Masaki Takamoto

Theoretical discharge coefficient of a critical circular-arc nozzle with laminar boundary layer and its verification by measurements using super-accurate nozzles

Abstract The discharge coefficient of a circular-arc critical Venturi nozzle is derived theoretically by combining theories to calculate mass flow defects caused by the core flow distribution and the laminar boundary layer. The equation obtained is verified by measurements using a constant volume tank system and nozzles of similar shape machined by super accurate lathes, which achieved mirror finish without polishing thus resulting in a machining error of less than 1 μm. The agreement of the theoretical and measured discharge coefficients is better than 0.04% at Reynolds numbers larger than 8×10 4 , the minimum used. The equation derived is in an analytical form, which enables an estimation of the effects of specific heat ratio as well as nozzle shape.

Development of a calibration facility for small mass flow rates of gas and the uncertainty of a sonic venturi transfer standard

Abstract A calibration facility based on the gravimetric method has been developed at NRLM for small mass flow rates of gas. This calibration facility establishes a primary gas flow measurement standard with a combined standard uncertainty of ±0.105% at maximum, for mass flow rates up to about 5 g/min. Two differently sized sonic venturis were tested using this facility and the results show that they can work well as a flow transfer standard for small mass flow rates. It is also shown that these sonic venturis can be used to establish flow transfer standards with a combined standard uncertainty of ±0.112% for the larger venturi and ±0.089% for the smaller venturi.

New measurement method for very low liquid flow rates using ultrasound

Abstract A very small ultrasonic flowmeter for liquids with measuring pipe diameter down to 0.5 mm was developed using disk ultrasonic transducers. The transducer has a hole in the center and the measuring pipe passes through the hole. The vibration mode in the radial direction of the transducer was used, and ultrasound was transmitted and received from outside the pipe wall. The flowmeter can measure a liquid flow rate below 1 ml/min, which corresponds to a Reynolds number of about 40 based on the measuring pipe diameter. The standard deviation of flow rate measurement was 0.01 ml/min (1%) at the flow rate of 1 ml/min.

Development of a new diverter system for liquid flow calibration facilities

Abstract The diverter system is a key component in achieving a high-accuracy liquid flow rate standard using a static gravimetric system with a flying start and stop method. A new system with double diverting wings has been developed in order to reduce the diverter timing error that dominates the uncertainty in the calibration of flowmeters. The basic concept of the new system is that each wing should move in the same direction at the beginning and end of measurement. The diverter timing error has been estimated using a small prototype in a water flow circuit in order to make a comparison between the performance of the new system and those of conventional systems with a single diverting wing. The results show that the jet flow condition has little effect on the timing error estimated by the double-wing method, although the error with the single-wing system is dependent on the liquid flow rate. Therefore, the triggering of the timing system can be easily adjusted over a wide range of flow rate by using the new diverter system. Furthermore, this system is adopted for a new calibration facility for hydrocarbon flow measurements at NMIJ.

Choking phenomena of sonic nozzles at low Reynolds numbers

Abstract The choking phenomena of sonic nozzles were investigated for the Reynolds number range from 40 to 30 000 for nitrogen gas. The results showed that the critical back pressure ratio is a function of the Reynolds number only, with different characteristics for different nozzle shapes. In ISO-type toroidal-throat Venturi nozzles, the minimum Reynolds number satisfying the choking condition is about 40 and the critical back pressure ratio is only about 0.05 at this minimum Reynolds number. It was also found that the critical back pressure ratio has a local minimum value around Reth=4000 and that the local maximum value is around Reth=10 000 due to the change in characteristics of the boundary layer in the diffuser. On the other hand, the critical back pressure ratio in quadrant nozzles decreases monotonically with decreasing Reynolds number, unlike the former nozzle, and the minimum Reynolds number necessary for choking is estimated to be approximately the same as that in the Venturi nozzle.

