焓，表征系统中所有的总能量，它是内能与压力位能之和.
对1公斤工质而言，用符号i表示
单位是kcal/kg.
即i=u+APv
kcai/kg。
式中u---内能
kcai/kg.
...P---压力
kgf/㎡.
...v---比容
m³/kg.
...A---功的热当量
A=(1/426.9)kcal/kg*m.
或者以G公斤工质的焓用I表示：I=Gi.
通过工质的热力性质表可查到该工质在某温度（T）时所对应的压力、比容、比重和两态焓值。
蒸汽焓值计算
焓值计算：H=2022.7+1.6675×T+2.9593×10^(-4)×T^2-1.2690×10^9×P/T^2.7984-1.0185×10^23×P^2/T^8.3077
P－MPa，T－KH－kJ/kg
一阶拟合：
Linear model Poly1:
f(x) = p1*x + p2
Coefficients (with 95% confidence bounds):
p1 = 1.569 (1.528， 1.61)
p2 = 2507 (2504， 2511)
Goodness of fit:
SSE: 3469
R-square: 0.9916
Adjusted R-square: 0.9914
RMSE: 8.414
Linear model Poly1:
f(x) = p1*x + p2
Coefficients (with 95% confidence bounds):
p1 = 1.67 (1.659， 1.682)
p2 = 2504 (2503， 2504)
Goodness of fit:
SSE: 252.6
R-square: 0.9994
Adjusted R-square: 0.9994
RMSE: 2.271
Linear model Poly1:
f(x) = p1*x + p2
Coefficients (with 95% confidence bounds):
p1 = 1.777 (1.765， 1.789)
p2 = 2502 (2501， 2503)
Goodness of fit:
SSE: 295.6
R-square: 0.9993
Adjusted R-square: 0.9993
RMSE: 2.456
二阶拟合：
Linear model Poly2:
f(x) = p1*x^2 + p2*x + p3
Coefficients (with 95% confidence bounds):
p1 = -0.002719 (-0.002911， -0.002526)
p2 = 2.036 (2.002， 2.071)
p3 = 2499 (2498， 2500)
Goodness of fit:
SSE: 195.7
R-square: 0.9995
Adjusted R-square: 0.9995
RMSE:
蒸汽焓值计算
焓值计算：H=2022.7+1.6675×T+2.9593×10^(-4)×T^2-1.2690×10^9×P/T^2.7984-1.0185×10^23×P^2/T^8.3077
P－MPa，T－KH－kJ/kg
