A Comparative Evaluation Of Heat Transfer And Friction Behavior Of A Square Channel With Sharp And Rounded Edge 45° Ribs At Wide Range Of Reynolds Numbers Using Experimental And Numerical Computation

An investigation of heat transfer and friction behavior for a fully developed flow in a square channel roughened with 45° ribs was conducted over a wide range of Reynolds numbers (Re) from 6,000 to 180,000. Two types of ribs were investigated, namely a) sharp edge and b) rounded edge ribs. The ratio of rib height to channel hydraulic diameter (e/Dh) and the ratio of pitch to rib height (p/e) were 0.063 and 10, respectively. The round ribs have fillet on all edges and the fillet radius was set to half of the rib height (e/2). Experimental data are validated by comparing the results of the sharp edge ribs with data available in existing literature in Re ranging from 6,000 to 70,000. An extensive investigation was performed at higher Re up to 180,000 for both types of ribs. In both cases, flow becomes fully developed after 8Dh for all the Re values. The results show that rounding the ribs’ edges causes lower heat transfer than the sharp edge ribs for all the Re. The rounded edge ribs cause less and less heat transfer than the sharp edge ribs with increasing Re (e.g., at Re≈180,000, rounded ribs causes~17% lower heat transfer). On the contrary, the rounded edge ribs result in only 4%-5% lower friction than the sharp ribs. In addition to the experimental studies, numerical studies were also conducted by solving steady Reynolds Averaged Navier Stokes (RANS) equations. These numerical simulations were performed by applying a periodic fully developed flow condition. Three different turbulence models, namely realizable k-ε, v2-f, and SST k-ω were used to solve the RANS equations. The results of each turbulence model are compared with the experimental data to shed light on the prediction capability of these models. It is found that SST k-ω shows excellent agreement for the heat transfer results for both cases. However, these three turbulence models do not predict the friction factor very reliably