Experimental Study on Heat Transfer of Heptane Pool Fire During the Whole Burning Process Under Different Initial Thickness Conditions

When the leaked liquid fuel is ignited, a pool fire with a certain fuel thickness could be formed due to the restriction of boundaries like fire dikes. The burning characteristics of pool fire during the whole burning process were experimentally studied. The initial thickness was set as 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm respectively. The pool diameter was set as 0.20 m, 0.30 m respectively. Results show that for the cases with initial thickness of 15 mm, 20 mm, 25 mm, 30 mm, there are four burning stages: pre-heating burning stage, steady burning stage, boiling burning stage, extinguishment stage. However, when the initial thickness is 5 mm, there is no boiling burning stage. During burning, the instantaneous mass loss rates under same fuel thickness in all cases increase with the initial thickness. Therefore, the time difference from 5 mm to 1 mm Δt5mm∼1mm will decrease with the increasing initial thickness because of the growing mass loss rate. Based on the law of energy conservation, a heat transfer model of the pool fire during the whole burning process was established. The calculation results show that during the whole burning process of pool fire, the vertical temperature distribution inside the pool fire would become higher and more uniform. Heat feedback (Q˙feedback) and heat loss (Q˙loss) would increase and Q˙feedback has a higher growth rate. Radiation heat feedback (Q˙rad), evaporation heat (Q˙evap), penetration heat flux (Q˙pe), transmission part of the reflected heat flux by the substrate (τQ˙ref), enthalpy change (ΔQ˙ h), the thickness of the boiling layer (δh) would increase during the whole burning. Heat conduction (Q˙cond) and the thickness of the gradient temperature layer (δg) would decrease during the whole burning. The case with larger initial thickness has smaller proportion of Q˙loss/Q˙feedback, the case with larger diameter has larger proportion of heat loss to heat feedback Q˙loss/Q˙feedback.