Steam Tables — Interactive Reference

Linear Interpolation Across All Table Columns

f = (X − X_1) / (X_2 − X_1) | 0 < f < 1 | Y = Y_1 + f · (Y_2 − Y_1) | applied with the same f to every column of the two bracketing rows

Variables: X = target value of the table's leading (independent) column — temperature (°C) on the saturated-by-temperature and superheated tabs, pressure (kPa) on the saturated-by-pressure tab; X_1, X_2 = leading-column values of the two rows that bracket X (X_1 < X < X_2) within the rows currently displayed, i.e. after any filter is applied — the filter narrows both the valid range and the available brackets; f = interpolation fraction (dimensionless, strictly between 0 and 1 — an exact table match, or a target outside the displayed range, produces no interpolated row); Y = interpolated value of any column: P_sat (kPa) or T_sat (°C), v_f, v_g, v (m³/kg), h_f, h_fg, h_g, h (kJ/kg), s_f, s_fg, s_g, s (kJ/(kg·K)); Y_1, Y_2 = that column's values in the bracketing rows (same units as Y); interpolated values are shown to 6 significant figures. Source: Cengel & Boles, Thermodynamics: An Engineering Approach, 8th ed., Ch. 3 'Properties of Pure Substances' (linear interpolation between property-table entries)

Saturation Temperature from Pressure (by-pressure tab)

T_sat(P) = T_1 + [(P − P_1) / (P_2 − P_1)] · (T_2 − T_1)

Variables: P = target saturation pressure (kPa); the full tabulation spans 0.6113 to 22089 kPa, but interpolation is carried out only over the rows left visible by the pressure filter (which keeps rows within ±50% of the filter value), so an unfiltered table is required to reach the full span; P_1, P_2 = bracketing tabulated saturation pressures (kPa); T_1, T_2 = tabulated saturation temperatures at P_1 and P_2 (°C); T_sat = interpolated saturation temperature (°C). Accuracy note: P_sat(T) is close to exponential, so linear interpolation in P is a first-order fit; over the coarse 5000-7500-10000-15000-20000 kPa spacing it reads about 1 °C low (6000 kPa gives 274.58 °C against a true value near 275.6 °C). Interpolating ln(P) against 1/T is the accurate practice. Source: Moran, Shapiro, Boettner & Bailey, Fundamentals of Engineering Thermodynamics, 8th ed., Ch. 3 (saturation temperature-pressure correspondence; interpolation in the pressure-entry saturation table)

Saturation-Line Column Identities

h_g = h_f + h_fg | s_g = s_f + s_fg

Variables: h_g = saturated-vapour enthalpy (kJ/kg); h_f = saturated-liquid enthalpy (kJ/kg); h_fg = latent heat of vaporisation (kJ/kg); s_g = saturated-vapour entropy (kJ/(kg·K)); s_f = saturated-liquid entropy (kJ/(kg·K)); s_fg = entropy of vaporisation (kJ/(kg·K)); subscript f = saturated liquid, subscript g = saturated vapour, subscript fg = the g − f difference. These columns are tabulated, not computed: the interpolation applies one fraction f column-wise, so it is linear and carries whatever residual the identity has in the two bracketing rows through to the interpolated row unchanged — it neither improves nor degrades it. Because the columns are independently rounded, residuals of a few tenths of a kJ/kg are normal, and the 240 °C row of the by-temperature table is inconsistent by 2.5 kJ/kg (h_f + h_fg = 1037.3 + 1764.7 = 2802.0 against a listed h_g of 2799.5). The entropy identity holds throughout to better than 0.0001 kJ/(kg·K). Source: Cengel & Boles, Thermodynamics: An Engineering Approach, 8th ed., Ch. 3 (definition of the f, g and fg property columns)

Degree of Superheat on a Selected Isobar

ΔT_superheat = T − T_sat(P)

Variables: ΔT_superheat = degrees of superheat above the saturation temperature (K; numerically identical to a °C interval); T = steam temperature read from the superheated table (°C); T_sat(P) = saturation temperature of the selected isobar (°C), displayed in the pressure selector and info line — 99.63 at 100 kPa, 120.23 at 200, 143.61 at 400, 158.83 at 600, 179.88 at 1000, 212.38 at 2000, 263.94 at 5000, 311.06 at 10000 kPa; P = selected isobar pressure (kPa). The page shows T and T_sat side by side; the subtraction is left to the reader and is not evaluated by the tool. Source: Cengel & Boles, Thermodynamics: An Engineering Approach, 8th ed., Ch. 3 (superheated vapour; degrees of superheat relative to T_sat at the same pressure)