Elliptic tube free convection augmentation: An experimental and ANN numerical approach

Experimental results of free convection thermal performance on the elliptical-tube outer surface at various inclination angles (θ) and heat fluxes (q) with artificial neural network modelling (ANN) and 3D ANSYS numerical evaluations are presented. The considered parameters include: axial distance (0.1 ≤ X/L ≤ 0.9), (0° ≤ θ ≤ 90°), and Rayleigh number (2.6 × 106 ≤ Ra ≤ 2.05 × 108). Bayesian regularization algorithm as a method of back-propagation technique is used for selecting the optimal ANN size. Results revealed that Nu increases with the increase in θ at constant Ra. Furthermore, θ = 90° gives higher values of Nu compared to all other elliptical-tube inclination angles at the considered Ra range. The elliptical-tube shape with major to minor diameter of (≈1.8) and at θ = 90° can be approximated as a vertical flat plate case. So, the elliptical-tube with θ = 90° is equivalent to two vertical-plates. The recapitulation of the ANN results indicates that, the highest Nu values exist at the tube two peripheral ends with (405 W/m2 ≤ q ≤ 885 W/m2) and Nu achieves the highest values at 555 W/m2. The current experimental data is correlated and compared with the ANN model output and other reported work in the literature.