COP	coefficient of performance
e	specific energy (kJ/kg)
g	gravitational acceleration (m2/s)
G	Gibbs function (kJ)
h	enthalpy (kJ/kg)
ke	kinetic energy (kJ/kg)
m	mass (kg)
N	mole number (kmol)
P	pressure (kPa)
pe	potential energy (kJ/kg)
Q	heat transfer (kJ)
R	gas constant (kJ/kg·K)
s	entropy (kJ/kg·K)
T	temperature (K)
u	internal energy (kJ/kg)
v	specific volume (m3/kg)
V	velocity (m/s)
V	volume (m3)
W	work (kJ)
X	exergy (kJ)
y	mole fraction
z	elevation (m)
Greek letters
η	efficiency
μ	chemical potential (kJ/kg)
ρ	density (kg/m3)
Subscripts
0	environmental state
act	actual
b	boundary
ch	chemical
env	environment
ex	exergy
gen	generation
H	high temperature
i	component i
in	input
m	mixture
L	low temperature
p	product
out	output
r	reactant
R	reservoir
rev	reversible
surr	surroundings
sys	system
Superscipts
˙	time rate
$¯$	per unit mole
0	standard reference state