Development of a transfer standard with sonic Venturi nozzles for small mass flow rates of gases

Abstract We have developed a transfer standard system with sonic Venturi nozzles for small mass flow rates of gases. The system is composed of a newly developed automatic pressure controller, two pressure sensors and one temperature sensor to measure the flow conditions in the upstream and downstream sides of a nozzle. The whole system is packed in a portable aluminum trunk. The data are sent to a laptop computer, and the results are displayed on the screen and are written to files. The system can calibrate a flow meter in the flow rate range from 10 mg/min to 100 g/min using ten different sonic Venturi nozzles with the expanded standard uncertainty ( k =2) being less than 0.2% for nitrogen. Examples of mass flow controller calibrations are given.

Installation effects on vortex shedding flowmeters

Abstract Numerous measurements of the effects of pipe fittngs on vortex shedding flowmeters are carried out as a contribution to flow metering standards. A water test line of 150 mm diameter is used in the experiments covering a Reynolds number range of about 2 × 10 5 to 10 6 . The effects of six kinds of piping configurations are examined at various upstream straight pipe lengths and all four kinds of liquid vortex shedding flowmeters, which were commercially available in Japan, are tested. The vortex shedding flowmeters are compared with a turbine meter in experiments designed to evaluate reproducibility of measurements. The uncertainty of the measured data is estimated at about 0.1%. It is found that the magnitude of each installation effect strongly depends on the design of the flowmeter. The experimental results are presented in detail and a table is given of the minimum upstream straight pipe lengths needed to suppress the effects to less than 0.5% for each of the tested flowmeters. This can be used as guidance in the installation of vortex shedding flowmeters.

CFD Aided Investigation of Multipath Ultrasonic Gas Flow Meter Performance Under Complex Flow Profile

This paper presents a systematic investigation of the influence of complex flow profiles on the performance of multipath ultrasonic gas flow meter by using computational fluid dynamics (CFDs) simulation. To guarantee the overall agreement between the CFD predictions and the measurements, the meshing approaches, generation of boundary layers, turbulence models, and wall treatment methods for CFD simulation are elaborated carefully. The performances of a multipath ultrasonic gas flow meter under complex flow profiles, regarding to an out-plane double-elbow with a half-moon block and an out-plane double-elbow with a half-moon block equipped with a Spearman conditioner, are investigated. The simulation results demonstrate that for complex flows with strong asymmetric and swirling velocity profiles inside an out-plane double-elbow pipeline with a half-moon block, a four-path ultrasonic flow meter located at 20-D right after the second elbow together with a Spearman conditioner installed 16-D upstream the meter is of providing a flow velocity estimation that the error is within ±0.5%, while the Reynolds number ranges from 3.25×103 to 3.25×105. The effect of sound path orientation on the performance of flow meter is also discussed.

Methods to calibrate a critical nozzle and flowmeter using reference critical nozzles

Abstract Methods to calibrate a critical nozzle and a flowmeter against reference critical nozzles are developed to replace the time-consuming conventional procedures. The discharge coefficient of a critical nozzle at a low Reynolds number was measured in a series connection with a reference nozzle in the upstream position, and its Reynolds number dependence was obtained by changing the reference nozzle. The dependence of similar critical nozzles with negligible machining error measured at low pressures using the series connections and at atmospheric pressure using a constant volume tank system coincide within ±0.04%. The same configuration was employed to measure the stability of the choking flow rate, which revealed premature unchoking phenomenon. The discharge coefficient of a critical nozzle under a reference condition was measured by a combination of three series connections with two reference critical nozzles at the upstream positions. Reynolds number dependence of a critical nozzle was measured using a combination of three series connections with four reference critical nozzles. These two methods require only one pressure gauge whose sensitivity is constant in a narrow range. An air flowmeter was calibrated at various volumetric flow rates against only one critical nozzle by controlling the upstream pressure of the nozzle.

Wet Steam Flowrate Calibration Facility

Newly developed wet steam flowrate calibration facility is introduced. It has a closed loop in which boilers generate a steam flow up to 800 kg/h. Steam flow of known wetness up to 12% is generated by cooling down a dry steam flow by a heat exchanger. The wetness is calculated from the enthalpy the heat exchanger draws from the dry steam flow. Analysis of the facility performance, calibration results of an orifice flowmeter calibration, and uncertainty analysis are described.Copyright