A Comprehensive Numerical Analysis on the Thermo-hydraulic Performance of U-Bend Tube with Spherical Dimple of Shell-and-Tube Heat Exchanger Subjected to Uniform/Non-uniform Magnetic Fields

Abstract

Heat exchangers are widely used in most heat transfer applications, and further improvements are necessary to limit the growing energy demand. In this context, performance improvement studies of shell-and-tube heat exchangers have gained importance. Although many studies have been conducted on this heat exchanger in the literature, research on the Utube channels remain limited. To address this gap in the literature, a detailed investigation of energy, entropy, and exergy analysis was conducted on this geometry using numerical methods. Both passive and active heat transfer enhancement methods were utilized to improve the thermo-hydraulic performance of the U-tube. As a passive method, dimpled fins and MWCNT-Fe₃O₄/water hybrid nanofluid at volume fractions of 0.001 and 0.003 were employed. As an active method, DC and AC (f = 2 Hz and square wave) magnetic fields with strengths of B = 0.16 T and 0.30 T were applied. The flow conditions in the analysis corresponded to the laminar flow regime at Dean numbers of 117.1, 175.7, and 234.2. Effects of hybrid nanofluid fractions, U-tube positions, flow regime, magnetic field strength, and current type on each other were discussed and compared in detail with previous results. Findings were carefully evaluated, and conclusions were drawn in the context of similar research. Results indicated that the U-tube position did not affect thermo-hydraulic performance. However, it was calculated that dimpled finned U-tube increased convective heat transfer by up to 30% compared to plain U-tube. Moreover, MWCNT-Fe₃O₄/water hybrid nanofluid at 0.003 volume fraction increased this rate by an additional 5.0%.