ADDITIVE MANUFACTURING FOR ADVANCED HEAT TRANSFER SOLUTIONS: FROM MATERIAL TO THERMAL MANAGEMENT APPLICATION

Additive Manufacturing (AM) is a general name for technology processes that produce parts stratifying layers of material instead of using subtractive conventional technologies. Although the availability of materials and their properties do not often achieve the same amount of those manufactured via traditional ways; the benefits of AM technologies are in the innovative shapes and complex geometries that can be manufactured. The AM technology is one of the fastest ways to prototype with free forms compared with expensive molds. In the thermal sector, the recent developments of high thermal conductivity and high-temperature resistance metals in fully dense parts made the AM attractive for several heat transfer applications: compact heat exchangers, heat sinks, electronic cooling, embedded cooling channels, micro-channels, structure lattice types, and triply periodic surface types. In this thesis, the use of AM is presented with particular attention to the thermal applications, with a general overview of the possible AM technology processes and the best achievable material properties. In addition, the benefits and the issues are then reported, with a focus on the thermal sector and the ongoing aspects that are keeping additive manufacturing a challenge to be used for industrial applications. Particular attention is given to the Powder Bed Fusion technology working with high laser power, to produce components with integrated cooling channel systems. The issue of such technology (L-PBF), after having characterized the best process parameters for fully dense material, is the high surface roughness inside the channels produced (Chapter 1). In this work, a first investigation of the process parameters of L-PBF and density and thermal properties is given in Chapter 2. Different methods to measure relative density and thermal conductivity are reported with experimental results of different high thermal conductivity metal samples produced via L-PBF. In Chapter 3, the surface roughness on walls at different building orientations is then studied and analyzed with an optical profilometer, to obtain a map of the L-PBF process parameters that modify the surface roughness quality. The surface roughness analysis is carried out using surface texture parameters to quantify the height of the surface roughness. Moreover, in Chapter 4, the fluid flow interactions between rough channels and water flow are studied and reported. The roughness influence is then investigated experimentally and numerically, focusing on the straight channels. The hydraulic performance are reported, while thermal performance is evaluated in other rough channels manufactured via L-PBF. An experimental correlation is proposed to predict the friction factor in a fully turbulence fluid regime from the surface texture parameters of the channel's internal and external thin walls. In Chapter 5, the results obtained from smoothed channels are reported. The manufactured channels via L-PBF were internally smoothed via a chemical milling process and the friction factor results were compared with the rough conditions. The experimental tests were realized with different samples and L-PBF machines. In Chapter 6, the results obtained from the smoothed channels were used to design cooling channels for the application of the L-PBF of integrated cooling channels in components for high heat flux applications, such as a nuclear fusion energy facility. A numerical model for experimental tests was designed, and the relative experimental setup was built. The experimental results were reported in terms of maximum temperature and pressure drop, and a numerical model was calibrated and compared with the experimental results.