The velocity distribution on ultrasonic flowmeter performance
Published on：2015-3-10 10:49:53 Hits：
USA TERRENCE A. GRIMLEY
Abstract: This paper introduces the single-channel and multi-channel ultrasonic flowmeter is installed under different conditions to test the situation, including the meter to measure the velocity distribution pipe upstream disturbance and common form of meter performance. Disturbance sources for testing a single elbow, double elbows and non-planar flat three forms of double elbow, some of which also comes downstream disturbance source rectifier. Measured ultrasonic flowmeter for single and multi-channel type each of two two brands. The test work was funded by the Gas Research Institute (GRI), and located on the Southwest Research Institute (SwRI) in the GRI study measuring device MRF completed. Test results show that: the gas metering station, the flow rate of a typical piping configuration upstream of the gas flow generated by the disturbance, at least 100 times the diameter of the straight pipe length to completely be eliminated. Ultrasonic flowmeter sensitivity of the velocity distribution of the development of the situation with its different types and different. Although the rectifier can be reduced velocity perturbations, but not always beneficial to the performance of the flowmeter. The test results also show that: meter performance drift velocity perturbations caused by the measured velocity profiles calculated.
Since the birth of the ultrasonic flowmeter, people will know the velocity distribution of the fluid forms a direct impact on the ultrasound beam passes through the fluid of the time difference, and the beam is projected through the time required to measure flow parameters, the geometric parameters of the measured value of its flowmeter together, we can calculate the corresponding single beam line measured average flow rate. However, the average speed of the flow meter to measure body needs at. From the line speed to the speed of the conversion method body, there are two options, one is to truly grasp the actual distributions of velocity, is the choice of one or more channels of a channel does not affect the flow velocity distributions of flow measurement. These forms can be pre-velocity distribution is assumed to be determined by the actual multi-path measurement. Single-type ultrasonic flowmeter are generally based on an assumed shape of the velocity distribution, the results are sensitive to deviate from its actual morphological; piping arrangement for a typical velocity distribution produced, the sensitivity of the multi-type ultrasonic flowmeter than single Road type to be small.
Are often used with other flow meters with the rectifier, but also can improve the performance of the ultrasonic flowmeter. Rectifier can be provided with the meter consistent with the requirements of the distribution form of the flow rate and / or eliminate the flow rate may reduce meter performance perturbations (e.g. vortex).
This paper describes the common pipe fittings (simplified, rectifiers optional) velocity distribution in relation to the impact of single and multi-channel ultrasonic flowmeter measurement of performance between the pipe and the flow rate by measuring the distribution of the meter and the upstream pipe fittings for flow measurement error contribution illustrates this relationship. In addition, the article also provides the use of computational fluid dynamics (CFD) to predict the ultrasonic flowmeter / process performance validation data. This validation results CFD model to predict the impact of improving the lot of pipe fittings prior to ultrasonic flowmeter performance accuracy, and these pipe fittings during the installation of the meter is possible frequently encountered.
Second, the test method
These tests are tests on gas research institute affiliated research measuring device located at the Southwest Research Institute conducted. Fittings for a variety of test configurations, test prototype has four units, single and multi-channel ultrasonic flowmeter 2 sets, all of which can be directly used for 8 in ultrasonic flowmeters for custody transfer, and by the manufacturer for free provided to this trial. Specific testing is done in order to go through the weighing tank calibrated critical flow nozzle as a benchmark of GRI-MRF high voltage circuit (HPL) conducted on. Test methods introduced in the past has been done (see Grimley and Bowles 1997 literature). Also in these test trials, with some tube assembly further comprises a rectifier.
Velocity profile is determined using the straight measuring tube designed for measuring the velocity distribution and design, and it replaces the meter under test, and after careful installation and commissioning, to ensure accurate positioning velocity measurement points. Automatic movement of the probe in the measurement system is installed outside the tube may be in the circumferential direction of the measuring tube on the use of four measurement position, and can detect the flow rate at any measuring point on the pipe diameter direction on.
For each section velocity distribution, dynamic pressure is measured using 45 o increments along the diameter of 7.981 in the direction of using 0.25 in steps. Pressure sensor is combined with a sensor (United Sensor) made three holes "W- probe." Center hole "W- probe" configuration integrated dynamic pressure can be measured and used to calculate the local flow velocity. Rotating the probe until the pressure balance on both ends are open, the rotation angle of the probe can be used for measuring the circumferential flow angle. And PC-based data acquisition system that can be measured by the motion control system based on stepper motor and control probe displacement, rotation and pressure values.
To ensure that the reference flow velocity measurement and MRF measure the velocity distribution measurement points on the critical flow nozzle synchronization, flow distribution measurement data acquisition system is also controlled by the MRF data acquisition system. The same calculation method as the reference flow rate, the average flow rate also used to correct the measured values of the flow velocity distribution for each point.
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