A two-dimensional and two-phase numerical model is presented for the smolder propagation in a horizontal polyurethane foam. The chemical processes considered include endothermic pyrolysis and exotherrnic oxidation deg...A two-dimensional and two-phase numerical model is presented for the smolder propagation in a horizontal polyurethane foam. The chemical processes considered include endothermic pyrolysis and exotherrnic oxidation degradation of polyurethane foam and exothermic oxidation of char. The governing equations are discretized in space using the finite element method and solved by the software package FEMLAB. Predicted profiles of solid temperature as well as evolutions of solid compositions （including foam, char and ash） are presented at an airflow velocity of 0. 28 cm/s. The computed average smoldering velocity is 0. 021 4 cm/s, and the average maximum temperature is 644. 67 K. Based on the evolutions of solid compositions, the packed bed can be obviously divided into four zones： unreacted zone, fuel pyrolysis and oxidation zone, char oxidation zone and fuel burned-out zone. Simultaneously, the effects of inlet air velocity and fuel properties （including thermal conductivity, specific heat, density and pore diameter） are studied on the smoldering propagation. The results show that the smoldering velocity and temperature have a roughly linear increase with increasing inlet air velocity; the fuel density is the most important factor in determining smoldering propagation; radiation has a non-negligible role on the smoldering velocity for larger pore diameters of porous material. The computational results are compared with the experimental data and a general agreement is reached.展开更多
Based on a three-step kinetic mechanism, a one-dimensional, time dependent, numerical model is presented for the smoldering propagation in a horizontally packed bed of cellulosic material. The kinetic processes includ...Based on a three-step kinetic mechanism, a one-dimensional, time dependent, numerical model is presented for the smoldering propagation in a horizontally packed bed of cellulosic material. The kinetic processes include pyrolysis and oxidation degradation of fuel and oxidation of char. Heat transfer between solid and gas is taken into account, and the diffusion coefficient varies with the temperature. Radiative heat transfer is included by using the diffusion approximation. The effects of airflow velocity and oxygen concentration are simulated on the smoldering velocity and the averaged maximum temperature of smoldering fuel. The results indicate that the spread rate varies linearly with increasing airflow velocity, and the inlet air velocity has little effect on the maximum temperature. The evolutions of gas species and solid compositions are predicted. The effects of frequency factors （A1, A2 and A3） are analyzed. Simulations show that the smoldering spread rate increases with increasing A2 （fuel oxidation）, but decreases with A1 （fuel pyrolysis） and A3 （char oxidation）.展开更多
基金The National Natural Science Foundation of China(No50476073)
文摘A two-dimensional and two-phase numerical model is presented for the smolder propagation in a horizontal polyurethane foam. The chemical processes considered include endothermic pyrolysis and exotherrnic oxidation degradation of polyurethane foam and exothermic oxidation of char. The governing equations are discretized in space using the finite element method and solved by the software package FEMLAB. Predicted profiles of solid temperature as well as evolutions of solid compositions （including foam, char and ash） are presented at an airflow velocity of 0. 28 cm/s. The computed average smoldering velocity is 0. 021 4 cm/s, and the average maximum temperature is 644. 67 K. Based on the evolutions of solid compositions, the packed bed can be obviously divided into four zones： unreacted zone, fuel pyrolysis and oxidation zone, char oxidation zone and fuel burned-out zone. Simultaneously, the effects of inlet air velocity and fuel properties （including thermal conductivity, specific heat, density and pore diameter） are studied on the smoldering propagation. The results show that the smoldering velocity and temperature have a roughly linear increase with increasing inlet air velocity; the fuel density is the most important factor in determining smoldering propagation; radiation has a non-negligible role on the smoldering velocity for larger pore diameters of porous material. The computational results are compared with the experimental data and a general agreement is reached.
基金Project supported by the National Natural Science Foundation of China (Grant No.50476073)
文摘Based on a three-step kinetic mechanism, a one-dimensional, time dependent, numerical model is presented for the smoldering propagation in a horizontally packed bed of cellulosic material. The kinetic processes include pyrolysis and oxidation degradation of fuel and oxidation of char. Heat transfer between solid and gas is taken into account, and the diffusion coefficient varies with the temperature. Radiative heat transfer is included by using the diffusion approximation. The effects of airflow velocity and oxygen concentration are simulated on the smoldering velocity and the averaged maximum temperature of smoldering fuel. The results indicate that the spread rate varies linearly with increasing airflow velocity, and the inlet air velocity has little effect on the maximum temperature. The evolutions of gas species and solid compositions are predicted. The effects of frequency factors （A1, A2 and A3） are analyzed. Simulations show that the smoldering spread rate increases with increasing A2 （fuel oxidation）, but decreases with A1 （fuel pyrolysis） and A3 （char oxidation）.
