Influence Of The Upstream Pipe Bends On The Measurement Errors Of An Ultrasonic Flowmeter

Ultrasonic flowmeter is a kind of non-contact flowmeter which uses theultrasonic wave to detect flow velocity so as to measure the flow rate. Due to itsgood stability, accuracy, wide measurement range, no pressure loses and low cost,ultrasonic flowmeter has been widely used in the industry, military, national defence,medicine and other fields. In this work the influence of pipeline conditions on anultrasonic flowmeter measurement error are maily studied. Numerical simulationshave been carried out to analyze the flow characteristics downstream of a planarsingle pipe bend and spatial double pipe bends, and the influences on themeasurement accuracy of an ultrasonic flowmeter. Simulations have also been madeto examine the effects of using a honeycomb flow conditioner and multi-channeldesign to improve the measurement accuracy. Main works and results are as follows:1. The influence of an upstream planer single pipe bend and spatial double pipebends to the measurement error of a single-channel ultrasonic flowmeter. The Fluentsoftware was used to simulate the internal flowfileds of a DN100ultrasonicflowmeter a flow range of0.1m3/h to120m3/h, and the length of straight pipe afterpipe bending is from2D to40D. The results show that, there are obviousphenomenon of secondary and vortex flow due to the upstream pipe bends. When theflow rate is less than5m3/h, the error curve is close to a horizontal line. In addition,the influence of a spatial double bends is greater than a planar single bend.2. The effect of a honeycomb flow conditioner to improve the measurementaccuracy of an ultrasonic flowmeter. The length of the honeycomb flow conditioneris100mm and the hexagon inner diameter is10mm. The conditioner is located at50mm upstream of flowmeter. By comparing the measurement errors with andwithout the flow conditioner, it is found that measurement error can be reduced about2%by using a honeycomb flow conditioner, when the flow rate is larger than3m3/h.When the flow rate is less than3m3/h, the measurement accuracy can also be improved with a honeycomb flow conditioner.3. Research on the multi-channels method to improve the measurementaccuracy of an ultrasonic flowmeter. Using Gauss-Legendre integration method tocalculate weight coefficients of each channel, according to the position and directionparameters of the channel. Effects of the bends on the measurement error have beenexamined at different arrangements, i.e. single-channel, double-channels andthree-channels. It is found that using the multi-channel method the velocityinformation of multi layers of the flow field can be obtained and the measurementaccuracy can be effectively improved. For instance, when the flow rate is larger than1m3/h and L=2D, the measurement error of single-channel design is larger than5%for the single bend, less than2%for double-channel, and less than1.5%forthree-channel. For the case of the double bend, the measurement error ofsinglechannel is larger than6%, less than4%for the double-channels, and and lessthan3%for the three-channels.