煤粉气-固两相流的超声衰减特性

摘要

In the premise of particulate phase distributed uniformly in the whole detection space, the McClements model and Bouguer-Lambert-Beer law model were applied to formulate the ultrasonic attenuation characteristics of pulverized coal gas -solid flow. The theoretical relation between the ultrasonic attenuation coefficients and the relevant parameters of two phase flow was established. By numerical simulations,the changing laws of the ultrasonic attenuation coefficients with particle volume fraction, ultrasonic frequency and particle size were analyzed. The results show that the higher the ultrasonic frequency is, the greater the attenuation coefficients are. The ultrasonic attenuation coefficients linearly increase with the increase of the particle volume fraction. If some fixed frequency is chosen, the slopes of attenuation -volume fractions curves can be confirmed by just testing ultrasonic attenuation coefficients under two volume fractions. So that testing of particle volume fraction corresponding to arbitrarily ultrasonic attenuation coefficients can be realized. If the coal particle sizes are in the range of 10 -200 μm with the same volume fraction, the ultrasonic attenuation coefficients monotonically decrease with the increase of the particle size. But if the pulverized coal particle size is more than 200 μm, the ultrasonic attenuation coefficients are no longer sensitive to the pulverized coal particle size.%以颗粒相在整个检测空间内均匀分布为前提,采用McClements理论和Bouguer-Lambert-Beer定律共同描述煤粉气-固两相流中超声衰减特性,建立超声衰减系数与气-固两相流相关参数的理论关系,通过数值模拟,分析超声衰减随着颗粒相体积分数、超声频率、颗粒粒径变化的规律.结果表明,超声频率越高衰减系数越大；声衰减系数随着颗粒相体积分数的增大线性递增；选用某固定频率检测,测得2个体积分数下的声衰减系数即可确定衰减-体积分数曲线斜率,从而实现任意衰减系数对应的颗粒相体积分数测量；在相同的体积分数下,煤粉颗粒粒径为10～200 μm,声衰减系数随着颗粒粒径的增大单调递减,当煤粉颗粒粒径大于200 μm时,声衰减系数对煤粉颗粒粒径不再敏感.