Quantitative inner heat transfer for cable fire: a numerical study and effects of core diameter and insulation thickness

Inner heat transfer by the metal core plays an important role in the flame spread of cables but little quantitative information is known. Series of calculations are conducted for the detailed inner temperatures and heat fluxes of five typical commercial cables with different core radii and insulation thicknesses by the flame heating at bottom. The results show that cable size has a significant and complex effect on the transient and final thermal structures in cables when heated. In the flame heating region, the core temperatures increase much faster and also be finally higher for thinner cable than thicker one. In the far-flame preheating region, the longitudinal temperature drops more slowly for thicker cables, which indicates that the strong inner core thermal channel enhances the cable preheating at farther locations. The results also indicate that the radial heat fluxes at the core-insulation interface are normally not larger than 30 kW m-2 under the heating condition here. However, for the longitudinal heat fluxes along the cable core, they can be as large as 1000 kW m-2 for thin cables. Finally, it illustrates that there is a negative correlation between the inner core temperatures and the heat flux distributions when the cable is heated on one side. The quantitative results for the heat transfer by metal core are important for cable fire modeling and optimal design of new fire-resistant cables.