A	heat exchange area, m2
ARS	Solar Absorption System
ASU	Air Separation Unit
C	cooler
COP	Coefficient of Performance
CP	compressor
E	Expander
HX	Recuperative Heat Exchanger
L	Lagrangian
LNG	Liquefied Natural Gas
LS	Liquid separator
MRC	Mixed-Refrigerant Cycle
MX	Mixer
ORC	Organic Rankine Cycle
RC	Rectification Column
SMR	Steam Methane Reforming
SP	Splitter
TV	Throttling Valve
Lattin Letters
${\mathrm{c}}_{\mathrm{p}}$	specific heat at constant pressure, kJ/kg/K
E	fraction of gas expanded in the expander, kg expanded gas/kg compressed gas
Ex	exergy, kJ
e, ex	mass exergy, kJ/kg
f	objective-function integrand
g	constrain function
h	specific enthalpy, kJ/kg
I	exergy destruction due to internal irreversibility, kJ
J	objective function
$\dot{\mathrm{m}}$	mass flow rate, kg/s
p	pressure, Pa
P	power, W
$\dot{\mathrm{S}}$	entropy rate, W/K
s	specific entropy, kJ/kg/K
$\dot{\mathrm{Q}}$	heat transfer rate, W
${\mathrm{q}}_{\mathrm{f}}$	specific cooling capacity of the gas, kJ/kg
${\mathrm{q}}_{\mathrm{iz}}$	heat penetration due to imperfect insulation, kJ/kg compressed gas
${\mathrm{q}}_{\mathrm{n}}$	cooling loss due to the temperature difference at the hot end of the heat exchanger, kJ/kg
T	temperature, K
U	overall heat transfer coefficient, W/m2/K
W	work, kJ
w	specific mechanical work, kJ/kg
${\mathrm{w}}_0$	mechanical work consumption to obtain 1 kg of liquefied gas, kJ/kg liquid
y	fraction of liquefied gas, kg liquid/kg compressed gas
Subscripts
0	environment, in equilibrium with the environment
C	Claude–Heylandt cycle
c	cold
cp	compressor
e	exit
ex	exergetic
f	forward gas stream
gen	generated
$\mathrm{G}({\mathrm{O}}_2+{\mathrm{N}}_2)$	gaseous mixture of oxygen and nitrogen
h	hot
i	inlet, irreversibility, summation index.
iz	insulation
L	loss
L,1t	single-throttling Linde–Hampson cycle
L,2t	double-throttling Linde–Hampson cycle
$\mathrm{L}\left({\mathrm{O}}_2\right)$	liquid oxygen
M	mean
min	minimum
n1	hot end of the first recuperative heat exchanger HX1
n2	hot end of the second recuperative heat exchanger HX2
n3	hot end of the throttling-stage heat exchanger HX3
opt	optimal
P	Pinch
r	returning gas stream
Rb	reboiler
t	throttle
t1	throttle valve upstream of the expander (TV1)
t2	throttle valve of the throttling stage (TV2)
Q	heat
$\Delta {\mathrm{T}}_{\mathrm{n}}$	temperature difference at the hot end of the heat exchanger
Superscript
Q	associated with heat transfer
RC	Rectification Column
Greek Symbol
Δ	difference
${\eta }_{\mathrm{T},\mathrm{c}\mathrm{p}}$	compressor isothermal efficiency
$\eta$	efficiency
λ	lagrangian multiplier
Ψ	share of an exergetic loss or destruction in the fuel consumption