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

Abstract

Several studies have been conducted to enhance 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) x103, longitudinal pitch ratios (PL =1.44, 1.54, 1.64, 1.74, 1.84, and 2.04), and transverse pitch ratios (PT =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−ε model is selected to evaluate the turbulence effect of the fluid flow. The results showed that an increase in PT significantly affects the heat transfer as compared to PL. 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¯ increases and the friction factor f decreases. At a constant PL, the minimum f was varied with Re and PT. The maximum values of the effectiveness ε and the efficiency index η were achieved for (PT = 1.64; PL = 2.04) at Re=1.78 × 103, and (PT = PL = 1.64) at Re> 1.78 × 103. 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¯, f, and ε 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.