Numerical Analysis On Dynamic Flow Characteristic Of Ultrasonic Heat Meter Flow Measurement With U Type Reflector

Recently, with urban construction and development, environmental issues and energycrisis appear constantly, so urban central heating has gained widespread attention becauseof its positive effect on the environment protection and energy saving. The speed of theheating development will be faster with the rapid development of economy and thecontinuous improvement of people’s living standard. Due to requirements of householdheat metering, household heat meter becomes the common measuring equipment of theuser in central heating system. The reliability of the heat meter measurement can directlyaffect the rationality of the charge on heat metering, and affect the energy saving effect ofcentral heating system ultimately.The measurement accuracy of the ultrasonic heat meter was related to the flow in thepipe. The stability of the instantaneous line velocity on the central axis reflected thestability of the soundtrack velocity in the unsteady state, and also, the stability of thedifference between the average line speed and the average surface speed indicated thereliability of flow measurement, the reliability was showed by the flow correctioncoefficient K. The flow measurement accuracy required that, the value K should remainstable relatively in the measurement range of different flow rates.Based on ultrasonic heat meter with U type reflector in the measuring pipe in thispaper, the physical model was built as big as the real object, and the numerical method oflarge eddy simulation was applied for the numerical calculation on the flow characteristicsin pipes and the distribution of flow fluid. In addition, the stability of the instantaneous linevelocity on the central axis and correction coefficient K of heat meter flow metering wereanalyzed under different speed and reduced channel area in the pipeline. At the end, theeffects of pipe length before and after the heat meter on the measurement accuracy werealso computed and analyzed.The flow fluid characteristics was analyzed in this paper, it could be seen thatsymmetric eddy appeared at the back of the upstream cylinder, while the high-speed flowarea growing alternately and eddies with different sizes occurred at the back of the downstream cylinder. It was found that the value K increased with the decline of Renumber, but the pressure loss decreased with the loss of the Re number. Analysis showedthat, when the Re number was in the large range, the value K was close to the test value K,in the meanwhile, the decrease of the reduced channel area can improve the stability of thevalue K and increase the pressure loss between the import and export of the pipeline. Inaddition, it was obtained by analysis that, the upstream pipe length can affect the correctionvalue K of the heat meter, while the downstream pipe length has no effect on it.The research results in this paper have certain reference significance to internalstructure optimization of ultrasonic heat meter and the study of flow characteristics.