Kyung-Am Park

The evaluation of critical pressure ratios of sonic nozzles at low Reynolds numbers

Abstract A sonic nozzle is presently used as a reference flow-meter in the area of gas flow-rate measurement. The critical pressure ratio of the sonic nozzle is an important factor in maintaining its operating condition. ISO 9300 suggested that the critical ratio of a sonic nozzle should be a function of area ratio. In this study, 13 nozzles designed according to ISO 9300, with diffuser half angles of 2°–8° and throat diameters of 0.28 to 4.48 mm were tested. The testing result for the angles of 2°–6° are similar to that of ISO 9300. But the critical ratio for the nozzle of 8° decreases by 5.5% in comparison with ISO 9300. However, ISO 9300 does not predict the critical pressure ratio at Reynolds numbers lower than 10 5 . To express the critical pressure ratio of sonic nozzles at low Reynolds numbers, it is found that the critical pressure ratio should be related as a function of Reynolds number rather than area ratio, as used by ISO 9300. A correlated relation of critical pressure ratios and low Reynolds numbers for small sonic nozzles is suggested in this investigation, with an uncertainty of ±3.2% at 95% confidence level.

Effects of cavitation and plate thickness on small diameter ratio orifice meters

Abstract High differential pressure drop is frequently required in the process line of electric power plants. However, cavitation produced by a high pressure drop could damage the pipe and pump blades. In these experiments, the effects of cavitation and plate thickness for small-bore diameter (d) to pipe diameter (D) ratio ( β = d/D) orifice plates were evaluated in a 100 mm diameter test section of a water flow calibration facility. Three size orifice meters were tested with β = 0.10, 0.15, and 0.33 and no bevel on the throat. The cavitation number at inception was measured to be 1.0 to 1.2 for all experiments. Although cavitation occurred in all experiments, the discharge coefficient was affected by cavitation only for the smallest bore ( β = 0.10) and thickest plate tested, 7.0 mm or t/d = 0.70 where t is the plate thickness. Thickness seemed to influence the discharge coefficient only for the β = 0.10 plate. But the trends in the results for thickness were not conclusive and could be attributed to edge sharpness.

Effects of inlet shapes of critical venturi nozzles on discharge coefficients

Abstract The discharge coefficients of critical venturi nozzles were obtained in a high-pressure gas flow standard system, which was a gravitational weighing system. The calibration uncertainty of a critical venturi nozzle of about 8 mm throat diameter was ±0.08% and ±0.14% at upstream stagnation pressures of 4 MPa and 1 MPa, respectively. The discharge coefficients of critical venturi nozzles fabricated according to ISO specifications are in good agreement with ISO correlation. The discharge coefficients for small inlet radius decrease significantly as the inlet length becomes short, owing to separation at the sharp inlet. For nozzles having long inlet radius, the effects of inlet length on the discharge coefficients were relatively small, but the effects become significant at the short inlet length. The effect of separation at the inlet is stronger than that of the boundary layer growth. The experimental results provide excellent support for the shape of critical venturi nozzles suggested by ISO specifications.

CIPM key comparison for low-pressure gas flow: CCM.FF-K6

A key comparison between seven national metrology institutes in the area of low-pressure gas flow was organized by the Comit? International des Poids et Mesures (CIPM) and the Working Group for Fluid Flow. A set of eight critical flow venturis with dedicated, redundant pressure and temperature sensors was used as the transfer standard at flows between 4.4 g/min and 260 g/min. Preliminary testing in the pilot lab determined temperature operating bounds and corresponding uncertainties. The transfer standard contributed a standard uncertainty of <0.026% to the comparison, primarily due to environmental temperature effects, the pressure sensors, and gas properties (the critical flow function and molecular mass of moist air). Redundant measurements by the transfer standard and the star pattern testing were valuable for maintaining low transfer standard uncertainty. The results supported equivalence between the labs with the largest difference between any two participants at any of the flows tested being 0.308%. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Measurement of gas flowrate by using a heat pulse

Abstract A heat pulse was used to measure gas flowrate. Direct current was supplied to a manganin wire wound around a stainless steel tube, which was connected at both ends to vinyl tubes in which thermocouples were installed. A switch, amplifier, comparator and timer were used to generate the heat pulse and to measure the transit time, which was strongly dependent on the consumed power rate and pick-up position. As the power rate decreased, the transit time increased. Also, it was found that the pick-up position should be close to the heater to get a short transit time. The linear range with the heat pulse was up to about 1:10 with a standard deviation of 0.042. It is expected that this sensor would make a good flow measurement device with optimization of pick-up position, power consumption rate and heater material.

Characteristic Research of Sonic Nozzles Using Step-Down Procedure in Low Reynolds Number (Keynote Paper)

The aim of this investigation is to develop the minute flow measuring technology to calibrate sonic nozzles at the low flow rate and low pressure without the expensive primary standard system. With this calibrated sonic nozzles, calibration service of flow meters to industry will be available. In this experiment, eight sonic nozzles with the throat diameter of 0.2 mm were manufactured according to the specifications of ISO 9300, and then four out of eight nozzles, which have most close values of the rate of discharge coefficients for a pair of nozzles, were selected. At first, all the four nozzles for the stagnation pressure range of 200∼600 kPa were calibrated in the standard system. Then, for the rest of the whole experiments, the step-down procedure was adopted to reduce the stagnation pressure range of the nozzle, 3∼600 kPa. It was proven that the step-down procedure can be done over and over with small additional uncertainty.Copyright

Performance Enhancement of Wet Gas Flow Meter

Wet gas flow meters are used in the gas flow meter manufacturing industries as a reference meter. Also those meters are used for gas flow measurement in many areas. Oil is suggested for sealing fluid in a wet gas flow meter. But water is used because of cheap and easy handling fluid in the industries. In this case, the inlet gas flow rate is different with the outlet gas flow rate because the evaporation of water in the chamber. It is important to estimate the rate of water evaporation and effects on flow measurement error. The humidity of wet gas in the outlet of a flow meter was measured. Flow measurement error due to water evaporation is about 2%. Those results will be useful for flow measurement error reduction of wet gas flow meter using water as sealing fluid. The new developed wet gas meter measured pulse and frequency in encoder through magnetic coupling between the chamber and an encoder. The flow quantity was compensated with adjustment of flow rate error. So the rangeability and error of flow measurement were enhanced remarkably.Copyright