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.
Columnar grained and single crystal superalloy blades and vanes for gas turbine applications are made by directional solidification process. In this process, the ceramic mould is subjected to high temperature 1500-1600uC. In order to improve refractoriness of the shell, fine alumina was added to the filler. The fine alumina reacted with silica in the binder forms mullite. The kinetics of formation of mullite and its effects on improvement of refractoriness was studied. Refractoriness is also improved by reducing the amount of sodium in the binder system which is used as a stabiliser. Binders with sodium 0?43 and 0?05% were used for making the shells. This paper would discuss improvement in the shell refractoriness and dimensional stability of the castings of gas turbine components made from Ni base superalloys by directional solidification process.
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