$A$	Surface area of square cross-section duct (m2)
C	Specific heat (kJ·kg−1·K−1)
Dh	Hydraulic diameter (m)
$h(exp)$	Experimental average nanofluid heat transfer coefficient (W·m−2·K−1)
$h(sim)$	Simulated average nanofluid heat transfer coefficient (W·m−2·K−1)
k	Thermal conductivity (W·m−1·K−1)
L	Duct length (m)
$Nu(exp)$	Average nanofluid Nusselt number obtained from experiments
$Nu(sim)$	Average nanofluid Nusselt number calculated from CFD analysis
Pe	Peclet number
Pr	Prandtl number
q	Heat flux (W/m2)
Re	Reynolds number
Tb	Bulk temperature (K)
Tw	Duct wall temperature (K)
$\overline{U}$	Average fluid velocity (m·s−1)
u	The x-component of the velocity (m−1·s−1)
v	The y-component of the velocity (m−1·s−1)
w	The z-component of the velocity (m−1·s−1)
Greek Symbols
γ	Ratio of the nano-layer thickness to original particle radius
μ	Viscosity (Pa s)
μwnf	Nanofluid viscosity at duct wall temperature (Pa s)
$\varphi$	Nanoparticle volume fraction (%)
$\rho$	Density (kg·m−3)
Subscripts
bf	Base fluid
i	Inlet
nf	Nanofluid
o	Outlet
p	Solid nanoparticles
w	Wall