Smoldering processes occurring in nature is accompanied by the presence of air which affects the regression rates. Smoldering accompanied by air is the leading cause of deaths in residential fires and a source of safety concerns in commercial aircrafts. One aspect which has not been addressed in the field of smoldering combustion is the way the smoldering regression rates are affected by the presence of forced air. The work attempts to synthesize a comprehensive view of smoldering combustion accompanied by varying air flow at selected velocities. The separation distance between the external source and the fuel, velocity of the flow and the surface orientation of fuel are the key controlling parameters investigated in this work. The investigation is carried out with the aid of an experimental setup with incense sticks as pilot fuel. Results state that, variable forced flow has significant effects on the smoldering process. The extent of the effect varies for different controlling parameters. This study will be helpful in determining the time required to control the smoldering combustion process which is the reason behind most of the fires including the on-flight fires in aircrafts.
Smoldering is flameless combustion that occurs on the surface of the condensed phase that is very difficult to detect and which causes serious fire risks in residential and industrial areas by the presence of turbulent winds. Statistics show that major fire accidents are due to smoldering for example cigarettes. Smoldering combustion is also a great concern in space facilities like ISS since the zero gravity environments can increase the rate of smoldering propagation. The main motivation of this paper is to design and develop the wind tunnel in order to study the effect of aerodynamic and combustible properties on the smoldering. A wind tunnel is an effective tool that is used to study the aerodynamic effects of air or smoke when it is allowed flowing past the solid bodies. The specific measurements that are required to construct the wind tunnel are mentioned in this paper, as well as the materials used in various sections of the wind tunnel are discussed. The power source and light source used for the visualization of the turbulent wind flow past the burning fuel are discussed. A low-speed tabletop wind tunnel is first designed using CATIA and then fabricated using necessary tools. The results from these experiments can be used to know how the combined effect of both laminar and turbulent flow on smoldering combustion is more harmful than the normal combustion.
Burning is an inevitable process that happens in nature and has a massive impact on life. Technically, burning or combustion emphasizes on the reaction process that consumes oxidizer and fuel to deliver heat and burnt products. Based on the direction of reaction propagation and fuel orientation, burning or combustion is classified in to forward or reverse combustion. Forward combustion is a process which comprises of movement of air and the propagation of ignition zone in the same direction while in reverse combustion, air moves opposite to the direction of the propagation of the ignition zone. Forward combustion escalates rapidly in solid fuels when compared to reverse combustion. The conductivity of the burning solid fuel, convection due to the atmospheric air around and buoyancy effects which takes place due to the difference in air densities plays a major role in the forward combustion process. In this work, thin uniform cross-sectioned solid materials such as matchsticks, candles and incense sticks have been considered as fuel to investigate forward flaming and smoldering. The experiments were carried out in ambient atmospheric conditions. The results based on visualizations suggest that the orientation of the fuel has a greater impact on burning rates and provides us the information on how to burn it in a beneficial way.
Most of the forest fires and building fires are occurring due to the low-temperature flame-less phenomenon called smoldering combustion. The present study is carried for the understanding of fluid flow patterns over the fuel and also fuel under smoldering combustion. The fuel equipped here is a hexagon since most of the modern architectural shapes for buildings, parking lots, hexagon-shaped houses, honeycomb-patterned facades, etc. Regression rates are calculated for the fuel under smoldering. For experimentation, a tabletop wind tunnel is fabricated, and an axial fan is fixed with a speed regulator to investigate the smoldering combustion under the flow and behavior of the fluid flow. The results suggest that the smoldering phenomenon is significantly dependent on the orientation, flow speed and the direction of smoldering with respect to the flow.
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