Mixed convection boundary layer flow from a horizontal circular cylinder in a nanofluid

Purpose - The purpose of this paper is to study the steady mixed convection boundary layer flow of a nanofluid past a horizontal circular cylinder in a stream flowing vertically upwards for both cases of a heated and cooled cylinder. Design/methodology/approach - The resulting system of nonlinear partial differential equations is solved numerically using an implicit finite-difference scheme known as the Keller-box method. This method is very efficient for solving boundary layer problems. Findings - The solutions for the flow and heat transfer characteristics are evaluated numerically for various values of the parameters, namely the nanoparticle volume fraction phi and the mixed convection parameter lambda at Prandtl number Pr = 1 and 6.2. Three different types of nanoparticles considered are Cu, Al2O3 and TiO2 by using water-based fluid with Pr = 6.2. It is found that for each particular nanoparticle, as the nanoparticle volume fraction phi increases, the skin friction coefficient and heat transfer rate at the surface also increase, and it also leads to the increment of the value of mixed convection parameter lambda which first gives no separation. Research limitations/implications - The results of this paper are valid only up to the value of lambda = lambda(0) (<0) below which a boundary layer solution does not exist. Practical implications - The results obtained can be used to explain the characteristics and applications of nanofluids, which are widely used as coolants, lubricants, heat exchangers and micro-channel heat sinks. Nanofluids usually contain the nanoparticles such as metals, oxides, or carbon nanotubes, whereby these nanoparticles have unique chemical and physical properties. Originality/value - The results of this paper are important for the researchers working in the area of nanofluids. The paper is well prepared and presented. The results are original, new and important from both theoretical and application point of views.