Effects of convective motion in n-octane pool fires in an ice cavity

Abstract

The effects of convective flows in n-octane pool fires in an ice cavity were investigated and it was found that a new set of parameters to the classical problem of bounded pool fires arises under these unique conditions. To systematically understand these parameters, two sets of experiments were performed by burning n-octane in cylindrically shaped ice cavities of 5.7 cm diameter. The first set of experiments was intended to provide a clear understanding of the geometry change of the cavity and displacement of the fuel layer. The results of these experiments showed that the rate of melting of the ice walls were higher in areas where the fuel layer was in contact with ice than in places where the flame was present. Due to the melting of the ice walls, a ring-shaped void was formed around the perimeter of the cavity. In the second set of experiments, the change in the temperature of the fuel layer was measured by use of multiple thermocouples at different locations inside the ice cavity. The results of the temperature analysis showed that the lateral temperature gradient of the fuel layer was an increasing function of time, whereas the vertical temperature gradient was a decreasing function of time. Using these experimental results, two dimensionless numbers (Marangoni and Rayleigh) were calculated. The Marangoni number represents the surface tension driven flows in the fuel layer and the Rayleigh number represents the buoyancy driven flows in the fuel layer. The results of this study showed two major convective phases; in the first half of the burning time, the buoyancy driven flows (Rayleigh) were dominant, while Marangoni convection was dominant in the second half of the burning time. The role of these mechanisms in affecting the flow and melting the ice is discussed.