A	heat exchange surface, m2
$c_v$	specific heat, Jkg−1K−1
D	diameter of the piston, m
h	convective heat transfer coefficient, Wm-2K-1
I	current, A
k	losses factor in regenerator, -
K	heat exchanger conductance, WK−1
m	mass, kg
n	engine rotation speed, rot.s−1
p	pressure, Pa
Q	heat, J
$\dot{Q}$	heat transfer rate, W
R	gas constant, Jkg−1K−1
S	stroke of the piston, m
T	temperature, K
U	voltage, V
V	volume, m3
W	work, J
$\dot{W}$	mechanical power, W
Greek symbols
$\gamma$	adiabatic exponent, -
$\phi$	rotation angle, °
${\phi }_0$	phase lag angle, °
ε	volumetric compression ratio (Vmax/Vmin), -
$\eta$	efficiency, -
Subscripts
C	compression
ε	depending on ε
E	expansion
d	displacer
h	hot on working gas side
l	low on working gas side
m	dead
max	maximum
min	minimum
p	piston
rev	reversible
reg	regenerator
v	constant volume (specific heat)
wl	low on source side
wh	hot on sink side