A Tutorial on Thermodynamics’ Phase Diagrams and Charts

Abstract

This note follows our earlier online public book, Engineering Thermodynamics – Concepts and Laws: An Informal Presentation, shared on ResearchGate.net in July 2026. Here, the focus shifts to explaining phase diagrams in key thermodynamic coordinates—namely P‑v, T‑v, P‑T, T‑s and h‑s. Mastering these diagrams and learning to use thermodynamic tables are essential steps toward the study of practical applications such as power plants, refrigeration systems, air conditioning and combustion processes. While the main development of our earlier book emphasizes thermodynamic derivations based on the ideal-gas model, students should also develop a clear visual understanding of phase behavior and real-substance property relations. For that reason, this supplementary section on phase diagrams is included to present, in a concise and accessible way, the interpretation of regions such as compressed liquid, saturated mixture, saturated vapor, superheated vapor, and the critical state, together with the use of common thermodynamic charts. Its purpose is not to replace the established textbooks or duplicate worked examples, but to complement them by offering another reference perspective. Since meaningful study in thermodynamics often requires consulting more than one source, this addition is intended to help students build the habit of connecting formal derivation with graphical interpretation and physical insight.