Experimental study of ullage height on the burning rate and heat transfer of medium-scale heptane pool fires

Abstract

Ullage height (the distance between the fuel surface and the pool upper rim) is one of the most important and widely recognized factors that affect the burning rate and heat transfer of pool fires. This study investigated the effects of ullage height on the burning rate, heat feedback, and radiation fraction of medium-scale pool fires. Heptane pool fires were tested with a diameter (D) of 30 cm and the non-dimensional ullage height (h/D, h is the ullage height) being varied from 0 to 1.48. Results show that the non-dimensional burning rate tends to decrease exponentially with h/D. It has been proved that the current models used to predict the burning rate of pool fires are not applicable to those medium-scale pool fires that are affected by the ullage height. The radiative, conductive, and convective heat feedback rate overall decrease with the ullage height. The conductive heat feedback fraction weakly depends on h/D. The radiative heat feedback fraction firstly decreases then stabilizes with h/D, while the convective heat feedback fraction shows an opposite trend. The radiative fractions firstly increase then decrease with h/D. This paper presents a new correlation with considering the ullage height and the mean beam length within the pool ullage. The universality and accuracy of the proposed model were verified by comparing it with extensive experimental data, where D varied from 10 cm to 35 cm, and h/D varied from 0 to 2.0.