Accuracy in evaluating convective heat transfer coefficient by RANS CFD simulations in a rectangular channel with high aspect ratio and 60° tilted staggered ribs

A numerical analysis of heat transfer characteristics of an air flow through a narrow rectangular channel of 1:10 aspect ratio with ribbed surfaces has been carried out, by means of a CFD commercial code, exploiting Reynolds Averaged Navier-Stokes (RANS) equations. The channel is 120 mm wide, 840 mm long, with 60° tilted staggered ribs. Ribs have a square cross section with two different side heights (2 mm and 4 mm) and three different values of dimensionless pitch (10, 20 and 40). The numerical results have been compared with experimental data obtained by the authors inside a ribbed channel both with same geometry and operating conditions as one numerically modelled. Agreement between numerical and experimental data on convective global heat transfer coefficient, i.e., averaged over the whole channel, is discussed for the six different configurations considered. Moreover, performances are presented by considering at the same time both heat transfer enhancement and pressure-drop penalization, highlighting strengths and weaknesses per each configuration. This work is aimed at finding a suitable configuration of a CFD model with RANS that will allow authors to apply it to the range of dimensionless pitches and side heights during early design-phases of parametric studies.