Numerical investigation of the entropy generation of forced convection flow of a non-Newtonian nanofluid inside a twisted double-pipe heat exchanger

The aim of this study is to numerically investigate various aspects influencing the entropy production in a twisted double-pipe heat exchanger. In the inner tube, a combination of copper oxide (CuO) nanoparticles in the base fluid (solution of 0.5 wt% Carboxymethyl Cellulose in water) was used as the non-Newtonian nanofluid. In the space between the two pipes, water flowed in the opposite direction with the Reynolds number (Re) of 1000. The effect of nanoparticle concentration (φ), nanofluid Reynolds number and twist pitch on the results were investigated. The results show that increasing Re from 500 to 2000 increases the thermal and frictional entropies. Also, increasing φ from 0 to 3% reduced both types of entropy. At Re=2000, increasing φ from 0 to 3% caused a decrease of 9.2%, 15.3% and 11.8% for thermal, frictional and total entropies, respectively. In addition, increasing the twist pitch increased them especially for thermal entropy. Also, it was observed that for all the considered values of φ, the Bejan number increases with increasing Re, and at a constant Re, increasing φ causes it to increase slightly.