Microchanneled devices: structural analysis of deformations during diffusion bonding process

This Master Thesis in Mechanical Engineering analyses the mechanical resistance of the channelled structure constituting a Printed Circuit Heat Exchanger (PCHE) during the building process. A PCHE is a particular type of heat exchanger which is made by different laminae, machined by chemical etching to create pseudo-circular channel. The plates are welded together via Diffusion Bonding (DB). The DB is a welding technique based on the junction of pieces thanks to the contact of the different interfaces of the components to be welded, putting them in contact at high temperature without any external material. This procedure is helped by the presence of the external pressure and the elevate temperatures improve the phenomenon of the grain growth, fundamental process of that technique. We perform the joining in a Hot Isostatic Pressure (HIP) furnace: a particular oven with controlled atmosphere, able to create a homogeneous pressure inside its structure. The goal of the engineer is finding the better compromise between temperature, time and external pressure to ensure an elevate mechanical resistance of the welding but a deformation of the channels under a certain threshold limit that is considered acceptable for the performances of the final product. The STV Italia hosted me for an internship experience. This company is leader in chemical etching and they want to tailor a slice of the PCHEs market passing from producer of semi-finished product (the etched laminae) to create a own final serie of heat exchangers. This Thesis is subdivided in a first part where the processes, the standards and a more general overview of the problems can born during the creation of the PCHE are described. The second part is an accurate analysis of the forces present in the block made which will create the PCHE. We desire to verify the static resistance of the channels during the process. An algorithm is created by myself to verify the static validation. Changing some geometrical parameters of the plates constituting the block we analyse the influence of the different changes in the static validation. The goal is finding a tool to get a starting point from the static validation, in order to extend the studies in a further way as next steps of the know-how in PCHEs production.