Heat transfer study of natural circulation serpentine-shaped loops

Abstract

Wide range of industrial applications have been utilized natural circulation loops due to heat transport achieved without the aid of any fluid-moving machinery. Moreover, it has been commonly used either two-phase-rectangular- or square-shaped loops owing these geometries promote satisfactory heat transfer and buoyancy forces performance, however, these two geometries require structural elements of considerable size for certain applications. Therefore, this study thoroughly examined a novel design of 10- and 14-elbow-single-phase-serpentine-shaped loops set in vertical configuration for improving cold water dispensers’ systems in a so called side-by-side refrigerator with the size restriction of its cabinet dimensions. Furthermore, when the application was not constricted to the use of water, numerical tests of heat transfer analysis for three working fluids commonly employed in industrial processes, namely, ethylene glycol, ethanol, and air, also was done. Both loops had the same surface area exposed to the heat source and heat sink, along with the total volume within the loops and the pipeline diameter were equal in the two cases. From the procured results, on one hand, when water was used and Reynolds number was increasing, employing the 10-elbow loop, an increase in internal Nusselt number of 24.5% was obtained. On the other hand, when ethanol was used an increase of Nusselt number of 27.28% was achieved. Finally, a great influence of the height of the loop on the increase of buoyancy forces was observed, hence, higher values for Rayleigh number were obtained when 14-elbow loop was utilized instead of 10-elbow loop; nonetheless, higher values of Rayleigh number did not result in greater values of Nusselt number, concluding that a smaller number of elbows promoted a better heat transfer performance under the operation conditions of the present work.