Numerical analysis of the effect of longitudinal and transverse pitch ratio on the flow and heat transfer of staggered drop-shaped tubes bundle

Several studies have been conducted to enhancement the performance of heat exchangers. In the recent decades, shifting from the bluff bodies to more streamlined ones received more attention. The drop-shaped tube is one of the most propitious options for building a better heat exchanger core. This is because of the aerodynamic profile characteristics of the drop-shaped tube. The present work has been conducted to clarify fluid flow and heat transfer across staggered drop-shaped tubes bundle at various longitudinal and transverse pitch ratios. The investigation is performed at Reynolds numbers Re= (1.78-18.72) x 10(3), longitudinal pitch ratios (P-L =1.44, 1.54, 1.64, 1.74, 1.84, and 2.04), and transverse pitch ratios (P-T =1.24, 1.44, 1.64, and 1.82). Ansys Fluent software package is used to predict the flow pattern around tubes. The RNG k - epsilon model is selected to evaluate the turbulence effect of the fluid flow. The results showed that an increase in P-T significantly affects the heat transfer as compared to P-L. An increase in the transverse pitch ratio from 1.24 to 1.82 enhances the heat transfer by 2.18 - 10.53% for the considered Re range. As the Re increases, the average Nusselt number (Nu) over bar increases and the friction factor f decreases. At a constant P-L, the minimum f was varied with Re and P-T. The maximum values of the effectiveness epsilon and the efficiency index eta were achieved for (P-T = 1.64; P-L = 2.04) at Re =1.78 x 10(3), and (P-T = P-L = 1.64) at Re> 1.78 x 10(3). The drop-shaped tubes bundle showed its superiority over a circular one in terms of high thermal-hydraulic performance under the same operating conditions. Finally, generalized (Nu) over bar, f, and s correlations for the studied models were predicted, providing a useful reference for future studies or for the design of heat exchangers employing drop-shaped tubes. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study confirmed that the drop-shaped tubes bundle can achieve higher thermal performance, with the transverse pitch ratio having a more significant impact on heat transfer efficiency. The maximum values of the effectiveness and efficiency index under a constant longitudinal pitch ratio depend on the Reynolds number and transverse pitch ratio.