Abstract
The performance augmentation of the heat exchangers is a deal between heat transfer improvement and pressure loss penalty. There is no study investigating this deal as the thermal performance index of the heat exchangers filled by hybrid nanofluid and porous media. The thermophysical properties of TiO2–Al2O3/water are available in the literature, but no study is dedicated to evaluating the flow characteristics of such a hybrid nanofluid, especially in a porous material. This paper is intended to explore the heat transfer and pressure loss of a turbulent convective flow of hybrid nanofluid (TiO2–Al2O3/water) and porous media in a double-pipe heat exchanger with a counter flow. Hot water flows in an annular pipe to warm cold nanofluid flow in an inner pipe. The effect of two porous media is examined for inserting in the inner pipe. Hybrid nanofluid increases the heat transfer (maximum 6%) and pressure loss (maximum 11%). The thermal performance index of the hybrid nanofluid in the aluminum porous media is less than 0.6, while this for the copper media is more than 1. Correlations for the calculations of the Nusselt number and friction factor of the turbulent hybrid nanofluid flow in porous media are missing in the literature. So, for the first time, equations were proposed for finding the Nusselt number and friction factor of the hybrid nanofluid in both empty and porous pipes.