本文基于对流体在近临界区流动热力学的分析,提出了用等熵压缩度来描述可压缩流体的流动特性。分别计算了氮、氢、氧和甲烷等流体在理想气体.近临界流体和近不可压缩流体等各种流动条件下,通过文丘里时的膨胀因子;进而估计了把建立于理想气体理论基础上的ASME规范的膨胀因子的计算公式用于上述非理想流体时的典型误差。 Based on the analysis of fluid thermodynamics in the near-critical region, this paper presents the isentropic compressibility to describe the flow characteristics of compressible fluid. We calculate the expansion factors of the fluids such as nitrogen, hydrogen, oxygen and methane under the venturi condition under various flow conditions, such as ideal gas, near-critical fluid, near-incompressible fluid, and so on. Furthermore, The ASME specification for the expansion factor is calculated using the typical error for the above non-ideal fluid.