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In this paper, the compound heat transfer of convection and radiation in an internal circulating fluidized bed for low temperature oxidation of pulverized coal was numerically simulated. The numerical prediction about the compound heat transfer characteristics and its relationship of convection and radiation was compared with the experimental measurements of low temperature radiation. The discrete ordinate model (DOM) was employed to investigate the radiation heat transfer in the low temperature oxidation internally fluidized bed, and user-defined function (UDF) was compiled by considering the effect of the particle flow emissivity on radiation heat transfer. The convection heat transfer coefficient increases with the increase of gas inlet volume flow rate and initial bed material height, however, thermal radiation coefficient was opposite. An increase of the thermal flux results in an increase of the surface temperature of the fluid and the heater surface, and the thermal transfer coefficient between bed material and heater surface is also increased. The results have the application reference to complex thermal transfer design of circulating fluidized bed systems wherein thermal radiation transfer must be considered as a significant mode. [ABSTRACT FROM AUTHOR]

In this paper, a 3D two-phase simulation involving the complex heat transfer characteristics within a vertical cylindrical fluidized bed was conducted numerically. The accuracy of mathematical modeling has been validated by comparing with the experimental results. The discrete ordinate model (DOM) was employed to investigate the radiation heat transfer in a fluidized bed. The user-defined function (UDF) was compiled by considering the effect of the particle flow emissivity on radiation heat transfer, and coupled the two-phase flow field by using the gray and non-gray model respectively. The results show that the non-gray model can better depict the selected absorption of radiation wavelength in two-phase flow heat transfer than gray model. Furthermore, under high heat flux density conditions, the proportion of radiation heat transfer increases gradually with the increase of heat flux, which can reach about 40% of the total heat transfer coefficient. Meanwhile, other factors about radiation heat transfer such as initial solid packing height, inlet gas velocity, and other conditions were studied and consistent with the thermal experimental regularity. The findings demonstrated that the radiation heat transfer and it's modeling play an important role in two-phase heat transfer of fluidized bed. [ABSTRACT FROM AUTHOR]

The heat transfer performance of a tube heat exchanger has great significance for the metal smelting, catalytic cracking and combustion performance in the fluidized bed reactor. In this paper, a three dimensional Eulerian–Eulerian simulation for the vertical heater tube to bed heat transfer within a baffle type internal circulating fluidized bed (ICFB) was conducted numerically and the results were compared to experimental ones. Gidaspow's drag correlation was adopted to describe the interaction between the gas and solid phases in the ICFB. Temperature and heat transfer coefficient were numerically analyzed under different operating conditions as same as the experimental setup. The effects on the heat transfer characteristic of input heat flux, air inlet velocity, and initial solid packing height were investigated as the average temperature was compared with the experimental data in the literature. The simulation results showed that along the height of the bed, the velocity of the solid particles increases, lateral movement of the particles from the low-speed area to the high-speed area can be observed at the bottom of the acceleration area. The convective heat transfer coefficient of solid particles is the main component of heat transfer in the dense phase zone, with the increase of the initial solid packing height, the average convection heat transfer coefficient between the fluid and the heated surface is shown an upward trend. By comparing the experimental datas, it can be concluded that the numerical simulation of the flow and heat transfer process of the inner circulating fluidized bed by the Eulerian-Eulerian method is in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]