Water as a Thermal Engineering Fluid

Water (H₂O) is the most studied and widely used thermal fluid in engineering. Its exceptionally high specific heat capacity, latent heat of vaporization, and thermal conductivity — combined with its availability and non-toxicity — make it the baseline reference fluid for virtually all heat transfer and thermodynamic calculations. Water's thermodynamic properties are strongly temperature- and pressure-dependent, exhibiting well-characterized phase transitions at its triple point, normal boiling point, and critical point. The anomalous density maximum at 4 °C, the large latent heats at fusion and vaporization, and the high dielectric constant further distinguish water from other common fluids and underpin its unique role in natural and industrial systems.

General Thermodynamic Properties
Property SI Units US Customary Units
Boiling Temperature (at 101.325 kPa) 99.974 °C 211.953 °F
Melting Temperature (at 101.325 kPa) 0 °C 32 °F
Triple Point Temperature 0.01 °C 32.02 °F
Triple Point Pressure 0.00604 atm  |  0.00612 bar  |  611.657 Pa  |  0.08871 psi
Critical Temperature 373.946 °C 705.103 °F
Critical Pressure 217.7 atm  |  220.6 bar  |  22.06 MPa  |  3200 psi
Critical Density 0.322 g/cm³ 20.10 lbm/ft³
Maximum Density (at 4 °C / 39.2 °F) 999.975 kg/m³ 8.345 lbm/gal (US)
Specific Weight (at 4 °C / 39.2 °F) 9.806 kN/m³ 62.43 lbf/ft³
Bulk Modulus of Elasticity 2.15 × 10&sup9; Pa
Thermal Expansion Coefficient (avg 4–100 °C, non-linear) 4.2 × 10−4 1/K
Heat Capacity and Thermal Energy Properties
Property SI Units US Customary Units
Specific Heat — Liquid Water (at 15 °C) 4.187 kJ/(kg·K) 1.001 Btu/(lbm·°F)
Specific Heat — Ice 2.108 kJ/(kg·K) 0.5035 Btu/(lbm·°F)
Specific Heat — Water Vapor 1.996 kJ/(kg·K) 0.4767 Btu/(lbm·°F)
Latent Heat of Fusion (at 0 °C) 334 kJ/kg 144 Btu/lb
Latent Heat of Vaporization (at 100 °C) 2256 kJ/kg 970 Btu/lb
Chemical and Molecular Properties
Property Value
Molar Mass 18.01527 g/mol
Ionization Constant pKw (at 25 °C) 13.995
Neutral pH (at 25 °C) 6.9976
Water Property Calculators

Explore the full set of water property calculators on KasperCalc:

Density Specific Heat Capacity Boiling Points at Pressures Thermal Conductivity Viscosity Prandtl Number Enthalpy and Entropy Ionization Constant (pKw) Heat of Vaporization Saturation Pressure Liquid Gas Equilibrium Melting Points at High Pressure Thermal Expansion Coefficient Thermal Diffusivity Gasses Dissolved in Water — Diffusion Coefficients

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