气液两相流含气率超声测试方法研究

Ultrasonic method for gas-liquid two phase flow void fraction measurement

超声波在流体中传播时对流场不产生扰动和压力损失,是两相流过程参数检测的一种重要手段。采用编码信号的超声技术,可在相同发射功率条件下获得比传统单脉冲信号更高的信噪比和分辨率。为了准确测试气液两相流含气率,采用超声衰减法,利用FPGA技术设计并实现了一种基于线性调频编码激励和脉冲压缩信号技术的超声检测系统;研究气液两相流中气泡的结构尺寸与气相含率的测试方法。实验测试结果表明,编码激励信号对气液两相流气泡结构尺寸敏感,通过适当的修正方法可实现两相流含气率的准确检测,在一定气泡尺寸范围内,检测精度可达±5%。研究工作为采用基于编码激励信号的脉冲压缩超声测试技术应用于两相流参数的检测提供了方法基础。

Transmission of ultrasonic wave in fluid does not cause disturbance and pressure loss to the flow field,which is therefore an important test means of two-phase flow process parameters.Using ultrasonic technique with coded signal and pulse compression method can achieve higher signal-to-noise ratio and resolution than using traditional single pulse signal while maintaining the same transmission power.In order to realize the accurate measurement of the void fraction in gas liquid two phase flow,the basic principle of two-phase flow test based on ultrasonic attenuation method is introduced.An ultrasonic testing system based on linear frequency modulation coded excitation and pulse compression signal was designed and implemented using FPGA.The size of the gas bubbles in liquid,and the void fraction of gas-liquid two phase flow were tested with the proposed system and method.The experiment results show that the coded excita tion signal is sensitive to the size of the bubbles in gas liquid two phase flow; and using appropriate correction method,accurate measure ment of the void fraction can be achieved.Within a certain range of the bubble size,the measurement accuracy can reach ± 5%.This study lays a foundation for the ultrasonic testing technology based on the pulse compression with coded excitation signal in two phase flow process parameter measurement.