Density and speed of sound of methane + n-heptane binary mixtures were measured at a temperature equal to 303.15 K and at pressures ranging from 10 MPa to 70 MPa. The measurements were performed in pure n-heptane and eight different mixtures with methane molar percentage ranging from 20 % to 95 %. Speed of sound data was obtained by a pulse-echo technique working at 3 MHz whereas density data were acquired from a vibrating U-tube densimeter. Isothermal and isentropic compressibilities were derived from both measurements in the same conditions. Finally, partial molar volumes, excess molar volume, excess isothermal compressibility as well as excess speed of sound and excess isentropic compressibility were estimated at the same conditions and the relative excess properties were represented as a function of methane content. From these measurements, it was observed that the large difference in compressibility of pure components provoked significant deviations to ideal behavior with relative excess values that can reach − 20 %, − 100 % and 200 % of the ideal properties for molar volume, isothermal compressibility and speed of sound, respectively. Moreover, a small clustering effect at high dilution of n-heptane at 30 MPa was brought forth to light by evaluating the partial molar volumes.

中文翻译：

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在 T = 303.15 K 和 p = 10 至 70 MPa 时，甲烷 + 正庚烷的密度、声速、可压缩性和相关的过剩特性

在等于 303.15 K 的温度和 10 MPa 到 70 MPa 的压力下测量甲烷 + 正庚烷二元混合物的密度和声速。测量是在纯正庚烷和八种不同的混合物中进行的，其中甲烷摩尔百分比范围为 20% 至 95%。声速数据是通过在 3 MHz 下工作的脉冲回波技术获得的，而密度数据是从振动 U 型管密度计获得的。等温压缩率和等熵压缩率源自相同条件下的两种测量结果。最后，在相同条件下估计偏摩尔体积、过量摩尔体积、过量等温压缩率以及过量声速和过量等熵压缩率，并且相对过量性质表示为甲烷含量的函数。从这些测量中，观察到纯组分的可压缩性的巨大差异引起了与理想行为的显着偏差，相对过量值可以达到摩尔体积、等温压缩性和声速的理想属性的 - 20 %、- 100 % 和 200 %，分别。此外，通过评估偏摩尔体积，揭示了在 30 MPa 下高稀释正庚烷时的小聚集效应。