Simulation of the Heat Transfer Mechanism of Flame Spread over Liquids

摘要

Flame spread over liquids is of current interest because of its importance to fire safety and the curiosity of combustion researchers studying the fundamental heat transfer mechanism of this phenomenon. The major heat-transfer process between the flame's leading edge and the liquid is a highly transient phenomenon involving both liquid and gas phases. These interact with each other through the exchanges of momentum, heat, and mass. The liquid convection ahead of the flame is unique, complex and plays an important role in the spreading procexx. In our past studies we focused on obtaining accurate and detailed measurements of flow and temperature for both liquid and gas phases and fuel concentrations generated by the flame. To enhance our understanding of the heat-transfer mechanism, this paper focuses on simulating the liquid-convection flow experimentally by suddenly mixing two liquids each having different surfacetension properties. The first liquid simulated the heated liquid beneath the flame at high temperature and low surface tension. The second one simulated the unburned upstream liquid at room temperature and higher surface tension. Both liquids were mixed suddenly through the surface only. The velocity profiles were visualized experimentally suing the 2-D Laser-Sheet Particle-Tracking (LSPT) technique. The preliminary results showed that, if we can choose successfully the two liquids that match the properties of the liquids underneath and ahead of the flame, a good similarity between the velocity profiles of mixing of two liquids and of those from real flame spreading experiment can be obtained. As a result the liquid flow patterns ahead of the flame can be simulated accurately in order to apply the 3-D holographic imaging technique which is limited because of the distortion of the reference beam by temperature and density gradient, to better understand the mechanism of heat transfer ahead of the flame.