$a$, $x$, $y$	Intermediate variables
$C$	Thermal capacity rate (kW/K)
$C_p$	Specific heat at constant pressure (kJ/(kg·K))
$E$	Effectiveness of heat exchanger or ecological function (kW)
$\overline{E}$	Dimensionless ecological function
$k$	Specific heat ratio
$M$	Mach number
$N$	Number of the heat transfer unit
$\dot{Q}$	Heat absorbing rate or heat releasing rate (kW)
$\overline{P}$	Dimensionless power density
$T$	Temperature (K)
$U$	Heat conductance (kW/K)
$u$	Heat conductance distribution
$\overline{W}$	Dimensionless power output
Greek symbols
$\eta$	Efficiency
$\pi$	Pressure ratio
$\tau$	Temperature ratio
Subscripts
$H$	Hot-side heat exchanger
$L$	Cold-side heat exchanger
$wf$	Working fluid
$1,2,3,4,5,2s,5s$	State points