Nwosu et al. [1] presented a review and parametric investigation into nanofluid viscosity models. The purpose of the present discussion is to draw the attention of readers that Nwosu et al. [1] did not refer to some nanofluid viscosity equations, which are available in literature. Different examples for the missing nanofluid viscosity equations are given below.

Nwosu et al. [1] mentioned the empirical model of Maïga et al. [2] for ethylene glycol (EG)–γAl2O3 nanofluid. It should be noted that Nwosu et al. [1] did not mention the empirical model of Maïga et al. [2] for water–γAl2O3 nanofluid. This empirical model for water–γAl2O3 nanofluid was
$η=ηnfηbf=1+7.3ϕ+123ϕ2$
(1)
Nwosu et al. [1] mentioned the...