Effect of differentially heated tubes on natural convection heat transfer in a space between two adiabatic horizontal concentric cylinders using nano-fluid

Abstract In the present numerical study, the free convective flow between several differentially hot and cold tubes enclosed in a space between two horizontal adiabatic coaxial cylinders which filled with three different kinds of nano-fluids is investigated. The effects of influential aspects including; location of heat source/sink, number of tubes, Rayleigh number (Ra), volume concentration (ϕ) and type of the nanoadditives on the isotherms, streamline, stream function and average Nusselt number ( N u ¯ i ) are explored. The governing equations are solved numerically employing control-volume based finite volume technique. For pressure-velocity coupling, the Semi-Implicit Method is utilized. According to the obtained results, usage of nano-fluid leads to the considerable enhancement of heat transfer in the studied cavity. For all the examined configurations with two cylinders, the configuration 30° has the most N u ¯ i values which is followed by configurations 60° or 0°, 90°, 120°, 150° and 180°, respectively. It is clearly seen that for all the assessed configurations with three cylinders, the highest to lowest N u ¯ i respectively belongs to the Case 2C, Case 2A and Case 2B. Moreover, for all the investigated configurations with four cylinders, the highest and lowest N u ¯ i respectively occurs at Case 3B and Case 3A.