Steam Tables Theory
Introduction
Steam tables provide thermodynamic properties of water and steam at various temperatures and pressures. They are essential for designing boilers, turbines, heat exchangers, and other thermal equipment. Modern calculations use equations from IAPWS (International Association for the Properties of Water and Steam).
Phase Diagram
Water exists in three phases depending on temperature and pressure:
Compressed Liquid
T < Tsat at given pressure. Subcooled water.
Saturation (Two-Phase)
Liquid and vapor coexist at Tsat and Psat.
Superheated Vapor
T > Tsat at given pressure. Dry steam.
Critical point: Tc = 373.95°C, Pc = 22.064 MPa. Above this point, liquid and vapor phases are indistinguishable.
Key Properties
Specific Enthalpy (h)
Energy content per unit mass (kJ/kg). Used in energy balances.
h = u + Pv
Specific Entropy (s)
Disorder measure per unit mass (kJ/kg·K). Used for cycle analysis.
Specific Volume (v)
Volume per unit mass (m³/kg). Inverse of density.
Internal Energy (u)
Microscopic energy per unit mass (kJ/kg).
Saturation Properties
At saturation, properties are denoted with subscripts:
- f = saturated liquid (fluid)
- g = saturated vapor (gas)
- fg = difference (hfg = hg - hf = latent heat)
For two-phase mixtures, use quality (x) - the mass fraction of vapor:
h = hf + x × hfg
s = sf + x × sfg
Common Applications
Boiler Design
Calculate heat input: Q = ṁ(hout - hin)
Turbine Work
Isentropic expansion: W = ṁ(h1 - h2s)
Heat Exchanger
Heat duty from steam condensation: Q = ṁ × hfg
IAPWS Formulations
This calculator uses IAPWS-IF97 formulation, which divides the steam tables into 5 regions with specific equations for each. The formulation provides:
- Valid range: 0 - 800°C, 0 - 100 MPa
- Accuracy: better than industrial measurement precision
- Consistency at region boundaries
References
- IAPWS-IF97: "Revised Release on the IAPWS Industrial Formulation 1997"
- Çengel, Y.A. "Thermodynamics: An Engineering Approach"
- Smith, Van Ness, Abbott "Introduction to Chemical Engineering Thermodynamics"