Development of a gravimetric system using a conical rotating double-wing diverter for low liquid flow rates

Abstract

An improved gravimetric system for low flow rates was developed at National Metrology Institute of Japan (NMIJ) to perform calibration method of flying-start-and-stop. The present paper describes the main features of the gravimetric system comprising three main components – a compact and umbrella-like conical rotating double-wing diverter, a weighing tank with a chimney-like inlet structure, and a liquid discharge mechanism using a suction nozzle – with explanation of the design considerations behind each feature. Performance tests show that, under the most unfavorable conditions, diverter timing error relative to liquid collection time is below 0.003% whereas evaporation rate of weighing tank relative to amount of liquid collection is below 0.005%. Dependency of diverter timing error on flow rates due to liquid collection loss was also revealed, and this shortcoming was improved by either one of the two following countermeasures: adjustment of nozzle sizes or modification of wing shape. These two measures are both effective in achieving a consistent timing error with varying flow rates. The overall performance results confirm the gravimetric system's capability in performing low flow calibration.