液态和超临界态二氧化碳的非线性声学性质

Nonlinear acoustical properties of liquid and supercritical carbon dioxide

根据美国国家标准局提供的二氧化碳在液态和超临界态下的声速、密度、比定压热容、膨胀系数等物理参数数据库中数据,计算了二氧化碳在液态和超临界状态下的声速压力系数、声速温度系数和非线性声参量几个非线性声学参数。分析归纳了液态二氧化碳和超临界二氧化碳的非线性声学特性,对比分析了液态二氧化碳、超临界二氧化碳和一般有机液的非线性声学特性。详细分析了二氧化碳在临界点附近的非线性声学特性。研究表明,液态二氧化碳表现出类似于一般液体在常温常压下的非线性声学特性;超临界二氧化碳的声速压力系数、声速温度系数和非线性声参量值可为正值或负值,其值随压力或温度的变化具有一定的规律性。压力越大温度越低,超临界二氧化碳的非线性声学特性越接近液态二氧化碳或一般液体。在临界点附近区域,3个参量值随压力或温度的变化出现正负最大值间的跳跃变化。

Several acoustic parameters including the pressure coefficient of ultrasonic velocity, temperature coefficients of ultrasonic velocity and the nonlinear acoustic parameter of liquid and supercritical carbon dioxide at different temperatures and pressures were calculated by using data of sound velocity, density, specific heat at constant pressure and bulk coefficient of expansion of carbon dioxide provided by the National Institute of Standards and Technology, USA. The nonlinear acoustical characteristics of liquid and supercritical carbon dioxide were analyzed and summarized. The nonlinear acoustical characteristics of supercritical carbon dioxide were contrasted with those of liquid carbon dioxide and common organic liquid. The nonlinear acoustical characteristics around the critical angle were analyzed in detail. Investigation indicated that the nonlinear acoustical characteristics of liquid carbon dioxide resembled common organic liquid at normal temperature and normal pressure. The values of pressure coefficient of ultrasonic velocity, temperature coefficients of ultrasonic velocity and the nonlinear acoustic parameter of supercritical carbon dioxide might be positive or negative and the values changed with temperature and pressure regularly. The higher the pressure and the lower the temperature, the more the nonlinear acoustical characteristics of supercritical carbon dioxide agreed with those of liquid carbon dioxide or common organic liquid at normal temperature and normal pressure. Near the critical region, the change of these three parameters with temperature and pressure had a jump between positive and negative maximum.