微波谐振腔测量蒸汽湿度非等动能取样误差分析

为了准确计算微波谐振腔的取样误差,分析了非等动能取样原理,针对2种不同的取样端,采用拉格朗日方法计算水滴运动轨迹,得到了不同工况和水滴尺寸下由于取样偏差导致的湿度测量误差.结果表明：当马赫数较小时,取样误差受水滴尺寸影响较小;而马赫数较大时,取样误差不仅与水滴尺寸密切相关,而且明显受工况的影响;通过优化谐振腔的取样端结构,可以有效减小由于取样产生的测量误差;由于电厂汽轮机排汽马赫数较小,通过取样修正,微波谐振腔可以达到较高的取样精度.

Analysis of Non-isokinetic Sampling Deviation for Measurement of Steam Humidity in Microwave Cavities

To accurately calculate the sampling deviation of microwave cavity,the non-isokinetic sampling principle was analysed,based on which measurement errors of wetness due to sampling deviation were obtained by computing the trajectory of droplets in two sampling ends of different structures through Lagrangian method under different conditions and droplet sizes.Results show that sampling deviation is less affected by the droplet size at low Mach number,while an obviously close relation with it has been seen as well as working conditions at high Mach number.It is found that optimizing the sampling end of the cavity can effectively reduce the measurement error.Since the Mach number of steam turbine exhaust is relatively low in power plant,therefore higher precision of sampling may be reached for measurement of steam humidity in microwave cavity via appropriate correction of sampling errors.