Experimental and numerical study to optimize flow and heat transfer of airfoil-shaped turbulators in a double-pipe heat exchanger

Abstract

This paper analyses heat and flow transfer in a double-pipe heat exchanger (DPHE). In the DPHE, the turbulators are added to the inner tube to raise its thermal performance. Although this approach increases the heat transfer, the pressure drop raises, leading to greater energy consumption. Therefore, the design of the turbulator should be optimized. This study optimizes the heat transfer and pressure drop of a DPHE with symmetrical 4-digit NACA airfoils with zero angle of attack as a turbulator. These airfoils have been exploited in a DPHE for the first time to reduce pressure drop according to their negligible production vortices. The thermal performance of four types of airfoil-shaped turbulators with different sets of the thickness (t), pitch ratio (PR), and Reynolds number (Re) have been assessed through experimental and computational fluid dynamics. In this context, the correlation of the Nusselt number (Nu) and friction factor (f) has been computed experimentally. Then, an objective function including the friction factor minimization and Nusselt number maximization has been optimized through Genetic algorithm to find the Pareto front. The results highlighted that ƞ enhances under small sets of Re. Further, an increase of t and PR drop result in a greater f and Nu, raising ƞ in overall. Finally, the maximum ƞ = 1.91 has been reached under Re = 6000, t = 0.3, and PR = 1.11.