To verify the measurement capability and performance of the newly established primary low-pressure gas flow standard, a mercury-sealed piston prover, at the National Institute of Metrology of Thailand (NIMT), a bilateral comparison with the piston prover at the Center for Measurement Standards (CMS, Taiwan) was conducted. The piston prover at NIMT has a measurement capability of 5 mL/min to 24 L/min flow range with a relative expanded uncertainty smaller than 0.13 %, whereas that of the system at CMS is 2 mL/min to 24 L/min with 0.10 % expanded uncertainty. The transfer standard (TS) used was a set of three critical flow venturis (CFV’s) with dedicated thermometers. The TS was used at eight flow rates of dry air ranging from 42 mL/min to 14.5 L/min at 0 ℃ and 101.325 kPa (0.055 g/min to 18.87 g/min). Comparison showed that the differences in the normalized average discharge coefficient between NIMT’s measurements and the reference values based on CMS’s results were smaller than 0.06 % throughout the range of flow tested. The En values for the flow measurements at NIMT with reference to CMS were all well less than unity. The equivalence between the two participants was thus demonstrated.

Low-pressure gas measurements are of increasing interest in the process industry for both control purposes and emission measurements. Industrial measurement environments include some very challenging components, such as:
• Dust, particles, vapor, water droplets, etc.
• Temperatures up to 1200 °C
• Pipe diameters of 1 to 10 m
Ultrasound flow measurement techniques have many advantages for such industrial measurement problems. Currently, a major problem is the lack of transducer technology that is sufficiently robust to operate in the presence of the above given industrial components. For the purpose of producing more robust technology, a gap discharge sound transmitter has been developed. Theoretical and experimental studies of the gap discharge transmitter indicate that flow measurement performances in the range of 1-2 % of the actual flow is achievable.
Based on this gap discharge transmitter, an experimental ultrasound gas flowmeter was designed. The design features a gap discharge transmitter and piezo-based receivers. The design was tested in a real industrial environment. The test environment included heavy dust and water vapor in an exhaust pipe at a pelletization plant at LKAB, Kiruna, Sweden. The pipe diameter is 3 m, the pressure is ambient, and the gas flow speed is in the range of 5-20 m/s. The flow conditions were highly turbulent, using a straight pipe length ten times the pipe diameter in front of the experimental flowmeter. This paper presents the experimental gap discharge ultrasonic flowmeter design, the experimental setup and some measurement data. These data indicate that the gap discharge transmitter is feasible for operation in an industrial environment. Further preliminary flow measurement data demonstrate the feasibility of using a gap discharge transmitter as the sound-emitting source in an ultrasonic gas flowmeter.

Orifice plates can be contaminated by oil, grease, pipeline sludge or other liquids or solids. Experience shows that sometimes the contamination extends to the sharp edge of the orifice plate, but that on many occasions any possible contamination near the edge is cleaned by the flow. The latter case is investigated here. In some of the existing sets of data the contamination in the form of soft deposits used to gather the data means that interpretation is not straightforward; so Computational Fluid Dynamics (CFD) was used to assist in the interpretation.
In the experimental work the contamination was simulated by sticking circular metal discs of defined thickness and radius to the plates so as to leave an untouched region in the neighbourhood of the sharp edge. The effect of this contamination was measured in nitrogen at 63 bar absolute. CFD was used to investigate similar contaminated plates.
A contamination angle was defined, and the CFD predictions were plotted against the contamination angle. The simulations for a diameter ratio, β, equal to 0.6, almost lie on a single curve. The β = 0.2 and β = 0.4 points lie above this curve and the β = 0.75 points lie below the curve. The new NEL experimental data are compared with the CFD and the Advantica data on coated plates with a clean ring as in ISO/TR 12767.
It is clear from the experimental data, as indeed from the CFD, that although the ratio of the thickness of the contamination to the distance from the orifice edge is the most important effect on the shift it is not the only effect. An equation for the percentage shift in discharge coefficient was derived to fit the experimental data: this has an uncertainty of 0.28 % based on 2 standard deviations. The CFD are in remarkably good agreement with the experiments and support the inclusion of the new model in a revision of ISO/TR 12767.

It is often difficult to realize calibrated accuracy of a flow metering system over measurement range when it is installed under hostile and perturbed flow conditions. Though widespread studies are reported in literature on individual characteristics of meters, comparative evaluation of the performance of these devices under real life installation situations is relatively inadequate. Present study compares classical venturi, cone, standard orifice and new slotted orifice and four hole orifice meters. Experiments are carried out to investigate the effects of single elbow, double elbow in and out of plane, reducer, and expander on the response characteristics of these devices. Discharge coefficients and pressure loss characteristics are analyzed and compared. Pressure and velocity variations created by the flow element restrictions with adjacent meter tubing are also analyzed with computational fluid dynamic simulations. Minimum upstream straight pipe lengths to suppress the effects for each of these tested flow meters are proposed.

There are several relatively new differential producing meters that are available for end users. Each meter claims to have advantages over other meter types, specifically orifice meters. Meter types discussed include; cone meters, Venturi meters, multi-ported averaging pitot tubes, multi-holed orifice plates, and diagnostic differential meters. This paper is intended to be used by purchasers of these meters to help them obtain the best meter for their application. The operating principles of these meters will be explored. This paper will look at the claims that the manufacturers of these meters make in terms of accuracy, required upstream lengths, and diagnostic capabilities. Another important aspect of these meters is industry’s reaction to these meters. Should these meters be included in standards documentation? What data needs to be collected to properly develop standards, and what standards exist to help develop these meters? Additionally, the implementation of these meters and metering systems is discussed with the intent of developing system uncertainties. From a calibration facility perspective, many issues have been observed with differential metering systems. Several of these issues will be discussed in detail along with their associated implications.