Experimental investigation of heat transfer in additive manufactured channels with different Prandtl

Additive manufacturing of metal alloys allows to create completely new designs for components that require to be actively cooled, such as gas turbines. The parts can now be printed with an uniform and distributed pattern of internal microchannels, leading to a better heat exchange. These channels, however, present a roughness pattern different from the one observed on conventionally manufactured channels, and this changes the flow behaviour in terms of pressure drop and heat exchange performance. This thesis aims to study the different behaviour of AM-manufactured channels and the impact that their relative roughness has on two adimensional parameters: Darcy friction factor for the pressure losses and Nusselt number for the heat exchange performance. The fluid used was distilled water, which allowed to test at various Prandtl numbers by changing its temperature. This test rig concept started two years ago, and the procedures and theoretical models have been improved by each student. In September 2023, a new model has been developed to gather more accurate results, using the Joule effect to internally generate heat in the metallic test object. An important part of the work has been creating a numerical model to estimate the heat transfer coefficient at the interface between the wall and the water, using Siemens Star CCM+ thermal and electrical solvers. The pressure loss results resemble what is already found in literature for conventional sand-grain roughness on the Moody diagram. The Nusselt number is affected in a different way, and the different roughness type has different results when compared to previous sand-grain correlations. Another different phenomenon observed is the effect of the Prandtl number, not following previous correlations such as Dittus-Boelter.