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 (theta) 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 degrees <= theta <= 90 degrees), and Rayleigh number (2.6 x 10(6) <= Ra <= 2.05 x 10(8)). 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 theta at constant Ra. Furthermore, theta = 90 degrees 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 (approximate to 1.8) and at theta = 90 degrees can be approximated as a vertical flat plate case. So, the elliptical-tube with theta = 90 degrees 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/m(2) <= q <= 885 W/m(2)) and Nu achieves the highest values at 555 W/m(2). The current experimental data is correlated and compared with the ANN model output and other reported work in the literature.