Although buoyancy and cracking reactions are strongly coupled in the active cooling process

most of the previous studies consider only one of these factors

and their coupling relationship has not been considerably examined. In this work

this coupling relationship was numerically investigated with complete consideration of different cases of heating

and in the view of energy transport and conversion. By comparing with the no-gravity case (NGC)

the results indicate that buoyancy has a significant effect on the bottom-heated case (BHC) and side-heated case (SHC)

but has little influence on the top-heated case (THC) owing to the different magnitudes of secondary flow. The heat transfer of the BHC and SHC was significantly enhanced by the secondary flow

but their energy conversion was simultaneously impaired. The conversion of the BHC and SHC was approximately half that of the THC and NGC. For all cases

by analyzing the energy transport ways

the cross section can be classified into three regions in the heating direction. Laminar conduction dominates in region I

but gradually fails in region II

where its role is replaced by other energy transport ways. In region III

convection dominates the energy transport for BHC and SHC

whereas turbulence dominates for THC and NGC.