Energy-Efficient Downsizing of Ribbed Confinements for Heat Exchange Applications

Abstract

Downsizing double-pipe heat exchangers is possible by deploying ribs on the two sides of the heat exchangers. The shape of these ribs, along with two key geometric variables—pitch and height, are crucial in the selection of energy-efficient rib configurations. This is because the enhancement in heat transfer performance comes at the cost of increased pressure drop. Thus, the goal of this numerical investigation is to identify favorable rib shapes and explore the effect of truncation on triangular ribs, which was found to be absent in existing literature. Truncation can address challenges with existing triangular ribs and is expected to greatly affect the performance of conventional triangular ribs. To explore this conclusively, an unbiased and exhaustive analysis is carried out by comparing the performance of confinements with modified and regular triangular ribs, keeping plain confinements as the baseline. Furthermore, the effects of two principal design variables—rib height and rib pitch—are explored for each shape, over a wide range considering essentially all possible combinations. Separate results are presented for the inner and outer confinements of the double-pipe heat exchangers (pipes and annuli) to allow for the extrapolation of results for a wide range of applications employing internal flows in pipes and annuli. A phenomenological model is developed to classify the thermal and hydraulic performance of each confinement and identify optimal geometrical configuration and identify best-performing design(s). Once optimal rib pitch-–height combinations are identified, performance at this optimal combination is evaluated at different Reynolds numbers, spanning from 10,000 to 30,000.