The first and second law analyses of thermodynamics for CoFe<inf>2</inf>O<inf>4</inf>/H<inf>2</inf>O flow in a sudden expansion tube inserted elliptical dimpled fins

Abstract

In this paper, thermo-hydraulic performance and entropy generation of the sudden expansion tube with elliptical dimpled fins (DFs) at different directions was computationally performed at different Reynolds (Re) numbers ranging between 100≤Re≤2000 using cobalt ferrite/H2O (CoFe2O4/H2O) nanofluid (NF) (0.0≤φ≤ 2.0). The novelty of this study is to investigate the effect of the elliptical DF and its arrays in the sudden expansion tube in terms of thermodynamics laws (energy and entropy generations). While the sudden expansion ratio (D2/D1) is 2.5, elliptical dimple width (a) and height (b) show variations between 4 and 8 mm. In addition, the distances among elliptical DFs (P) are taken as P = 10, 15, and 20 mm while the diameter (D1) and length (L1) of the inlet tube are D1=8 mm and L1=375 mm. The diameter (D2) and length (L2) of the tube with the sudden expanding and elliptical DFs are D2=20 mm and L2=1125 mm, respectively. The study comprehensively exhibits results of the thermo-hydraulic performance and entropy generation based on numerical data. The results demonstrated that the highest heat transfer rate is recorded by the case of DT3, and DT3 enhances the convective heat transfer rate by 221%, and increases the pressure drop by 17.38% at Re=2000 compared to smooth tube (ST). It was observed that as the Re increases, the performance evaluation criteria (PEC) gradually increases too, and the highest PEC has been obtained for DT3 as 2.11 at Re=2000. The entropy generation (EnG) was also evaluated in terms of both geometric designs and volumetric concentrations. Moreover, the best total EnG was found around 17% for DT3 at the Re=1000 and φ=2.0% compared to ST using H2O. Consequence of the applied analyses, the use of elliptic DFs in a sudden expansion tube enhances the convective heat transfer rate and decreases total EnG.