Non-grey radiative heat transfer modelling in LES-CFD simulated methanol pool fires

Non-grey radiation modelling of gas-phase combustion products is performed during runtime of large eddy simulations (LES) of 30cm, 20kW methanol pool fires, based on the experiments of Klassen and Gore (1992) and Weckman and Strong (1996). FireFOAM, the turbulent flame solver part of open source CFD platform OpenFOAM®, was modified to include a new array of gas radiation models. Two grey and three non-grey implementations of the weighted-sum-of-grey-gases (WSGG) are compared in terms of both accuracy and CPU efficiency, along with a 'box' model based on the exponential wide band model (EWB) but specially optimised for fire scenarios. Turbulence-radiation interactions (TRI) are taken into account for the self-correlation of temperature in the emission term of the radiative transfer equation (RTE). Non-grey WSGG models consistently performed better than their grey counterparts, but the two newer WSGG correlations based on up-to-date spectral databases did not perform noticeably better or worse than the older WSGG model, which is a departure from other studies in oxy-fuel conditions. The work also showed that TRI is very important for the accurate prediction of the pool surface radiant feedback and the total radiant output. Some recommendations are made for the fire and radiation community

LNG vapour cloud dispersion modelling and simulations with OpenFOAM

Growth in demand for Liquefied Natural Gas (LNG) has increased calls for further research and development on LNG production and safer methods for its transportation. This paper presents the implementation of numerical models for dispersion of evaporated LNG in the open atmosphere. The developed model incorporates in its formulation LNG spill and pool formation into a source model. It is then coupled with a Computational Fluid Dynamics (CFD) approach in OpenFOAM for dispersion calculations. Atmospheric conditions such as average wind speed and direction were used to resolve wind boundary layers. The model also accounts for the humidity effect and its influence on air-density and buoyancy change. Verifications have been conducted using the experimental results from Maplin Sands series of tests by comparing the maximum evaporated gas concentration in every arc in relation to the release point. The results show good agreements between the model’s predictions and experiments

Two-step method for radiative transfer calculations in a developing pool fire at the initial stage of its suppression by a water spray

A procedure based on two-step method is suggested to simplify time-consuming spectral radiative transfer calculations in open flames containing scattering particles. At the first step of the problem solution, the P1 approximation is used to calculate the divergence of radiative flux, and it is sufficient to determine the flame parameters. The second step of solution is necessary to obtain the radiation field outside the flame, and this can be made independently using the ray-tracing procedure and the transport source function determined at the first step. Such a splitting of the complete problem results in much simpler algorithm than those used traditionally. It has been proved in previous papers that the combined two-step method is sufficiently accurate in diverse engineering applications. At the same time, the computational time decreases in about two orders of magnitude as compared with direct methods. An axisymmetric pool fire at the initial stage of fire suppression by a water spray is considered as the case problem. It is shown that evaporating small water droplets characterised by a strong scattering of infrared radiation are mainly located in regions near the upper front of the flame and one can observe the scattered radiation. This effect can be used in probe experiments for partial validation of transient Computational Fluid Dynamics (CFD) simulations

Thermal breakage of window glass in room fires conditions - Analysis of some important parameters

In a compartment fire, the breakage and possible fallout of a window glass has a significant impact on the fire dynamics. The thermal breakage of glass depends on various parameters such as glass type, edge shading, edges conditions and constraints on the glass. The purpose of the present study is to investigate some of the key parameters affecting the thermal breakage of window glass in fire conditions using a recently developed and validated computer tool. Fallout is not within the scope of this study. Different boundary conditions of the glass pane (unconstrained and constrained) subjected to fire radiant heat are investigated. The analysis shows that to prevent glass thermal breakage, it is important to provide enough spacing between the frame and glass pane to accommodate the thermal expansion, and constraints on the glass structure should be avoided. The zones where the glass is likely to crack first are shown. The study also quantifies the effects of glass edge conditions on its thermal breakage in fire conditions; such analysis has not been reported in the literature due to its complexity and the statistical nature of edge flaws. The results show that an ordinary float glass mostly used in windows, with the “as-cut” edge condition would break later and is stronger than a ground edge or polished edge glass for the scenarios investigated. The study demonstrates how a predictive tool could be employed for a better understanding of thermal breakage of window glass in fires and for design guidance

