A${}_1$, A${}_2$	coefficient for viscosity
C${}_k$	coefficient for thermal conductivity
D${}_h$	hydraulic diameter, (m)
h	heat transfer coefficient, (W/(m${}^2$K))
k	thermal conductivity, (W/(m K))
KR	conductivity ratio
H	slot-to-plate distance, (m)
Nu	Nusselt number
p	pressure, (Pa)
Pr	Prandtl number
R	residual
Rc	cylinder radius, (m)
Re	Reynolds number
Rew	rotational Reynolds number
Sc	distance between the cylinders, (m)
T	temperature, (K)
u, v	velocity components, (m/s)
w	slot width, (m)
W	weight function
x, y	Cartesian coordinates, (m)
Greek Characters
$\alpha$	thermal diffusivity, (m${}^2$/s)
$\varphi$	solid volume fraction
$\nu$	kinematic viscosity, (m${}^2$/s)
$\rho$	density, (kg/m${}^3$)
$\omega$	rotational speed, (rad/s)
$\Delta T$	temperature difference, (K)
Subscripts
c	cold
h	hot
m	average
nf	nanofluid
p	solid particle
Abbreviations
ANN	artificial neural network
EBE	energy balance equation
MSE	mean square error
NF	nanofluid
NP	nanoparticle
PST	panel surface temperature
PV	photovoltaic
PV-T	photovoltaic thermal
RCC	rotating circular cylinder
SVF	solid volume fraction
T-RCC	twin rotating circular cylinder