The effect of inlet temperature on the irreversibility characteristics of non-Newtonian hybrid nano-fluid flow inside a minichannel counter-current hairpin heat exchanger

Abstract

The goal of this work is to examine the influence of entering temperature on the entropy generation characteristics of a minichannel hairpin heat exchanger with counter-flow configuration. The working fluids are water and hybrid water–Fe3O4/carbon nanotubes (CNTs) nano-fluid (NF) that flows through the annulus side and tube side of the heat exchanger, respectively. It is assumed that the NF is non-Newtonian, and its thermal conductivity and viscosity are temperature dependent. The impact of volume fraction of Fe3O4 ($$\varphi_{\text{FF}}$$) and CNT nanoadditives ($$\varphi_{\text{CNT}}$$) as well as the Reynolds number of NF ($$Re_{\text{nf}}$$) on the Bejan number and irreversibilities due to heat transfer and fluid friction are also assessed. It was found that augmenting the temperature difference between the fluids entering the heat exchanger results in a decrease in the frictional irreversibility and an increase in the global thermal and total irreversibilities and global Bejan number. Additionally, the outcomes depicted that the global frictional and total irreversibilities and the global Bejan number intensify by boosting the $$Re_{\text{nf}}$$ and $$\varphi_{\text{CNT}}$$, while the increase of $$\varphi_{\text{FF}}$$ first leads to the reduction and then the increase of these parameters.