The impact of spacing ratios on thermal-hydraulic performance of a cam-shaped tube in a four-tube staggered configuration

Abstract

Comprehensive experimental and numerical studies were conducted to investigate the effects of longitudinal and transverse spacing ratios (S_L^⁎ and S_T^⁎) on fluid flow and heat transfer characteristics of the downstream tube in a staggered tube bank consisting of four cam-shaped tubes. Using cam-shaped tubes improved the thermal-hydraulic performance of the tube bundle by enabling a more compact arrangement and reducing drag coefficient. Various configurations (Model D to O) were examined, with S_L^⁎ ranging from 3 to 6 and S_T^⁎ ranging from 1.25 to 2 at a constant Reynolds number of 26,870 with a uniform heat flux on the rear tube. Numerical simulations using an unsteady three-equation k-kl-ω turbulence model demonstrated strong agreement with our experimental data, confirming the model's accuracy. The results revealed that the configuration with S_T^⁎ = 1.25 and S_L^⁎ = 3 (Model D) significantly reduced the drag coefficient of the rear tube by 122 % compared to a single cam-shaped tube (reference case). The maximum Nusselt number was obtained at S_T^⁎ = 2 and S_L^⁎ = 3 (Model L), resulting in a 39.05 % enhancement compared to the reference case. Furthermore, reducing S_L^⁎ from 6 to 3 while keeping S_T^⁎ values constant significantly enhanced thermal-hydraulic performance. Notably, Model D achieved the highest performance, with an improvement of 212.8 % compared to the reference case, while minimizing the tube bundle volume.