Projeto de concepção, prototipagem e comissionamento de uma bancada experimental para determinação do coeficiente de transferência de calor por ebulição externa em um bloco de aço girante no processo de têmpera

Abstract

The quenching plays a fundamental role in the metallurgical industry, since, in addition to improving the toughness and ductility of steel, it optimizes its mechanical properties in general, and is present in the manufacturing process of products intended for the automotive and oil industries. The quenching is a fundamental heat treatment in large steel tubes and, since it is a complex procedure, knowing the variables involved facilitates process control and allows computational simulation, saving time and resources. One of the main parameters involved in quenching by immersion in a cooling fluid is the heat transfer coefficient. Since quenching involves different boiling regimes, it is more complex to determine the heat transfer rates. This work consists of the design, construction and commissioning of a mechanism capable of simulating the cooling process of a solid steel tube, at high temperature, in a similar way to that observed in the industry. The project consisted of adapting a masonry tank developed to determine the external heat transfer coefficient in quenching processes of steel tubes in steady state to operate in transient mode. The tank, which already had a test specimen whose shaft was connected to a gear motor, in addition to a cooling system with a chiller and water recirculation by pumping, received a mechanism driven by pneumatic cylinders, responsible for rapidly raising the water level to cover the test specimen. Type K thermocouples were distributed radially in the cylinder body, as well as on the surface and in the middle of the tank. A higher-speed data acquisition system was also incorporated to allow the capture of temperatures during the transient regime. The commissioning of the test bench and validation of the preliminary results was completed with the survey of the cooling curve. A mathematical model, based on finite differences, was implemented in the MatLab® software to numerically estimate the value of the heat transfer coefficient from the cooling curves of the test specimen. The convection coefficient curves were plotted for several experimental tests, with different execution times, including tests with the static and rotating cylinder. The results were qualitatively compared with related works available in the literature, since, as the experimental conditions are unique, there are no numerical results similar to those obtained.