The Effect of Specimen Thickness on Critical Heat Flux and Effective Thermal Inertia Calculations Using Cone Calorimeter and Ignitability Test Apparatus

Abstract

To investigate the differences in critical heat flux for ignition measured by cone calorimeter (CCM) and ignitability test apparatus (IGA), 9.5 mm-thick lauan plywood was tested. CCM tests were carried out in horizontal and vertical orientations. The measured critical heat flux was 14.4 kW/m2 in horizontal CCM, 15.2 kW/m2 in vertical CCM, and 15.0 kW/m2 in IGA. Thermal inertia was apparently measured as 0.369kWs/(m4.K2) in horizontal CCM, 0.585kWs/(m4.K2) in vertical CCM, and 0.231kWs/(m4.K2) in IGA. In addition, the effect of specimen thickness on the measured values of the critical heat flux and the thermal inertia was analyzed. Unsteady one-dimensional finite difference method was applied to heat conduction equation through the specimen. As to the critical heat flux, heat loss from the heated surface is dominant if the specimen thickness is more than 21 mm. Thus, the critical heat flux by vertical CCM is the largest, while the value by IGA is smallest. The effect of heat loss from the specimen back surface is dominant in the case of thin specimens. Under such conditions, IGA gives maximum value in contrary.