Related Resources: thermodynamics

Thermodynamic Functions , Typical Symbols and Units

Heat Transfer Engineering
Thermodynamics

Thermodynamic Functions, Typical Symbols and Units

Definitions

1. Intensive properties are independent of mass.
2. Extensive properties are proportional to mass.
3. Specific properties are extensive properties that are expressed on a per-mass basis; shown in lowercase.

Function	Symbol(s)	Unit (I-P or SI)
Absolute pressure	P	lbf / in2 or Pa
Absolute temperature	T	°R or K
Volume	V	ft3 or m3
Specific volume	v = V / m	ft3/lbm or m3/kg
Internal energy	U	Btu or kJ
Specific internal energy	u = U/m	Btu/lbm or kJ/kg
Enthalpy	H	Btu or kJ
Specific enthalpy	h = u +Pv = H/m	Btu/lbm or kJ/kg
Entropy	S	Btu/°R or kJ/K
Specific entropy	s = S/m	Btu/lbm-°R or kJ/kg·K
Gibbs free energy	G = h - Ts	Btu/lbm or kJ/kg
Helmholtz free energy	A = u - Ts	Btu/lbm or kJ/kg

For a single-phase pure component, specifying any two intensive, independent properties is sufficient to determine all the rest.

Heat capacity at constant pressure:
c_p = ( ∂h / ∂T )_P Btu/lbm-°R or kJ/kg·K

Heat capacity at constant volume:
c_V = ( ∂u / ∂T )_V Btu/lbm-°R or kJ/kg·K

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Source

• Source: Reprinted with permission from 2013 ASHRAE Handbook - Fundamentals, ASHRAE: 2013.