Experimental Investigation of High Prandtl Number Flow in Additive Manufactured Channels

Sammanfattning: Additive manufacturing (AM) rapidly evolves and expands into new industries dueto its great design freedom and time savings. Injection molding is an excellentindustry where AM can help reduce cooling time by printing complex coolingchannels for more effective and uniform cooling. This not only simplifies the extensive machining of complex cooling channels but also increases profitability, which is heavily influenced by cooling time. Regardless of the advantages, AM components have a natural and random surface roughness that varies depending on the material and technology. Although increasing surface roughness improves thermal performance, it also increases unwanted pressure loss. This thesis aims to assemble and validate a test rig for the commonly used cooling media – water. Followed by experimental testing with both smooth and AM rough mini-channels to compare the difference in results for pressure loss and convective heat transfer coefficient. Data collected were evaluated using the Darcy friction factor for pressure loss and the Nusselt number for the convective heat transfer coefficient quantification, respectively. In the heat transfer experiment, a one-dimensional constant heat flux boundary condition was applied with the streamwise linear discretization method. Results show a good agreement of smooth and rough channel results for the Darcy friction factor to the prediction done by theoretical correlations and compared to results from the air. Nusselt number results of the smooth channel were in line with theoretical correlations; however, as the water Prandtl number increases, the correlations seem to underpredict the heat transfer performance in high Reynolds numbers. Furthermore, the heat transfer enhancement of the AM rough channel increased overall by 2.5 times compared to the smooth channel in laminar to early turbulent flow regimes. These results established a ground for continuous experimental testing but also revealed unknowns regarding the effect of high Prandtl number on heat transfer in turbulent flow regimes.