Saturated Liquid Enthalpy Calculator and Formula

A saturated-liquid enthalpy calculator estimates the specific enthalpy of a substance at its saturation temperature or pressure using a property table or equation of state. Entering a temperature or pressure alone is not enough to calculate a dependable value unless the substance and a suitable source of thermodynamic properties are also specified.

Formula

This calculator returns the supplied saturated-liquid specific enthalpy directly:

h_f = h_f(T_sat, substance, reference convention)

h_f is saturated-liquid specific enthalpy, in kJ/kg.
T_sat is the saturation temperature, in °C. It identifies the state but does not determine enthalpy by itself.
Substance is the working fluid, such as water or a refrigerant. This simple calculator does not select it.
Reference convention is the enthalpy zero used by the property source. Enthalpy values are relative, so the convention matters when comparing numbers.

The calculator’s input h_f must be looked up in a validated thermodynamic property table or produced by a reliable property model for the specified fluid, saturation state, and reference convention. The output simply reports that value to two decimal places. It does not estimate properties from temperature or pressure. This distinction is essential: there is no universal formula giving saturated-liquid enthalpy from temperature alone.

Worked Example

The defaults illustrate the reporting step for water at its normal boiling point, using a conventional steam-table value of 419.17 kJ/kg for saturated liquid at 100 °C. The value is supplied as an input because this calculator does not contain a steam-property table.

Set the saturation temperature: T_sat = 100 °C.
Look up the saturated-liquid enthalpy for water at 100 °C in a consistent steam table: h_f = 419.17 kJ/kg.
Enter 419.17 in the saturated-liquid specific enthalpy field.
Report h_f = 419.17 kJ/kg.

The reported result is the same as the calculator’s first output, rounded to two decimal places. If a different table, fluid, or enthalpy reference is used, the input and result may differ. The example is not a claim that the calculator independently obtains the property.

Assumptions

The supplied enthalpy value already corresponds to a saturated liquid state, not a saturated vapor or a two-phase mixture.
The temperature and enthalpy come from the same substance and a consistent property source.
The source uses a clearly understood enthalpy reference convention; the calculator does not convert between conventions.
The value is specific enthalpy per unit mass, not total enthalpy.

What Saturated Liquid Enthalpy Means

A saturated liquid is a liquid at the boundary where it is about to boil at a given pressure, or about to condense at a given temperature. Its temperature and pressure are linked by the saturation curve. For a pure substance at equilibrium, specifying one saturation property fixes the other, subject to the substance and the range in which the property data apply.

Specific enthalpy, usually written h, is an energy property per unit mass. It is commonly tabulated in kJ/kg in engineering references. The subscript f is a widely used convention for the saturated-liquid state; g commonly indicates saturated vapor. The difference h_fg = h_g − h_f is the enthalpy of vaporization per unit mass at that saturation condition.

Enthalpy is not an absolute energy reading with one universal zero. Property tables choose a reference state, then report changes from it. Two reputable tables can therefore show different enthalpy values if their reference conventions differ, even though calculated energy balances remain consistent when values from one convention are used throughout.

How to Find the Property Value

Use a reference appropriate to the fluid and conditions. A steam table is suitable for water and steam; other working fluids require their own tables or validated property software. Check whether the table is organized by saturation temperature or saturation pressure, and confirm the units and reference convention before copying a number.

Identify the pure substance or mixture and the desired saturation condition.
Find the saturation temperature or pressure in the matching property source. If given a pressure, do not use a temperature table without first finding the corresponding saturation temperature.
Read the saturated-liquid enthalpy column, typically labeled h_f or saturated liquid.
Check the unit, reference state, and whether interpolation is needed between tabulated entries.
Enter h_f in kJ/kg. Convert other units before entering: 1 kJ/kg = 1,000 J/kg, and 1 Btu/lbm is approximately 2.326 kJ/kg.

For values between table rows, interpolation may be reasonable when the data are smooth and the interval is small. Near the critical point or across a phase boundary, property changes can be rapid, so use a suitable model or denser data rather than assuming a coarse linear interpolation is accurate.

Using the Result in Energy Calculations

Specific enthalpy becomes useful when combined with mass flow or mass. For a fixed mass m, total enthalpy relative to the source’s reference is H = m h, with H in kJ if m is in kg and h is in kJ/kg. For a steady flow, the enthalpy-rate contribution is ṁh, where ṁ is in kg/s; its units are kJ/s, equivalent to kW.

For example, saturated liquid at a boiler outlet is not automatically the same state as liquid entering a pump or leaving a heat exchanger. Use the actual state at each point in an energy balance. If a state is a mixture of liquid and vapor, use quality x and the mixture relation h = h_f + xh_fg, where x ranges from 0 for saturated liquid to 1 for saturated vapor. This relation does not apply to a compressed (subcooled) liquid without appropriate properties.

Common Errors and Calculator Limits

Assuming temperature alone determines a universal answer: the fluid matters, as do the property model and reference convention.
Entering saturated-vapor enthalpy: h_g is not h_f. Check the table heading carefully.
Mixing units: a value in J/kg entered as though it were kJ/kg is too large by a factor of 1,000.
Mixing reference conventions: use one consistent source in a calculation. A standalone enthalpy number cannot reliably reveal which zero was selected.
Confusing specific and total enthalpy: kJ/kg is not kJ. Multiply by mass only when total energy is needed.

This page is deliberately a transparent property-value calculator, not a built-in thermodynamic database. It cannot validate whether the entered number matches the selected temperature or pressure, because no fluid or property source is encoded. For engineering design or safety-critical work, verify properties against an authoritative source and check the complete system calculation. Where bench work is involved, follow your lab method, the safety data sheet (SDS) and your supervisor.

Frequently Asked Questions

How do I calculate saturated liquid enthalpy?
Identify the fluid and saturation temperature or pressure, then obtain h_f from a suitable property table or model. This calculator formats the property value you enter; it does not generate it from temperature alone.

Is saturated liquid enthalpy the same as heat of vaporization?
No. Saturated-liquid enthalpy is h_f. Heat of vaporization per unit mass is h_fg = h_g − h_f at the same saturation condition.

Does saturated liquid enthalpy depend on pressure or temperature?
For a pure substance at saturation, temperature and pressure are linked. The enthalpy depends on the saturation state and the substance, and the displayed number also depends on the reference convention.

Why do two steam tables give different enthalpy values?
They may use different reference states, units, rounding, or property formulations. Compare the conventions and use one source consistently throughout an energy balance.

What is the difference between h_f and h_g?
h_f is specific enthalpy of saturated liquid; h_g is specific enthalpy of saturated vapor. Their difference is h_fg, the enthalpy change associated with vaporization at saturation.

Formula used

in t | Saturation temperature | °C | 100 | -273.15
in hf | Saturated liquid specific enthalpy | kJ/kg | 419.17 | 0
out hf | Saturated liquid specific enthalpy | kJ/kg | hf | 2

Each line is one input (in, sel, list) or one result (out: label, unit, formula, decimals). How the calculators work

Method: the standard formula for this calculation with the constants and conversion factors written on the page, rounded as each result states. See method and constants, the disclaimer or report an error.