Empirical Determination of the Isoenthalpic and Isoentropic Equations of State of Polyethylene Based on the Pressure–Volume–Temperature–Entropy Equation of State

Abstract

The isoenthalpic and isoentropic equations of state of polyethylene (PE) have been determined based on the empirical pressure–volume–temperature–entropy equation of state, P–V–T–S Eos. The three dimensional plot, 3D plot, for the isoenthalpic Eos consists of the variables pressure (P_H), volume (V_H), temperature (T_H), and entropy (S_H) satisfying the condition that the enthalpy, H, is constant, while the 3D plot for the isoentropic Eos consists of the P_S, V_S, T_S and H_S satisfying the condition that the entropy, S, is constant. The 3D T_H–P_H–V_H plot determined for the isoenthalpic Eos for PE showed a considerable difference from the 3D T_S–P_S–V_S plot for the isoentropic Eos for PE. The thermodynamic derivative, ${\left(\frac{\partial V}{\partial T}\right)}_H,$ for the isoenthalpic Eos with constant H in PE was positive, while the ${\left(\frac{\partial V}{\partial T}\right)}_S$ for the isoentropic Eos with constant S was negative. Thermodynamic derivatives for the isoenthalpic and isoentropic equation of state have been evaluated based on the experimental 3D plots and discussed in terms of the thermodynamic relations.

Keywords:

• isoenthalpic equation of state
• isoentropic equation of state
• polyethylene
• pressure–volume–temperature–entropy equation of state