steam table function最可靠，有數值化的公式。只要飽和曲線，溫度對應壓力那部份就可。

下面是以前從網上收集的EXCEL巨集中節錄出計算蒸汽飽和壓力用的。


Function VAPP(T)
' ****************************************************************
' * DAMPFDRUCKKURVE NACH IFC 68 *
' * T = SIEDETEMPERATUR in K *
' * VAPP = SIEDEDRUCK in bar *
' * VAPP = -1: TEMPERATUR AUSSERHALB BEREICH *
' ****************************************************************
'
Dim AK(12), BK(4), Tz(12)
Tc = 647.3
Pc = 221.2
'
AK(1) = -4.0596821
AK(2) = 5.1322555
AK(3) = -1.1842407
AK(4) = 0.11779592
AK(5) = -0.005157642
AK(6) = -0.0014689537
AK(7) = 0.00053622818
AK(8) = 0.00012455399
AK(9) = -0.000049154288
AK(10) = 0.000046302565
AK(11) = 0.000015301334
AK(12) = -0.00002095453
BK(1) = 2
BK(2) = 0.95
BK(3) = 1.45220717
BK(4) = -0.84878953
TR = T / Tc
If TR < 0.421 Or TR > 1.658 Then GoTo Bereich:
U = (BK(1) * (1 / TR - BK(2)) ^ 0.4 - BK(3)) / BK(4)
Tz(1) = 1
Tz(2) = U
For I = 3 To 12
Tz(I) = 2 * U * Tz(I - 1) - Tz(I - 2)
Next I
Sum = 0
For I = 1 To 12
Sum = Sum + AK(I) * Tz(I)
Next I
PR = Exp(Sum)
VAPP = PR * Pc
GoTo Ende:
Bereich: VAPP = -1
Ende:
End Function