Effect of scale formation on the emissivity of austenitic stainless steels in an annealing furnace

Abstract. The aim of this thesis was to develop a mathematical model to describe the effect of scale growth of austenitic stainless steels on the emissivity during the annealing process. The model is intended to be suitable for industrial use, so the temperatures, atmospheres and holding times used in annealing tests were chosen to match industrial conditions in stainless steel making. The experimental work consisted of simulating the annealing of cold rolled AISI 316L on an industrial scale annealing- and pickling line. The experiments were performed in a vertical tube furnace and the analysis was performed using a GDOES and FESEMEDS microscope. Emissivity measurements were performed under the same conditions as the annealing experiments, which made it possible to find out how the formed scale layer affects the emissivity. In all cases it was noted that a higher temperature and longer holding time would cause a higher amount of oxidation. Correspondingly, the emissivity values increased as the thickness of the scale layer increased. The results of the experimental work were fitted into mathematical models executed using the Python programming language. Different oxidation time laws were tested, of which the best performing one was selected for the final model. The Arrhenius equation was used to calculate equilibrium constants, activity coefficients and frequency factors. In the model, a regression line was used to predict emissivity, which was determined from the measurement data by multivariate regression analysis.Hilseenmuodostumisen vaikutus austeniittisten ruostumattomien teräksien emissiivisyyteen hehkutusuunissa. Tiivistelmä. Tämän työn tavoitteena oli kehittää matemaattinen malli kuvaamaan austeniittisten terästen hilseenkasvun vaikutusta emissisiivisyyteen hehkutusprosessin aikana. Malli on tarkoitettu sopivaksi teolliseen käyttöön, joten hehkutuskokeissa käytetyt lämpötilat, atmosfäärit ja pitoajat valittiin vastaamaan ruostumattoman teräksen valmistuksen teollisia olosuhteita. Työn kokeellisessa osassa simuloitiin kylmävalssatun AISI 316L:n hehkutusta teollisen mittakaavan hehkutus- ja peittauslinjalla. Kokeet suoritettiin pystyputkiuunissa ja näytteiden analysointiin käytettiin GDOES- ja FESEM-EDS-mikroskopiaa. Emissiivisyysmittaukset suoritettiin samoissa olosuhteissa kuin hehkutuskokeet, jolloin saatiin selville, miten muodostunut hilsekerros vaikuttaa emissiivisyyteen. Kaikissa tapauksissa havaittiin, että korkeampi lämpötila ja pidempi pitoaika aiheuttivat enemmän hapettumista. Vastaavasti emissiivisyyden arvot kasvoivat hilsekerroksen kasvaessa. Kokeellisen työn tulokset sovitettiin matemaattisiin malleihin, joiden toteutus suoritettiin käyttämällä Python ohjelmointikieltä. Erilaisia hapettumisen aikalakeja testattiin, josta parhaiten suoriutunut valittiin lopulliseen malliin. Tasapainovakioiden, aktivoitumisenergioiden ja taajuustekijöiden laskemiseen käytettiin Arrheniuksen yhtälöä. Mallissa emissiivisyyden ennustamiseen käytettiin regressiosuoraa, joka määritettiin mittausdatan pohjalta monimuuttujaregressioanalyysillä

Development of flat flame burners for industrial heat transfer applications

Several industrial processes involve the heating of long and thin strips. One such process is the decarburising annealing of electrical steel. Published research suggests that rapid heating of up to 100◦C/s during the decarburising annealing process significantly improves the magnetic properties of these steels. In this investigation, it was shown that the currently used technology of radiant tube burners was not optimal for the heating of these type of products. Therefore, the main objective of this project was to develop a novel type of burner that produced a flat wall attached flame by means of the Coanda effect. Due to its unique flame geometry, the burner achieved the required heating rates. The behaviour and fundamental characteristics of isothermal and reacting Coanda flows were investigated. A combination of laser diagnostics, temperature measurements and visual observations were used to obtain information about the flow. A precessing vortex core that contributes to the flat flow profile was identified. A hysteresis behaviour between different flow states was observed. Critical factors that affect the onset and stability of the Coanda flame were determined; being the most relevant ones the applied swirl intensity, the flow rate, the relation between plate height and the nozzle outlet, the equivalence ratio and the nozzle geometry. Subsequently, the experimental results were used to validate numerical simulations. The numerical simulations were used to conduct a parametric analysis for the burner geometry optimisation. The optimised burner was compared to a radiant tube burner via CFD simulations. It was found that the Coanda burner had lower radiant heat flux than the radiant tube burner. However, this downside was compensated by an increase in the total radiating area in the furnace. The use of the proposed Coanda burner in the decarburising annealing process had the potential to cause an increase in heating rate, a reduction in energy requirement, a reduction in NOx emissions, a reduction in heating time, an increase in temperature homogeneity of the load, and a reduction in volume furnace with the consequential reduction in start-up times. Thus, the proposed technology has the potential to reduce the energy intensity of the annealing process and, because of the increased heating rate, improve the magnetic properties of the final product

Cumulative index to NASA Tech Briefs, 1986-1990, volumes 10-14

Tech Briefs are short announcements of new technology derived from the R&D activities of the National Aeronautics and Space Administration. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This cumulative index of Tech Briefs contains abstracts and four indexes (subject, personal author, originating center, and Tech Brief number) and covers the period 1986 to 1990. The abstract section is organized by the following subject categories: electronic components and circuits, electronic systems, physical sciences, materials, computer programs, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

NASA Tech Briefs, June 1996

Topics: New Computer Hardware; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery/Automation; Manufacturing/Fabrication; Mathematics and Information Sciences;Books and Reports

NASA Tech Briefs, September 1987

Topics include: NASA TU Services; New Product Ideas; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Fabrication Technology; Machinery; Mathematics and Information Sciences; Life Sciences

NASA Tech Briefs, June 1995

Topics include: communications technology, electronic components and circuits, electronic systems, physical sciences, materials, computer programs, mechanics, machinery, manufacturing/fabrication, mathematics and information sciences, life sciences, books and reports, a special section of laser Tech Briefs

The Twenty-Fifth Lunar and Planetary Science Conference. Part 3: P-Z

Various papers on lunar and planetary science are presented, covering such topics as: impact craters, tektites, lunar geology, lava flow, geodynamics, chondrites, planetary geology, planetary surfaces, volcanology, tectonics, topography, regolith, metamorphic rock, geomorphology, lunar soil, geochemistry, petrology, cometary collisions, geochronology, weathering, and meteoritic composition

Bibliography of Lewis Research Center technical publications announced in 1993

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1993. All the publications were announced in the 1993 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses