How to use this calculator

Pick the substance and the two properties you know, such as the pressure and entropy after an isentropic turbine, or the pressure and enthalpy after a throttling valve. The calculator finds the phase and every other property, plus the saturation values at that pressure or temperature: everything you would otherwise read and interpolate from the tables.

Finding the phase

Given T and PP > P_sat(T): compressed liquid; P < P_sat(T): superheated vapor

Given P and h (or s, u, v)h_f < h < h_g: mixture, x = (h − h_f)/h_fg

Mixturey = y_f + x(y_g − y_f) for y = v, u, h, s

Worked example

Steam at 4 MPa and 500 °C (the default)

T_sat at 4 MPa is 250.35 °C, below 500 °C, so the steam is superheated.
From the equation of state: v = 0.08644 m³/kg, u = 3100.3 kJ/kg, h = 3446.0 kJ/kg, s = 7.0922 kJ/kg·K, matching Çengel Table A-6.

Frequently asked questions

Why might my textbook differ in the last digit?

Printed tables round to a few digits and you interpolate linearly between rows. This calculator evaluates the same equation of state the tables were made from at exactly your state, so it is at least as accurate.

Which reference state is used?

Water: u = 0 and s = 0 for saturated liquid at the triple point (0.01 °C), the international standard. R-134a: h = 0 and s = 0 for saturated liquid at −40 °C (the ASHRAE convention used by Çengel). Differences in h or s between two states don’t depend on the reference.

What about air?

Air is treated as an ideal gas, as in Çengel Table A-17: h, u and s° depend only on temperature, and P_r and v_r handle isentropic processes.