RCAAP Repository

The heat affected zone (HAZ) is the most susceptible region for corrosion occurrence in a welded joining. Besides microstructural variations, the corrosion susceptibility of HAZ is increased by stresses that act on it (residual ones, related to welding thermal cycles, added to external stresses) and also by stress concentration factors connected to the geometry of the weld edge (toe). Machining (grinding) of the weld edge is used to increase the smoothness (concordance) between the weld bead and the base metal. However, such techniques do not eliminate problems associated to the presence of inclusions, porosity and segregation, which increase corrosion wear. TIG Dressing technique has been used for reducing fatigue crack occurrence from stresses generated in the weld edge. The use of this technique is expected to increase the concordance between weld bead and base metal and to reduce the tensile residual stresses in the surface (tensile stresses increase the HAZ corrosion susceptibility). Therefore, the effect of external stresses concentrated at the concordance between weld bead and base metal on corrosion wear at the weld edge of the HAZ was evaluated. Both machining and TIG Dressing techniques were used to smoothen the concordance. The effects of tensile stresses, superficial finishing and microstructural variations in the HAZ were quantified by the wearing after submitting the samples to chloriteion medium. Wear in MIG/MAG and TIG Dressing HAZ were assessed using optical microscopy by using a mask that reveals the corrosion area in terms of linear dimension of the welded and bended samples. From the obtained results, it was observed that the TIGDressing technique led to lower wear in the HAZ, especially when using pure argon as shielding gas. By using electrochemical measurements, it was observed the HAZ of the weld edge of the bead from TIG Dressing is the most susceptible region for corrosion wear and anodic dissolution occurs.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

This thesis deals on the development an autonomous system, able to move within a culture accurately and effectively, being functional and economically viable in small cultures, which constitute the most percentage to agricultural production area in Colombia. A system capable to mapping the boundaries of culture it has develop with sub metric GPS in free signal without real time correction, and generate an innovative and proprietary methodology that integrates many different systems to a level pilot of one hectare. The GPS data are stored in a file and used for limits correction with software developed, using methods of interpolation and optimization with cubic splines, to make the distribution of culture and establishment the points of automatic positioning to the vehicle within the culture. With these coordinates, the trajectories are generate using A* algorithm to move between two points fulfilling the tasks of culture, interacting with a remote computer over wireless network Xbee. The result is a vehicle capable of dispensing liquid fertilizer with an error less than 3% by volume, with the possibility of moving in a culture following the trajectory generated by A* algorithm with error less than 10 cm, based on the embedded sensing in the vehicle and supervised by remote computer.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

The present research deals with an experimental study of the heat transfer and pressure drop of nanofluids composed by carbon nanotubes and distilled water in single-phase flow inside a horizontal straight tube. An experimental bench has been developed and constructed whose the main component was a horizontal brass tube electrically heated by tape resistors wrapped on the external surface. Experimental results have been obtained for a wide range of mass velocities, 600 up to 3200 kg/s.m2, (Reynolds varying from 2300 to 30000) corresponding to the transition and turbulent flow regimes. The specific heat flux varied from 10 to 18 kW/m2. Tests were conducted for three different temperatures at the test section inlet, 10, 15 and 20 C. Other effects on the heat transfer coefficient were also analyzed such as: aspect ratio of the carbon nanotubes; mass concentration and nanoparticle deposition on the wall. The thermal-hydraulic performance obtained for the nanofluid was higher in comparison with distilled water.The experimental results were compared with the leading correlations from the literature. Finally, an empirical correlation for the heat transfer coefficient was proposed, with a very good agreement in relation to the experimental results using nanofluids.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior