A	area, m2
Ao	total heat transfer area, m2
cp	specific heat, J/(kg·K)
d	pin diameter, m
dp	pressure difference between the leading and trailing edges of a pin, Pa
Fd	flow depth, m
Fh	fin height, m
Fp	fin pitch of the louvered fin, m
h	heat transfer coefficient, W/(m2·K)
k	thermal conductivity, W/(m·K)
$\stackrel{\mathrm{-}}{P}$	fan power per unit frontal area, W/m2
p	pressure, Pa
Δp	pressure drop, Pa
$\stackrel{\mathrm{-}}{Q}$	heat transfer rate per unit frontal area, W/m2
Q	heat transfer rate, W
Re	Reynolds number
Sx	streamwise pin pitch, m
Sy	transverse pin pitch, m
Δs	size of the first layer element on fin surface, m
T	temperature, K
ΔTm	logarithmic mean temperature difference, K
Tw	tube wall temperature, K
U	velocity, m/s
u	velocity vector, m/s
Subscripts
a	air
c	cross-section with minimal flow area
in	inlet
N	streamwise position number
out	outlet
f	fin
Superscripts
L	leading edge of the pin
T	trailing edge of the pin
Greek symbols
μ	dynamic viscosity, kg/(m·s)
ρ	density, kg/m3
Abbreviations
CFD	computational fluid dynamics
LFFTHXs	louvered-fin and flat-tube heat exchangers
PFFTHXs	pin-fin and flat-tube heat exchangers