Enhanced Heat Transfer Mechanisms in a Horizontal Annular Heat Exchanger Utilizing a Central Tubular Heater

The efficiency of various industrial processes is contingent upon the heat transfer enhancement and fluid flow dynamics within horizontal annular heat exchangers. This study, therefore, investigates these factors, utilizing a heater with the capacity to vary between 400 W and 600 W, connected to an alternating current (AC) voltage regulator. Cold water, with flow rates ranging from 2.5 to 5 gallons per minute (GPM), circulates in a closed-loop system. The central objectives of this research are to elucidate the heat transfer characteristics, including heat transfer coefficient, Nusselt number, friction factor, and flow regime, and to derive a new empirical correlation for the Nusselt number (Nu) and the friction factor (f) within a horizontal annular heat exchanger incorporating a central tubular heater. The experimental evidence demonstrates an increase in the heat transfer coefficient (h) and the Nusselt number (Nu) with the rise in Reynolds number (Re). The peak heat transfer coefficient was observed at a heat rate of 450 W, commencing at 1893 W/m2·K when Re=4813 and reaching a maximum of 3886 W/m2·K when Re=10127. Additionally, the mean Nusselt number (Nu) was found to range between 89 at Re=4813 and 183 at Re=10127. Conversely, the friction factor (f) decreased as the Reynolds number (Re) increased. The transition from a laminar to a transitional flow regime was observed at Re=8000. The empirical correlations derived from this study were Nu = 0.145Re0.671 Pr0.4and f = 1.4219 Reâ��0.277 with mean absolute percentage errors (MAPEs) of 10.64% and 25.70%, respectively. These findings have the potential to significantly enhance the performance of horizontal annular heat exchangers in various industrial applications.