$B$	Parameter to characterize $\left[1/\left(1-R^{{*}^2}\right)\right]$
$Be$	Bejan number
$Br$	Brinkmann number
$Br{\mathsf{\Omega }}^{-1}$	group parameter
$C_1-C_2$	Constants
$c_p$	Specific heat at constant pressure (J/g K)
$D$	Parameter to characterize $\left(1-\beta \right)/\left(1+\beta \right)$
h1	heat-transfer coefficient at inner wall (W/m2·K)
h2	heat-transfer coefficient at outer wall (W/m2·K)
$I_1-I_4$	constants, depends on aspect ratio
$k$	thermal conductivity (W/m·K)
$N_s$	dimensionless entropy-generation number
$N_{HT}$	entropy generation due to heat transfer
$N_{FF}$	entropy generation due to fluid friction
Nu	Nusselt number
Nu1	Nusselt number at the inner wall of the annulus
Nu2	Nusselt number at the outer wall of the annulus
$P$	Parameter to characterize ${\left[R^{*}{}^2/\left(1-R^{{*}^2}\right)\right]}^2$
q1	lower wall heat flux (W/m2)
q2	upper wall heat flux (W/m2)
$r$	radial coordinate (m)
$r_1$	inner radius of the annulus (m)
$r_2$	outer radius of the annulus (m)
$R$	Dimensionless radial coordinate
$R^{*}$	aspect ratio of the annulus
$S_G$	volumetric entropy generation (W/m3·K)
$T$	temperature (K)
$\overline{T}$	average temperature (K)
$T_1$	inner wall temperature (K)
$T_2$	outer wall temperature (K)
$v_z$	axial velocity (m/s)
$v_{\theta }$	tangential velocity (m/s)
$V$	dimensionless velocity
$z$	axial coordinate (m)
Greek symbols
$\beta$	degree of asymmetry
$\omega$	rotational speed (rad/s)
$\mathsf{\Omega }$	temperature-difference parameter
$\theta$	dimensionless temperature
${\theta }_m$	dimensionless bulk mean temperature
${\theta }_{mc}$	dimensionless mean temperature
$\varphi$	tangential coordinate
$\mathsf{\Phi }$	viscous-dissipation function
$\mu$	dynamic viscosity (kg/m·s)
Subscripts
$f$	initial fluid
$m$	mean