Josep Arnaldos

Mathematical models and calculation systems for the study of wildland fire behaviour

This is a review of the most important work in wildland fire mathematical modelling which has been carried out at different research centres around the world from the beginning of the 1940s to the present. A generic classification is proposed which allows wildland fire models to be sorted. Surface fire spread models, crown fire initiation and spread models, spotting and ground fire models are reviewed historically and the most significant ones are analysed in depth. The last two sections are dedicated to wildland fire behaviour calculation systems based on the reviewed models. The evolution and complexity of these systems is analysed in parallel with the development of new technologies. Special attention is given to the tools most commonly in current use by forestry agencies.

Hazard and operability (HAZOP) analysis. A literature review

Hazard and operability (HAZOP) methodology is a Process Hazard Analysis (PHA) technique used worldwide for studying not only the hazards of a system, but also its operability problems, by exploring the effects of any deviations from design conditions. Our paper is the first HAZOP review intended to gather HAZOP-related literature from books, guidelines, standards, major journals, and conference proceedings, with the purpose of classifying the research conducted over the years and define the HAZOP state-of-the-art.

Experimental study of burning rate in hydrocarbon pool fires

Experimental results on hydrocarbon pool fires are reported. Experiments on gasoline and diesel oil pool fires with diameters of 1.5, 3, and 4 m were carried out and burning rate was determined through the measurement of the variation in fuel level as the fire proceeded. The instantaneous value of burning rate was thus established as a function of time. This allowed the analysis of the transient periods at the beginning (fire development) and end (fire extinction) of the whole process, as well as the determination of the average burning rate during steady-state fire as a function of pool-fire diameter. The effect of wind speed on burning rate was also studied. Finally, a set of conclusions were drawn from experimental results.

Historical analysis of accidents in the transportation of natural gas

The purpose of the present analysis is to determine the main features of accidents occurring in the transportation and distribution of natural gas (in a gaseous state). A survey of 185 accidents taken mainly from the database MHIDAS has been performed. Of these, 131 (70.8%) occurred in transport systems, 32 (17.3%) in process plants, 13 (7.0%) in storage plants and nine (4.9%) in domestic/commercial activities. The 131 accidents occurring in gas pipes were selected for further analysis. The data show that the most frequent accident was explosion (86 cases, 65.6%) followed by loss of containment (63 entries, 48.1%) and fire (56 entries, 42.7%). The cause of the accident was identified for 90 cases (68.7%). Of these, the most frequent causes were mechanical failure (39 entries, 43.3%), impact failure (37 entries, 41.1%) and human error (32 entries, 35.6%); of the specific causes, impact failures due to excavating machinery were especially numerous (21 cases, 23.2% of known causes). The consequences of the accidents, in terms of both human and economic losses, are assessed. Finally, some conclusions are given about the risks involved in natural gas transportation.

Fluidization at vacuum conditions. A generalized equation for the prediction of minimum fluidization velocity

The hydrodynamical behaviour of fluidized beds at reduced pressures is studied. The minimum fluidization velocity is strongly influenced by pressure, decreasing as pressure increases. The well-known equation of Wen and Yu and two equations proposed for the calculation of umf at reduced pressures are tested; the comparison with experimental data shows that they can be applied only over restricted pressure ranges. The relationship between flow rate, pressure and pressure drop at conditions ranging from high vacuum to high pressure is analysed for the different flow regimes (molecular, slip, laminar, transition and turbulent). A generalized equation is found which predicts fairly well the value of umf at vacuum conditions, atmospheric pressure and high pressures.

Magnetically stabilized fluidization: modelling and application to mixtures

Abstract A mathematical model of the magnetically stabilized fluidized bed, based on the arrangement of particles following field lines, is proposed. Magnetic stabilization has also been applied to fluidized beds with mixtures of magnetizable and non-magnetizable particles (sintered nickel—silica, steel—copper, steel—silica). The behaviour of these systems is studied, as well as the influence of the magnetic material mass fraction on the delay of bubbling. The results obtained show that the magnetic stabilization can be applied not only to the fluidization of magnetizable materials but also to non-magnetizable particles, if a certain fraction of magnetizable material is present. Correlations are proposed to calculate the transition velocity as a function of gas—solid properties and operating conditions.

HIGH TEMPERATURE INCIPIENT FLUIDIZATION IN MONO AND POLYDISPERSE SYSTEMS

Tests have been made on the behaviour of fluidized beds at high temperature (15-950°C). Bed materials used were silica sand of different sizes. Bed voidage at minimum fluidization conditions was found to be dependent on temperature rise and on increase in Reynolds number. Plots of bed voidage function, bed voidage and Ar versus Remf show a change in the behaviour at Reynolds numbers between approximately 0.75-2. This is explained in terms of a variation in the fluid flow pattern inside the bed: at very low Remf creeping flow exists, but at higher values of Reynolds number, separation of boundary layer takes place and a wake appears at the rear of the particle, creating a low pressure zone. This contributes to attractive forces between particles at the minimum fluidization conditions, decreasing the value of ϵmf. If Remf increases, the separation point moves towards the rear of the particle and the wake shrinks; attractive forces decrease, and ϵmf increases. Data on umf , both for monodisperse systems and ...

Determination of flame emissivity in hydrocarbon pool fires using infrared thermography

A methodology is proposed for the determination of flame emissivity in hydrocarbon pool fires using infrared thermography. Experiments on gasoline and diesel oil pool fires with diameters of 0.13, 0.18 and 0.5 m were carried out, determining the flame emissivity for these types of fires in transition regime and turbulent regime. Also analysed was the evolution of the flame emissivity depending on the pool diameter, and a new correlation for the estimation of the emissivity depending on the above mentioned diameter was obtained.

Prediction of transition velocities and hydrodynamical regimes in fluidized beds

Abstract Amongst the diverse fluid velocities establishing the existence of the different fluidization regimes, only minimum fluidization velocity has been extensively studied. Although an increasing number of communications have been devoted in the last decade to circulating fluidized beds, the prediction of the velocities over which bubbling, turbulent and fast fluidization exist is still difficult. Even the existence of the different fluidization regimes is not perfectly established. In this communication, the diverse correlations available for the calculation of u c , u k and u tr are analysed and compared to experimental data. Conclusions are derived about their adequacy, and a simple map is proposed for the operating conditions over which each fluidization regime exists.

Analytical expressions for the calculation of damage percentage using the probit methodology

Abstract In the modelling of accidents, difficulties arise when introducing data from figures and tables into a computer code. In order to solve this problem in relation to the estimation of the consequences of an accident on the population, analytical expressions for converting Probit variables into probability percentages and vice-versa, are presented. The results obtained have been compared with the results found in tables and figures from references. Very good agreement between the commonly used values and those obtained from the analytical expressions has been found.