An Investigation On The Flow Behaviors Of An Ultrasonic Heat Meter

Ultrasonic heat meters are commonly used in home heating systems. In this paper, an investigation was carried out with focus on the flow behaviors of some typical ultrasonic meter models. Computational Fluid Dynamics (CFD), experimental verification and PIV experiments were combined during the study. Two different configurations of ultrasonic heat meters were considered. As a first step, the characteristics of flow field and a series of parameters were obtained with CFD methods, including the shape of reflector, Reynolds number, the aspect ratio of pipe. Secondly, an experimental examination was carried out on the performance of an ultrasonic heat meter with PIV method. The main works can be summarized as follows:The average speed between two reflecting plate is an important parameter affecting the measurement accuracy of ultrasonic flow meter. Further, the average speed is related to flow field of the flow meter which contains different stages. It was found that two jets are formed in the wake of the upstream reflector. Meanwhile, there exists a quiescent zone at the back of the reflectors. The direction and strength of the jets, as well as the size and stability of the quiescent zone are all affected by the cross-sectional distribution of the incoming pipe flow. Moreover, the two jets intersect at the front of the measuring pipe. Because the size of measuring pipe is relatively small, the flow converges into the pipe becomes stable as a result of momentum dissipation. Based on the above observations, improvement strategies were proposed, including a regulator device in front of the heat meter, column-type reflectors, a deflector device on the front end of the measuring pipe and increasing the aspect ratio, etc. It was demonstrated that the performance of ultrasonic heat meter were significantly improved after the modifications.A PIV measurement was carried out to explore the connection between the flow characteristics and the performance of an ultrasonic heat meter. The tests were mainly conducted with the consideration of two cases. In the first case the flow fields at different flow rates were examined where the inlet-installation condition was a straight pipe. The experimental results showed that under low flow conditions the flow field behaves obviously unsteady, which is mainly responsible for the deviation of the measurement. In the second case, a ball valve was installed upstream of the heat meter to analyze the installation effect on the measurement accuracy. The results, in combination with that of the first case, revealed that the characteristics of the adaptability are consistent with the stability of the inner flow. That is, the more stable the flow field is, the more adaptively the heat meter can be applied. Furthermore, a multi-parameter analysis showed that the Reynolds number is a key non-dimensional parameter to characterize the measurement accuracy of small scale flow meters.