HOT SURFACE IGNITION
An image of the heated plume provides an indication that there is a near and far field region above the plate and this is borne out by highly resolved temperature measurements. A significant difference in the thermal transport mechanism is observed at an x/D of 0.05
Insight into the differences in the flowfield were uncovered using laser light flow visualization, where a horizontal laser sheet was passed over the heat disk and highlighted a cellular structure within the near field. As the one moves into the far field these structures break down leading towards a well mixed thermal field.
One major source of engine and machinery fires may be attributable to the leakage of flammable fluids onto hot surfaces and its subsequent ignition. ESI has conducted in-depth analysis of this phenomenon using Schlieren and Laser sheet visualization techniques over a uniformly heated circular flat plate. In addition to acquiring experimental data, a computational analysis of the flow field was performed.
This difference in the thermal mechanism was also confirmed by ESI through Modeling & Simulation studies. The difference in the thermal energy transport, is highlighted by the local fluid temperature in the near field (< 5 mm above the plate) is very different than the temperature in the far field (approximately > 10 mm above the plate).
Hot surface ignition may be easily realizable if the conditions are such that the elevated temperature of a surface is above the auto-ignition temperature of a leaking fluid. This may be observed from the following images where kerosene is dripped from a tube onto a hot plate. In the initial case the surface temperature is 250 deg C, and in the second case at 550 deg C. This latter temperature provides instantaneous combustion of the leaking fuel.