High-efficiency heat transfer devices by innovative manufacturing techniques

In the present thesis, novel methods devoted to develop high heat transfer efficiency devices have been presented. These methods rely on both novel manufacturing techniques, belonging to the class of additive manufacturing (AM), and thermal and fluid-dynamics studies and optimization procedures. As a first result, optimization of a traditional heat exchanger from a real application, i.e. million of units produced per year, is presented; That is manufactured by extrusion. A thermal fluid-dynamic model is experimentally validated (from an industrial experimental test rig) and used for optimization purposes. Results demonstrate there is room for efficiency optimization even in well established heat transfer devices configurations based on traditional manufacturing techniques. Then, an experimental rig for ''in house'' thermal characterization is designed. It guarantees high precision measurement of small convective heat fluxes (forced air) on enhanced solutions investigated hereinafter, namely micro-structured surfaces and small heat transfer devices. To deal with that challenge, an innovative convective heat flux sensor is developed. That exploits the concept of thermal guard to avoid any spurious perturbation between the flow field and investigated surfaces, while it allows to cancel out terms due to spreading conduction phenomenon. Results demonstrate remarkable accuracy in direct measurement of convective heat fluxes through this novel concept. Relying on the proposed experimental rig, various methods for enhanced convective heat transfer are experimentally investigated. Firstly, regular patterns of micro-protrusions are studied. Effect of fluid-dynamics and geometrical length on heat transfer performances are discussed. More important, they have been applied to develop an optimization procedure tailored to deal with AM techniques. Results from both experimental investigation and optimization procedure suggest the existence of an optimal value of protrusion height, that maximize performance-to-cost ratio for patterns made by AM. Then, surface roughness of components built by DMLS has been investigated as an augmentation heat transfer technique. Surface roughness is controlled varying DMLS process parameters and its effect on convective heat transfer is measured. The results demonstrate a remarkable enhancement in convective heat transfer due to DMLS artificial roughness, in the investigated configurations. That preliminary study unveils the potential of AM artificial roughness as an heat transfer enhancement techniques. It has been considered, by academic and industrial institutions, as an important step towards development of next generation gas turbine components and electronic cooling devices. Finally, extreme flexibility in shape of parts built by DMLS is exploited to design and fabricate in one step an unconventional heat transfer device, called Pitot heat exchanger. Enhanced heat transfer efficiency is achieved, with regard to standard heat exchangers. Nevertheless, the most important achievement has been to highlight unusual morphologies allowed by AM can pave the way to revolutionary changes in conceiving and designing heat transfer components