031”) to3.18mm (0.125”) and with various diffuser geometries. Testdata was obtained over an inlet pressure range from subatmospheric41 kPa (6.0 psia) to 965 kPa (140 psia).American National Standard ASME/ANSI MFC-7M-1987entitled “Measurement of Gas Flow by Means of Critical FlowVenturi Nozzles” gives the design parameters for CFV’s, andpredicts the choking pressure ratio for throat Reynolds numbersexceeding 200,000. For lower Reynolds numbers, the datapresented in this paper will indicate where more stringentdesign parameters must be followed to insure accuratemeasurement.