Calculation of the Thermodynamic Properties of Methane up to 30 MPa Using a New Equation of State with Regular and Scale Parts and Few Constants

IF 1 4区物理与天体物理 Q4 PHYSICS, APPLIED High Temperature Pub Date : 2024-03-12 DOI:10.1134/s0018151x23020037

P. P. Bezverkhii, O. S. Dutova

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Abstract

The heat capacities \({{C}_{v}}\), C_p and speed of sound W of methane were calculated by a new equation of state with few adjustable constants. The equation includes a new regular part with 13 coefficients and a scale part with 6 coefficients with a regular crossover function containing two fitting parameters. The constants in the equation of state were determined using only (p, ρ, T) data for СH₄; no data on \({{C}_{v}}\), C_p, and W were employed, except for the data on isochoric heat capacity \({{C}_{v}}\) in the ideal-gas state and value of \({{C}_{v}}\) at 100 K on the liquid branch on the liquid–vapor equilibrium curve. The calculated values of \({{C}_{v}}\), C_p, and W are close to the experimental and tabulated values in the regular region. Calculations in the critical region uses universal critical indices α, β, γ according to the three-dimensional Ising model. A discrepancy with the tabulated data is caused by application of the scaling equation of state. The calculated values are compared with the predictions by the known crossover equations of state for СH₄. The root-mean-square error in the description of СH₄ pressure is σ_р = 0.5%, the mean absolute deviation is 0.3%, the uncertainty in \({{C}_{v}}\) does not exceed 5%.

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使用带有常规和比例部分以及少量常数的新状态方程计算 30 兆帕斯卡以下甲烷的热力学性质

摘要甲烷的热容 \({{C}_{v}}\)、Cp 和声速 W 是通过一个新的状态方程计算得出的，其中可调常数很少。该方程包括一个由 13 个系数组成的新的正则部分和一个由 6 个系数组成的比例部分，其中正则交叉函数包含两个拟合参数。状态方程中的常数只使用了 СH4 的 (p, ρ, T) 数据来确定；除了理想气体状态下的等时热容 \({{C}_{v}}\) 数据和 100 K 时液气平衡曲线液态分支上的\({{C}_{v}}\) 值外，没有使用 \({C}_{v}}\)、Cp 和 W 的数据。在常规区域，\({{C}_{v}}\)、Cp 和 W 的计算值接近于实验值和表格值。在临界区的计算中，根据三维伊辛模型使用了通用临界指数 α、β、γ。由于应用了比例状态方程，与表格中的数据存在差异。计算值与 СH4 的已知交叉状态方程的预测值进行了比较。СH4压力描述的均方根误差为 σр = 0.5%，平均绝对偏差为 0.3%，\({{C}_{v}}\) 的不确定性不超过 5%。

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来源期刊

High Temperature 物理-物理：应用

CiteScore

1.50

自引率

40.00%

发文量

审稿时长

4-8 weeks

期刊介绍： High Temperature is an international peer reviewed journal that publishes original papers and reviews written by theoretical and experimental researchers. The journal deals with properties and processes in low-temperature plasma; thermophysical properties of substances including pure materials, mixtures and alloys; the properties in the vicinity of the critical point, equations of state; phase equilibrium; heat and mass transfer phenomena, in particular, by forced and free convections; processes of boiling and condensation, radiation, and complex heat transfer; experimental methods and apparatuses; high-temperature facilities for power engineering applications, etc. The journal reflects the current trends in thermophysical research. It presents the results of present-day experimental and theoretical studies in the processes of complex heat transfer, thermal, gas dynamic processes, and processes of heat and mass transfer, as well as the latest advances in the theoretical description of the properties of high-temperature media.