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T. Mušič, G. Bobovnik, J. Kutin
Liquid level detection in standard capacity measures with computer vision

The article presents a computer vision system for liquid level detection in standard capacity measures that can be used for automating measurements or preforming them in inaccessible places. The developed computer vision system consists of a digital camera and a computer program in the LabVIEW environment. The acquired images are processed and corrected for different distortions (parallax, lens and tilt distortion). By using the edge detection method, liquid level is detected and corrected for all distortions. The computer vision system was tested using water in a laboratory environment on the standard capacity measure with a nominal capacity of 100 l. The measurement results acquired with the automated computer vision system were compared with the readings made by an operator and the agreement is found to be satisfactory.

U. Primožič, G. Bobovnik, J. Kutin
PVTt primary flow standard for small gas flow rates

A PVTt primary flow standard operates on the principle of determining the change of density of the measured gas in the tank of a known volume and the corresponding time interval. The PVTt standard presented in this paper is based on the diverter-operated flying start and finish method. It contains the gas collection tank that is constructed as a dismountable assembly, which enables determining its internal volume by dimensional measurements. The standard is designed for the flow range from 0.12 mg/min to 12 mg/min and it achieves the relative expanded measurement uncertainty between 0.12% and 0.24%. We performed a comparison of the realized PVTt flow standard with the piston-prover flow standard for flow rates above 1.2 mg/min, and the results were found successful in view of normalized errors, En.

G. Bobovnik, J. Kutin
Effects of inclination of a clearance-sealed piston prover on the leakage flow rate

The leakage flow rate represents one of the most important contributions to the uncertainty of the measured gas flow rate at the bottom limit of the measuring range in a clearance-sealed piston prover. In order to successfully minimize its uncertainty contribution, it is necessary to understand the effects related to the reproducibility of the piston's travelling path relative to the cylinder and to the ability to position the piston prover in the ideal vertical position. The paper deals with an experimental study of the leakage flow rate in the inclined piston prover. The test results show that the leakage flow rate slightly increases with the inclination of the flow cell and that the leakage flow rate is correlated to the pressure inside the flow cell of the piston prover. The results indicate that such relationship could also be applied for predicting the leakage flow rate in a non-inclined piston prover.

Chen Hui-yu, Cui Li-shui
Experimental Investigation to Measure the Natural Flow by Gas Laser Doppler Laser Doppler Velocimetry

In order to solving the natural gas flow measurement problem about measuring flow under the complicated conditions and the measurement traceability of large diameter instruments, a set of optical natural gas flow metering devices based on Laser Doppler Velocimetry was established, translating the traditional flow volume measurement into pipeline section velocity field measurement to achieve the accurate measurement of natural gas flow. Results show that: the facility can achieve 1.45Mpa, 500m³/h the largest experiment measuring ability and the expanded uncertainty was 1.42% (k = 2); The relative deviation between the experimental results and the standard flow based on the ultrasonic flowmeter was 0.09% ~ 2.93%; The results verify the feasibility of optical method measuring natural gas flow, and the established experiment system can be used for broader flow range of the research of high pressure natural gas flow measurement.

H. Warnecke, C. Kroner, D. Schumann, J. Tränckner
Cavitating Herschel Venturi nozzle test rig

Cavitation is a phenomenon, which is typically associated with negative effects, for example damage at propellers in water. However, there are various applications in which cavitation is exploited advantageously such as injection nozzles in diesel engines or cleaning with an ultrasonic bath. A new application is the deployment of cavitating nozzles in liquid flow measurements. The novelty of the application means from a metrological point of view the requirement to analyse potential influencing factors on the measurement quality in-depth. These comprise among others the installation conditions of the nozzles in a test rig or the additivity of flows when more than one nozzle is used. Furthermore, comprehensive insights into cavitation processes for different liquids are desirable with the view on a broad range of cavitation nozzle applications in liquid flow measurements.
First investigations are carried out for different fluids including liquid mixtures such as white spirits. A detailed analysis of the pressure measurement in front and at the back of the nozzles gives further information about how fast the flow rate changes and about the cavitation process itself. This is of relevance for a possible application, in which flow rate profiles are used to assess flow meter performance under dynamic loads. Such load profiles e.g. serve as input for a test rig with cavitation nozzles to assess the performance of domestic water meters.

