Steam tables / Saturated vapour enthalpy h_g

Enthalpy of dry saturated steam against temperature

The total heat in a kilogram of dry saturated steam, h_f plus h_fg, peaking at 2,803.3 kJ/kg near 235 °C. Computed from IAPWS-IF97.

h_g is h_f plus h_fg, the total heat in a kilogram of dry saturated steam, and the shape of it surprises people. It rises, peaks at 2,803.3 kJ/kg around 235 °C, and then turns back DOWN. Past that point the latent heat is falling faster than the sensible heat is climbing, so a hotter kilogram of saturated steam carries less energy than a cooler one.

Arrive here from a chart on the steam tables page and the temperature you dialled in comes with you, marked on the curve and bolded in the table that prints beside it. The sheet is then about one operating point rather than about water in general.

Table units — bar, °C, m³/kg, kJ/kg. Both columns of pressure, absolute and gauge, either way.

Saturated vapour enthalpy h_g kJ/kg

Vapour enthalpy, h_gf^e
°C	bar a	psig	kJ/kg
0	0.006112	-14.6	2,500.9
25	0.0317	-14.2	2,546.5
50	0.1235	-12.9	2,591.3
75	0.386	-9.1	2,634.6
100	1.014	0.0	2,675.6
125	2.322	19.0	2,713.1
150	4.761	54.4	2,745.9
175	8.924	115	2,772.7
200	15.55	211	2,792.1
225	25.49	355	2,802.3
250	39.76	562	2,801.0
275	59.46	848	2,785.1
300	85.88	1,231	2,749.6
325	120.5	1,733	2,684.5
350	165.3	2,383	2,563.6
373.946	220.6	3,185	2,087.2

Everything else at 100 °C
Saturation pressure	1.0142 bar a
On the gauge	0.0 psig
Latent heat of vaporisation	2,256.5 kJ/kg
Specific volume, saturated vapour	1.672 m³/kg
Saturated liquid enthalpy h_f	419.1 kJ/kg

The rest of the state at 100 °C (default)

Saturation pressure	1.0142 bar a · 0.0 psig
Latent heat of vaporisation	2,256.5 kJ/kg
Specific volume, saturated vapour	1.672 m³/kg
Saturated liquid enthalpy h_f	419.1 kJ/kg

Saturated vapour enthalpy h_g along the whole saturation line

Temperature°C	Temperature°F	Pressurebar a	Pressurepsig	Saturated vapour enthalpy h_gkJ/kg	Saturated vapour enthalpy h_gBTU/lb
0	32.0	0.006112	-14.6	2,500.9	1,075.2
25	77.0	0.0317	-14.2	2,546.5	1,094.8
50	122.0	0.1235	-12.9	2,591.3	1,114.1
75	167.0	0.386	-9.1	2,634.6	1,132.7
100	212.0	1.014	0.0	2,675.6	1,150.3
125	257.0	2.322	19.0	2,713.1	1,166.4
150	302.0	4.761	54.4	2,745.9	1,180.5
175	347.0	8.924	115	2,772.7	1,192.0
200	392.0	15.55	211	2,792.1	1,200.4
225	437.0	25.49	355	2,802.3	1,204.8
250	482.0	39.76	562	2,801.0	1,204.2
275	527.0	59.46	848	2,785.1	1,197.4
300	572.0	85.88	1,231	2,749.6	1,182.1
325	617.0	120.5	1,733	2,684.5	1,154.1
350	662.0	165.3	2,383	2,563.6	1,102.1
373.946	705.1	220.6	3,185	2,087.2	897.4

Every row is a call into IAPWS-IF97 made when this page was built, not a transcription. Gauge pressure is absolute minus one standard atmosphere, 101.325 kPa, so it is negative everywhere below 99.97 °C, which is where water actually boils at one atmosphere, and a real barometer is never exactly that anyway.

Learning zone

The turnover, and what it costs

The peak at 235 °C is the whole economics of a steam plant in one bend of one line. Below it, raising pressure gets you a kilogram carrying more heat. Above it, raising pressure gets you a kilogram carrying LESS. The sensible heat going in keeps climbing, the latent heat coming out is collapsing faster, and past the turnover the second term wins.

What a coil actually receives

h_g is the number a heat exchanger is sized against, and it is the number a wet main quietly takes away. Steam at a dryness fraction of 0.9 carries h_f plus 0.9 h_fg, so at 100 °C that is 2,449.9 kJ/kg instead of 2,675.6. The coil was sized for the second number. That is the argument for drip legs and properly sized traps on a main, said as arithmetic rather than as advice.

IAPWS R7-97(2012), regions 1 to 5 implemented in full · saturation line from 0 °C to 373.946 °C · computed at page build, never transcribed

The other curves on this line

← Steam tables: every curve, both full tables and the saturated and superheated panels

The saturation dome, the Mollier h–s chart and the T–s diagram