THE USE OF CRITICAL FLOW VENTURI NOZZLES WITH SATURATED WET STEAM

This paper describes the results of an investigation into the use of c ritical flow venturi nozzle flowmeters with wet saturated steam. The r eal-gas flow coefficient has been calculated using the equations of st ate for steam, which show the steam behaviour to be far from ideal alo ng the saturation line. The nozzle was calibrated using superheated st eam and the mass flow rate measured using a condensate weightank was s een to agree with the flow rate measured by the nozzle to within +2%, although up to half of this uncertainty may be due to the uncertainty in the calibration rig and in the measured parameters used in the nozz le equation. The nozzle was then calibrated in saturated steam with dr yness fractions down to 84%. The nozzle can still be used by including a wet steam correction factor in the flow rate calculation, or a more practical approach might be to precede the nozzle by an efficient ste am/water separator, assume the steam then to be dry saturated and acce pt an uncertainty in the mass flow of 3%.