Numerical investigation of the effect of cross-section on the hydrothermal and irreversibility features of water/Fe₃O₄ ferrofluid flow inside a twisted tube in the presence of an external magnetic field effect

This paper studied the heat transfer and entropy generation rate of water-Fe₃O₄ magnetic nanofluid flow inside three twisted tubes with square, triangular, and elliptical cross-sections at the absence and presence of a magnetic field (MF) effect for Reynolds number (Re) range of 400–800, pitch distance (Ps) range of 25–75 mm as well as the nanoparticle concentration (φ) range of 1%, 2%, and 4%. Based on the results, the increase in Re from 400 to 800 escalated convective heat transfer coefficient (h) by 33.98% (or 4.66%), 23.97% (or 18.46%) and 31.36% (or 20.91%) in the square, triangular, and elliptical twisted tubes, respectively, under the absence (or presence) of the MF. At P=50 mm and φ=2%, the MF improved h by 21–45%, 21–26%, and 0–16% within the Re range of 400–800 for the square, triangular, and elliptical twisted tubes, respectively. Nearly 60% and 50% pressure drop observed as Re escalated from 400 to 800 in the absence and presence of the MF, respectively. The highest performance evaluation criterion (PEC) (i.e. 1.45) and the lowest PEC (i.e. 0.91) were obtained for the square twisted tube at Re=400 and elliptical tube at Re= 800, respectively. The highest and lowest PEC of the square twisted tube (i.e. 1.88 and 1.45) at Re=400 were observed for P=50 mm and φs of 4% and 2%, respectively. In the presence of the MF effect, nearly 37–48% (or 32–35%) increase in the S˙_fr (or S˙_th) were obtained at Ps of 25–75 mm against the cases without the MF effect.