Scale Modeling of Puffing Frequencies in Pool Fires Related with Froude Number

Abstract

Quantitative investigation of the gravity effect was performed for small-sized acetone and kerosene pool fires. Several investigations on the behavior of pool fires have been conducted to understand the physical model. In their primary papers, it was mentioned that the buoyancy effect on the motion of pool fires was significant to understand the characteristics such as flame height, oscillatory frequency, and so on. Under these circumstances, in this investigation, a centrifuge was used to create elevated gravity fields and to examine the gravity effect. Small-scale pool fires were observed under various high gravity fields. Regions of stable flame, puffing flame and irregular oscillatory flame were categorized to make a map related with the gravity level and pool diameter. Flame height decreased and oscillatory frequency increased with an increase in the gravity level. Behavior of the flame height was agreed quantitatively with the scaling prediction presented by Orloff and Heskestad. Puffing phenomena observed under various gravity fields were summarized with the relationship between Strouhal and Froude number. As the result, an empirical equation expressed by St = 0.517Fr -0.502 could be obtained. From this equation, puffing frequency could be estimated for a flame of various pool diameters varying from 0.01 to 50m.