Development of a gravimetric system using a conical rotating double-wing diverter for low liquid flow rates. (August 2017) - Cheong, Kar-Hooi
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. Highlights: An improved gravimetric system for low flow rates was developed. The system comprises a diverter, a weighing tank and a liquid discharge mechanism. Diverter timing error relative to liquid collection time is below 0.003%. Evaporation rate relative to amount of liquid collection is below 0.005%. Nozzle size adjustment or wing shape modification improves diverter's performance.