Modelling of Heat Transfer, Gas Flow and Stress in Porous Material with Thermal Decomposition

The governing equations of heat transfer and gas flow within a cylindrical porous material which causes thermal decomposition are simplified to derive approximate models for evaluating the inner gas pressure and the effort of the convection heat transfer, respectively. The combination of these models with the existing previous stress model gives a model for not only evaluating the thermal stress but also stress due to gas pressure. The models are adapted for a green carbon rod during carbonization. The numerical results reveal the following useful facts: 1) Both the gas pressure and the stress due to the gas pressure approximately increase in proportion to specimen diameter and the square root of heating rate. 2) The releases of gaseous tar and H ₂ promote the convection heat transfer rate within the specimen because they change the thermophysical properties of the gas phase as well as increase the gas flow rate. 3) The release of H ₂ essentially raises the gas pressure and the stress due to the gas pressure and moreover has a particularly strong influence on the overall-stress peak at about 1000 K.