D. Jonker, W. M. Dlamini, R. M. Molefe
Flow Instability Evaluation at the NMISA Gas Flow Laboratory

Interlaboratory comparison and verification measurements performed in the Gas Flow Laboratory indicated stability problems in the flow ranges below 50 mL/min and above 30 L/min. Initially the stability problems in the low flow range below 50 mL/min were attributed to the flow cell used as reference standard. The unstable measurements above 30 L/min were attributed to the lack of sufficient pressure drop in the flow path from the gas cylinder to the measuring point. However, further measurements performed indicated that this might not be the cause of the instabilities experienced. To further investigate the matter, a second reference standard was acquired, and the flow path was lengthened and equipped with more pressure regulators to ensure better pressure control and a larger pressure drop. This paper discusses the methods to determine the causes of the instability, the measurements performed, analysis of the measurement results and measures implemented to eliminate further problems.
This paper includes a discussion of the possible flow instability generated by the insertion of thermistors in the flow path to perform temperature measurements of volume flow devices. The Flow Laboratory regularly receives volumetric flow devices and to calculate standardised flow conditions, it is necessary to measure the gas temperature and pressure at the unit under test (UUT) location. Emphasis is given to the determination of the immersion depth and measurement position of the temperature sensor in the flow path to ensure no, or negligible, disturbances in the gas flow path.

Jos van der Grinten, Bodo Mickan
Combining three independent traceability chains for high-pressure gas flow in Germany

Currently all measurement capabilities for high-pressure gas flows in Germany are based on a single traceability chain. However, there are three primary standards available that can be made traceable without mutual dependencies. In this study PTB investigates the benefits of combining three independent traceability chains. The applied method is identical to the harmonization of the high-pressure cubic metre of natural gas [1]. For two G1000 transfer reference meters the measurement uncertainty decreases from 0.110% to 0.089%. For the working standards the CMCs decrease from 0.156% and 0.175% to 0.142% and 0.163% respectively. When only two chains are used the CMCs of the working standards improve with approximately 0.01%. More scenarios are explored. The development of a new primary standard with a CMC of 0.10% has the potential to improve the CMCs of the working standards with approximately 0.02%.

M. Olbrich, E. Schmeyer, M. Bär, M. Sieber, K. Oberleithner, S. Schmelter
Identification of coherent structures in horizontal slug flow

Multiphase flow measurement devices are significantly affected by the occurring flow pattern, such as, e.g., slug flow, leading to large uncertainties. In this context, the slug flow pattern in horizontal pipes is investigated with the aim of finding a statistical characterization of the structures in space and time. For this, two different instances of slug flow are analyzed with a snapshot proper orthogonal decomposition and an additional mode coupling algorithm, which provides an energy-ranked mode basis of the underlying coherent structures. For the considered flows, the most energetic mode pair has been identified with the corresponding slugging structures. Thereby, the temporal and spatial information of these mode pairs enables a statistical characterization of the slugs. In this context, a length scale, a dominant frequency, and an energy representation of the slugging structures is obtained from this method.

Felipe Jaloretto, Marcelo Souza de Castro
Uncertainty Analysis for Multiphase Flow: A Case Study for Horizontal Air-Water Flow Experiments

This work describes the procedure used to define the measurements uncertainties of experiments in horizontal air-water two-phase flow performed in order to identify influences due to pipe diameter. These experiments were performed with 4 different pipe diameters, always using the same test section length, therefore varying the length-by-diameter (L/D) ratio. Several parameters were measured, such as fluid flow, pressure, temperature and pressure drop; other parameters were calculated, such as the superficial velocities of each fluid, as well as their respective properties. The main parameters studied were the flow patterns for different velocity configurations and the two-phase pressure drop to be used for model improvement, thus the importance of uncertainties analysis. The sources of uncertainty were defined, detailed, systematically studied and quantified. The flow maps with its uncertainties could show the regions a pattern can be defined, and the plots of two-phase pressure drop variation with diameter validated the homogeneous model as a good approach to calculate pressure drop

S. Schmelter, M. Olbrich, E. Schmeyer, M. Bär
Numerical simulation, validation, and analysis of twophase slug flow in large horizontal pipes

Multiphase flow, especially two-phase gas-liquid flow, is of great importance for a variety of applications and industrial processes, for example in the nuclear, chemical, or oil and gas industries. In this contribution, we present simulation results for gas-liquid slug flow in large horizontal pipes. Six test cases with different oil, water, and gas flow rates are considered, which cover a wide range of different slug flows. The numerical predictions are validated by comparison with experimental data obtained from video observations, which have been recorded at NEL as part of the European research project “Multiphase flow metrology in oil and gas production”. The relative error of the mean liquid level between experiment and simulation is less than 10.8 per cent for all but one test cases. Furthermore, a frequency analysis is performed. The single-sided amplitude spectrum as well as the smoothed power spectral density are calculated. For both, experimental and simulation data, one observes an increase of the dominant frequencies if the ratio of liquid and gas superficial velocity is increased.

Page 179 of 977 Results 1781 - 1790 of 9762