FLAMES

Author: MUÑOZ MIGUEL ANGEL.
Year: 2005.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: Sala d'Audiovisuals d'Enginyeria Química.
Place of preparation: ETSEIB, EDIFICI H PLANTA 4 Campus SUD.

Summary: Although there is abundant literature describing studies, both theoretical and experimental, on the thermal radiation from the flames, the estimation of the characteristics of large fires remains uncertain, mainly due to lack of large-scale experimentation and the difficulty presented at the time to measure some of the parameters involved in the calculation. For example, it is known that the large amount of smoke produced by burning of hydrocarbons leads to a decrease of power emisivo of flame, but this effect has not been quantified correctly and in addition it is not known precisely power emisivo each the portions that make up this kind of flames, namely that it is smoke-free and that is covered by this. In the present study we have experimentally determined the main parameters that are used in estimating the effects of the fires. It has a pilot plant, which has been remodeled and expanded for this work and has five rafts that allow testing of oil fires in the open air of 1.5 to 6 meters in diameter. A system of thermocouples can measure the temperature distribution in the flame, both radial and axial. Also, a system of communicating vessels used to obtain the combustion rate as a function of time. The experiences have been obtained data from the flame temperature, combustion rate, video footage (Visible and IR) radiometric data, data on the influence of wind speed, etc.. We analyzed further experimental data of large-scale fires that have taken place in the CERTEC (Center d'Estudis of Risc Technology) since 1999. Experimental data possible to determine the variation of the main variables that characterize fire âvelocidad combustion flame shape, height and slant, etc.â depending on the essential parameters of the fire (diameter of the tank, fuel type , wind speed). Using the technique of infrared thermography (IR images) identified the main emission properties of the fires, such as the power emisivo and the fraction of energy radiated by the flame or heat flux incident. In addition, it has developed a new methodology based on the superposition of IR images VHS, which has determined the distribution of power emisivo into flame and no bright light, as well as the area covered by each of them and their corresponding powers emisivos average. The data obtained and correlations to improve the modeling of fires raft. To corroborate the effectiveness of correlations and improve the methodology used to estimate the effects of the fires using models semiempíricos, has made a comparative study of a number of models of solid flame. The result has been established and the most appropriate methodology has been proven effective correlations developed here.

Author: FERRERO FABIO.
Year: 2005.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: ETSEIB-PAVELLÓ G-2A. PLANTA.
Place of preparation: ETSEIB, EDIFICI H PLANTA 10 Campus SUD.

Summary: Though the number of studies on pool fires is relevant, the characteristics of boilover are not yet totally understood. Boilover is one of the most dangerous phenomena that can occur when the fuel is burning above a water layer; in this situation, due to heat transfer from the flame, water can reach ebullition and the consequent eruptive expulsion of vapour bubbles, drags fuel into the flame, increasing the thermal effect and the dimension of the fire. The phenomenon can present itself in two forms, depending on the fuel layer thickness, the hot zone boilover and the thin layer boilover, which boundaries are not yet well defined. Thus, this work can prove to be very important, since it aims to step forward in the knowledge of boilover, by defining in a clearer form its mechanisms and its effects, at a scale representative of a real fire scenario. The experiments realized concerned thin layer boilover, due to economical and security limitations; nevertheless, when it was possible, data have been extrapolated to situations of hot zone boilover. In order to carry on the study, an experimental facility was remodelled and enhanced; the facility has 5 circular pools of diameter ranging from 1.5 to 6 m. A series of thermocouples was used to determine the fuel and water temperatures. Other thermocouples were employed to analyze flame temperature distribution. Moreover, from the experiences much information was obtained, such as burning rate values, video-recordings (in the visible and IR field), intensity of radiation emitted to the exterior, atmospheric condition evolution, etc. Data proceeding from three experimental series, performed by CERTEC (Centre d'Estudis del Risc Tecnològic) since 1999, were analyzed. In great detail, the fundamental parameters of thin layer boilover (on-set time, pre-boilover burned mass ratio, boilover intensity, radiation intensity, etc.) as a function of the characteristics of the experiments (pool diameter, fuel type, fuel thickness, etc.) were studied. New correlations to estimate average and maximum flame length during the stationary period and the thin layer boilover, were obtained. Effects of the phenomenon on flame tilt and pulsation were also considered. Moreover, in order to calculate the increase to apply to safety distances in case of occurrence of the phenomenon, a semi-empirical model to estimate thermal effects during thin layer boilover was determined. The analysis of the distribution of the temperatures inside the water layer showed that, working with small fuel layers, there is no formation of a proper hot zone. It was only possible to determine a much reduced high temperature zone, which did not increase in thickness or temperature and has been named pseudo hot zone. Finally, a mathematical model to predict temperature distribution inside the liquid layer (fuel and water) during the process that leads to thin layer boilover was developed. The model, which showed the great importance of the convection inside the fuel for the heat transfer, was later modified and extended, in order to simulate the boilover phenomenon in a general form. The predictions of the model fit very well experimental data from this thesis and from previous publications. Furthermore, the results obtained allowed to observe that a combination of Prandtl and Fourier number can help in deciding the possibility and the type of boilover.

Author: SERRANO HUERTAS CLARA.
Year: 2005.
University: CASTILLA-LA MANCHA [www.uclm.es].
Place of defense: ESCUELA TÉCNICA SUPERIOR DE INGENIEROS INDUSTRIALES.
Place of preparation: ESCUELA TÉCNICA SUPERIOR DE INGENIEROS INDUSTRIALES DE CIUDAD REAL.

Summary: The gasification is a technology that raises a lot of interest because it allows the elimination of waste agroforestry spot, through its use in small facilities gasifier / engine parala producing electricity or mechanical. This is a partial oxidation process which gives a combustible gas, low calorific value, which consists mainly of CO, H2 and inert gases. Given the paucity of information concerning the caracterizaicón gas gasification combustion processes, this paper has obtained the combustion rate and the delay time to autoencendido this hydrogen-rich fuel. The modeling of the blast and autoencendido gas has been carried out through you program CHEMKIN, renowned in the field of combustion, which allows for the consideration of a detailed kinetic mechanism for the oxidation of gas. Carrying out this study in a wide range of conditions of pressure, temperature and composition, it has been possible to obtain correlations for combustion parameters mentioned. In addition, through the use of two pumps spherical combustion, and without optical access, it has been contrasting the results of combustion rate, as well as information on the regime of the flame propagation under different conditions of pressure and dosado. We have also studied the phenomena of stretch and cellularity of the flame, both phenomena by quantifying the number of Markstein, and the number of Lewis in the mix. Thus, this work contributes to the caracterizaicón not only gas gasification, but also mixtures H2/CO/N2 typical processes reformed.