An infrared scattering by evaporating droplets at the initial stage of a pool fire suppression by water sprays

The computational analysis of downward motion and evaporation of water droplets used to suppress a typical transient pool fire shows local regions of a high volume fraction of relatively small droplets. These droplets are comparable in size with the infrared wavelength in the range of intense flame radiation. The estimated scattering of the radiation by these droplets is considerable throughout the entire spectrum except for a narrow region in the vicinity of the main absorption peak of water where the anomalous refraction takes place. The calculations of infrared radiation field in the model pool fire indicate the strong effect of scattering which can be observed experimentally to validate the fire computational model

Two-step iterative method for radiative transfer calculations in axisymmetric flames containing absorbing and scattering particles

The discrete ordinates and finite volume methods used in most fire simulations codes for radiative transfer calculations suffer from high computing overheads. A procedure based on two-step iterative method is suggested to simplify time-consuming spectral radiative transfer calculations in open flames containing scattering particles. At the first step of the problem solution, the P1 approximation is used to calculate the divergence of radiative flux, and it is sufficient to determine the flame parameters. The second step of solution is necessary to obtain the radiation field outside the flame, and this can be made independently using the ray-tracing procedure and the transport source function determined at the first step. Such a splitting of the complete problem results in much simpler algorithm than those used traditionally. It has been proved in previous papers that the combined two-step method is sufficiently accurate in diverse engineering applications, especially in the scattering media. At the same time, the computational time decreases in about two orders of magnitude as compared with direct methods. An axisymmetric pool fire suppressed by a water spray is considered as the case problem in the present paper to analyze the effect of radiation scattering by evaporating water droplets. The strong effect of scattering on radiative power field in the flame is obtained computationally for the first time

A comparative analysis of shielding of thermal radiation of fires using mist curtains containing droplets of pure water or sea water

The paper is focused on comparative computational modelling of the attenuation of fire radiation by water mists of pure water or sea water. The use of sea water in fire protection could be a more convenient and practical choice in coastal areas, on offshore installations or transported ships. The spectral absorption and scattering properties of both water droplets and salt particles formed by evaporation of sea water droplets are considered. A combined heat transfer problem is based on a combination of the spectral radiative transfer in a mist curtain, the kinetics of water evaporation, and convective heat transfer along the curtain. The developed computational model is used to analyze the radiative heating and evaporation of droplets of pure water and more complex multi-phase processes in droplets of sea water at all stages of the process. The numerical results for the case problem indicate sufficiently good shielding quality of a sea-water mist curtain. The suggested approach is expected to be useful for important engineering applications in fire protection

Towards gender-informed adaptation planning in the Sudanian zone of Mali Analysis of climate change vulnerability

Understanding the linkages between gender and vulnerability is crucial for proposing sustainable gender-responsive climate-smart solutions. This study compared the vulnerabilities of male (MHHH) and female household heads (FHHH) in the Sudanian zone of Mali using Cinzana in the Segou region as a case study. We used semi-structured questionnaire interviews and focus group discussions for data collection. The questionnaires were randomly administered to 233 household heads (23% women). The Livelihood Vulnerability Index (LVI) method was used to assess vulnerability to climate change. The results showed that livelihoods in the Sudanian zone of Mali are vulnerable to climate change. Female household heads (FHHH) were found to be more vulnerable. FHHH recorded higher values for six out of the eight LVI major components used in the vulnerability assessment: socio-demographic index, livelihood strategies index, social network index, food index, natural disasters and climate variability index and agricultural production system index. The study proposes a number of interventions for improving the adaptive capacity of FHHH to climate change and variability: improving access to financial resources, improving access to radio for receiving weather information, encouraging FHHHs involvement in farmer-based groups for peer-learning; and promoting the development of policy initiatives that ensure the mainstreaming of gender into agricultural development programs